General Science & Technology for UPSC [Prelims] Examinations

General Science-1-Biochemistry and Cell Biology

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Prelims MCQ Topics

Basic Features of Life, Living and Nonliving properties of Viruses, Comparison of Carbon and Silicon in terms of life, Polarity of Water and its implications for life, Role of Cations and Anions in our body, Hypernatremia, Hyponatremia, Types of Carbohydrates, Lipids, Unsaturated Fat and Saturated Fat; Trans and Cis Fats; Good Fats or Bad Fats, Thermal Properties of Fats and Lipids; Cholesterol-Importance, Sources, Types and control; Proteins-Types and Composition, Amino Acids, Peptide Bonds, Examples of Common Proteins, Enzyme-Functions and Industrial Uses, DNA & RNA Differences, Basics on how do they work; Various Vitamins; Deficiency diseases, Cell-structure and major organelles, Prokaryotic and Eukaryotic cells, Difference between Plant cells and Animal cells, Mitosis and Meiosis


Basic Features of Life

Biology is the science of living things or organisms.  Scientific evidence suggests that life began on Earth approximately 3.5 billion years ago by variously proposed mechanisms.

Basic Features

Life is considered a characteristic of organisms that exhibit all or most of the certain phenomena such as Homeostasis, organization, growth, adaptation, response to stimuli and reproduction.

  • Homeostasis is the regulation of the internal environment to maintain a constant state. For example: electrolyte concentration or sweating to reduce temperature.
  • Organization means that any living organism is made of one or more cells and cells serve as basic unit of life.
  • Metabolism refers to life-sustaining chemical transformations within the cells of living organisms. Metabolic reactions are of two types viz. anabolism and catabolism. Anabolism refers to transformation of energy by converting chemicals and energy into cellular components. Catabolism refers to decomposing organic matter. Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
  • Growth refers to increase in size in all of parts of an organism. To grow, the organisms need to maintain a higher rate of metabolism than catabolism.
  • Adaptation is the ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism’s heredity, diet, and external factors.
  • Response to stimuli can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms.  A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
  • Reproduction is the ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.

Are Viruses Living Organisms?

Viruses are most often considered replicators rather than forms of life. They have been described as “organisms at the edge of life, because

  • They possess genes
  • They evolve by natural selection
  • They replicate by creating multiple copies of themselves through self-assembly.

However, viruses do not metabolize and they require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic molecules.

Living propertiesNon-living properties
The presence of DNA or RNA (but never both)The absence of cell.
Structural diversityThe lack of protoplasm.
Geneticity and parasitic propertiesNo any reproduction and growth outside the living cell.
Sensitivity and evolutionStored in the form of crystal outside the living cell.
Capable of spreading the diseaseThe lack of metabolic activities like nutrition, digestion

Carbon Bonds – The Basic Feature of Life on Earth

Life on earth is carbon based because carbon makes up 18 percent of the weight of the human body. Due to its unique electron configuration, carbon needs to share electrons. It can form four covalent bonds with other carbon atoms or a variety of other elements.

Comparison of Carbon and Silicon

We note here that technically, life on Earth could be based on silicon also because this element has the same bonding properties as carbon. However, there is much less silicon than there is carbon on Earth. Further, Carbon wins the competition on many accounts as follows:

  • The bonding versatility of Carbon allows it take on many forms: long side chains that make up fatty acids and cell membranes, ring structures that compose hormones and sugars, and even simple gaseous molecules like methane (CH4) or carbon dioxide (CO2). Silicon has not those capabilities.
  • While carbon is perfectly comfortable in a variety of different structures (rings, long chains, multi-ring chains, and double-bonded carbon catenations), silicon’s analogous structures are comparatively unstable and sometimes highly reactive. Additionally, such analogous silicon compounds may never occur in nature; the largest silicon molecule ever observed had only six silicon atoms. In contrast, some carbon-based molecules can have tens of thousands!

Molecules of Life

Four chemical elements that make up the majority of living biological matter are Carbon, Hydrogen, Oxygen and Nitrogen. Organisms are made of both organic and inorganic substances.

Inorganic substances

Some of the most common inorganic substances needed for life are water, mineral salts, molecular oxygen, molecular carbon dioxide etc. Out of them, water is the most abundant inorganic substance in almost all animals and plants. Mineral salts are simple, inorganic substances made up of metallic chemical elements, such as iron, sodium, potassium, calcium and magnesium, or of non-metallic elements, such as chlorine and phosphorus. The mineral salts are found in two forms viz. solubilized ions (such as sodium and potassium ions in cells) or non-solubilized form such as calcium in our bones.

Organic Molecules

There are many types of organic molecules that are important for living organisms. Out of them, four molecules viz. nucleic acids (DNA & RNA) , Proteins, Carbohydrates and Lipids are referred to as bio-organic molecules because they are essential to living organisms and contain carbon. These perform the basic functions of life such as structural functions (compose, surround and maintain organs, membranes, cell organelles, etc.), energy functions (chemical reactions in metabolism), control and informative functions (genetic code control, inter and intracellular signalling etc.) and enzymatic functions (facilitation of chemical reactions).

These molecules are much more complex and made of sequences of carbon chains bound to other elements called polymers or biopolymers or giant polymers. They are also called macromolecules– the molecules which have molecular weight greater than 1,000 Daltons.

These four kinds of Macromolecules are quite diverse in terms of structure, size, and function. Some of the common features of all of them are as follows:

  • All are comprised of single units linked together to create a chain. Similar to a freight train with many cars. All the monomers or single units contain carbon.
  • All monomers are linked together through a process known as dehydration synthesis, which literally means “building by removing water.”
  • All polymers are broken down by the same method called hydrolysis. Hydrolysis means “breaking with water.”

Carbohydrates, lipids, and even proteins can be metabolized for energy. ATP and related compounds are used as temporary energy storage vehicles. The comparative value of the common energy sources for cells is given below:

  • Carbohydrate  → 4 kcal/g
  • Fat → 9 kcal/g
  • Protein → 4 kcal/g

Importance of Water for Life

Water is the basis of life. There are various properties of water that make it basis of life. These include its molecular polarity, high specific heat, its boiling and melting points which allow it to remain liquid in most environments on Earth, its acid-base neutrality, small molecular size and low chemical reactivity.

Water as solvent

It serves as fundamental solvent for the chemical reactions in living organisms and is the main means of substance transportation between cells and tissues. It is responsible for correct temperature for life of an organism and is either regent or product of chemical reactions. All important macromolecules are produced by dehydration synthesis and broken down by hydrolysis.

Water in Human Body

Water makes around 65% of human body mass. It makes 90% of our brain, 85% of muscles and 25-40% of bones.  Children have a greater proportion of water in their body in comparison to elders.

1. Polarity of Water

In water, two hydrogen atoms are attached to one central atom of oxygen by covalent bond, making an angular spatial structure. Since the hydrogen atoms lend electrons to the oxygen; oxygen atom becomes more negative while the hydrogen atoms become more positive. The spatial geometry of water makes it thus a polar molecule with negative and positive poles. If a molecule is polar, it will be attracted to other polar molecules. This can affect a wide range of chemical interactions, including whether a substance will or will not dissolve in water, the shape of a protein, and the complex helical structure of DNA.

Water and working of a microwave Oven

Water is the most common example of a polar molecule and that is also the reason that when we put a potato in a paper plate in a microwave, potato gets hot but not the paper plate. If we put the potato in a wet paper plate, it would get cooked along with Potato.

The implication of water being a polar molecule is that it works as an excellent solvent for polar substances because the electrical activity (attraction and repulsion) of its poles helps in the separation and the mixing of these substances, giving them more movement and thus increasing the number of molecular collisions and the speed of chemical reactions. On the other hand, water is not a good solvent for non-polar substances.

Water Soluble and Fat Soluble Substances

Water-soluble substances are polar molecules, meaning that they have electrically charged areas. Fat-soluble substances are non-polar molecules, meaning that they are electrically neutral.

2. Role of Water for Enzyme Activity

There can be no enzyme activity without water. The enzymes need water and correct pH to do their job. The pH is result of release of hydrogen cations (H⁺) and hydroxyl anions (OH⁻) by the acids and bases in water solutions.

Significance of heat capacity of water

The specific heat of water is 1 cal/gram °C. This implies that there is 1°C per gram change in its temperature per every addition or subtraction of 1 cal of energy. This is a very high value (compare it with ethanol that has 0.58 cal/g°C, and mercury that has 0.033 cal/g°C). This feature of water makes it an excellent thermal protector against temperature variations. Even if there is a sudden external temperature change, the internal biological conditions are kept stable in organisms containing enough water.

Mineral Salts and Ions

Inorganic substances made of metallic elements such as iron, sodium, potassium, calcium and magnesium, or of non-metallic elements, such as chlorine and phosphorus. The mineral salts are found in two forms viz. solubilized ions (such as sodium and potassium ions in cells) or non-solubilized form such as calcium in our bones.

Cations and Anions

Ions are atoms or molecules that are electrically charged due to losing or gaining electrons {electrons are negatively charged as we all know}.

  • The cations are ions with positive charge. A cation is formed when a neutral atom or molecule loses electrons (gains positive charge). Important cations in our body are sodium (Na+), potassium (K+), calcium (Ca++), iron (Fe++, Fe+++), magnesium (Mg++), zinc (Zn++) and manganese (Mn++).
  • Anions are ions with negative electrical charge. An anion is formed when a neutral atom or molecule gains electrons (gains negative charge). Important anions in our body are chloride (Cl), phosphate (PO₄), bicarbonate (HCO₃), nitrate NO₃) and sulphate (SO₄).

Role of mineral salts in osmotic regulation

In our body, mineral salts along with glucose, proteins and urea are key substances for osmotic regulation. These molecules being inside or outside of the cell generate a larger or smaller osmotic gradient between intracellular and extracellular space.

Role of mineral salts in nervous system

The mineral salts play important role in the creation of electric voltage at cellular level. This cellular electric activity depends on the concentration of the cations and anions between inner and outer surfaces of the cell membrane. This is very important function which allows the neurons work.

Role of mineral salts in enzyme activity

pH regulation is very important because some enzymes work only under certain pH range. The mineral salts play important role pH regulation. Further, some minerals work as cofactors of enzymes and without them, enzymes cannot work.

1. Importance of Sodium

Sodium is a necessary ion in both plants and animals. In plants, it’s a micronutrient that aids in metabolism. It also serves as substitute for Magnesium for several functions in plants such as opening and closing of stomata. Excessive sodium in soil would result in lower water potential, reducing uptake of water from soil by plants.

In animals, Sodium is necessary for maintenance of electrolyte balance; fluid balance; generation of the nerve impulses, heart activity, blood volume, blood pressure, osmotic equilibrium, pH and many metabolic activities. In humans, table salt is the most important source of Sodium. A human needs half gram sodium every day, which can be obtained from 1.2 to 1.5 grams of table salt. However, generally we take more than that required amount. In excessive amount, salt would promote hypertension.

Hypernatremia, Hyponatremia and Thirst

In human body, the brain part hypothalamus and pituitary glands control the balance of sodium and water concentration in extracellular fluids. If a person loses too much body water, the sodium concentration in blood will rise higher than normal. The hypothalamus would sense it and would result in thirst. This condition is also known as Hypernatremia. On the other hand, if we drink lots of water, it would reduce concentration of sodium in blood, which is called Hyponatremia.  This would cause loss of water as urine. We note here that when a severally hydrated person is rescued from desert or ocean, he would have very high blood sodium concentration. This must be slowly and carefully treated because rapid correction of Hypernatremia can result in brain damage from cellular swelling.

2. Importance of Calcium

Calcium is present in almost all cells and plays important role in physiology and biochemistry in both plants and animals. In plants, Calcium and Potassium ions both work in tandem in the opening and closing of stomata. In some cases, Sodium can work in place of Potassium in case of deficiency of the later. Without Calcium, the mitotic spindle cannot form during cell division and thus needed for healthy plant growth. Further, Calcium ion is an essential component of cell walls and cell membranes. It is needed to stabilize the permeability of cell membranes. This is very important function in fruits where without Calcium; the cell walls would become weak and will not be able to hold the fruit content. Calcium is also stored in plants and provides some mechanical strength.

In animals and humans, Calcium plays important role in muscular contraction, blood coagulation, formation of bone tissue, teeth, motility of the sperm cells and transmission of the nerve impulses. Bones serve as storage site for Calcium and when needed, Calcium is released from Bones into blood. It remains in the blood as dissolved ion or bound to serum albumin. This function is controlled by Parathyroid gland and its parathyroid hormone.

3. Importance of Iodine

Iodine is needed for proper functioning of the thyroid. Iodine deficiency creates hypothyroidism also known as goitre.

4. Importance of Chloride

Like Sodium, chloride also actively participates in the osmotic regulation. Both sodium and chloride play important role in acid-base balance of an organism.


Carbohydrates are compounds of Carbon, Hydrogen and Oxygen and are known as Hydrates of Carbon. The common formula of all Carbohydrates is Cm(H2O)n, where m and n may be different values. However, Deoxyribose Sugar of DNA is an exception and its molecular formula is C5H10O4. Sugars, starch and cellulose are some of the common examples of Carbohydrates.


Carbohydrates are classified in several ways. Monosaccharides (single unit sugars) are grouped by the number of carbon molecules they contain: For example, triose has three pentose has five and hexose has six.  Carbohydrates are also classified by their overall length (monosaccharide, disaccharide or polysaccharide) or function.

  • Monosaccharides are simple carbohydrates molecules that cannot be broken down into smaller molecules of other carbohydrates. Glucose and fructose are examples of Monosaccharides.
  • Disaccharides are carbohydrates made up of two monosaccharides and which are missing one molecule of water (dehydration). The chemical bond between two monosaccharides is known as a glycosidic bond. Table sugar Sucrose is a disaccharide made of one molecule of glucose and one molecule of fructose. Maltose is also a disaccharide that consists of two glucose molecules. Lactose or milk sugar is another disaccharide made of one molecule of galactose and one molecule of glucose.
  • Oligosaccharides are carbohydrates made of maximum of 10 Monosaccharides.
  • Polysaccharides are polymers of monosaccharides made of more than 10 units. Common examples of polysaccharides are cellulose, starch, glycogen, chitin etc. Polysaccharides do structural and storage functions. Storage polysaccharides (glycogen and starch)  store energy while structural polysaccharides (cellulose and chitin) provide support for organisms without a bony skeleton

Hexose Sugars and Pentose Sugar examples

Hexose sugars are carbohydrates made of six carbon atoms. Glucose, fructose and galactose are all examples of hexose. Hexose sugars are energy sources for the metabolism.

Deoxyribose and Ribose sugars are fundamental components of DNA and RNA respectively. Both of these are pentose sugars.


Lipids refer to a group of molecules comprising fats, oils, phospholipids, waxes and steroids. All lipids are hydrophobic and don’t dissolve in water. However, they dissolve in organic solvents. The backbone of all lipid compounds is Glycerol or Glycerine. Glycerol is a sugar alcohol, made of a linear chain of three carbon atoms and three hydroxyl groups. It is soluble in water.

Hydrophobic and Hydrophilic molecules

Hydrophobic molecules are molecules which don’t dissolve in water (hydro = water, phobia = fear). Hydrophilic molecules dissolve in water (philia = friendship). Water is a polar substance. The thumb rule is that “equal dissolves equal”, so, hydrophobic substances are non-polar molecules whereas hydrophilic molecules are polar molecules. Fats and oils are hydrophobic molecules, meaning that they are non-polar and insoluble in water. Lipids in general are molecules with a large non-polar extension, making them soluble in non-polar solvents, such as benzene, ether and chloroform. There exist some amphipathic lipids (example Phospholipids) which are soluble in water as well as organic solvents.

Fats and Oils

The fats are triglycerides made of three molecules of fatty acids bound to one molecule of glycerol. Thus, fats are also known as triesters of glycerol. Fats are not soluble in water but soluble in organic solvents.


Phospholipids are molecules made up of one molecule of glycerol bound to two molecules of fatty acids and also one phosphate group. They are main components of the cell membranes. Phospholipids are amphipathic molecules, meaning that they have a non-polar portion, due to the long fatty acid chains, and a polar portion, due to the phosphate group. They dissolve in water as well as organic solvents.


Steroids are another class of lipids, which have a unique chemical structure. They are built from four carbon-laden fused ring structures.  Bile salts, cholesterol, the sexual hormones estrogen, progesterone and testosterone, corticosteroids and pro-vitamin D are examples of steroids. Their functions are as follows:

  • Aldosterone : Maintains water and salt balance by the kidney, controls blood pressure
  • Bile acids : Produced by the liver, help in the digestion of dietary lipids
  • Cholesterol : Provides stability and flexibility to cell membranes
  • Cortisone : Carbohydrate metabolism
  • HDL (high density lipoproteins) and LDL (low density lipoproteins): Lipid-protein combinations that transport lipids in the blood
  • Testosterone, estrogens, progesterone: Maintain sex characteristics. Allow reproduction to occur.

Saturated and Unsaturated Fats

In Saturated fats, the Carbon molecule is bound to as many hydrogen molecules as many it is possible. Thus, all C-C bonds in saturated fats are single bonds only. There are no double or triple bonds in saturated fats. Generally, saturated fats are solid at room temperature. Examples of saturated fat are ghee, cream, cheese, butter etc.

In unsaturated fats, double and triple C-C bonds are found, and thus there is a possibility of adding few more hydrogen atoms. Generally, unsaturated facts are liquid at room temperature. If there are more than carbon-carbon double / triple bonds present, such fat is called Poly Unsaturated Fatty Acid (PUFA). Examples of such PUFA include palmitoleic acid, oleic acid, myristoleic acid, linoleic acid, and arachidonic acid.

Hydrogenation: Converting Unsaturated Fat to Saturated Fat

The unsaturated fatty acids have double bonds, and therefore have fewer hydrogen atoms than maximum possible. The process of hydrogenation can convert an unsaturated fat into saturated fat by adding extra hydrogen atoms to it. Thus, hydrogenation converts liquid vegetable oils into solid or semi-solid fats. This reaction is the basis of Vegetable Oil industry and is achieved in the presence of some catalysts such as nickel, palladium or platinum metals. This method has prevented oxidation and thus rancidity and has allowed for the development of foods with less animal and saturated fats. However, the consumption of hydrogenated fatty acids increases risk of heart disease, because the fats cause a change in the structure of targeted unsaturated fatty acids. Kindly note that majority but not all  double / triple bonds broken during hydrogenation of unsaturated fats.  Hydrogenation may also result in creation of unsaturated fats with peculiar hydrogen atoms arrangement called “Trans Fats”.

Trans and Cis Fats

Cis and trans are terms that refer to the arrangement of the two hydrogen atoms bonded to the carbon atoms involved in a double bond in unsaturated fats. There are no cis or trans types in saturated fats because they have single bonds only.

In the cis arrangement, the hydrogen atoms are on the same side of the double bond. In the trans arrangement, the hydrogens are on opposite sides of the double bond.

We note here that most naturally occurring fats are Cis fats. Only a handful of naturally occurring fats are trans fats such as those found in milk and body fat of ruminants (such as cattle and sheep). Further, trans fats are generated during hydrogenation processing of polyunsaturated fatty acids in food production. They are outcome of the Partial Hydrogenation and not the complete Hydrogenation, because complete Hydrogenation would end the double bonds.

The process of hydrogenation adds hydrogen atoms to unsaturated fats, eliminating double bonds and making them into partially or completely saturated fats. However, partial hydrogenation, if it is chemical rather than enzymatic, converts a part of cis-isomers into trans-unsaturated fats instead of hydrogenating them completely.

Impacts of Trans fats on health

The consumption of trans fats has been shown to slightly increase the levels of bad cholesterol (LDL) in the blood. However, as per recommendations of the US National Academy of Sciences (NAS), trans fats are not essential and provide no known benefit to human health”, whether of animal or plant origin. While both saturated and trans fats increase bad cholesterol; the trans unsaturated fats also lower levels of good cholesterol. In this way, trans fats increase the risk of heart diseases.

Good Fats or Bad Fats

One thing is clear that no fats are “bad,” as fats are excellent sources of energy and help to maintain the health of the body. However, Fat is only bad if it is too much. There are several fats that are considered essential (the omega-6 and omega-3 fatty acids)-in other words, they are substances that our bodies require for maintenance but that we cannot manufacture. These are considered to be “good” fats. Comparatively, the fats we don’t need to ingest are often dubbed as “bad.”

Thermal Properties of Fats and Lipids

Fats are poor heat conductors and they also form thick layers of fatty tissue (called adipose tissue) when accumulated in an organism. This is the reason that they serve as good thermal insulators. In cold climate fauna such as polar bears, seals and whales, adipose tissue helps the maintenance of internal body temperature.

Fats as source of Energy

In carbohydrates are the main energy sources for aerobic cell respiration. However, when carbohydrates are absent or deficient, the body can use lipid (and also proteins) to break them and get energy.


Cholesterol refers to a subclass of lipids known as steroids. Cholesterol is also the molecule from which steroid hormones and bile acids are built.

Importance of Cholesterol

Cholesterol is a steroid of fat used to maintain the strength, permeability and flexibility of cell membranes. It also serves as a precursor for the biosynthesis of sex hormones, bile acids, and vitamin D.

Sources of Cholesterol

Cholesterol is predominantly synthesized in our body in Liver and also provided in food. Food also supplements Cholesterol. All foods containing animal fat contain cholesterol to varying extents. Major dietary sources of cholesterol include cheese, egg yolks, beef, pork, poultry, fish, and shrimp. Cholesterol is not found in significant amounts in plant sources. However, ingested cholesterol is esterified. This esterified cholesterol is poorly absorbed. That is the reason that cholesterol intake in food has little effect on total body cholesterol content or concentrations of cholesterol in the blood. In our body, Liver secretes it in a non-esterified form (via bile) into the digestive tract. Typically about 50% of the excreted cholesterol is reabsorbed by the small intestine back into the bloodstream.

Transport of Cholesterol in Lipoproteins

Cholesterol is only slightly soluble in water; it can dissolve and travel in the water-based bloodstream at exceedingly small concentrations. Since cholesterol is insoluble in blood, it is transported in the circulatory system within lipoproteins.

There are several types of lipoproteins in blood, called, in order of increasing density, chylomicrons, very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). The more lipid and less protein a lipoprotein has, the less dense it is.

Control of Cholesterol: Statins

Statins are a group of drugs that work to lower cholesterol Levels, particularly the “bad cholesterol”. Low-density lipoprotein known as LDL. The drugs work in two ways. First, they block an enzyme that is needed for cholesterol production. Second, they increase LDL membrane receptors in the liver.


Proteins are made up of chains of amino acids bound by bonds called peptide bond. There are some 22 different known amino acids which can compose proteins. There may be many more unknown to us.

Functional Versatility of Proteins

Numerous combinations of amino acids can form different polypeptide chains and thus a great variety of proteins can be produced. Consequently, proteins can take different configurations and thus play role in a lots of biological processes.  Thus, there are several types of Proteins which do specific functions as follows:

  • Defensive Proteins: Antibodies that respond to invasion
  • Enzymatic Protein: Increase the rate of reactions, build and breakdown molecules
  • Hormonal Proteins: Insulin and glucagon, which control blood sugar
  • Receptor Proteins: Cell surface molecules that cause cells to respond to signals
  • Storage Proteins: Store amino acids for use in metabolic processes
  • Structural Proteins: Major components of muscles. Skin, hair, horns etc.
  • Transportal Proteins: Haemoglobin carries oxygen from lungs to cells

Formation of Proteins

Amino acids are the basic units of proteins. There are 22 known amino acids and many more might be there unknown to us. Each amino acid has at least one carboxyl group –COOH, one amine group – NH₂ and an hydrogen atom –H. Further, there is a variable radical called -R. All of these are bound to a central carbon atom as shown below:

The R may be a complex chain of carbon atoms, or simply a methyl group or even a hydrogen atom. R is what distinguishes one amino acid from others. Two amino acids are bound by a peptide bond as mentioned above. The peptide bond is such that carboxyl group of one amino acid is connected to the nitrogen atom of the amine group of another amino acid. A molecule of water is released when such bond is established as shown below:

As shown above, many amino acids can bind through these peptide bonds and create linear chains. We note here that the same amount of amino acids can create different proteins because the difference depends on the types of amino acids or on the sequence in which they form the protein.

A chain of more than 50 peptide molecules is called Polypeptide. Proteins have very complex structural patterns of these polypeptides. They require up to four levels of structure in order to be functional. The four levels of Protein Structure are as follows:

  • Primary: Polypeptide chain of up to 500 amino acids covalently bonded. The sequence is important and unique for each polypeptide.
  • Secondary: The formation of hydrogen bonds between nearby amino acids causes the polypeptide chain to twist and/or pleat.
  • Tertiary: Distant amino acids form bonds and associations in reaction to changes that occur in the secondary level.
  • Quaternary: Two separate polypeptide chains intermingle to form a molecule that has a larger, more complex structure than that found in the other protein levels.

This structural complexity makes the proteins so versatile that relatively slight environmental changes cause a shift in structural levels that may be sufficient to radically change the function of the protein.

Further, the secondary, tertiary and quaternary structures of a protein are spatial structures. If there is any change in that spatial structure, the protein will denature and cease to do the function which it was supposed to do. This denaturation may or may not be reversible. The factors that cause such denaturation include change in temperature, change in pH, change in concentration of solutes in surrounding environment etc. This is the reason that organisms need to maintain stable internal temperature and pH so that proteins including enzymes etc. can do their normal jobs.

Cooking and Denaturation of protein

When we cook food, proteins become denatured. This is the reason that the boiled eggs become hard and cooked meat become firm. In an unboiled egg, the egg white is transparent and liquid. When its boiled or cooked, egg white turns opaque and solid mass.

Essential and Non-essential amino acids

Some 12 of the 22 known amino acids can be synthesized in our body. These are non-essential. Essential amino acids are those that the body is not able to synthesize and which need to be taken as diet. Examples of some of the essential amino acids are {don’t cram→} phenylalanine, histidine, isoleucine, lysine, methionine, threonine, tryptophane and valine.

Examples of Common Proteins

  • Myosin protein when bound to actin produces a muscle contraction.
  • CD4 is a membrane protein in some lymphocytes, the cells that are infected by HIV.
  • Albumin is an energy storage protein and also an important osmoregulator of blood.
  • Keratin is a protein with a structural function and which is present in the epidermis and skin appendages (hair, nails) of vertebrates.
  • Immunoglobulins are antibodies, specific proteins that attack and inactivate foreign agents that enter the body.
  • Reverse transcriptase is the enzyme protein responsible for the transcription of RNA and the formation of DNA in the life cycle of retroviruses.
  • Haemoglobin is the protein that carries oxygen from the lungs to cells.
  • Insulin is a hormone secreted by the pancreas that participates in the metabolism of glucose.


Enzymes are proteins that act as biological catalysts. They decrease the amount of energy needed (activation energy) to start a metabolic reaction. Without enzymes, organisms are not being able to harvest energy and nutrients from food. One common example is the Lactose intolerance. Lactose intolerance is the inability to produce lactase, the enzyme that breaks down milk sugar (lactose).

Functions of Enzymes

Enzymatic reactions can build up or break down specific molecules. The specific molecule an enzyme works on is the substrate. In the function of the Enzyme, Shape is very critical. We note that enzymes are complex proteins with specific three dimensional spatial shapes. The “active site” of an enzyme is the area where substrate binds and the reaction takes place. How an enzyme reacts with its substrate is similar to how a lock and key work. There are minor bonds that form between the enzyme and substrate until locking and unlocking is done.

Anything affecting the shape of the key would make the key unable to lock and unlock.

Naming of Enzymes

The naming of the enzymes is peculiar. Individual enzymes are named by adding the suffix “ase” to the name of the substrate with which the enzyme reacts. For example enzyme amylase controls the breakdown of amylose (starch), hydrolases control hydrolytic reactions; proteinases control protein breakdown; synthetases control synthesis reactions. However, some enzymes retain their name from older system when this ‘ase’ nomenclature was not adopted. Examples are trypsin and pepsin, both digestive enzymes that breakdown protein.

Applications of Enzymes

Enzymes are used in the chemical industry and other industrial applications when extremely specific catalysts are require. For example:

  • Amylases from fungi and plants are used in Food Processing Industry. For Instance, production of sugars from starch, such as in making high-fructose corn syrup.
  • Proteases are used by the biscuit manufacturers to lower the protein level of flour.
  • Trypsin enzyme is used in the making of Baby Foods
  • Several enzymes are used in making wines and whiskeys. Enzymes from barley are released during the mashing stage of beer production.
  • Cellulases, pectinases are used in packing juices; they help to clear the cellulose from juice.
  • Rennin, derived from the stomachs of young ruminant animals (like calves and lambs) are used in the dairy industry to produce Cheese.
  • Papain obtained from Papaya is used as a softener in meat cooking.
  • Amylases, Xylanases, Cellulases and ligninases are used in Paper Industry.
  • A class of drugs called protease inhibitors are powerful HIV-fighting medications Protease inhibitors prevent T-cells that have been infected with HIV from making new copies of the virus.

Enzymes and pH

Since changes in temperature and pH can cause the structure of a protein to change, every enzyme has criteria that must be met in order for it to perform its function. For example, the amylase that is active in the mouth cannot function in the acidic environment of the stomach; pepsin, which breaks down proteins in the stomach, cannot function in the mouth.

Spinach TNT and Enzymes

TNT is a dangerous explosive. Spinach contains a powerful enzyme called nitro-reductase that is able to neutralize TNT by converting it to other compounds that are less dangerous. Through additional reactions, these less-harmful compounds can be converted to carbon dioxide gas.

Enzyme cofactors

Few enzymes need other associated molecules to do their job properly. These molecules are called enzyme cofactors. They can be organic ions like mineral salts, or organic molecules, or Vitamins. Inactive enzymes which are not bound to their cofactors are called apoenzymes. Active enzymes bound to their cofactors are called holoenzymes.

Use of Enzyme Inhibitors in Health Science

Substances that “simulate” substrates can bind to the activation center of enzymes, thus blocking the true substrates from binding to these enzymes and paralyzing the enzymatic reaction. These “fake substrates” are called enzyme inhibitors. Many Pharma drugs such as some antibiotics are enzyme inhibitors that block enzyme activity. We note here that Penicillin {first antibiotic discovered} inhibits the enzymes necessary for the synthesis of peptidoglycans, a component of the bacterial cell wall. Using this would block growth of the bacteria and this is what won Nobel Prize for Alexander Fleming for discovery of penicillin. Similarly, some antiretroviral drugs called “protease inhibitors” are used against HIV infection. Protease is an enzyme necessary for the construction of the  human immunodeficiency virus (HIV) after the synthesis of its proteins within the host cell. The protease inhibitor binds to the activation center of the enzyme blocking the formation of the enzyme-substrate complex and enzyme activity, thus stopping viral replication.

Nucleic Acids

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are nucleic acids. Nucleic acids are molecules comprised of monomers known as nucleotides. These molecules may be relatively small (as in the case of certain kinds of RNA) or quite large (a single DNA strand may have millions of monomer units) individual nucleotides and their derivatives are important in living organisms. ATP, the molecule that transfers energy in cells is built from a nucleotide as are a number of other molecules crucial to metabolism.

DNA and RNA molecules are responsible for hereditary information that controls the protein synthesis in living organisms. They are called nucleic acids because they were first discovered within the nucleus of the cell by a Swiss biochemist Friedrich Miescher.

Location of DNA and RNA

In prokaryotic cells, DNA and RNA are found dispersed in the cytosol, the fluid space inside the cell. In eukaryotic cells, DNA and RNA are found within the cell nucleus and also in mitochondria and chloroplats. Further, RNA is also the main component of nucleolus and ribosome in eukaryotic cells.

Composition of DNA and RNA

Both DNA and RNA are formed by sequences of nucleotides. A Nucleotide is made of one molecule of a pentose sugar (Deoxyribose in DNA and Ribose in RNA) bound to one molecule of phosphate and to one nitrogenous base.

While remaining things are same, the nitrogenous bases are of five types viz. Adenine (A), Guanine (G), Cytosine (C), Thymine (T) and Uracil (U).

Out of them, adenine and guanine are called Purines (because they have fused ringed structure), while cytosine, thymine and uracil are called Pyrimidines (because they have single ring structure). Further, while both DNA and RNA consist of adenine, guanine and cytosine; thymine is only found in DNA and uracil in RNA. This is shown in below image:

The nucleotides are joined together supported by the backbone of the sugar and phosphate. These nucleotide chains are long and may be either single stranded, or single stranded folded onto itself or double stranded. Whenever the strand folds onto itself or two strands come together for making a double stranded structure, the nucleotides are joined together with hydrogen bond between nitrogenous bases. This is called base pairing. The rule of base pairing is such that:

  • In DNA, Adenine links to thymine (A-T) while cytosine links to guanine (C-G).
  • In RNA, Adenine links to uracil (A-U) and cytosine links to guanine (C-G).

The RNA is either single stranded or a single strand folded onto itself. Its structure would look something like this:

However, DNA is double helix in its structure. The double helix structure of DNA was discovered by Watson, Crick and Wilkins.

Different Functions of DNA and RNA

DNA contains the genetic instructions used in the development and functioning of all known living organisms. It is a medium of long-term storage and transmission of genetic information. On the other hand, RNA plays an important role in the process of translating genetic information stored in DNA into protein products. In other words, DNA is the boss who has all instructions. RNA is his assistant who takes blueprint (via a process called transcription) to produce different proteins from him and then plugs it into cellular machines called ribosome. Ribosomes are the sites of protein synthesis.

How DNA and RNA Work?

As discussed above, DNA is the hereditary material that contains the genetic code for long term storage. RNA takes that blueprint from DNA via transcription and plugs that blueprint in protein factories called Ribosomes. The ribosomes produce required protein in a process called translation. There are three types of RNAs viz. ribosomal RNA (rRNA), messenger RNA (mRNA), and transfer RNA (tRNA). All of them originate from DNA itself as copy of one the strands of DNA. The resultant RNA has same sequence as the other strand of DNA, except that uracil will replace thymine. The ribosomal RNA is the structural component of  the protein making factories (Ribosomes). Messenger RNA carries the genetic message from DNA to Ribosome. Transfer RNA is the smallest of three types and it carries amino acids to Ribosomes during translation process. This entire process is called Central Dogma in biology.

Vitamins and Minerals

Vitamin is an organic non-protein substance that is required by an organism for normal metabolic function but cannot be synthesized in sufficient quantity by that organism. In other words, vitamins are crucial molecules that must be acquired from outside sources. While most vitamins are present in food, vitamin D for example, is produced as a precursor in our skin and converted to the active form by sunlight.

Vitamins are classified by their biological and chemical activity, not their structure. Thus, each “vitamin” refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals is grouped under an alphabetized vitamin “generic descriptor” title, such as “Vitamin A”, which includes the compounds retinal, retinol, and four known carotenoids.

Vitamin ARetinol, retinal, and four carotenoidsFatNight-blindness, Hyperkeratosis, and KeratomalaciaOrange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, liver
Vitamin B1ThiamineWaterBeriberi, Wernicke-Korsakoff syndromePork, oatmeal, brown rice, vegetables, potatoes, liver, eggs
Vitamin B2RiboflavinWaterAriboflavinosisDairy products, bananas, popcorn, green beans, asparagus
Vitamin B3Niacin, niacinamideWaterPellagraMeat, fish, eggs, many vegetables, mushrooms, tree nuts
Vitamin B5Pantothenic acidWaterParesthesiaMeat, broccoli, avocados
Vitamin B6Pyridoxine, pyridoxamine, pyridoxalWaterAnaemia peripheral neuropathy.Meat, vegetables, tree nuts, bananas
Vitamin B7BiotinWaterDermatitis, enteritisRaw egg yolk, liver, peanuts, certain vegetables
Vitamin B9Folic acid, folinic acidWaterMegaloblast and Deficiency during pregnancy is associated with birth defects, such asneural tube defectsLeafy vegetables, pasta, bread, cereal, liver
Vitamin B12Cyanocobalamin, hydroxycobalamin, methylcobalaminWaterMegaloblastic anaemiaMeat and other animal products
Vitamin CAscorbic acidWaterScurvyMany fruits and vegetables, liver
Vitamin DCholecalciferolFatRickets and OsteomalaciaFish, eggs, liver, mushrooms
Vitamin ETocopherols, tocotrienolsFatDeficiency is very rare; mild hemolytic anemia in newborn infants.Many fruits and vegetables, nuts and seeds
Vitamin Kphylloquinone, menaquinonesFatBleeding diathesisLeafy green vegetables such as spinach, egg yolks, liver

Important Facts on Vitamins

Vitamin A (Retinol)

Vitamin A is required in the production of rhodopsin, the visual pigment used in low light levels. This is why eating foods rich in vitamin A is often said to allow an individual to see in the dark, although the effect they have on one’s vision is negligible.

Vitamin A is also essential for the correct functioning of epithelial cells. In vitamin A deficiency, mucus-secreting cells are replaced by keratin producing cells, leading to xerosis.

Vitamin B (Thiamine)

Vitamine B (Thiamine) deficiency produces beriberi, Wernicke-Korsakoff syndrome, and optic neuropathy.

Beriberi is a neurological and cardiovascular disease. The three major forms of the disorder are dry beriberi, wet beriberi, and infantile beriberi. Dry beriberi is characterized principally by muscular dysfunctions, while Wet beriberi is associated with mental confusion, muscular atrophy, edema. Infantile beriberi occurs in infants breast-fed by thiamin-deficient mothers.

Vitamin C (Ascorbic Acid)

Ascorbic acid is found in plants and animals where it is produced from glucose.  Humans are unable to make ascorbic acid. This Vitamin is also an antioxidant and antioxidant properties of ascorbic acid are only a small part of its effective vitamin activity.

Vitamin D (Calciferol)

Calciferol is not actually an essential dietary vitamin in the strict sense, as it can be synthesized in adequate amounts by most mammals exposed to sunlight.

Vitamin E (Tocopherol)

Vitamin E is a series of organic compounds consisting of various methylated phenols. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was given the name “tocopherol” or birth carrying vitamin.

There are eight forms of Vitamin E. In general, food sources with the highest concentrations of vitamin E are vegetable oils, followed by nuts and seeds including whole grains. The highest sources of Tocoferol are Wheat germ oil (215.4 mg), Sunflower oil (55.8 mg), Almond oil (39.2 mg), Sunflower seed (35.17 mg) and Almond (26.2 mg).

Vitamin E deficiency causes neurological problems due to poor nerve conduction. It has been linked to Age-related macular degeneration (AMD), Alzheimer’s disease. Vitamin E is widely used as an inexpensive antioxidant in cosmetics and foods. Vitamin E containing products are commonly used in the belief that vitamin E is good for the skin; many cosmetics include it. The function is mainly associated with Vitamin E being a powerful antioxidant. It also plays important role in skin health.

Vitamin K1 (Phylloquinone)

Phylloquinone is an electron acceptor during photosynthesis. Its best-known function in animals is as a cofactor in the formation of coagulation factors II (prothrombin), VII, IX, and X by the liver.  It found in highest amounts in green leafy vegetables because it is directly involved in photosynthesis. It may be thought of as the “plant form” of vitamin K.

Vitamin K2 (menaquinone)

It may be thought of as the “animal form” of vitamin K. Bacteria in the colon (large intestine) can also convert K1 into vitamin K2.

Vitamin B5 (Pantothenic acid)

Animals require pantothenic acid to synthesize coenzyme-A (CoA), as well as to synthesize and metabolize proteins, carbohydrates, and fats.

Vitamin B7 (Biotin)

Biotin is a coenzyme for carboxylase enzymes, involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis. It is also known as Vitamin H. Biotin deficiency is rare and mild, and can be addressed with supplementation.

It is caused by the consumption of raw egg whites (two or more daily for several months) due the avidin they contain, a protein which binds extremely strongly with biotin, making it unavailable. The defecinecy causes hairloss and skin problems mainly.

Vitamin B6 (Pyridoxine)

Pyridoxine assists in the balancing of sodium and potassium as well as promoting red blood cell production. It is linked to cardiovascular health by decreasing the formation of homocysteine.

Pyridoxine may help balance hormonal changes in women and aid the immune system. Lack of pyridoxine may cause anemia, nerve damage, seizures, skin problems, and sores in the mouth.

Vitamin B3 (Niacin)

It is also known as nicotinic acid and vitamin PP. Niacin is used to increase levels of HDL in the blood and has been found to modestly decrease the risk of cardiovascular events in a number of controlled human trials.

Vitamin B9 (Folic acid)

Also known as Vitamin M and Folate, Vitamin B9 is essential to numerous bodily functions. The human body needs folate in DNA synthesis and repair. It is also important in cell division and growth during pregnancy. Children and adults both require folic acid to produce healthy red blood cells and prevent anaemia. Deficiency can result in many health problems, the most notable one being neural tube defects in developing embryos.

Pandemic deficiency diseases

Deficiency diseases of five vitamins are called Pandemic deficiency diseases. These include:

Niacin Deficiency (Pellagra)

Vitamin C Deficiency (Scurvy)

Thiamine Deficiency (Beriberi)

Vitamin D Deficiency (Rickets)

Vitamin A Deficiency (Night Blindness)

Cell Biology

A cell is a functional basic unit of life discovered by Robert Hooke in Cork cells and is the smallest unit of life that is classified as a living thing, and is often called the building block of life. In the beginning of the 18th century, Antonie van Leeuwenhoek, a Dutch tradesman and scientist built a microscope and drew the protozoa from rainwater and bacteria from his own mouth. He is known as the “Father of Microbiology”.

In 1665 Robert Hooke discovered cells in cork, then in living plant tissue using an early microscope. He was the first person to use the term “cell”.

Largest and smallest cells

The organisms which have a single cell are unicellular and the organisms that have multiple cells are multicellular.  There are 1 trillion cells is a human body. The size of a typical cell is 10 micrometer and largest cells in human body are nerve cells called neurons. The largest known cells are unfertilized ostrich egg cells which weigh 3.3 pounds. Pleuropneumonia-Like Organisms (PPLO) which are now known as Mycoplasma are the smallest cells.

Cell Theory

Cell Theory was proposed by Scheilden and Schwann and this theory stated that:

  • The body of all organisms is made up of cells
  • New cells arise from the pre existing cells
  • Cells are structural units of all organisms
  • Cells are units of all biological functions.

Before the discovery of the cell, people were unaware that living organisms were made of building blocks like cells.

Prokaryotic and Eukaryotic cells

Prokaryotic cells are primitive cells in which there is no enclosed nucleus. Eukaryotic cells are those with a nucleus enclosed by a membrane. Bacteria and blue green algae are examples of prokaryotic cells. Algae, plants and animal cells are eukaryotic cells.

Cell Components

Cell Membrane / Plasma Membrane

The cell membrane or plasma membrane is the outer membrane of a cell.  Cell membrane is found around all cells and is selectively-permeable. Cell membrane encloses the cell itself, maintaining specific conditions for cellular function within the cell.

It controls the movement of substances in and out of cells. Main function of cell membrane is to protect the intracellular components from the extracellular environment. The cell membrane facilitates the transport of materials needed for survival. The movement of substances across the membrane can be active (with use of energy) or passive (diffusion without use of energy). Exocytosis and endocytosis are the processes by which the materials are taken in or out of a cell.  The cell membrane plays an important role in the respiration and electron transport chains.

Cell wall

Cell walls are found in plants, fungi and prokaryotic cells. They work like a bulwark or a pressure vessel, preventing over-expansion when water enters the cell. Cell walls are absent in animals and protozoa.

  • Major components of the cell wall in plants are Cellulose, hemicelluloses and pectin. In the industrial uses, the cellulose is mainly obtained from wood pulp and cotton and used to produce the textiles and paper.
  • Cell walls of Fungi are made of Chitin. Chitin is the same substance that makes the exoskeleton of arthropods (insects etc.)
  • The cell walls of diatoms are composed of silicic acid.
  • The Bacterial cell walls are made of peptidoglycan which is also called murein.


Nucleus is the master of a cell. It controls the cell functions such as metabolism, reproduction and development. It consists of Nuclear membrane, Nucleoplasm, Nucleolus and Chromatin. Kindly note that Mammalian red blood cells have no nucleus.

1. Nuclear Membrane

The nuclear membrane is a double membrane and the space between the two membranes is called pronuclear space. The outer membrane is continuous with the endoplasmic reticulum which indicates its firm position in the cell. During the cell division the membrane disintegrates and reappears once the division is almost complete.

2. Nucleoplasm

Nucleoplasm is a transparent and gel like matrix. It contains the nucleolus, chromatin threads and Ribosomes.

3. Nucleolus

Nucleolus also disappears in the later phase of cell division and reappears once the process is almost complete. It is made of RNA and protein and is the site of RNA synthesis.

4. Chromatin

Chromatin, dispersed in the nucleus, is a set of filamentous DNA molecules attached to nuclear proteins called histones. Each DNA filament is a double helix of DNA and therefore a chromosome.

The Cytoplasm

Part of a cell that is enclosed within the cell membrane except the nucleus is cytoplasm. Cytoplasm contains organelles, such as mitochondria, Golgi bodies, Endoplasmic reticulum, Plastids etc. Cytoplasm is the site where most cellular activities occur, such as metabolism, glycolysis, cell division, protein synthesis etc.  It is divided into two parts, the inner, granular mass is called the endoplasm and the outer, clear and glassy layer is called the cell cortex or the ectoplasm. The cell membrane is the outermost layer of the cytoplasm.

Major Cell Organelles

There are two kinds of organelles in the cytoplasm viz. living and non living. The living organelles include the Plastids, Mitochondria, Endoplasmic reticulum, Golgi Bodies, Ribosome, lysosomes, Micro bodies such as peroxisomes, Microtubules, Centrosomes, Cilia and Flagella. The nonliving substances, called ergastic substances include the reserve products such as carbohydrates Fats, Oils and nitrogenous substances, Secretary products such as pigments, enzymes and nectar and execratory products such as tannins, resins, latex, alkaloids, essential oils, mineral crystals etc.


Plastids are major organelles found in the cells of plants and algae. The term plastid was used by Schimper for the first time. Major function of the plastids includes photosynthesis, storage of products like starch. They are of 3 types:

  • Leucoplasts: Colorless plastids,
  • Chloroplasts: Green plastids.
  • Chromoplasts: Colored plastids.

The plastids are of various shapes and have the ability interchange between the above forms & and many shapes. For example due to continuous absence of the sunlight the green chloroplast may turn to colourless leucoplasts.  In tomato, when it ripes, the chloroplasts change into Chromoplasts and this turns the color of tomato from green to red.

The leucoplasts don’t have any color. So they have no role in photosynthesis. Their major function is of storing. On the basis of the stored material they have been divided into 3 types viz. Amyloplats (which store the carbohydrates), Elaioplasts (which store the fats) and Aleuroplats (which store proteins).

Chloroplasts have a green pigment in them called Chlorophyll. They are responsible for photosynthesis. The number, shape and size of the chloroplasts vary from plants to plants. In higher plants they are biconvex in shape.

Each chloroplast is covered by a double membrane envelope. This envelope is made up of lipoproteins. The space between these two membranes is called periplastidial space. Inside these membranes are located the membrane-bound compartment called thylakoid which is basically a sac. This sac has stacks of disks referred to as “grana”, (singular: granum). Each grana is connected to other grana by intergrana or stroma thylakoid. The space enclosed by a thylakoid is called lumen. All lumens are collectively called thylakoid space. Each chloroplast has 40-60 grana. The inner side of the thylakoid membrane has some particles which are called quantasomes. Each quantasome has around 230-250 chlorophyll pigments.

Why Chlorophyll is green?

The chlorophyll absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. But it is a poor absorber of green and near-green portions of the spectrum, hence the color of the tissues which contain chlorophyll is Green. The chlorophyll was first isolated by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817.

What are Carotenoids and how they are related to Vitamin A?

There are two types of pigments Chlorophyll a and Chlorophyll b. Apart from these pigments, there are Carotenoids occurring in the chloroplasts and Chromoplasts. These Carotenoids are responsible for different colours. There are more than 600 known Carotenoids. Among them the most important are carotenes and Xanthophylls.  Carotenes are pure hydrocarbons, means they are basically made up of Carbon and Hydrogen. The Xanthophylls have oxygen too.

The Carotenoids absorb blue light of the spectrum generally.

Absorption of blue light serves a major purpose and that is they save the chloroplasts from the photo damage.

  • Most fruits have Carotenoids. The Beta carotene is one example which gets converted into Vitamin A.
  • Beta carotene is the precursor of Vitamin A.
  • Vitamin A occurs in many forms. One form of Vitamin A is retinal, which is vitamin A aldehyde. The four kinds of Carotenoids viz. beta-carotene, alpha-carotene, gamma-carotene, and beta-cryptoxanthin can be converted in human beings in retinal.
  • This retinal form of Vitamin A is a Chromophore and is responsible for its color, it absorbs certain wavelengths of visible light and transmits or reflects others.
  • Retinal binds to some proteins called Opsins in the Eye’s retina. This Vitamin A + Opsins bond is the chemical basis of vision.

The Carotenoids also get converted to another type of Vitamin A called Retinol. Retinol is fat-soluble vitamin important in vision and bone growth. All Retinol, retinal (aldehyde form), retinoic acid (acid form) and retinyl esters (ester forms) are converted from the carotenes and thus important for Human vision.


Mitochondria (singular: mitochondrion) are the power houses of the cells. They were discovered by Fleming; however the term was used by Benda & Meeves. Another name for mitochondria is Chondriosomes. They are absent in Prokaryotic cells.

Since they are the “Power houses of the Cells” the number of mitochondria in cells is directly proportional to the metabolic activity of the cells. This means that the more active a cells is metabolically, more is the number of mitochondria in that cell. This is the reason that number of mitochondria is maximum in muscular cells.

The shape of the mitochondria may be spherical, filamentous or even rod shaped. Like the chloroplasts, they are also bound by double unit membranes.  The space between these two membranes is called perimitochondrial space. The liquid inside these membranes is called matrix. The matrix contains the enzymes. Apart from the enzymes matrix contains ribosomes, double stranded DNA and RNA.

Due to presence of double stranded DNA along with the RNA and Ribosome, the mitochondria are called semiautonomous structures. Both chloroplasts and mitochondria are semiautonomous structures.

Role of Mitochondria in Krebs cycle

Mitochondria are the sites of oxidation of food material. This oxidation is called aerobic respiration. It is carried out by Krebs cycle or TCA cycle. The Krebs cycle is also known as Citric Acid Cycle and is basically a series of enzyme-catalyzed chemical reactions.  The raw material in the Krebs cycle is carbohydrates, fats and proteins and the final products are Carbon Dioxide and Water and Energy.  The usable energy which is produced by the Krebs cycle is in the form of ATP which is Adenosine triphosphate.  The correct name of ATP is Adenosine-5′-triphosphate.

Endoplasmic Reticulum

The interconnected network of tubules, vesicles, and cisternae within cells is called “Endoplasmic reticulum”. The term was coined by Keith R. Porter in 1945. The tubules are narrow long structures, vesicles are round structures and cisternae are long, flat unbranched structures which are parallel to each   other. They are of two types, Rough endoplasmic reticulum (appears rough because it has ribosomes on it) which synthesize proteins and the smooth endoplasmic reticulum which synthesize lipids and steroids, metabolize carbohydrates and steroids, and regulate calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins.

Another function of the endoplasmic reticulum is that it provides the mechanical support to the cytoplasm and provides larger surface area for exchange of materials and transportation.

During the cell division, the endoplasmic reticulum organizes the nuclear envelope at the telophase stage of cell division.

Golgi Apparatus

These are named after Camillo Golgi who identified them in 1898. The size of the Golgi body changes as per the metabolic activity of the cells and they are bigger in young cells and metabolically active cells. Function of the Golgi apparatus is to process and package proteins, polysaccharides and lipids. During the cell division they provide a cell plate. At the end of the cell division (telophase) the Golgi vesicles fuse and make the new plasma membrane.  The Lysosomes which digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria etc. are formed by the Golgi body. Golgi Bodies, unlike the Chloroplasts and Mitochondria are bound by the single membranes.


Lysosomes are very small sacs with irregular shapes. These are bags of Hydrolytic or digestive enzymes and so also called Suicide Bags. The major function is the autolysis of a cell by release of the enzymes within the cells. It also helps in the intracellular digestion of dead, injured or defective cells. Intracellular digestion of the material taken from the endocytosis.


Ribosomes were discovered by Palade in 1955. They are not enclosed by any unit membrane. They are made up of RNA and proteins.


These are also sac like structures bound with single membranes. They have enzymes and take part in the metabolism of fatty acids, respiration and many other metabolic processes.


They are mainly found in plants particularly in plants the fat storage tissues of germinating seeds such as castor seed. The major function is in the conversion of the fatty acids in Carbohydrates.


Spherosomes are present in the endosperm and cotyledons of seeds. They have the enzymes which are necessary in synthesis of oils and fats.


Centrioles are present in animal cells mostly and not in higher plants. They organize the spindle fibers in cell division.

Cilia and Flagella

Both Cilia and Flagella are present in the motile cells. Both help in cell mobility. Both are made up of fibrils. When they cut in a section, they show 9+2 arrangement which shows that they have 9 pairs of fibrils on the circumference and 2 pairs of fibrils at the centre.

Prokaryotic and Eukaryotic cells

There are two groups of cells. All cells are either prokaryotic or eukaryotic. Prokaryotic cells are primitive and don’t possess a well defined nucleus. Eukaryotic cells have a nucleus.

DifferenceProkaryotic CellsEukaryotic cells
ChromosomesNo true chromosomes are found. Chromosomal material is called PlasmidTrue chromosomes are present.
Cell TypeGenerally unicellular, some blue green algae are multicellular.Generally multicellular
Sexual ReproductionAbsent. Only Genetic recombination is found.Present through meiosis.
Cell organellesMitochondria, Chloroplasts, Golgi Bodies, Lysosomes, Endoplasmic reticulum and Peroxisomes are absentThese are Present
ChlorophyllSince there is no chloroplast, the chlorophyll scattered in the cytoplasmPresent in Chloroplast
Cell size1-10um (smaller)10-100um (Large and larger)
ExamplesBacteria and Blue green algaeAnimal and Plant cells

In prokaryotic cells DNA material remains scattered in the Cytoplasm only. Further, same compartment is used in the Prokaryotic cells for synthesis of RNA and protein while in the Eukaryotic cells the RNA is synthesized in the Nucleus while the protein in the cytoplasm. There is no sexual reproduction in Prokaryotic cells and only genetic recombination is present in the name of sexual reproduction while in eukaryotic cells, the true sexual reproduction is present.

Difference between Plant cells and Animal cells

The animal cells don’t contain the cell wall and the outer boundary of the animal cells is cell membrane. In Plant cells the cell wall is present which is made up of mostly cellulose, is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism.

In bacteria the cell wall is made of peptidoglycan. There are no plastids in animal cells. There is no photosynthesis in animal cells. Cytokinesis which is a process by which cytoplasm of a single eukaryotic cell is divided to form two daughter cells, is by equatorial furrowing from periphery to the centre in animal cells and by disk formation in plant cells.

In animal cells the ribosome are of 55S and 80S types while in the plant cells they are of 70s and 80S types.

Cell Division

The cell division is of two types viz. Mitosis and Meiosis.


In mitosis the mother cell divides into two daughter cells which are genetically identical to each other and to the parent cell. In mitosis:

  • The number of the Chromosomes in Parent and daughter cells remains constant
  • The parent and daughter cells are similar in all respects.
  • The parent and daughter cells are genetically identical
  • The purpose of Mitosis is growth by increasing number of cells.
  • In most plants and animals the regeneration of the lost parts and vegetative propagation in some plant species takes place by Mitosis.

In Meiosis, the number of chromosomes is divided into half in this process.  Meiosis is required to create the Gametes in animals and Spores in other organisms. Meiosis is a prerequisite for sexual reproduction in organisms with Eukaryotic cells.

5. Significance of Meiosis

The cell division in the reproductive cells takes place by Meiosis. In meiosis the number of the chromosomes is reduced to half of that in the parent cells.  Meiosis maintains the number of Chromosomes constant in all sexually reproducing organisms.

Programmed cell death

Apoptosis, or programmed cell death is a process by which cells deliberately destroy themselves. The process follows a sequence of events controlled by nuclear genes. In this process, the chromosomal DNA breaks into fragments, and this is followed by breakdown of the nucleus. The cell then shrinks and breaks up into vesicles that are phagocytosed by macrophages and neighbouring cells.

Significance of Apoptosis

Apoptosis plays an important role in maintaining the life and health of organisms. During human embryonic development apoptosis removes the webbing between the fingers and toes; it is also vital to the development and organization of both the immune and nervous systems.

How cells become Cancerous?

Cancer is caused by the unrestrained growth of cells. Cells that do not “follow the rules” of normal cell cycling may eventually become cancerous. This means that the cells reproduce more often than normal, creating tumors. Usually this happens over an extended period of time and begins with changes at the molecular level. Our body has trillions of cells and all cells replicate in normal fashion. However, some agents may change the way genes carry the information regarding the cell division and thus cells become cancerous. Such genes are called Oncogenes and such agents are called Carcinogens.

In normal cells, there are have types of genes that are important in determining whether or not cancerous tissue can form. These genes control the production of proteins that affect the cell cycle. Proto-oncogenes are DNA sequences that promote normal cell division. By mutation, these genes may be converted into oncogenes, which promote the overproduction of cells. Another class of genes, known as tumor-suppressor genes prevents excess reproduction of cells. Mutation in these genes can also allow cells to become cancerous.

How Cyanide kills cells?

Cyanide acts by inhibiting the enzymes cells need for oxygen utilization. Without these enzymes, a cell cannot produce ATP and will die. Very small amounts of cyanide naturally occur in some foods and plants. For example. cyanide is present in cigarettes and in the smoke produced by burning plastics.

How carbon monoxide kills people using heating appliances using fossil Fuels?

Because of its molecular similarity to oxygen, haemoglobin can bind to carbon monoxide instead of oxygen, and this subsequently disrupts haemoglobin’s efficiency as an oxygen carrier. Carbon monoxide in fact has a much greater affinity (about 300 times more!) for haemoglobin than oxygen. When carbon monoxide replaces oxygen, this causes cell respiration to stop, leading to death. The particular danger of carbon monoxide poisoning lies in the fact that a person exposed to high levels of this toxin cannot be saved by being transporting to an environment free of the poison and rich with oxygen. Since the haemoglobin remains blocked, artificial respiration with over pressurized pure oxygen must first be performed to return the haemoglobin to its original function and the body to normal cell respiration.

What is impact of Coffee on Cellular level?

Caffeine affects cells by stimulating lipid metabolism and slowing the use of glycogen as an energy source. As a whole, the body responds to caffeine by extending endurance, allowing us to stay awake for longer periods of time or perform extra activities. Adverse effects of excess caffeine intake include stomach upset, headaches, irritability, and diarrhoea.

General Science-2: Plant Kingdom

Prelims MCQ Topics

Common Plant Viral Diseases, Common Human Viral Diseases, Meaning of H and N in Influenza Virus, Difference between Hepatitis A, B and C, HIV and AIDS, Difference between Dengue and Chikungunya, Viral encephalitis and Japanese encephalitis, Industrial and Scientific Applications of Viruses. Gram Positive and Gram Negative Bacteria, Pasteurization, Biological Nitrogen Fixation, Bacteria in Industry and Everyday Life, Bacterial Diseases, MDR and XDR TB, Various uses of Fungi; Various uses and Hazards of Algae, Common Bryophytes, Pteridophytes and Gymnosperms, Angiosperms basic features, Double Fertilization, Types of Pollination, Monocots and Dicots, Roots and root modifications, Stem and Stem Modifications; Types of Leaves, Types of Fruits and examples; Dendrochronolgy, Xylem and Phloem-their use in plant life; Photosynthesis and Plant Hormones

Biological Classification

When we classify the organisms into hierarchical series of groups on the basis of their evolutionary relationships, it is called Systematics. Classification is a subtopic of Systematics which deals with ordering of organisms into groups and taxonomy is the study of principles and procedures of classification. Nomenclature is the process of naming an organism so that this particular organism is known by same name all over the world. Currently, the scientists follow binomial nomenclature in which any organism is denotes by a name with two components viz. Genus and Species. For example, Mango is named as Mangifera indica, whereby, Mangifera is its Genus and indica is its species. While first letter of Genus is always capitalized, first letter of species is always in lower case. For example:

  • Tomato → Solanum lycopersicum
  • Potato → Solanum tuberosum
  • Brinjal →Solanum melongena

In the above example, Tomato, Potato and Brinjal belong to same genus while they are different species. We note here that for plants, scientific names are based on agreed principles and criteria, which are provided in International code for Botanical Nomenclature (ICBN). Animal taxonomists have evolved International Code of Zoological Nomenclature (ICZN).

Taxonomical Hierarchy

Species is the smallest taxonomical unit and refers to a group of individual organisms which interbred among themselves and produce fertile offspring when they interbred. The group of related species is called Genus. Related Genera {General is plural of Genus} are kept in a family, related families are kept in Order. Related Orders are kept in classes. Classes comprising animals like fishes, amphibians, reptiles, birds, mammals etc. constitute the next higher category called Phylum. Generally animals are subdivided into phyla, while plants are subdivided into Divisions. All animals/plants belonging to various phyla/divisions are assigned to the highest category called Kingdom. The below graphic shows position of humans in above taxonomic ranks:

Five Kingdom Classification

Initially, the scientists had put all the living organisms into two Kingdoms viz. Plantae and Animalia. However, there were some problems such as – this classification did not distinguish between Eukaryotes / Prokaryotes, unicellular / multicellular, photosynthetic / non-photo synthetic organisms. Later, they divided the entire living world into five Kingdoms viz. Monera, Protista, Fungi, Plantae and Animalia. This five kingdom classification was based on several features such as cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.

  • All the prokaryotes were kept in Monera. This Kingdom comprises mainly Bacteria and blue green algae.
  • All unicellular eukaryotes were kept in Protista. This kingdom comprised of Algae and Protozoa.
  • All fungi were kept in Kingdom Fungi while multicellular plants and animals were kept in Plantae and Animalia respectively.

In the above classification, Viruses have not been included because of their pseudo-living nature.


Virus is a Latin word, literally meaning “poison”. Tobacco Mosaic Virus was the first Virus discovered by Russian scientist Dimitri lvanovsky in 1892. A Virus is an extreme micro, parasitic non-cellular nucleoprotein particle which can persist only if it is inside any living organism. This means that all viruses are parasites.

Salient Features

Viruses are very small acellular and infectious particles which can be seen only by an electron microscope. They can pass through bacteria-proof filters. They cannot be grown on artificial media in the laboratory. They are not cells and they behave as living organisms inside the host tissue only where they can multiply. They lack functional autonomy. They are not affected by antibiotics but can be made inactive by chemotherapy and thermotherapy. They react to stimuli such as light, radiations, chemicals, heat etc.

Viruses have been excluded from the biological classification because they are not living things in first instance. However, they do posses some properties of the both living and non-living.

Living propertiesNon-living properties
The presence of DNA or RNA (but never both)The absence of cell.
Structural diversityThe lack of protoplasm.
Geneticity and parasitic propertiesNo any reproduction and growth outside the living cell.
Sensitivity and evolutionStored in the form of crystal outside the living cell.
Capable of spreading the diseaseThe lack of metabolic activities like nutrition, digestion

There are three types of Viruses viz. Plant Viruses, Animal Viruses and Bacteriophage (viruses that are parasites on bacteria).


The sizes of viruses normally range from 40 to 350 nm. The smallest virus is of Hepatitis B (42nm), while largest Virus is Pandoravirus. The shapes of Viruses are also variable ranging from spherical (polio virus), rod-shape (TMV), tadpole-like (bacteriophages), polyhedral (adenovirus) and of other types.

A virus is made of three components viz. a protein capsid, nucleic acid and a thick outer layer. Viruses may contain either DNA or RNA but not both together. Generally, plant viruses are RNA viruses while animal viruses are DNA viruses. Further, Bacteriophage is always a DNA virus. Viruses produce diseases in plants, animals and human beings.

Plant Viral Diseases

Common plant viral diseases are Tobacco mosaic, Cauliflower Mosaic Sandalwood spike, Sugarcane mosaic, Bean mosaic, Aster yellow, Bunchy top of Banana, Leaf Curl of Papaya, Potato leaf roll, Twisted leaf disease of Tomato etc.

Use of TMV in Research

The Tobacco Mosaic Virus has become a popular tool for scientific research. The main reason is that it is available in large quantities and it does not infect animals. After growing a few infected tobacco plants in a greenhouse and a few simple laboratory procedures, a scientist can easily produce several grams of virus. As a result of this, TMV can be treated almost as an organic chemical, rather than an infective agent. Tobacco mosaic virus (TMV) and Cauliflower mosaic virus (CaMV) are frequently used in plant molecular biology. Of special interest is the CaMV 35S promoter, which is a very strong promoter most frequently, used in plant transformations.

Animal and Human Diseases

Common animal viral diseases include African horse sickness, Foot and mouth disease of cattle, Virus pneumonia of pigs, Rabies etc. Common human viral diseases include Influenza, Measles, Herpes, Dengue, Smallpox, Mumps, Common cold, Hepatitis, AIDS. The recent viral pandemics / epidemics include Ebola Virus Disease, Rift Valley fever, Bolivian hemorrhagic fever, Crimean Congo Hemorrhagic Fever, SARS, and MERS etc.

Human Viral Diseases

Common animal viral diseases include African horse sickness, Foot and mouth disease of cattle, Virus pneumonia of pigs, Rabies etc. Common human viral diseases include Influenza, Measles, Herpes, Dengue, Smallpox, Mumps, Common cold, Hepatitis, AIDS. The recent viral pandemics / epidemics include Ebola Virus Disease, Rift Valley fever, Bolivian hemorrhagic fever, Crimean Congo Hemorrhagic Fever, SARS, and MERS etc.


Flu is caused by influenza virus, which is a highly mutant virus. Influenza generally spreads through air via cough or sneezes. There are three species of Influenza Virus viz.  Influenza-A, Influenza-B, and Influenza-C. Out of them, Influenza A infects birds and mammals. It has very high rate of mutation, and this is the reason that so many different strains of influenza virus are found. In a first, they don’t infect humans, but if they do so, they cause devastating pandemics. The common Influenza outbreaks caused by Influenza-A strains include H1N1 (swine flu) in 2009; and H5N1 (Bird Flu) in 2004. H1N1 is the same strain which causes seasonal outbreaks of flu in humans on a regular basis. Since doctors have found it very hard to predict who will develop complications, it has been dubbed a “Jekyll and Hyde” virus.

Meaning of H and N in Flu

Various strains of Virus differ in certain proteins on the virus surface — hemagglutinin (HA) and neuraminidase (NA) proteins. The scientists give them different names on this bases.

Influenza B and C are less common and are less mutants in comparison to A.

Hepatitis / Jaundice

Hepatitis literally means inflammation of the liver. There are three major types of Hepatitis virus viz. Hepatitis A virus, Hepatitis B virus (HBV) and Hepatitis C Virus (HCV).

  • A is acute (acute means short term), B is acute as well as chronic (Chronic means long term) while C is almost chronic.
  • A spreads easily, B spreads relatively less easily and C spreads rarely.
  • A spreads via food, water etc. and can infect many people at once. For example, a food handler in a restaurant can spread Hepatitis A to many people at once; B spreads by blood or other body floods. C spreads only by blood.
  • A gets better on its own but can be serious in older people; B is common in India, Asia and Africa.  We note here that Amitabh Bachchan has recently revealed that he has lost 75% of is liver to Hepatitis B. C is even more dangerous.
  • A and B can be prevented by vaccination, but not C. However, there are medicines available to treat C.


Human immunodeficiency virus (HIV) also known as human T-lymphotropic virus-III (HTLV-III), lymphadenopathy-associated virus (LAV), and AIDS-associated retrovirus (ARV) is a retrovirus. {Retrovirus means it replicates via reverse transcription} in host cell. It transmits via anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, breastfeeding or other exposure to one of the above bodily fluids.

Due to weakened immune system the person is attacked by infections caused by bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune system that HIV damages.

What is the difference between human immunodeficiency virus (HIV) and AIDS ?

The term AIDS applies to the most advanced stages of HIV infection. The Center for Disease Control (CDC) definition of AIDS includes all HIV-infected people who have fewer than 200 CD4+ T cells per cubic millimetre of blood. (Healthy adults usually haveCD4 + T cell count of 1,000 or more.) The definition also includes 26 clinical conditions (mostly opportunistic infections) that affect people with advanced HIV disease.

Opportunistic infections are common in people with AIDS. HIV affects nearly every organ system. People with AIDS may develop various cancers such as Kaposi’s sarcoma, cervical cancer and cancers of the immune system known as lymphomas. Besides the people infected with AIDS often have systemic symptoms of infection like fevers, sweats (particularly at night), swollen glands, chills, weakness, and weight loss.


Smallpox is one of the three diseases (other two Guinea worm and Polio) that have been eradicated from India. Smallpox was eradicated globally in 1980s. This Virus has been used in biological warfare also. British used smallpox as a biological warfare agent during seven years war in 18th century.


Chickenpox or varicella is caused by Varicella Zoster Virus (VZV).


Polio virus is an enterovirus which means that the route of entry of this virus is through the gastrointestinal system. It’s an RNA virus.  Polio is usually spread via the fecal-oral route (i.e., the virus is transmitted from the stool of an infected person to the mouth of another person from contaminated hands or such objects as eating utensils). Some cases may be spread directly via an oral to oral route.


Both measles and German measles (rubella) are caused by viruses; and are rashes on the skins. German measles is accompanied by a blotchy red rash. The patient sometimes suffers a slight cold prior to the appearance of the rash. German measles can be dangerous for pregnant women, who have no immunity for the virus. It is called German measles because it was German physicians who first described this disease. Mild upper respiratory affect, high temperature that can last for four days and conjunctivitis are some symptoms of measles.

Rubella or German measles

Rubella (German measles) spreads when infected person coughs or sneezes. It causes a rash, a slight fever, aching joints, headaches, runny nose and red eyes. The virus spread by sneezes or coughs can lead to serious birth defects if contracted by pregnant woman. In 2015, the North and South America region have become the first region of the world to eradicate Rubella. There are no home-grown cases in five years.


Dengue virus is transmitted by a bite of female mosquito of any of two species of mosquitoes of the genus Aedes.

The mosquito, which typically bites humans in the daylight hours, can be easily recognized because of its peculiar white spotted body and legs.

Outbreak of the disease typically occurs in summer season when the mosquito population reaches its peak.

Unlike malaria, which is a major health concern in rural areas, dengue is equally prevalent in the urban areas too. In fact, it is predominantly reported in urban and semi-urban areas.

A severe form of the infection is known as dengue hemorrhagic fever (DHF). DHF can be fatal. Because of the severe joint pain, dengue is also known as break-bone fever.

DHF is characterized by a fever that lasts for 2 to 7 days, with general signs and symptoms consistent with dengue fever. In addition to these symptoms, if a patient suspected with dengue experiences decrease in platelets or an increase in blood haematocrit, it becomes more certain that the patient is suffering from the infection.  Platelets are cells in blood that help to stop bleeding, while haematocrit indicates thickness of blood. The smallest blood vessels become excessively permeable allowing fluid component to escape from blood vessels to organs of the body.  This may lead to failure of circulatory system, which might also cause death.


This disease is caused by Chikungunya virus transmitted by both Aedes aegypti and Aedes albopictus.  The mosquitoes usually transmit the disease by biting infected persons and then biting others. The infected person cannot spread the infection directly to other person.

Symptoms of Chikungunya fever are most often clinically indistinguishable from those observed in dengue fever. However, unlike dengue, haemorrhagic manifestations are rare and shock is not observed in Chikungunya virus infection. It is characterized by fever with severe joint pain (arhralgia) and rash.


Rabies or hydrophobia is found among dogs, cats, bats and other wild mammals. The transmission to humans occurs through the saliva of contaminated animals, mainly through bites. The rabies virus is neurotropic and attacks the central nervous system in a fast and lethal fashion. The prevention of the disease is done through the prophylactic vaccination of animals and humans. The treatment is done with an anti-rabies serum containing specific antibodies against the virus.

Yellow Fever

Yellow fever is a viral infection that occurs mainly in Central Africa and in the Amazon region of South America. It is prevented through vaccination and is transmitted by many species of mosquitoes of the Aedes genus, including Aedes aegypti. The infection causes clinical manifestations that range from asymptomatic cases to lethal fulminant cases. Generally, the disease begins a with fever, chills, discomfort, headache and nausea and evolves to jaundice (increase of bilirubin in blood, after which the disease is named), mucosal and internal hemorrhages, hemorrhagic vomiting and kidney failure.

Prevention is done by regular mass vaccination and the vaccination of travelers to endemic areas. The fight against the vector mosquito is also an important prophylactic measure.

Acute Encephalitis Syndrome

Encephalitis refers to acute Inflammation of the brain. There are two main types of encephalitis viz. viral encephalitis and Japanese encephalitis. While Viral encephalitis is caused by water-borne enterovirus; Japanese encephalitis is caused by mosquito Culex tritaeniorhynchus and Culex vishnui. Every monsoon sees an outbreak of acute encephalitis syndrome, or AES, diseases. Japanese encephalitis and viral encephalitis diseases; and both of these make the Acute encephalitis syndrome, or AES. This disease is called a poor man’s disease and affects largely to paddy farmers.

Other Notes on Viral Diseases

  • Common Cold is caused by a rhinovirus
  • Hepatitis (inflammation of the liver, jaundice)
  • Rabies (transmitted by bites from infected bats, raccoons, dogs)
  • Polio (may cause paralysis)
  • Smallpox (eradicated from the world in 1977 through vaccination)
  • Yellow Fever is a viral hemorrhagic fever transmitted by infected mosquitoes.

Industrial and Scientific Applications of Viruses

Since Viruses contain the characteristics of both living and non-living organisms, they are utilized in the field of Biotechnology research.  Bacteriophage can be used in water preservation as it can destroy the bacteria and keep water fresh. Here are some other applications of Viruses:

  • Molecular Biology, Cellular Biology, Molecular genetics, such as DNA replication, transcription, RNA processing, translation, protein transport, and immunology.
  • Virotherapy uses viruses as vectors to treat various diseases, as they can specifically target cells and DNA. It shows promising use in the treatment of cancer and in gene therapy.
  • The viruses represent largest reservoirs of unexplored genetic diversity on Earth. They can be used as alternative to the antibiotics because of the high level of antibiotic resistance now found in some pathogenic bacteria.
  • Viruses contain protein and this property can be used in production of various proteins such as vaccine antigens and antibodies.
  • In nanotechnology, viruses can be regarded as organic nanoparticles. Because of their size, shape, and well-defined chemical structures, viruses have been used as templates for organizing materials on the nanoscale.
  • It’s relatively easy to synthesize a new Virus. First synthetic virus was created in 2002, which is actually a DNA genome (in case of a DNA virus), or a cDNA copy of its genome (in case of RNA viruses). Ability to synthesize viruses has far-reaching consequences, since viruses can no longer be regarded as extinct; as long as the information of their genome sequence is known and permissive cells are available. Currently, the full-length genome sequences of 2408 different viruses (including smallpox) are publicly available at an online database.
  • Viruses can cause devastating epidemics in human societies. They can be weaponised for biological warfare.

Virus and Aquatic Ecosystem

A teaspoon of seawater contains about one million of Viruses, making them the most abundant biological entity in aquatic environments. They are useful in the regulation of saltwater and freshwater ecosystems. The Bacteriophage, which is harmless to plants and animals, play the most important role here. They infect and destroy the bacteria in aquatic microbial communities, comprising the most important mechanism of recycling carbon in the marine environment. However, the organic molecules released from the bacterial cells by the viruses stimulate fresh bacterial and algal growth. Viruses are useful for the rapid destruction of harmful algal blooms that arises generally from the Blue Green algae and often kills other marine life. Viruses INCREASE the amount of Photosynthesis in Oceans and are responsible for reducing the amount of carbon dioxide in the atmosphere by approximately 3 gigatonnes of carbon per year.


General Information about Bacteria

The bacteria are unicellular microorganisms which were first observed and reported by Anton Von Leeuwenhoeck in 1676. All bacteria are unicellular and prokaryotic. Their size and shape varies as per the species. Majority of Bacteria are in the size range of 0.5 to 50 µ, the smallest bacterium is “pasteurella” which is 0.7µ and largest bacteria Beggiota is 15-22 µ in size.

Different shapes of Bacteria

Bacteria are the monocellular microorganisms which are found in almost places in singleton form or in group. The cellular wall of the bacteria is thick and it is made from chitin, Murine etc. They have different shapes such as Coccus (spherical), Bacillus (rod shaped), Vibrio (comma shaped) and Spirillum (cork screw shaped)

G+ and G- Bacteria

Gram staining is a method to identify some of the bacteria on the basis of some chemical properties of their cell wall.  Not all bacteria can be identified on the basis of gram method. If a bacterium can be judged using this method, it would be called Gram variable otherwise Gram indeterminate. can be classified by using this technique are called Gram variable. What is basically done is to color the cell walls using a stain called Crystal violet. If a bacteria has lipids and peptidoglycan in its cell wall, it would appear violet in microscope and will be called gram positive. Otherwise, they would be called gram negative.

The cell wall of Gram positive bacteria is thicker and more peptidoglycan in comparison to gram negative bacteria. Further, a chemical called Teichoic acid is present in + and absent in – bacteria.


The tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells is Flagella. It helps in locomotion. If bacteria have no Flagella, then it is called atrichous.

Nutrition in Bacteria

Bacteria are autotrophic, heterotrophic as well as saprophytic. The autotrophic bacteria are either photo-autotrophic or chemo-autotrophic. Some bacteria grow on the dead and decaying material and they are called Saprophytes. The bacteria that grow on plants and animals are called parasitic bacteria. The bacteria which make mutually beneficial association are called symbioants. Chemotropic bacteria use chemicals to produce energy. For example, Hydrogen bacteria use Hydrogen and as source of energy. Similarly, Sulphur bacteria are capable of oxidation of the reduced Sulphur compounds such as Hydrogen Sulphide (H2S), Inorganic Sulphur etc.


In bacteria reproduction takes place by two methods viz. Asexual and Sexual. Asexual reproduction happens via binary fission which is similar to mitosis. Sexual reproduction occurs via conjugation, transduction and transformation.

Applications of Bacteria


Pasteurization is one of the methods of preservation of products such as milk, alcoholic beverages etc. at higher temperatures. Pasteurization is defined as the process of heating products to a particular temperature and holding it at that temperature for a particular time till the pathogenic (disease causing) micro-organisms are destroyed causing minimum change in composition, flavor and nutritive value of products such as milk.

  • There are two methods of pasteurization (of milk) in general use. One is low temperature holding (LTH) method in which milk is heated to 62.8°C (145F) for 30 minutes in commercial pasteurizers (or) large closed vats which are heated by steam coils, hot water jackets etc.
  • The other method (i.e.) high temperature short time (HTST) method in which the milk is heated to 71.7°C (161F) for 15 seconds.

The heating is accomplished by electricity (or) hot water and requires a heat exchange system, which preheats raw, cold milk and cools the hot pasteurized milk. Please note that Pasteurization conditions are not sufficient to destroy thermo-resistant spores (reproductive part of microorganisms).  Thus, Pasteurization does not sterilize the products but kills only those organisms that grow most readily at low temperatures. The surviving organisms must be kept from multiplying by constant refrigeration.

Nitrogen Fixation

The Nitrogen Fixation is the procedure by which atmospheric Nitrogen is converted into ammonia. The Nitrogen fixation is one of the important components of the Nitrogen cycle.

Nitrogen fixation can be biotic or abiotic. The examples of abiotic processes are lightening, Industrial processes such as Haber-Bosch Process, and combustion. The biotic nitrogen fixation was discovered by Martinus Beijerinck.

How does it work?

Two molecules of ammonia are produced from one molecule of nitrogen gas, at the expense of 16 units of ATP and a supply of electrons and protons (hydrogen ions):

N2 + 8H+ + 8e- + 16 ATP = 2NH3 + H2 + 16ADP + 16 Pi

Please note that exclusively the prokaryotes do this reaction. The enzyme used is called nitrogenase. The nitrogenase enzyme has two kinds of proteins viz. Iron Protein, and Iron-Molybdenum protein. The N2 is is bound to the nitrogenase enzyme complex. The Fe protein is first reduced by electrons donated by ferredoxin. Then the reduced Fe protein binds ATP and reduces the molybdenum-iron protein, which donates electrons to N2, producing HN=NH. There are two more cycles and each requires electrons donated by ferredoxin) HN=NH is reduced to H2N-NH2, and this in turn is reduced to 2NH3 .

Thus in summary
  • 16 ATP are used in BNF (Biological Nitrogen Fixation)
  • Two minerals viz. Iron and Molybdenum play important role in BNF.
  • End product is ammonia + Hydrogen
  • Enzyme used is Nitrogenase
Role of Bacteria

Both anaerobic bacteria as well as the aerobic bacteria do biological nitrogen fixation however, the process occurs in absence of Oxygen and thus is anaerobic process. Further, biological nitrogen fixation is done by both free living and symbiotic bacteria. The notable examples are given below:

  • Free living aerobic bacteria: Azotobacter
  • Free living anaerobic bacteria: Clostridium, purple sulphur bacteria
  • Symbiotic in legumes and pulses: Rhizobium (found in root nodules)
  • Symbiotic in sugarcane: Glucoacetobacter diazotrophicus (found in stem knots)
  • Symbiotic in other plants: Frankia, Azospirillum
Why BNF occurs only in anaerobic conditions?

The enzyme nitrogenase is susceptible to destruction by oxygen. Many bacteria cease production of the enzyme in the presence of oxygen that is why many nitrogen-fixing organisms exist only in anaerobic conditions. Some aerobic bacteria which carry out the Nitrogen Fixation use another protein called Leghemoglobin to bind the oxygen and bring its level down.

BNF in Legume Plants

Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with plants such as pulses, groundnut, clover, soybeans, alfalfa, lupines, peanuts etc. They contain symbiotic bacteria called Rhizobium within nodules in their root systems. Further, it is not necessary that ONLY symbiotic bacteria are able to fix nitrogen by BNF. It is also NOT necessary that only leguminous plants do this. BNF is also found in sugarcane in which such bacteria live in stem nodules. Moreover, fixed nitrogen is released only when the plant dies. This helps to fertilize the soil.

Bacteria in Nitrification

Nitrification is the process in which the ammonia is converted into Nitrate. Nitrification is a two step process and based upon these two steps, the bacteria are divided into Nitrosifying and Nitrite-Oxidizing bacteria. Example of Nitrosifying bacteria is Nitrosomonas, which converts the Ammonia (NH3) into Nitrite (NO2-). Example of Nitrite-Oxidizing bacteria is Nitrobacter which are able to oxidize the Nitrite and crate Nitrate (NO3-).

Bacteria in Industry and Everyday Life

Some other notable used of bacteria include in Dairy Industry, Food Industry, Soil Health, Bioremediation, Biotoilet

Dairy Industry

In Dairy Industry, Lactobacillus bacteria are used in fermentation of lactose sugar to form lactic acid (in curd). Lactobacillus in combination with yeasts and molds, have been used for thousands of years in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt.

Food Industry

The Bacillus megatherium bacterium is used in the Flavoring of Tea and Tobacco. Acetobacter aceti is used in preparation of vinegar from Alcohol.

Industrial Uses

Clostridium acetobutylicum is able to produce acetone from acetic acid as well as butanol from butyric acid. In Biogas plants, the bacterium called Methanobecterium is used for production of Methane. Bacteria are useful in the Fibre ratting in which the fibres of Jute, hemp and Flax are prepared. Clostridium butyricum is used in the process and these bacteria hydrolyze the middle lamella of these plant fibres. Microbial mining, which is the bacteria and other microorganisms are cultured in container and then used to bring these processes e.g., copper extraction, iron extraction; which involves bacteria called Ferro-oxidans.

Bacteria in soil formation and soil fertility

As soon as a fresh rock is exposed to a biological environment certain organisms, notably the bacteria take possession of it. There is an instance of increased production of organic matter and it results in formation of soil contents. There are many bacteria which decompose the rotten substances like dung, dead residues of animals etc. Some bacteria enhance the fertility of the soil by means of denitrification especially of plants Rhizobium bacteria are found in the roots of the plants which nitrified (transformed) atmospheric nitrogen into the nitrates. Such nitrates act like fertilizers and along with the growth of the plants fertility of the soil is also enhanced.

Other uses
  • Bacteria work as natural scavengers as they are able to decay huge amount of plant, animal and human waste.
  • Using biotechnology techniques, bacteria can also be bioengineered for the production of therapeutic proteins, such as insulin, growth factors or antibodies.
  • Some bacteria living in the gut of cattle, horses and other herbivores secrete cellulase, an enzyme that helps in the digestion of the cellulose contents of plant cell walls. Cellulose is the major source of energy for these animals. generally plant cells contain cellulose.the bacteria present in the stomach of cattle will help in the digestion of cellulose.
  • Escherichia coli that live in the human large intestine synthesize vitamin B and release it for human use. Similarly, Clostridium butyclicum is used for commercial preparation of riboflavin, and vitamin B.
  • Bacillus thuringiensis (also called BT), a Gram-positive, soil dwelling bacterium is used for Pest Control and producing Bt crops.
  • Bioremediation techniques such as Oil zapper use bacteria.
  • Many antibiotics are used from bacteria. Some of them are Bacitracin, Polymyxin B, Streptomycine, Erythromycine, neomycin-B, Chloramophenicol etc.
Antibiotics (medicines)Bacteria
StreptomycinStreptococcus groseis
Tyrothrycin-ABacillus brevis
Polymyxin-BBacillus polymixa
BacitracinB.Subtilis, Bacillus Licheniformis
Pleasant smell of the earth after the first shower

Pleasant smell of the earth after the first shower (earthy odour) is caused by the production of a series of streptomycete metabolites called geosmins.

These substances are sesquiterpenoid compounds and unsaturated compound of carbon, oxygen and hydrogen. The geosmins first discovered has the chemical name trans-1, 10-dimethyl-trans-9-decalol; however, other volatile products produced by certain species of Streptomyces may also be responsible for the characteristic smell.

Oil Zapper

‘Oilzapper’ technology was developed by ONGC-Teri Biotech Ltd (OTBL), a joint venture between ONGC and TERI. This technology was first used by OTBL in Mehsana in Gujarat to eliminate an oil spill and manage the sludge created from the first oil well in the region. The water became clean and subsequently a home to a variety of birds.

Bacteria in the Bio-Digester Toilet

Bio-Digester Toilet is a decomposition mechanized toilet system by means of which the sludge(Human Waste), the fecal matter is decomposed to bits in the digester tank using a specific high graded bacteria further converting them into methane and water, discharged further to the desired surface.  The Bio-digester toilet is total maintenance-free system & does not require any sewage system. The specific high graded bacteria involved in these bio-digester toilets carries on to further auto generation on their own because of their supreme quality.  Bio-toilet technology is based on anaerobic biodegradation of organic waste by unique microbial consortium and works at a wide temperature range. The bacterial consortium degrades night soil at temp as low as -20 degree C and produces colourless, odourless and inflammable gas containing 50 – 70% methane.

This bacterial consortium has been made through acclimatization, enrichment and bio-augmentation of cold-active bacteria collected from Antarctica and the other low temperature areas.

Bacterial Diseases

Common Bacterial diseases include Diarrhoea, Dysentery, Typhoid, Whooping Cough, TB, Diphtheria, Cholera etc.


Diarrhea can be caused by all sorts of parasites including viruses, Bacteria and protozoa.  Most common virus causing Diarrhoea in adults is Norovirus.  Most common virus causing Diarrhoea in children below 5 years is rotavirus. A rotavirus vaccine Rotavac has been recently launched in India.

Most common bacteria causing Diarrhoea is campylobacter; others are salmonellae, shigellae and some strains of Escherichia coli (E.coli).


Dysentery is usually caused by a bacterial or protozoan infection or infestation of parasitic worms, but can also be caused by a chemical irritant or also viral infection. The most common cause of the disease in developed countries is infection with a bacillus of the Shigella group (causing bacillary dysentery). Infection with the amoeba Entamoeba histolytica can cause amoebic dysentery


Typhoid is transmitted by the ingestion of food or water contaminated with the feces of an infected person, which contain the bacterium Salmonella enterica enterica. The bacteria perforate through the intestinal wall and are phagocytosed by macrophages. It is a G- short bacillus that is motile due to its peritrichous flagella.

Whooping Cough

Pertussis or Whooping cough is a highly contagious bacterial disease caused by Bordetella Pertussis.


Tuberculosis is caused by various strains of Mycobacterium, usually Mycobacterium tuberculosis. It usually attacks the lungs but can also affect other parts of the body. It is spread through the air when people who have active infection cough, sneeze, or spit. In most cases the disease is asymptomatic, latent infection, and about 10% latent infections eventually progresses to active disease. If untreated, it killed 50% of its victims.


TB that is resistant at least to isoniazid  and rifampicin  the two most powerful first-line anti-TB drugs is called the Multi-drug-resistant tuberculosis (MDR-TB). It develops because the when the course of antibiotics is interrupted and the levels of drug in the body are insufficient to kill 100% of bacteria. This means that even if the patient forgets to take medicine, there are chances of developing MDR-TB. MDR-TB is treated with secondline of antituberculosis drugs such as a combination of several medicines called SHREZ (Streptomycin+isonicotinyl Hydrazine+Rifampicin+Ethambutol+pyraZinamide)+MXF+cycloserine.


When the rate of multidrug resistance in a particular area becomes very high, the control of tuberculosis becomes very difficult. This gives rise to a more serious problem of extensively drug-resistant tuberculosis (XDR-TB). XDR-TB is caused by strains of the disease resistant to both first- and second-line antibiotics. This confirms the urgent need to strengthen TB control.

2. Extent of TB

One third of the world’s population is thought to be infected with M. tuberculosis, and every second a new infection occurs. About 80% of the population in many Asian and African countries test positive in tuberculin tests.  The highest number of deaths from TB is in Africa Region.

3. HIV and TB

HIV and TB form a lethal combination, each speeding the other’s progress. TB is a leading cause of death among people who are HIV-positive. In Africa, HIV is the single most important factor contributing to the increase in the incidence of TB since 1990. Tuberculosis was declared a global emergency by the WHO in 1993.

4. BCG

BCG (Bacillus Calmette-Guérin) was the first vaccine for TB that discovered in 1905 by Albert Calmette and Camille Guérin. Once WHO declared TB a global emergency, BCG vaccine along with DOTS was used in more than 192 countries as a preventive therapy. However, there was a controversial side of BCG vaccination that it showed variable efficacy, that depended on geography. It was concluded that BCG efficiency goes down as one gets closer to equator. There were several explanations to this phenomenon. One such theory said that in areas where there are high levels of background exposure to tuberculosis, every susceptible individual is already exposed to TB prior to BCG, which is why the natural immunizing effect of background tuberculosis duplicates any benefit of BCG. This means that BCG is less effective in the area where the Mycobacteria are less prevalent. Another theory says that Variable efficacy is because of the Genetic variation in BCG strains.

5. DOTs

DOTS, is an acronym for Directly Observed Treatment, Short course. The DOTS strategy represents the most important public health breakthrough of the decade, in terms of lives which will be saved. It is based largely on research done in India in the field of TB over the past 35 years.


Leprosy or Hansen’s disease is caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Leprosy has a high degree of stigma attached to it because of the fact that there was no cure for the disease till the eighties and also due to disfigurement caused by the disease.

Some drugs such as rifampicin, clofazimine, and dapsone are used to treat Leprosy.


Diphtheria is caused by Corynebacterium diphtheriae, an anaerobic Gram-positive bacterium. It is an acute respiratory disease caused by bacteria, which leads to a thick coating in the nose, throat or airway. Diphtheria takes its name from Greek word ‘dipthera’ referring to the leathery membrane or coating that grows on the tonsils, throat and in the nose.

Diphtheria is a purely vaccine-preventable disease and effective vaccine is available.


Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting.

Kingdom Fungi

Fungi are among the most primitive members of the plant kingdom. Study of the fungi is called mycology. The fungi are non-chlorophylous, nucleated, non-vascular, thallophytic micro organism and due to lack of chlorophyll they do not prepare their own food. The fungi are among the thallophytes or plants with a thallus, which are simple plants, have no roots, stems, flowers and seeds- structures we commonly associate with higher plants. The thallus of a fungus is usually made of branching threads called hyphae.

Why Photosynthesis does not take place in Fungi?

Fungi lack chlorophyll and cannot prepare their own food and depend on other organism for nourishment. On the basis of nourishment the fungi are of three types –

  • Saprophytes: The fungi which obtain their food or do nutrition from decayed moist leaves, moist dead wood or by some other useless rotten residues or organic substances. The fungi like Rhizopus, Penicillium etc are saprophytes.
  • Parasites: The fungi which obtain their food by taking or sharing  the food of any other organisms. The fungi like Ustilago, Puccinia etc that are harmful parasites.
  • Symbiotic: The fungi, which coexist with other plants and facilitate water and mineral salt and plants prepare food for them. The microbe lichen is the best example of symobiotic fungus.

Benefits of Fungi

Soil Formation and Fertility

The fungi decompose moist residues of leaves, dead wood, animal along dung and other rotten organic substances into another, which act like manures, and thus soil becomes more fertile.


There are various fungi which are used as food. Agaricus and Morchella are used in the forms of vegetables (mushrooms) fungi. Aspergillus, penicillium are used in cheese industry, yeast a (a type of fungi) like Saccharomyces cervisiae is used in making double roti (bread dough). Wines, beers are also prepared by the alcoholic fermentations of the yeasts.

Nitrogen fixation

The fungi like Rodoturela do the process of nitrogen fixation due to which the fertility of the soil is enhanced.


In the fungi  there are various types of antibiotics which are utilized in making medicines like chloromycetin, neomycin, streptomycin, teramycin etc.

Chemical Industry

Various types of acids and chemical substances are prepared. Aspergillus gallomyces and Pencillium glaucum are used in the Gallic acid. Similarly Gluconic acid and Fumeric acid are prepared by the fungi Aspergillus niger and Rhizopus nigricans respectively.

Enzymes and Vitamins

By the fungi and some yeast, various types of enzymes are prepared. The enzymes amylase is prepared from Aspergillus orizae. Similarly, invertase is prepared by yeasts.  Various vitamins like vitamin B is prepared from Streptomyces griseus.


Bioremediation by means of Fungi is called Mycoremediation. Fungi have been shown to biomineralize uranium oxides, suggesting they may have application in the bioremediation of radioactively polluted sites. Some fungi are hyperaccumulators, capable of absorbing and concentrating heavy metals in the mushroom fruit bodies.

Pest control

Beauveria bassiana, Metarhizium spp, Hirsutella spp, Paecilomyces (Isaria) spp, and Lecanicillium lecanii have been used in Pest Control. One gene-one enzyme hypothesis was formulated by scientists who used the bread mold Neurospora crassa to test their biochemical theories. Aspergillus nidulans and the yeasts, Saccaromyces cerevisiae and Schizosaccharomyces pombe, have a long history of use to investigate issues in eukaryotic cell biology and genetics, such as cell cycle regulation, chromatin structure, and gene regulation.

Common fungal diseases

Wart disease of potato, Late blight of potato, Green ear disease of bajra, Rust of wheat, Loose smut of wheat, Tikka disease of groundnut, Red rot of sugarcane, Brown leaf spot of rice, Ergot disease of rye, Powdery mildew of wheat etc.

Common animal and human fungal diseases include Athlete’s foot scabies, Scabies , Ring worm, Meningitis, Asthma, Baldness, Aspergillosis etc.


Lichens are symbiotic associations of fungi and algae. In this association, the fungi (called mycobiont) facilitate water, minerals, vitamins, etc to the algae and algae (called phycobiont) prepare carbohydrate by the process of photosynthesis and supply the food to the fungi. Study of lichens is called Lichenology. Lichens are most commonly found on the trees. Lichens are useful and by the help of these various economic activities can be observed. Lichens are capable to indicate air pollution, water pollution, heavy metals as well as radioactive particles. Lichens like Reindeer mosses, Iceland moss etc are utilized as food stuffs.

Kingdom Plantae


Algae (seaweeds) are usually aquatic, either marine or fresh water plants. A few algae also occur in terrestrial habitats such as moist soils, wet rocks, tree trunks, etc. These are unicellular or multicellular, autotrophic plants which don’t have vascular tissues {tissues that provide mechanical strengh} and their body are called thallus.

Types of algae

Algae have been divided on the basis of nature of pigments present in them and the mode of storing food. These pigments give them specific color.

1. Green Algae or Chlorophyceae

Green algae have chloroplast and chlorophyll in their cells. Examples are Chlamydomonas, Volvox, Spirogyra, Ulothrox, Oedogonium and Chara are some example.

2. Brown algae or Phaeophyceae

Brown algae store food in the form of laminarin and mannitol. Many of brown algae are called Kelps. Ectocarpus, Laminaria, Sargassum are common examples of brown algae.

3. Red Algae or Rhodophyceae

Red algae are red because of a pigment called Phycoerythrin. Most red algae are found in marine habitats. They store food in Floridean starch. Common examples are Gracilaria, Porphyra etc.

4. Blue Green Algae or Cyanophyceae

Blue green algae are most primitive algae and are prokaryotic. Modern classification puts them in Kingdom Monera along with bacteria.

Economic Importance of Algae

Nitrogen fixation and Biofertilizers

There are many species of blue-green algae capable of fixing atmospheric nitrogen in the soil and are used as biofertilizers. Common examples are Anabaena and Nostic. Anabaena, in association with water fern Azolla contributes nitrogen and also enriches soils with organic matter.

5. Other Uses
  • Many green algae such as Chlorella, Ulva, Caulerpa, Enteromorpha, etc. are used as food. Chlorella has about 50% protein and 20% of lipid and carbohydrates. Chlorella also yields an antibiotic chlorellin.
  • Agar is obtained from the Red algae Gracilaria and Agar is used as a culture medium for growing of microbes in labs. Agar is also used in Food and Pharmaceuticals.
  • Carragineen which is used in the Dairy industry is obtained from a red alga called Chondrus crispus. It is also used in cosmetics and Pharma.
  • Alginic acid, which is used as a stabilizer and thickening agent is obtained from Laminaria, the brown algae.
  • Dynamite is prepared with the cell walls of Diatoms.
  • Brown algae Laminaria is a good source of Iodine.
  • Macrocystis algae are source of Potash. It’s a brown algae (phaeophyceae ) and is largest algae among all.
Algal Hazards
6. Algal toxicity

Some algae are extremely poisonous to fishes. The blue-green alga Microcystis secretes hydroxylamine which kills aquatic life while Lyngbya and Chlorella may cause skin allergies in human beings.

7. Algal parasitism

The red alga Cephaleuros virescens causes Red Rust of Tea.

8. Algal blooms

Algae grow abundantly in water reservoirs where excess of nutrients are available to them. This algal growth floats on the water surface and look like foam or soap lather. It is called water bloom. Examples: Microcystis, Anabaena, Oscillatoria, etc.

Color of Red Sea

Red Sea is the part of the Mediterranean sea where a Blue green algae Trichodesmium grows profusely is called Red Sea. It is due to the presence of red Phycoerythrin in the cells of Trichodesmium.


The common word for Bryophytes is Moss, which are the first land plants in context with evolution of plants. The branch of science that deals with Bryophytes is called Bryology. Please note that Mosses don’t have a vascular tissue such as Xylem and Phloem, which we find in plants of higher orders. Due to this, they are also known as Atracheates which means no trachea. In India, S R Kashyap did a commendable job in the studies of Bryphytes and that is why is called Father of Indian Bryology.

Amphibians of Plant Kingdom

Bryophytes are called the “amphibians” of the plant kingdom. They can live on land but for reproduction and fertilization, need water essentially.

The Bryophytes were the first plants in which alternation of generation was seen for the first time in the embryophytes as Gametophyte→Mitosis → gametes →Sporophyte → Spores → Meiosis →Gametophytes.

Bryophytes: Important Points
  • One of the famous Bryophyte is Peat Moss. Its botanical name is Sphagnum. It grows in swamps and damp areas. This is one of the most economically important Bryophyte. In World War I, Peat moss was used as “dressing cotton’ for wounded soldiers. Peat is obtained from Sphagnum.
  • Physcomitrella patens is increasingly used in biotechnology. Prominent examples are the identification of moss genes with implications for crop improvement or human health and the safe production of complex biopharmaceuticals in the moss bioreactor.
  • Mosses play an important role in controlling soil erosion. They perform this function by providing ground cover and absorbing water.
  • Mosses are also indicators of air pollution. Under conditions of poor air quality, few mosses will exist.
  • Peat is used as fuel to heat homes and generate electricity. Bryophytes are among the first organisms to grow up in areas that have been destroyed by a fire or volcanic eruption.
Why Mosses are haploid in most of their lives?

Bryophytes commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems. Please note that in Bryophytes, the dominant phase of life is not the plant itself but one of its phases in reproduction called gametophytes. The only thing you need to remember is that gametophyte contains a single set of Chromosome and that is why the “Bryophytes are in Haploid state in most of their lives”.

At certain times, mosses produce spore capsules, which may appear as beak-like capsules borne aloft on thin stalks. These gametophyte produces male or female or both gametes (term used for sperms or ovum lower plants) by mitosis. When male and female gametes fuse, they make a diploid zygote, which develops by repeated mitotic cell divisions into a multicellular Sporophyte. This Sporophyte is diploid because it is a product of fusion of two haploid gametes. This Sporophyte is NOT independent in Bryophytes and needs to get nutritional support from the gametophyte.

Now, this diploid phase Sporophyte again produces sex cells via meiosis, which are called spores. During making of spores, the chromosome pairs are separated once again to form single sets. The spores are therefore once again haploid and develop into a haploid gametophyte. This is how the lifecycle of a Bryophyte goes on.


Pteridophytes are commonly known as Ferns. There are around 12,000 species of Ferns, many of them are generally used a decoration / ornamental plants.

1. Position of Pteridophytes in Evolution

In the evolutionary stages, Ferns are next advanced level after Bryophytes. Bryophytes don’t have the vascular tissues, but the Ferns have both xylem and phloem, thus they are the first vascular plants in terms of evolution of plant species. They have stems, leaves, and roots like other vascular plants. Further, in case of the Bryophytes, the dominant phase of life is gametophytes. This reverses from Pteridophytes ONWARDS. Thus in Pteridophytes, Gymnosperms and Angiosperms, the dominant phase of life is Sporophyte. This Sporophyte is NOT only independent but also long lived.

Pteridophytes differ from the advanced plants on the basis of the Reproduction procedures. They differ from gymnosperms and angiosperms as they do not have neither flowers nor seeds.

Economic Importance

Most of the Pteridophytes have ornamental value; they are grown as ornamental plants in gardens and homes. Some Pteridophytes such as Marsilea are rich source of starch and used as food material. Parts of Pteridium aquilinum or Pteridium esculentum, are used as a cooked vegetable in Japan and are believed to be responsible for the high rate of stomach cancer in Japan. It is also one of the world’s most important agricultural weeds, especially in the British highlands, and often poisons cattle and horses. Dryopteris filix-mas is used an anti-helminth means anti worm, used in Pharmacy.

2. Biofertilizer

The smallest fern Azolla has the capability of Nitrogen Fixation is used as a biofertilizers, especially in parts of Southeast Asia. Azolla has been used for thousands of years in China in paddy cultivation. Azolla is also known as Mosquito fern because of a myth, that when this plant is in bloom, no mosquito can cross its covering to the water in the water body to lay eggs.


Gymnosperms are called so because they have naked ovules / seeds. In terms of plant evolution, they are first seed-bearing plants. They are inferior to Angiosperms because in Angiosperms, the ovules are covered. Common gymnosperms include Conifers, Cycads, Ginkgo, and Gnetales.

Notable Points

  • Tallest plant of the world “Coast Redwood of California” is a gymnosperm.
  • Some Gymnosperms are called the “living fossils” because many of them represent the one of the few, if not the only, surviving members of a taxonomic group, with no close living relatives. Cycas and Ginkgo Biloba are examples of living fossils.
  • Canada Balsum, the sticky colourless and odourless liquid used in optical industry is obtained from a Gymnosperm.
  • Ephedrine is obtained from Ephedra which is a naturally growing Gymnosperm in Rajasthan.
  • Sago, which is a staple food in New Guinea and some other countries is obtained from Cycas revoluta and
  • Chilgoza is obtained from Pinus gerardiana, known as the Chilgoza Pine. Chilgoza is one of the most important cash crops of tribal people residing in the Kinnaur district of Himachal Pradesh, which seems to be the only place in India where Chilgoza pines are found.
  • Cedar wood is obtained from many species of the Gymnosperms. Similarly Chir wood is obtained from Chir Pine or Pinus longifolia. The Pinus species of Gymnosperms contain the “winged pollen grains”.


Angiosperms or flowering plants are the most advanced, most diverse and most dominant group of land plants. They are seed-producing plants and can be distinguished from the gymnosperms by a series of derived characteristics such as flowers, endosperm within the seeds, and the production of fruits that contain the seeds. They have developed from Gymnosperms over the period and replaced them as most dominant group of plants some 100 million years ago.

Main Features of Angiosperms

Benefit of Flowers

Due to Flowers, Angiosperms were able to adapt a wider range of ecological niches, making them largely dominate terrestrial ecosystems.

Reduced Male and Female Parts

Instead of cones in Gymnosperms, the Angiosperms have stamens, reduced male parts and an enclosed ovule. The Stamens are much lighter than the corresponding organs of gymnosperms and have contributed to the diversification of angiosperms through time with adaptations to specialized pollination methods. In some advanced species, the Stamens were modified to prevent self-fertilization, enabling further diversification.

Dominant Sporophyte

The main plant of Angiosperms is a Diploid Sporophyte which is divided into roots, stems and leaves. The male gametophyte in angiosperms is significantly reduced in size compared to those of gymnosperm seed plants. The smaller pollen decreases the time from pollination — the pollen grain reaching the female plant — to fertilization of the ovary; in gymnosperms, fertilization can occur up to a year after pollination, whereas, in angiosperms, the fertilization begins very soon after pollination. The shorter time leads to angiosperm plants’ setting seeds sooner and faster than gymnosperms, which is a distinct evolutionary advantage.

Double Fertilization

Double Fertilization is a rule on Angiosperms. This means that the Fertilization in Angiosperms involves the joining of a female gametophyte (megagametophyte, also called the embryo sac) with two male gametes (sperm).

Pollination in Angiosperms

In flowering plants, pollination refers to transferring pollen grains from the male anther of a flower to the female stigma.

Pollination taking place in a single flower is called self pollination, while pollination taking place between two flowers is called cross pollination. If the cross pollination is between flowers of a same plant, it will be called Geitonogamy, while if it takes place between two separate plants, it will be called as Xenogamy.  In some plants, the flowers are bisexual and closed called Cleistogamous. Here only self pollination takes place.

Insects (Entomophily) can facilitate the pollination, similarly can Wind (anemophily), Water (Hydrophily), Animals (Zoophily). Further, Hummingbirds, bats, monkeys, marsupials, lemurs, bears, rabbits, deer, rodents, lizards and other animals are common animals that carry pollens and help in pollination.

1. Pollination by Bats

Pollination done by Bats is called chiropterophily. Many fruits are dependent on bats for pollination, such as mangoes, bananas, and guavas. Bat pollination is an integral process in tropical communities with 500 tropical plant species completely, or partially, dependent on bats for pollination.

2. Pollination by Birds

The term ornithophily is used to describe pollination specifically by birds. Hummingbirds, sunbirds, honeyeaters, flowerpeckers, honeycreepers, and bananaquits are examples.  Plants pollinated by birds often have brightly colored diurnal flowers that are red, yellow, or orange, but no odor because birds have a poor sense of smell. Other characteristics of these plants are that they have suitable, sturdy places for perching, abundant nectar that is deeply nested within the flower. Often flowers are elongated or tube shaped. Also, many plants have anthers placed in the flower so that pollen rubs against the birds head/back as the bird reaches in for nectar.

3. Pollination by Lizards

Although lizard pollination has historically been underestimated, recent studies have shown lizard pollination to be an important part of many plant species’ survival. Not only do lizards show mutualistic relationships, but these are found to occur most often on islands. The lizard Hoplodactylus is only attracted by nectar on flowers, not pollen.

Monocots and Dicots

Angiosperms are classified into two categories viz. monocots and dicots. In monocots, seed has only one cotyledon while in dicots, seed has two cotyledons.

The key comparisons of these two groups are as follows:

  • The roots of monocots are lesser developed in comparison to dicots.
  • The petals in flowers of monocots are 3 or multiples of 3. The petals in flowers of dicots are four or five; it’s their multiples.
  • No secondary growth is found in monocots because their vascular tissue has no cambium. Secondary growth is found only in dicot plants.
  • Examples of monocots include grasses, bamboo, sugarcane, cereals, bananas, palms, lilies, orchids etc. Examples of Dicots include all the hardwood tree species, pulses and the most fruits, vegetables, species beverage crops and ornamental flowering plants.

Roots and root modifications

Roots of Angiosperms always move opposite to the sunlight. The soft parts of roots and root hairs absorb water and mineral salts from the soil. The root transports water and mineral salts to the stem and ultimately to the leaves. Some roots like of carrot, radish etc. store foods and in contingency plants use these foods. The roots are of following types:

  • Tap root: The radical of such root develops itself and forms a main root and such roots exist in dicotyledonous plants.
  • Conical shape: This type of root is thickened towards base but thin near the side of the plant. Example-carrot.
  • Napiform: This type of root is extremely thickened and becomes inflated spherical at the base (bottom) but it becomes extremely thin at the top of the plant. Examples-turnip, beet root etc.
  • Fusiform : This type of root is inflated in the middle portion, while towards bottom and top it becomes thinned. Example is Radish.
  • Pneumatophores : This type of root is found in salty soil of the sea and for the respiratory activities it undergoes towards negative geotropic. Examples are Rhizophora, etc.
Adventitious Roots

Adventitious roots originate from the stem, branches, leaves, or old woody roots, rather than the normal root system. For example in Strawberry and Willow. These roots develop to avoid stress or fight with the problem of nutrition deficiency or to get sufficient oxygen, or avoid too much oxygen. One more important work of these roots is to help in vegetative propagation in many plants. This ability of plant stems to form adventitious roots is utilized in commercial propagation by cuttings. Understanding of the physiological mechanisms behind adventitious rooting has allowed some progress to be made in improving the rooting of cuttings by the application of synthetic auxins as rooting powders and by the use of selective basal wounding.

Adventitious roots develop near the existing vascular tissue, so that they can connect to the xylem and phloem. There are several kinds of modifications such as:

  • Tuberous roots are without any definite shape; example: Sweet Potato.
  • Fasciculated root (tuberous root) occur in clusters at the base of the stem; example: asparagus, dahlia.
  • Nodulose roots become swollen near the tips; example: turmeric.
  • Stilt roots arise from the first few nodes of the stem. These penetrate obliquely down in to the soil and give support to the plant; example: maize, sugarcane.
  • Prop roots give mechanical support to the aerial branches. The lateral branches grow vertically downward into the soil and acts as pillars; example: banyan.
  • Climbing roots these roots arising from nodes attach themselves to some support and climb over it; example: money plant.
Modifications of adventitious roots
Fibrous rootOnion
Leafy rootBriophylem
Climbing rootBetel leaf, pothos
Buttress rootTerminolia
Sucking rootCuscuta
Respiratory rootJuicia
Epiphytic rootOrcede
Aerial rootOrcede
Assimilatory rootTinspora
Parasitic rootKascutta
Moniliform rootGrapes, bitter guard
Nodulose rootMango turmeric
Prop rootBanyan tree
Stilt rootMaize, sugarcane
Fasciculated rootDahlia

Stem in Angiosperms

On the basis of the position of the soil, stems are of three types:

  • Underground stem: The branch or part of the stem which intruses inside the soil is called underground stem. These  stems store the food in the stem, node, internode, bud and scale leaf are found. Examples- banana, potato, colocasia etc.
  • Sub aerial stem : If a few part of stem is inside the soil and rest is in air then such stem is called subaeriala stem. Examples-Grass root, water plant, etc.
  • Aerial stem : The stem which is completely confined and localized in air and entirely outside from the soil then it is called aerial stem. In this type of stem branches, leaves, node, internodes, buds flower-fruit etc are found. Examples-Grapes, lemons, roses etc.

To perform some specific works, stems sometimes do exclusive  works other than common work then shapes and sizes of the stems are changed and it is called modifications of stems. Usually there exists three types of modifications in the stems-

Underground modifications

In the diverse conditions, underground stems store their food inside the stems and become thickened and tuberous. There are various types of modifications occur in underground stem-

  • Stem tuber- Potato
  • Bulb – Onion, garlic, tulips, lilies etc.
  • Corm – Gladiolus, crocus, saffron etc.
  • Rhizome—Ginger, turmeric, arrow root etc.
Sub aerial  modifications

There are various types of modifications exists in such types of stem-‘

  • Runner – Grass root, mereilia etc.
  • Stolon – Mint, jasmine, straberi etc.
  • Offset – Water plant, pestia etc.
  • Sucker – Roses, gilly flower etc.
Aerial modifications

There also occur various types of aerial modifications-

  • Stem tendril – Grape.
  • Stem thorn – Lemon, roses, jujube, plum or Chinese date.
  • Phylloclade – Cactus.
  • Bublis – Ruscus.

Leaf in Angiosperms

Leaves prepare food for the plants. Respiratory activities are performed  by the leaves through stomata. Leaves perform the vascular and execratory activities of foodstuffs. Leave help in performing conducive reproduction and pollination. Some leaves work to store food-stuffs.

Leaves undergo through various modifications like the following—

  • Leaf spines : In this class of modification leaves transform into spines. Examples-Cactus, lemon etc.
  • Floral leaves : In this class of modification floral activities like calyx, corolla etc are performed by the leaves.
  • Bract : In this class of modification leaves become colored and fascinate the insects towards themselves.
  • Scaly leaves: Sometimes leaves modified themselves to protect buds and other soft organs of the plant, called scaly leaves. Sometimes scaly leaves also store the food-stuffs. Example-Garlic, onion, etc.
  • Leaf root : In this class of modification, leaves transform into roots. Example- Briophylem etc.
  • Leaf tendril : In this class of modification leaves take the form of tendrils. Example-Pea plant.
  • Storage leaves : In this class of modification leaves store foodstuffs and become thickened and tuberous.
  • Picher : In this class leaves accommodate to trap the insects and modified themselves in the form of bags. Example-Pitcher plant.
  • Bladder : In this class of modification, leaves transform themselves in the form of bladder to trap   the aquatic insects like utriculeria etc.
  • Leaf hooks : In this class of modification leaves turn like nails. Example-bignonia etc.
  • Phyllode : Australian acacia etc.

Main parts of a Typical Flower

A Flower is a composite system of modified leaves and knots, which directly participates in the reproductive activity and produces fruits and seeds. Usually a flower is composed from four modified leaves which are attached to the thickened receptacle thalamus. This receptacle thalamus has four types of cycle- calyx, corolla, androecium and gynoecium.

The flower which has all four cycles is called complete flower, while if any cycle be absent then it is called incomplete flower. The organelles calyx and corolla and called auxiliary organelles, while androecium and gynoecium and called necessary organelles.


This is an extremely outer cycle of the flower and it is green coloured cycle of sepals. The main work of calyx is to protect the soft parts of buds and performs photosynthesis. In some flowers, it becomes coloured and its main function to attract insects for the pollination.


This is the second cycle of the flower which is confined inside the organelle calyx.  Corolla is mainly composed from 2-6 petals and it is also colored  whose  main function  to fascinate insects for the pollination.


This is the third cycle of sepals which is the made from stamens. The stamen is the male sex organ of the flower. Each and every stamen has its three parts viz. Filament, Anther and Connective. The vital component of androecium is basically stamen and in which pollen grains are found in pollen sac.


This is the central part (fourth cycle) of the flower and it is the female sex organ  of the flower. Each and every gynoecium is made from one or more carpels and it produces female ovule. The carpel is made from three components- ovary, style and stigma.

Fruit in Angiosperms

The fruit is usually formed in the ovary of the plant and pericarp is formed from the mature ovary walls. But in the formation of some fruits like apple, jack fruit etc, calyx, corolla, thalamus etc participate and such fruits are called false fruits.

Usually pericarp has three layers outermost layer is called epicarp. Middle Layer is called mesocarp, while innermost layer is  called endocarp. Please note that Coconut coir is Mesocarp.

On the basis of fertilization of the flower there are two types of fruits-

  • True fruit – The fruit forms in the ovary of the flower by the process of fertilization and zygote formation is called true fruit.
  • False fruit : When fruit formation occurs other than ovary and flowers organelles like calyx, corolla, thalamus etc take place then it is called false fruit. Examples- Apple, jack fruit, pear etc.

But in angiosperms too much diversities are found in their fruits, thus on macro level there are three classes in them.

  • Simple fruit – bean, mustard, mango, lemon etc.
  • Aggregate fruit- strawberry, lotus, raspberry, custard apple etc.
  • Composite (multiple) fruit- jack fruit, mulberry, banyan, fig etc.
  • Accessory / False Fruit: Apple

Here is a list of some common Fruits and their edible parts. This list is important.

FruitsEdible parts
MangoMid. Pericarp
TomatoPericarp and perisperm
LitchiPulpy aerial
Ground nutSeed leaves and embryo
Wood appleMesocarp and endocarp
Jack fruitSepals, bract, seeds
WheatEndosperm and embryo
CorianderThalamus and seeds
Custurd applePericarp
Water chest nutSeed leaves
LemonJuicy pore
Chinese dateEpicarp and mesocarp
MulberryBract, sepals and seeds

In some plants without fertilization, fruits are produced through ovary and the process of this non-fertilization  is called  parthenocarpy and such fruits are seedless. Examples-banana, papaya, orange, grapes, etc.

Other Important Topics

Stomata in Plants

There exist various tiny openings (called pores) on the surface of the skin of stems and leaves called stomata which are surrounded by two kidney shaped guard cells. In a leaf the number of stomata vary from 14 to 1040mm². These stomata exchange the moisture and help in transpiration activities  in the plants.

Annual rings in age determination

The branch of botany under which annul a rings of the plant are studied is called dendrochronolgy. By the elevation of number of annual rings in the plants or trees, the ages of the plants or trees are estimated exactly. Please note that dendrochronolgy is applicable only to a period of a few thousand years and only in the few areas where old wood samples have been preserved, radiocarbon dating can date events up to sixty thousand years old.

How does it work?

Due to the chronological, climatic changes the core activities of the cambium of any plant that of any place is regularly changed. In spring season this activity is increased, while in the winter season it is decreased, consequently distinct annual rings form which is the indicative parameter of the year growth.

Plant Physiology Topics

Plant Tissues

In plants, there are two kinds of tissues viz. Meristematic tissues and Permanent Tissues.

Meristematic Issue

The Meristematic tissues are divisible and cells in these tissues retain the power of division, so that plant keeps growing. These tissues are found in the regions of plant growth such as apical tissues, buds, nodes, side of branches etc.

1. Apical Dominance by Meristematic Tissues

Apical Dominance means that in plants, one Meristem {regions of growth / Meristematic tissues} inhibits the growth of other Meristems. The result of this is that a plant has one clearly defined main trunk. The tip of the main trunk bears the dominant Meristem and grows rapidly. It is not shadowed by branches. If the dominant Meristem is cut off, one or more branch tips will assume dominance. The branch will start growing faster and the new growth will be horizontal. To get a bushy growth, the tip of the main trunk is removed. This mechanism is based upon Auxin hormone which is produced in the apical Meristem and transported towards the roots in the cambium.

Permanent Tissue

Permanent tissues are formed by the cells which lose the power of division. Cells in permanent tissue are either living or dead. These cells have thick cell walls. These tissues are either simple {made of similar types of cells} or complex {made of different types of cells, working as single unit}.

Simple Tissues

Simple permanent tissues are of three kinds viz. parenchyma, collenchyma and sclerenchyma. Parenchyma tissues are the most vital parts and centers of important physiological functions such as respiration, photosynthesis, storage, secretion etc. These tissues help in growth and repair, wound healing, formation of adventitious roots. In succulent plants (Succulent plants are water-retaining plants adapted to arid climate or soil conditions, such as Carissa carandas or Karonda), these tissues store water; while in aquatic plants they store air. The collenchyma tissue also has living cells but these cells are with thick cell walls and provide tensile strength. It works both as vital and mechanical tissues.  Sclerenchyma is made of dead cells and it works as mechanical tissues.

Complex Tissues

In plants, the complex tissues are Xylem and Phloem. Xylem (wood) conducts water and minerals from root to leaves and also provides mechanical strength. It remains at inner side in the root and in the form of wooden columns in stems as shown below:

Phloem or wood conducts the prepared food material from the leaves to the storage organs and growing organs. Generally Phloem is found outside the vascular cambium, but in some plants it may be found inside the pith also in the form of intraxylary phloem.

Why plants die when bark is removed?

Here we note that when bark of a tree is removed in a circular fashion all around near its base, it gradually dries up and dies because roots are starved of energy. This is because removal of bark means removal of phloem and absence of phloem would block transport of soluble organic material made during photosynthesis in leaves to root of the plant.

Other Tissues in Plants

Plants also have secretory tissues such as water stomata or hydathodes. The water stomata release water via a process called guttation in aquatic plants. Pistia (also called water cabbage / water lettuce) is one such aquatic plant that has water stomata. Further, some plants are insectivorous (example Nepenthes, Pitcher plant) which have secretory tissues that release some poisonous material to kill the insects. Further, in Rubber plants (Ficus elastica and Havea brasiliensis), the laticiferous tissue secretes latex, which is dried and processed to produce natural rubber.


Plants have the amazing ability to harvest energy from the sun using chlorophyll and convert it into carbohydrates. These carbohydrates serve as chief energy source for almost all living beings in the world, including plants themselves.

Photosynthesis is the process through which the food is prepared by the plant from chlorophyll, carbon dioxide (CO2) and water (H2O) in the presence of sunlight. The chemical involve in the photosynthesis is –

6CO2 + 12H2O ———- C6H12O6+6H2O+6O2

Most organisms that utilize photosynthesis to produce oxygen use visible light to do so, although there are plants which use infrared radiation too. Photosynthesis occurs in Chloroplats of plants and it done by Chlorophyll pigment. Magnesium is found in the chlorophyll of plant leave and in the nucleus of the chlorophyll on atom  of the magnesium  exists. The chemical substance chloroplast is called the nucleus of the photosynthesis.

Factors influencing photosynthesis

1. Light

Mainly, violet, blue and red light portion of sunlight is used for photosynthesis. Further, photosynthetic activity is maximum in low intensity light; as the intensity of the light increases photosynthetic activity decreases.

2. Temperature

As the process of photosynthesis is the complex chemical reaction of the various enzymes and these enzymes only being  normal to participate  in the chemical reaction up to a moderate and optimum temperature. Thus photosynthetic activity increase from 0°C to 37°C but 37°C onwards such activity decreases abruptly.

3. Carbon dioxide (CO2)

Up to a definite level on increasing the concentration of CO2, photosynthetic activity increases, but after the certain limit, the increase of its concentration does not affect the photosynthetic activity.

4. Water (H2O)

Due to the lack of water, the photosynthetic activity abruptly decreases because of steep fall of the rate of evaporation. In fact, the pores of the plant leaves become partially closed and ultimately the translocation of CO2 is disrupted through the leaves.

Why Peepal tree releases Oxygen all the time?

Most plants largely uptake Carbon dioxide (CO²)and release oxygen during the day (photosynthesis) and uptake oxygen and release CO² during the night (respiration). Some plants such as Peepal tree can uptake CO² during the night as well because of their ability to perform a type of photosynthesis called Crassulacean Acid Metabolism (CAM). However, they don’t release large amounts of oxygen during the night. CAM is one of the three types of photosynthesis pathways occurring commonly in plants; the other two being C3 and C4 pathways.

Plant Hormones

Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved to other locations, in other locations of the plant. Hormones also determine the formation of flowers, stems, leaves, the shedding of leaves, and the development and ripening of fruit. Plants, unlike animals, lack glands that produce and secrete hormones. Instead, each cell is capable of producing hormones. They affect which tissues grow upward and which grow downward, leaf formation and stem growth, fruit development and ripening, plant longevity, and even plant death. Hormones are vital to plant growth, and, lacking them, plants would be mostly a mass of undifferentiated cells.

There are various types of plant hormones.


Auxin is a group of plant hormones that produce a number of effects, including plant growth, phototropic response through the stimulation of cell elongation (photopropism), stimulation of secondary growth, api¬cal dominance, and the development of leaf traces and fruit. An important plant auxin is indole-3-acetic acid. (IAA and synthetic auxins such as 2,4-D and 2,4,5-T are used as common weed killers.)

  • They are basically weak organic acids which actively participate in the cell division and the cell elongates consequently thus plants growth occurs.
  • If some auxins hormones be applied on the flower of the plants then without fertilization and without seeds formation ovary wall becomes tuberous and forms the fruit. This is called the artificial parthenocarpy

Agent Orange

2,4-dichlorophenoxyacetic acid (2,4-dichlorophenoxyethanoic acid) is a synthetic auxin frequently used as a weed killer of broad-leaved weeds. When two herbicides 2,4,5-T and 2,4-D and mixed in equal parts, it is called Agent Orange, which was used by US in Vietnam war.


Gibberellins, or GAs, include a large range of chemicals that are produced naturally within plants and by fungi. They were first discovered when Japanese researchers, including Eiichi Kurosawa, noticed a chemical produced by a fungus called Gibberella fujikuroi that produced abnormal growth in rice plants.

  • Gibberellins are important in seed germination, affecting enzyme production that mobilizes food production used for growth of new cells. This is done by modulating chromosomal transcription. In grain (rice, wheat, corn, etc.) seeds, a layer of cells called the aleurone layer wraps around the endosperm tissue.
  • Absoption of water by the seed causes production of GA. The GA is transported to the aleurone layer, which responds by producing enzymes that break down stored food reserves within the endosperm, which are utilized by the growing seedling. GAs produce bolting of rosette-forming plants, increasing internodal length. They promote flowering, cellular division, and in seeds growth after germination. Gibberellins also reverse the inhibition of shoot growth and dormancy induced by ABA.


Cytokinins or CKs are a group of chemicals that influence cell division and shoot formation.

  • They were called kinins in the past when the first cytokinins were isolated from yeast cells.
  • They also help delay senescence or the aging of tissues, are responsible for mediating auxin transport throughout the plant, and affect internodal length and leaf growth.
  • They have a highly synergistic effect in concert with auxins, and the ratios of these two groups of plant hormones affect most major growth periods during a plant’s lifetime.
  • Cytokinins counter the apical dominance induced by auxins; they in conjunction with ethylene promote abscission of leaves, flower parts, and fruits.
  • The correlation of auxins and cytokinins in the plants is a constant (A/C = const.).


Ethylene is a gas that forms through the Yang Cycle from the breakdown of methionine, which is in all cells. Ethylene has very limited solubility in water and does not accumulate within the cell but diffuses out of the cell and escapes out of the plant.

  • Its effectiveness as a plant hormone is dependent on its rate of production versus its rate of escaping into the atmosphere. Ethylene is produced at a faster rate in rapidly growing and dividing cells, especially in darkness. New growth and newly germinated seedlings produce more ethylene than can escape the plant, which leads to elevated amounts of ethylene, inhibiting leaf expansion.
  • As the new shoot is exposed to light, reactions by phytochrome in the plant’s cells produce a signal for ethylene production to decrease, allowing leaf expansion. Ethylene affects cell growth and cell shape; when a growing shoot hits an obstacle while underground, ethylene production greatly increases, preventing cell elongation and causing the stem to swell. The resulting thicker stem can exert more pressure against the object impeding its path to the surface. If the shoot does not reach the surface and the ethylene stimulus becomes prolonged, it affects the stem’s natural geotropic response, which is to grow upright, allowing it to grow around an object.

Abscisic Acid

Abscisic acid (ABA) hormone activates the vascular cambium during mitosis cell divison and its presence slows down the stems growth. This hormone can be used in preventing the sprouting activities in seeds and buds. In dry stem it provokes the pores to close and consequently a downfall in the rate of evaporation takes place. The role of Abscisic acid in abscission of leaves is doubtful and not proved, please note it.

General Science-3: Animal Kingdom

Prelims MCQ Topics

Basic idea about the animals belonging to various taxonomic groups of animal Kingdom. Comparison of three classes of Arthropods, Cartilaginous and Bony Fish examples, Swim Bladder in Fishes, Amphibians – Adaptations to Terrestrial environments, Bird Adaptations for Flight, Common features of all mammals, Monotremes / Marsupials / Placentals


Note: In UPSC or state level examinations, questions are not asked directly regarding classification of the animals in GS Paper. The questions are generally odd man out type, which are easy and low hanging fruits if you have basic idea about various taxonomical groups given in this module. Two Example questions are given here:
Q-1: Consider the following:

  1. Sea Cow
  2. Sea Horse
  3. Sea Anemone

Which of the above is / are mammals?
{In this question Sea Cow (Dugong) is a mammal, while Sea Horse is a Fish. Sea Anemone is a Cnidarian; so correct answer is Only 1}
Q-2: Among the following organisms, which one does not belong to the class of other three? {CSE-2014}

  1. Crab
  2. Mite
  3. Scorpion
  4. Spider

{The above question is asking you to differentiate between Arachnids and Crustaceans among Arthropoda. This is discussed in this module}. Some more example Questions have been given in the end of this module.

Animal Kingd