General Science Questions (MCQs) for Competitive Examinations

Notes:

Steel is an alloy made by combining iron and other elements, the most common of these being carbon. When carbon is used, its content in the steel is between 0.2% and 2. 1% by weight, depending on the grade. Other alloying elements sometimes used are manganese, chromium, vanadium and tungsten. Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another.

Notes:
Rings of cartilage are present in the throat, specifically in the trachea or windpipe, to ensure that the air passage does not collapse. These semi-circular rings provide the necessary structural support to keep the airway open regardless of pressure changes that occur during breathing. This is very important for maintaining a clear, open path for air to flow into our lungs for respiration.

Notes:
Flowers emit fragrance to attract pollinators which are mainly insects. The fragrance plays a prominent role in the localization and selection of flowers by insects, especially moth-pollinated flowers, which are detected and visited at night. If they have become infested with herbivores like caterpillars, they attract beneficial insects like parasitic wasps with the help of scent signals from their leaves.

Notes:
A thick vein seen in the middle of the leaf is called the midrib. Pinnately veined leaves have one large central vein, called the midrib, which extends from the base of the blade to its tip. Other large veins branch off on each side of the midrib. The leaves of beech, birch, and elm trees have such a vein pattern.

Notes:
Composting is the depomposition of plant remains and other once-living materials to make an earthy, dark, crumbly substance that is excellent for enriching soil. It is the chief way to recycle wastes.

Notes:
Plants obtain nitrogen through their roots. In the soil, nitrifying bacteria change ammonia into nitrite (NO2 –) and then into nitrate (NO3 –), this process is known as nitrification. Furthermore, plants also absorb nitrogen in an organic form. Several organic compounds (compounds containing carbon) constitute the organic fraction of nitrogen in the soil. The organic matter in the soil exists as decomposing plant and animal residues, relatively stable decomposition-resistant compounds, and humus. The abundance of various forms of nitrogen can be altered by plant roots through the change in pH and secretion of organic compounds or oxygen.

Notes:
Infection is the invasion of an organism’s body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. Infectious diseases can be spread from one person to another, for example through contact with bodily fluids, by aerosols (through coughing and sneezing), or via a vector, for example a mosquito.

Notes:
The gap between the two neurons is called the synapse. It is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron. Synapses are essential to neuronal function : neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so.

Notes:
Humming birds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm (3–5 in) range. Indeed, the smallest extinct bird species is a humming bird, the 5-cm Bee Humming bird. These birds being the smallest are, capable of flying both in forward and back direction.

Notes:
Chameleons have specialized cells, chromatophores, which contain pigments in their cytoplasm, in three layers below their transparent outer skin. Dispersion of the pigment granules in the chromatophores sets the intensity of each color. Chromatophores contain pigments and reflect light, which are responsible for creating coloration. In chameleons, there are four types of chromatophores: xanthophores, erythrophores, iridiophores, and melanophores (Cooper and Greenberg, 1992).