General Science Questions (MCQs) for Competitive Examinations

Notes:
Plants that flower and fruit only once and then die are termed monocarpic or semelparous such as bamboo. The term was first used by Alphonse de Candolle. Other terms with the same meaning are hapaxanth and semelparous. The antonym is polycarpic, a plant that flowers and sets seeds many times during its lifetime; the antonym of semelparous is iteroparous. 

Notes:
As per the report of WWF the ten most endangered rivers emerge as: the Salween, La Plata, Danube, Rio Grande, Ganges, Murray-Darling, Indus, Nile, Yangtze and Mekong.

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The Cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, and that all cells come from pre-existing cells. Cells are called the ‘Building Blocks of Life’ or the ‘Basic units of Life’.

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Wilhelm Johannsen was a Danish botanist, plant physiologist and geneticist. His most well-known research concerned so-called pure lines of the self-fertile common bean. He was able to show that even in populations homozygous for all traits, i.e. without genetic variation, seed size followed a normal distribution. This was attributable to resource provision to the mother plant and to the position of seeds in pods and of pods on the plant. This led him to coin the terms phenotype and genotype and introduce the term gene. This term was coined in opposition to the then common pangene that stemmed from Darwin’s theory of pangenesis.

Notes:
Conditions which increase the rate of evaporation also increase the rate of transpiration. Transpiration is more rapid in hot, dry and windy conditions than it is in still or humid conditions. Plenty of light also speeds up transpiration. Factors that affect transpiration rate Factor Description Explanation Light In bright light transpiration increases The stomata (openings in the leaf) open wider to allow more carbon dioxide into the leaf for photosynthesis. Temperature Transpiration is faster in higher temperatures Evaporation and diffusion are faster at higher temperatures Wind Transpiration is faster in windy conditions Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf Humidity Transpiration is slower in humid conditions Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air.

Notes:
A heavy, silvery d-block element, Mercury is the only metal that is liquid at STP The only other elements that are liquid under these conditions is bromine.

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When a volume of air at a given temperature holds the maximum amount of water vapour, the air is said to be saturated. When relative humidity reaches 100 percent or is saturated, moisture will condense, meaning the water vapor changes to liquid droplets.

Notes:
White phosphorus is the most reactive form of phosphorus. It is made up of discrete P4 tetrahedra which are subjected to very high angular strain as the angles is 60 degrees. This high angular strain makes white phosphorus unstable and highly reactive. It ignites spontaneously at about 50°C, and at much lower temperatures if finely divided. Therefore, it is stored in cold water in brown coloured bottles.

Notes:
Oxidized forms of nitrogen include nitrite (NO2) and nitrate (NO3). Nitrogen mainly occurs in wastewater in this form. Because nitrite is easily oxidized to nitrate, nitrate is the compound predominantly found in groundwater and surface waters.

• 4NH4O —> 4NH4(+) + 4OH(–)
• 4OH(–) —> 2H2O + O2
• NH4 + O2 —> NO2(–) + 2H2O
• 2NO2(–) + O2 —> 2NO3(–)

Notes:
Methane is the most common gas that can cause explosions in coal mines. Methane is a colorless and odorless gas that is highly flammable and can easily be ignited by a spark or flame. When methane accumulates in high concentrations in the air in a coal mine, it can create a risk of explosion. This is why it is important for miners to monitor methane levels and take steps to prevent it from reaching dangerous levels.