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Ques What is definition of resistivity?
Resistivity of a substance is numerically equal to the resistance of the substance which is 1 metre in length and 1 square metre in cross section.
OR
Resistivity is the resistance across opposite faces of a cube of a given material of one metre side.
Ques Why is variation important for species and not necessarily for individuals? (Asked by: Ajaydeep)
Ans. The difference in the characters among the individuals of a species is called variation. Variation is the occurrence of differences among the individuals of a species.
Variation is necessary for species as it has been found that some variants become advantageous in the struggle for survival with respect of characteristics of an organism such as size, shape, physiology, mode of behaviour etc. Thus, variation helps in maintaining the differences between individuals and may make some or other more favourable with environment and making species more adaptable to environment.
Ques. What do you mean by Greenhouse effect? (Rohit Jain)
Ans. The trapping of outgoing heat by carbon dioxide layer in the air is green house effect or global warming. Increased level of CO2 in air traps more heat radiated from earth surface and leads to increased heating of Earth.
Ques. What is osmoregulation? (kani)
The control of water content and the mineral salts of the body is called osmoregulation. If there is excessive water in the body, then water may move into cells by osmosis. If there is less water then water will move out of cells.
The kidneys (helped by hypothalamus and pitutary gland) are responsible for osmoregulation.
Ques. How is presbyopia cured? Is it a form of hypermetropia? (Almas)
Ans. Presbyopia is a special kind of hypermetropia, which is caused mainly due loss of power of accommodation of the eye due to ciliary muscles being weak and eye lens becoming inflexible.
It is generally corrected in the same way as hypermetropia by using spectacles using convex lenses.
In some cases, when the person has both defects-myopia and hypermetropia, it is corrected by used of bifocal lenses, in which upper part is concave lens and lower part is convex lens.
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