Short Answer TypeState with reason any two possible consequences of elimination of decomposers
from the Earth.
Energy flow in a food chain is unidirectional. Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Write one difference between asexual and sexual mode of reproduction. Which species is likely to have better chances of survival - the one reproducing asexually or the one reproducing sexually? Justify your answer.
What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant though each new generation in a combination of DNA copies of two individuals?
List three main factors responsible for the speciation and briefly describe each one of them.
A trait may be inherited, but may not be expressed. Justify this statement with the help of a suitable example
Long Answer TypeList two reasons for carbon forming a large number of compounds. Name the type of bonding found in most of its compounds. Why does carbon form compounds mainly by this kind of bonding? Give a reason why the carbon compounds.
(i) Generally, have low melting and boiling points.
(ii) do not conduct electricity in the molten state.
The two characteristic properties of the carbon element which leads to the formation of a very large number of organic compounds are: Catenation and Tetravalency.
Catenation: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large chain molecules. This property is called catenation.
Tetravalency: Carbon has a valency of four. So, it is capable of bonding with four other atoms of carbon or atoms of some other monovalent element.
Covalent bonding is found in most of the carbon compounds.Carbon form compounds mainly by covalent bonding becauseThe bonds that carbon forms with most other elements are very strong making
these compounds exceptionally stable. One reason for the formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.
(i) Carbon compounds generally have low melting points and boiling points because The force of attraction between the molecules of carbon compounds is not very strong. These weak intermolecular forces make them very easy to pull apart from each other. Since they are easy to separate, carbon compounds have low melting and boiling points.
(ii) Carbon compounds do not conduct electricity in the molten state because bonding in carbon compounds does not involve any formation of ions.
(a) List the parts of the human eye that control the amount of light entering into it.
Explain how they perform this function.
(b) Write the function of retina in human eye.
(c) Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?
(a) Explain the following terms related to spherical lenses:
(i) optical centre
(ii) centres of curvature
(iii) principal axis
(iv) aperture
(v) principal focus
(vi) focal length
(b) A converging lens has focal length of 12 cm. Calculate at what distance the object should be placed from the lens so that it forms an image at 48 cm on the other side of the lens.
Switch
