Biology:2013:[Delhi ]:Set-III

The tapetum is the innermost layer of a microsporangium. It is found in a cluster of two in each lobe of the anther. It nourishes the pollen grains. If it malfunctions, then the pollen grains are provided with adequate nutrition. Hence, the anther is not able to produce mature viable male gametes.

The sharing of injection needles between two individuals can lead to the transfer of various diseases like AIDS from an infected person to a healthy person.

The enzyme is DNA polymerase. The property that is responsible for continuous and discontinuous replication of the two strands of a DNA molecule is that the enzyme catalyses the polymerisation of the nucleotides only in 5' to 3' direction during replication.

MOET technique is used to:
i) obtain a better breed of animals.
ii) produce economically important hybrids in a short period of time.

Plant cells have a cell wall which is made of cellulose. However, animal cells lack the cell wall and do not contain cellulose. Cellulase is an enzyme that digests cellulose. So, it is needed for digesting the cell wall before the genetic material can be isolated from the plant cells.

(a) Genetic diversity
(b) Ecological diversity

The Net Primary Productivity (NPP) of an ecosystem can be derived by using the following equation:
NPP = GPP (Gross Primary Productivity) – R (Respiratory Losses)

Convergent evolution is a process by which organisms of different origins individually develop the traits that are similar in function but different in their structure.

Both sweet potato tubers and potato tubers are underground fleshy structures. They perform the functions of storage of food and vegetative reproduction. However, both are different in origin as sweet potato is an adventitious root, whereas potato tuber is an underground stem.

(a) An allergy is the exaggerated response of the immune system to the antigen present in the environment. An antigen which can elicit such a response is called an allergen.
(b) Two unique characteristics of this system are:
i) Specificity, i.e. the response is elicited only to a specific antigen.
ii) Memory: There is a low intensity response to an antigen when the immune system encounters it for the first time. It is the primary response. The antigen specific antibodies are produced after this response, which ensures a fast and heightened response the next time the body encounters it.

Chorionic villi are finger-like projections that develop from the trophoblast layer of the zygote after it has been implanted in the uterine wall.
Functions of chorionic villi:
a) The projections from the uterine tissue interdigitate with the chorionic villi to form the placenta, which is the connecting link between the mother and the foetus.
b) It facilitates the supply of oxygen and nutrients to the embryo.