(i) (a) Species  A group of specific organisms with similar characteristics which are capable of compatible interbreeding to produce fertile offsprings
(b) Niche The way in which an organism functions in relation to the biotic and abiotic factors within its habitat that serves a purpose in its environment.
(ii) Increased selection pressure due to climatic or habitat change cause organisms to become specialised and have the optimum phenotype that is suited to the prevailing environment condition.
In the primary radiation, the six closely related species evolved as a result of the increasing water levels when the lake first filled. This change in the environment exerted a selection pressure on their river dwelling ancestors to adapt by developing different characteristics for survival, thus giving rise to the six species that could occupy more niches.

Predation is an interaction where one organism (predator) kills and eats the other weaker organisms called prey. Predation is a natural way of transferring the energy fixed by plants, to higher trophic levels.
Examples of predation include snake eating a frog, tiger killing and eating a deer, Predators keep prey population under control which otherwise could achieve very high population densities and cause instability in ecosystem.
They also help in maintaining a species diversity in a community by reducing the intensity of competition among competing prey species.

Figure I It is single population and all individuals are of the same species, i.e. all individuals interact among themselves and their environment in an intraspecific interaction.
Figure II It is a community and it contains three populations of species A,B and C. They interact with each other and their environment in as interspecific interaction.
Figure III It is a biome. It contains three communities of which one is in climax and other two are in different stages of development. All three communities are in the same environment and they interact with each other and their environment.

(i) The interaction in figure I parasitism (one organism is benefitted and other is harmed) and in figure II, the interaction is mutualism (both organisms are benefitted).

(ii) The doctors often use leech therapy after a microsurgery (attaching tissues and connecting thin arteries and veins). If the veins are not connected properly, excess blood can pool-blocking the entry of oxygenated blood and eventually leading to death of reattached tissue.
(iii) Leeches are used to treat such a condition due to the presence of hirudin in their saliva. Hirudin is an anticoagulant factor which prevents the blood from pooling in the reattached tissues.

Contractile nacuole helps in osmoregulation. Because of hypertonic, the water diffuses inside the cell constantly and gets collected in the contractile vacuole, which squeeze the extra water out of the cell periodically. Thus, keeping the internal environmental constant. In case marine organisms, this does not occur due to hogh salinity, therefore, there is no need of contractile vacuole.

Coral reefs are found in zone with salt concentration (salinity), optimal temperature and with a less siltation condition which fairly facilitate to colonise corals. Hence, are found in Talil Nadu and east coast of India. In case of high siltation and water flow, coral reef do not colonise.

S-shaped pattern of population growth from shows an initial gradual increase, followed by an exponential increase and then a gradual decline to a near constant level. It is different from J-shaped curve because J-shaped pattern shows exponential population growth and its abrupt crash after attaining the peak value.

A- When resources are not limiting the growth, plot is exponential.
B- When resources are limiting the growth, plot is logistic, K is the carrying capacity.

(a) Arctic tern    
(b) Tiger/Lion    
(c) Aphid    
(d) Chameleon    
(e) Glycosides (in Calotropis).