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.

(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.

(i) A - Exponential growth curve
B- Logistic growth curve
(ii) Logistic growth B is considered more realistic one because the resources are finite and become limited sooner or later.
(iii) K stands for carrying capacity which refers to the maximum number of individuals of a population that the given environment can sustain at a given time.
(iv) N symbolise population density, i.e. the number of individuals of a species in a given population per unit area.

(i) An individual has birth; a population has birth rate, i.e. the number of individuals added to a population by birth/hatching per capita in a given period of time.
(ii) An individual has death; a population has death rate, i.e. the number of individuals removed from a population due to death per capita in a given period of time.
(iii) An individual is either male or female, but a population has sex ratio, i.e. the number of males: .the number of females at a given time.

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