(I) The plants develop a thick cuticle to check transpiration. 
(il) They have sunken stomata.
(iii) The leaves are modified into spines or scales.
(iv) The stem becomes a phylloclade and helps in photosynthesis and storage of food and water.
(v) Sorne have their stomata open at night and dosed at day.
(vi) They may have deep tap root to reach the water available at lower layers of soil or even water table

 Vertebrates like bear undergo hibernation, to escape in time.
Angiosperms produce seeds and certain other vegetative structures to tide over unfavourable conditions in the habitat.

(i) In summer, we sweat profusely; the evaporation of sweat causes a cooling and brings down the body temperature.
(ii) In winter, we shiver, and that produces heat to raise the body temperature.

Heat loss or heat gain is a function of surface area.
Since small animals (like humming birds) have a larger surface area relative to their volume, they tend to lose body heat very fast, when it is cold outside.
They spend more energy to generate body heat through metabolism; considering the cost and benefit of maintaining   a constant internal temperature, small animals (humming  birds) are not found in polar regions.

a) These are places at high altitudes, i.e. 73,500 m above sea level.
Tourists may experience altitude sickness, whose symptoms include nausea, heart palpitations and fatigue.
Since the atmospheric pressure is low at high altitude, the body does not get enough oxygen.
But gradually, the body gets acclirnatised and stops experiencing altitude sickness.
(b) Heat loss or gain is a function of the surface area of the body.
 Small animals have a larger surface area relative to the volume of the body; hence they tend to lose body heat very fast, when it is  cold outside.
They have to spend more energy to generate body heat through metabolism; hence small animals are not found in polar regions.

Reproductive strategies:
(i) Some organisms breed only once in their life time-e.g. Bamboo, Pacific Salmon.
(ii) Some produce a large number of small-sized offspring-Oysters.
(iii) Some breed many times during their life time-e.g. birds.
(iv) Some produce a small number of large sized offspring, e.g. Mammals.

(i) Predation acts as a conduit for energy transfer across trophic levels.
(ii) It keeps the prey population under control.
(iii) It helps in maintaining species diversity in a community, by reducing the intensity of competition.
(iv) Biological control of pests is based on the principle of predation.

Fungi produce various kinds of thick-walled spores to survive under unfavorable conditions; they germinate when conditions become favorable.
Zooplanktons enter diapause, a stage of suspended development, under unfavourable conditions.
Bears go into hibernation during winter to escape in time of unfavourable conditions.

Symptoms include:
(i) nausea
(ii) fatigue, and
(iii) heart palpitations.
Adaptations are:
(i) Increase in breathing rate.
(ii) Increased production of red blood cells.
(iii) Decreasing binding capacity of haemoglobin.

(a) Commensalism
(b) (i) Orchids grow as epiphytes on mango tree or other fruit trees.
Orchids are benefitted by getting a shelter, while the tree is neither benefitted nor damaged.
(ii) Barnacles growing on the whale are benefitted to move where food is available.
(iii) The cattle egrets always forage near to where the cattle animals graze; the cattle animals stir up the ground and the insects are flushed out from the vegetation and make it easy for the egrets to catch them.
(iv) The clown fish living among sea anemones get protection from their predators, which stay away from the stinging tentacles of the sea anemone:
(c) Amensalism
Roots of certain plants secrete chemicals, which are harmful to the soil organisms.
The antibiotics secreted by certain soil fungi are harmful to soil fungi bacteria. (anyone)
(d) Interactions should be beneficial to all concerned. Avoid selfish or selfcentered people.

The chemical composition and pH of water are important to affect the animals.
Some animals can tolerate only a narrow range of salinity and are called stenohaline.
Some animals can tolerate a wide range of salinity and are called euryhaline.
Many freshwater fishes can not live for long in sea water and vice versa, because of the osmotic problems, they would face in such waters.
(b) (i) The leaves are reduced to spines.
(ii) The stem is green, flattened, spongy and takes over the function of photosynthesis .
(iii) A thick cuticle prevents loss of water.
(iv) They have a special photosynthetic mechanism (CAM), that enables their stomata to remain closed during day and open during night.
(c) Water is the most precious resource, use it judiciously and think of programs for its conservation.

The different ways to cope with abiotic stresses are:
(i) Regulation
(ii) Conformation
(iii) Migration and
(iv) Suspending.
(i) Regulation: Some animals maintain homeostasis by physiological means that ensure a constant body temperature, constant osmolarity of body fluids, etc; mammals maintain a constant body temperature.
(ii) Conformation: Those animals called conformers, which cannot maintain homeostasis, change their body temperature or osmolarity of body fluids according to the ambient environment.
(iii) Migration: If the stressful condition is localised, animals move away temporarily from the stressful environment to more hospitable area and return when the stressful conditions is over.
(iv) Suspending: Some animals avoid the stress by escaping in time; bears go into hibernation during winter and snails go into aestivation in summer. (any three)

(I) When resources are limiting, the population growth curve is sigmoid and it is represented by the equation:
\(dN/dt=rN\left( \frac { K-N }{ K } \right) \), where
N = population density at time t
r = intrinsic rate of natural increase
K = carrying capacity
When resources are not limiting, the growth curve is J shaped and is represented by the equation: dN/dt = rN 
\(N_{ t }={ N }_{ 0 }^{ e^{ rt } },where\)
\(N_{ t }\) =population density after time t
\(N_{ 0 }\)= population density at time zero
r = intrinsic rate of natural increase
e = the base .of  natural logarithm (2.71828)