(a) Temperature, water, light and soil.
(b) (i) Temperature influences the kinetics of enzymes and thereby the metabolism and other physiological functions of the organisms.
1. Organisms may be eurythermal and can tolerate a wide range of temperatures or stenothermal and can tolerate only a narrow range of temperatures.
(ii) Water is important to sustain life and productivity and distribution of plants is dependent on water.
1. Freshwater forms cannot thrive in sea water and vice versa.
(iii) Light influences photosynthesis of plants.
1. Light also influences the flowering in plants and timing of foraging, reproduction and migratory activities of animals.
2. Aquatic plants occupy different depths depending on their pigments and the light available.
(iv) Soil influences vegetation by the water holding capacity topography and its composition.

(a) Commensalism:
(i) It is the interspecific interaction where one species is benefitted by the association while the other is neither benefitted nor harmed. e.g: Sucker fish attached to a shark.
(b) Parasitism:
(i) It is the interspecific interaction where one species (called parasite) takes food and shelter from another living species (and damages the host in due course of time, the parasite is benefitted and the host is harmed, e.g: Tapeworm in the intestine of man.
(c) Camouflage:
(i) It is an adaptation, where the animal (organism) blends with the surroundings to escape detection by the predator. For e.g: Frogs have olive green skin with patches of chromatosphores to camouflage with the grasses.
(d) Mutualism:
(i) It is the interspecific interaction, where both the interacting species are mutually benefitted e.g: an alga and a fungus in a lichen and Rhizobium and Legume plant.
(e) Interspecific competition:
(i) It is an interspecific interaction, where organisms of two different species compete with each other for certain resources. e.g: Flamingoes and fishes competing for zooplanktons.

(a) Adaptations of desert plants and animals:
Desert Plants
(i) Plants have a very deep root system.
(ii) Stems become modified into fleshy and spongy structures or they become expanded, flat and green (phylloclade) to store water and to carry out photosynthesis.
(iii) Leaves are either small or have leathery surface, waxy cuticle and sunken stomata.
(iv) Leaves are modified into spines in cacti.
Importance of light to plants:
(i) Light is important to plants for photosynthesis and preparation of food materials.
(ii) Duration of light determines the flowering and fruiting in many Plants.
(iii) Availability of light is associated with temperature and it determines the functioning of enzymes.
Desert Animals
(i) They burrow into the soil and hide to escape from the above ground heat. 
(ii) Desert lizards manage to deal with high temperature by keeping the body temperature fairly constant by behavioural means. 
(iii) Kangaroo rats are capable of meeting their water requirement (up to 90%) from the metabolic water produced by oxidation of fat. 
(iv) They also concentrate their urine to a minimal volume (released urine in the crystallized form).
Behavioural adaptations in animals:
To cope up with the extremes in their environmental conditions, they show modified behaviour to suit the conditions, they show modified behaviour to suit the environmental conditions.
(i) Migration is an example, where the animals temporarily moves to a less stressful environmental.
(ii) The desert lizards basic in the sun and absorb heat when the body temperature drops below the comfort zone. But when temperature starts to increase they move into shade.
Effect of temperature:
(i) Temperature affects the enzyme kinetics and hence, the physiological functions animals have developed tolerance over a wide range of temperatures or only for a narrow range of temperature.
(ii) The levels of their thermal tolerance determine their geographical distribution.
Effect of water scarcity:
(i) In the absence of an external source of water, the kangaroo rat is capable of meeting all its water requirements through its internal fat oxidation.
(ii) It also concentrates its urine, so that minimal volume of water is used to remove excretory products in the crystallized form.
(b) Adaptations of plants to water scarcity.
(i) The plants develop a thick cuticle to check transpiration.
(ii) 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.

(i)Deserts cover about one fifth of the Earth's surface and occur where rainfall >500mm/year.
(ii) Rainfall is usually very low and concentrated in short bursts between long rainless periods. Evaporation rate regularly exceed rainfall rates.
(iii) Soils are course-textured, shallow, rock or gravely with good drainage and have no subsurface water. The finer dust and san~ particles are blown elsewhere, leaving heavier pieces behind. Sand dunes are common.
(iv) Mean annual temperatures range from 20-25° C. The extreme maximum range from 43.5 - 49° C. Minimum temperature sometimes drop to -18° C. Based on IlK temperature range, deserts can be H deserts and Cold deserts.
(v) Hot deserts such as the Sahara of North Africa and the deserts of the South western U.S., Mexico, Australia and Indi (Thar desert) occur at low latitudes.
(vi) Hot deserts have a considerable amount of specialized vegetation: (xerophytes aloe, agave, Opuntia species, Euphorbs royleana as well as specialized vertebra and invertebrate animals.
(vii) Soils have abundant nutrients because the need only water to become very productive and have little or no organic matter.
(viii) Only animals which can tap available water or capable of storing sufficient water and withstand the heat can survive in the desert. The animals include small nocturnal (active at night) carnivores. The dominant animals are burrowers and have cursorial, fossorial and saltatorial adaptations.
(ix) The animals stay inactive in protected hideaways during the hot day and come out to forage at dusk, dawn or at night, when the desert is cooler.
(x) The dominant animals of warm deserts are reptiles and small mammals. The Indian Spiny-tailed lizard, the black buck, the white-footed fox are the common fauna of the Thar deserts. There are also insects, arachnids and birds.

The two most characteristic forms of behavioral adaptations are migration and courtship. Migration allows the animals to find better resources or evade threat. Courtship is a set of behavioral patterns to find a mate to reproduce. Most nocturnal animals remain underground or inactive during the daytime. This is a modification of their feeding and activity pattern or habit or behavior.

Organisms belonging to different populations interact for food, shelter, mating or for other necessities. Interaction may be intra specific (interaction within the members of same species) or interspecific (among organisms of different species).
Intraspecific association is observed for all livelihood processes like feeding, territoriality, breeding, and protection.
Interspecific associations or interactions can be:
Neutral: Where different species live together but do not affect each other.
Positive: It is a symbiotic relationship ill which no organism in association is harmed and either one or both may be benefitted. It is of two types - Mutualism and Commensalism.
Negative: One or both of the interacting organisms will be affected as in case of competition, predation, and parasitism.

r-selected species k-selected species Smaller sized organisms Larger sized organisms Produce many offspring Produce few offspring Mature early Late maturity with extended parental care Short life expectancy Long life expectancy Each individual reproduces only once or a few times in their lifetime Can reproduce more than once in a lifetime Only a few reach adulthood Most individuals reach a maximum life span Unstable environment, density independent Stable environment, density-dependent

1. The pectoral fins and dorsal fins act as stabilizers or balancers and the caudal fin helps in changing the direction as a rudder.
2. Arrangement of body muscles in the form of bundles (myotomes) help in locomotion.
3. Stream lined structure helps in the swift movement of the animals in water.
4. Respiration by gills making use of gases dissolved in water.
5. Presence of air-bladders filled with air for buoyancy.
6. Presence of lateral-line system. They function as chemoreceptors which is helpful in echolocating objects in water.
7. Integuments rich in mucous glands are protected by scales.
8. Maintain water and ionic balance in its body with excretory structures.

(i) These forests occur in eastern North America, northeastern Asia, and western and central Europe.
(ii) Have well-defined seasons with a distinct winter. Moderate climate and a growing season of 140-200 days during 4-6 frost-free months distinguish temperate forests.
(iii) Annual temperature varies from -30⁰ C to 30⁰ C.
(iv) Precipitation (750-1500 mm) is distributed evenly throughout the year.
(v) Soil is fertile, enriched with decaying litter.
(vi) Canopy is moderately dense and allows light to penetrate, resulting in well-developed and richly diversified under storey vegetation and stratification of animals.
(vii) Flora is characterized by 3-4 tree species per km2. Trees have broad leaves that are lost annually such as oak, hickory, beech, hemlock, maple, basswood, cottonwood, elm, willow, and spring-flowering herbs.
(viii) Fauna consists of squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and black bear. Based on seasonal distribution of rainfall, the types of temperate forests are:
(ix) Moist conifer and evergreen broad-leaved forests: wet winters and dry summers.
(x) Dry conifer forests: dominate higher elevation zones; low precipitation.
(xi) Mediterranean forests: precipitation is concentrated in winter (1000 mm /year).
(xii) Temperate coniferous forests: mild winters, high annual precipitation (> 2000 mm /year).
(xiii) Temperate broad-leaved rainforests: mild, frost-free winters, high precipitation (> 1500 mm/ year), evenly distributed throughout the year.

(i) Grasslands occur in temperate and in the tropical regions.
(ii) They have hot summers, cold winters, and irregular rainfall.
(iii) Often they are characterized by high winds.
(iv) The low irregular rainfall is the factor which makes the difference between a temperate deciduous forest and a temperate grassland.
(v) Herbivores like antelope, bison, wild horse, jack rabbit, ground squirrel and prairie dogs are abundant.
(vi) Predators include coyotes, foxes, hawks and snakes.
(vi) In India, fauna of grasslands includes Elephant, Gaur, Rhino, Antelope.
(vii) Flora of grasslands include purple needle grass, wild oats, foxtail, ryegrass and buffalo grass.

(i) Texture of soil - The texture of soil is determined by the size of the soil particles. The types of soil include sand, silt and clay on the basis of their size differences.
(ii) Porosity - The space present between soil particles in a given volume of soil are called pore spaces., The percentage of soil volume occupied by pore space or by the interstitial spaces is called porosity of the soil.
(iii) Permeability of soil - The characteristic of soil that determines the movement of water through pore spaces is known as soil permeability. Soil permeability is directly dependent on the pore size. Water holding capacity of the soil is inversely dependent on soil porosity.
(iv) Soil Temperature - Soil gets its heat energy from solar radiation, decomposing organic matter, and heat from the interior of earth. Soil temperature effects the germination of seeds, growth of roots and biological activity of soil-inhabiting micro and macro-organisms.
(v) Soil water - In soil, water is not only important as a solvent and transporting agent, but also maintains soil texture, arrangement and compactness of soil particles, making soil habitable for plants and animals impactness of soil particles, making soil habitable for plants and animals.

Essential properties of water
(i) Water is one of the main agents in Pedogenesis (soil formation).
(ii) It is the medium for several different ecosystems
(iii) It is present as moisture in the atmosphere and the outer layers of the lithosphere and is uneven in distribution on the earth
(iv) Water is heavier than air and imparts greater buoyancy to the aquatic medium. This enables organism to. float at variable levels.
(v) Water has high heat capacity and latent heat, due to which it can withhold large amounts of heat. Thus, oceans and lakes tend to maintain a relatively constant temperature, and the biosphere is relatively thermostable.
(vi) Water is physically unique because it is less dense as a solid (ice) than as a liquid.
(vii) When water freezes (O°C), it contracts. The maximum density of liquid water occurs at 4°C. Below that, it expands markedly. This enables ice to float on the top of water bodies. Hence, only the surface of water bodies will freeze, while below the surface, water will be in liquid form, sustaining life).
(viii) Water is considered as the Universal solvent. It is the main medium by which chemical constituents are transported from abiotic components to the living components of an ecosystem
(ix) Water has high surface tension. This allows pollen, dust, and even water striders to remain at the surface of a water body even though they are denser than the water.

(i) Extremely cold climate
(ii) Low biotic diversity
(iii) Simple vegetation structure
(iv) Limitation of drainage
(v) Short season of growth and reproduction
(vi) Energy and nutrients in the form of dead organic material
(vii) Large population oscillations

S.No	R selected species	K selected species
1.	Smaller sized organisms.	Larger sized organisms.
2.	Produce many offspring	Produce few offspring
3.	Mature early	Late maturity with extended parental care
4.	Short life expectancy	Long life expectancy
5.	Each individual reproduces only once or few times in their life time	Can reproduce more than once in lifetime
6.	Only few reach adulthood	Most individual reach maximum life span
7.	Unstable environment density independent	Stable environment, density dependent

(i) The pectoral fins and dorsal fins act as stabilizers or balancers and the caudal fin helps in changing the direction as a rudder.
(ii) Arrangement of body muscles in the form of bundles (myotomes) help in locomotion.
(iii) Stream lined structure helps in the swift movement of the animals in water.
(iv) Respiration by gills making use of gases dissolved in water.
(v) Presence of air-bladders filled with air for buoyancy.
(vi) Presence of lateral-line, system. They function as rheoreceptors which is helpful in echolocating objects in water.
(vii) Integuments rich in mucous glands are protected by scales.
(viii) Maintain water and ionic balance in its body with excretory structures.