Cold deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer.
E.g. Ladakh region in India.

Forest is a broad term used to describe areas where there are a large number of trees. The major forest biomes are the Tropical forests and the Temperate forests.

Aquatic biome is the largest biome occupying 71% of biosphere.
The aquatic biomes on Earth are:
a) Freshwater biome (Lakes and Ponds)
b) Brackish water biome (Estuaries / Wetlands)
c) Marine biome (Coral reefs and abyssal zones)

(i) Anadromous migration - migration of fishes from sea to fresh water Eg. Salmon.
(ii) Catadromous migration - migration of fishes from fresh water to sea Eg. Eel

Hibernation and aestivation

Ethology is the scientific study of animal behaviour, under natural conditions.

Birds and mammals attain greater body size in colder regions than warmer regions (Bergmann's rule).

Stenohaline Animals	Euryhaline Animals
The animals which show tolerance only to a narrow range of salinities.	The animals which, can tolerate a wide range of salinities
Their distributional range is limited.	Their distribution shows a wide range

This is the level of exposure of plants to environmental factors that leads to neither injury nor reduction in growth and yield of crops.

1. Animals are known to modify their response to environmental changes (stress) in reasonably short time of spans. This known as Acclimatisation.
2. This is observed when people who have moved from the plains to higher altitudes show enhanced RBC count within a few days of settling in their new habitat. This helps them cope with lower atmospheric oxygen and higher oxygen demand.

(a) Commensalism
(b) Amensalism
(c) Predation

Temperature or degree of hotness and coldness is an essential and variable factor in any environment. It influences all forms of life by affecting many vital activities of organisms like metabolism, behaviour, reproduction, development and even death in the Biosphere.

Groups of species with comparable role and niche dimensions within a community are termed 'guilds'. Species that occupy the same niche in different geographical regions are termed 'ecological equivalents'.

Migration is a peculiar and unique kind of mass population movement from one place to another and back. To avoid the severe winter cold. Eg. Siberian cranes migrate from Siberia to Vedanthangal in Tamil Nadu and return back in spring.

The movement of organism in response to light, either towards the source of light as in Moths (positive phototaxis) or away from light (Earthworm (negative phototaxis).

The adaptations seen in animals to overcome extreme winters and summers are:
a) Formation of heat resistant spores
b) Formation of cysts (Entamoeba)
c) Presence of antifreeze proteins (Arctic fishes)
d) Hibernation (Winter sleep)
e) Aestivation (Summer sleep)
f) Migration

(i) The inherent tendency of all animal populations is to increase in number. But it does not increase indefinitely.
(ii) Once the carrying capacity of the environment is reached, population numbers remain static or fluctuate depending on environmental conditions.
(iii) This is regulated by many factors which are:
1. Density independent - Extrinsic factors
2. Density dependent - Intrinsic factors
(iv) Extrinsic factors include the availability of space, shelter, weather, food, etc.
(v) Intrinsic factors include competition, predation, emigration, immigration, and diseases.

S. No. Natality Mortality 1. It refers to the number of births per unit
population per unit time. e.g., per thousand
individuals per year in humans. It refers to the number of deaths per unit population per unit time. e.g., per thousand individuals per year in humans. 2. It adds new members to the population It removes members from the population 3. It increases the size of population. It decreases the size of population 4 Natality adds to population density Mortality reduces density of population 5 It maintains continuity of population It maintains health of population 6 It is high when population size is small and low when population size is large. Mortality is low when population
size is small and high when population size is large

(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.

(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) 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.

Biotic potential:
It is the maximum reproductive capacity of an organism under optimum environmental conditions.
Carrying capacity:
The maximum number of organisms live in a region can support without environmental degradation is called carrying capacity.
Environmental resistance:
Is the sum total of the environmental limiting factors, both biotic and abiotic which together act to prevent the biotic potential of an organism from being realized.

(i) Earthworms, land planarians secrete a mucus coating to maintain a moist situation for burrowing, coiling, respiration, etc.
(ii) Arthropods have an external covering over the respiratory surfaces and well developed tracheal systems.
(iii) Invertebrate skin, there are many cellular layers besides the well protected respiratory surfaces that help in preventing loss of water.
(iv) Some animals obtain their water requirement from food as partial replacement of water lost through excretion.
(v) Birds make nests and breed before the rainy season as there is the availability of abundant food. But during drought birds rarely reproduce.
(vi) Camels are able to regulate water effectively for evaporative cooling through the skin and respiratory system and excrete highly concentrated urine, and can also withstand dehydration up to 25% of their body weight.

Properties of soil
(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 the earth. Soil temperature affects 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.