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.

(i) The proportion of the age groups in a population is its age distribution attribute.
(ii) This determines the reproductive status of the population at the given time and is an indicator of the future population size.
(iii) Usually a rapidly growing population will have larger proportion of young individuals.
(iv) A stable population will have an even distribution of various age classes.
(v) A declining population tends to have a larger proportion of older individuals

No.	Tundra Biome	Taiga Biomes
1.	This is almost treeless plain in the northern parts of Asia, Europe, and North America.	Taiga is a forest of coniferous trees such as spruce, fir and pine.
2.	Winters are long with little daylight, summers are short, with long daylight hours.	Summer temperature ranges from 10octo 21oPc.
3.	Because of the severe winters, many of the animals are migratory. For E g: the many shore birds and water fowl such as ducks and geese, nest in the Tundra during the summer and migrate south for the winter.	Important migratory herbivores include moose, elk, deer and reindeer. Moose and reindeer migrate to the Taiga for winter and to Tundra for summers.