Q. 1. Describe the different biomes of the world and their characteristics.
Ans. 1. Tropical Rain Forest This biome is located in the equatorial regions wherever the annual rainfall exceeds 140 cm. This covers about 8 per cent of the earth’s surface but contains more than half of its flora and fauna.
Vegetation. Plant life is highly diverse reaching up to a framework of 200 species of trees per hectare. The warm, humid climate supports broad-leaved evergreen plants with distinct stratification into an upper storey and two or three understoreys. The tallest trees form an open canopy but the lower crown levels block most of the available light from the jungle floor. The jungle edge is a tangle of sun-loving woody climbers, also called lianas.
Animal life is abundant and diverse, including ground-dwellers and treedwellers. The animals include monkeys, snakes, anteaters, tropical birds, bats, large carnivores animals and a variety of fish in the rivers. Of all the species of insects known, nearly 70 to 80 per cent occur in the tropical rain forests.
2. Tropical Savanna Savannas are characterised by coarse grass and scattered trees on the margins of tropics where rainfall is seasonal. Wet seasons alternate with dry seasons. Plants and animals are drought-tolerant and do not show much diversity. This biome supports the greatest variety of hoofed herbivore species including the zebra, giraffe, elephant and several kinds of antelope. Kangaroos are found in the Savannas of Australia.
3. Mediterranean Scrub Forest This biome is also known as the Chapparal. This is marked by very limited winter rain followed by drought in the rest of the year. The temperature is moderate under the influence of cool, moist air of the oceans. The biome is characterised by broad-leaved evergreen vegetation. It is made up of fire resistant resinous plants and drought-adapted animals.
4. Deciduous Forest The deciduous forests are found in the temperate regions of north-central Europe, eastern Asia and the eastern United States. The annual precipitation ranges between 75 and 150 cm. With the onset of autumn most of the trees and shrubs become leafless. The vegetation comprises broad-leaved, hardwood trees such as oak, elm, birch, maple and hickory. The fauna includes frogs, salamanders, turtles, snakes, lizards, squirrels, rabbits, deer, bears, raccoons, foxes and song birds.
5. Grassland The principal grasslands are the prairies of Canada and the USA, the pampas of South America, the steppes of Europe and Asia and the veldts of Africa. The annual rainfall is between 25 and 75 cm. Winter blizzards and summer drought can be severe, wit periodic fire devastations. The dominant plant species comprise short and tall grasses. Animal species include larks, the burrowing owl, prong-horned antelopes, badgers, coyote, jackrabbit and bison.
6. Desert Deserts are characterised by extremely low rainfall and high evaporation rate. Even the water from the meagre rainfall is not available to plants because of the fast run-off. The days are extremely hot and the nights cold. The seasonal fluctuations of temperature are wide. Deserts are characterised by scanty flora and fauna. Desert plants include different kinds of acacias, cacti, euphorbias and other succulents.
Ants, locusts, wasps, scorpions, spiders, lizards, rattle snakes, a large number of insect-eating birds such as swifts and swallows, seed-eating quails, doves, desert rats, rabbits, foxes, jackals and various cats are the common desert animals.
7. Taiga In the northern conifreous forest or taiga, the growing period of plants is only about 150 days. As the physical conditions are variable, the organisms must be resistant to fluctuations of temperature. Pine, fir, cedar, hemlock and spruce constitute the dominant vegetation. In some areas the trees are so dense that little light reaches the floor of the forest. In humid areas mosses and ferns grow profusely. This biome is a good habitat for elks, deer, grouse, rabbits, squirrels, pumas, lynx and many species of insects.
8. Tundra A tundra consists of plains characterised by snow, ice and frozen soil for most part of the year. The main limiting factors for life are poor light and extremely low temperature. The snowfall is scanty. Vegetation is so sparse that it is also called the arctic desert. The biome is virtually treeless. It consists mainly of lichens, mosses, sedges, heaths, grasses and dwarf willow trees.
Seasonal thawing of the frozen soil occurs only up to a few centimetres depth allowing only shallow rooted plants to grow. Caribou, arctic hares, arctic foxes, reindeer, snow owl and migratory birds are common in this region.
Q. 2. Discuss human impact on the Ecosystem.
Ans. Man is an integral part of environment. Human beings are one of the species of the innumerable life forms. Man influences his environment with the help of his skill, knowledge, science and technology. Man has domesticated the animals and plants for greater human use.
He has tilled the land and raised crops. He gets many plants and products to meet his needs. New species have been evolved while the old species have extincted. In this way, man has tried to control the environment. Man has tried to exploit the resources of Biosphere. But he has disturbed the ecosystem in this attempt. Plants and animals have been introduced to new areas.
Their fast growth has changed the environment of new areas drastically. Human interference with the natural environment has modified or altered ecosystem in many areas. Deforestation for cultivation has changed the habitat of the organisms living in the forests. It has resulted in soil erosion. Excessive cultivation, over-grazing, and shifting agriculture have increased the rate of soil erosion.
Irrigation projects in dry areas have resulted into salinization of soil and spread of water borne diseases. Land, air and water have got polluted and have become unsuitable for human consumption. In recent years, environmental pollution and presence of chemicals in air, water and food has damaged human health.
Human interference has led to the deterioration of natural resources. Man is using water, land, soil and other resources at such an alarming rate that there will be serious shortage of these resources in the near future. Careless use may destroy them to such an extent that they may not be available to mankind. The hunting of animals has led to the extinction of certain species. Over-exploitation has caused a serious shortage. For example, mineral oil will not last long.
Thus, it is clear that most of the environmental problems are man induced. Man will have to live in harmony with the environment so that ecological balance is not disturbed.
Q. 3. Describe clearly the components of ecosystem.
Ans. Ecosystem is a set of physical conditions in which growth of organisms takes place. An ecosystem consists of two types of components, Living (biotic) and Non-living (abiotic).
1. Non-living or Abiotic components : The nonliving components of the ecosystem consists of chemical substances found in the soil, water and atmosphere. These chemicals are of two types; organic and inorganic.
(i) Inorganic substances : These include water, oxygen, carbon dioxide and minerals like phosphate, nitrates, etc.
(ii) Organic substances : These include carbohydrates, fats, proteins and vitamins.
(iii) Other abiotic elements : These include climatic conditions such as temperature, rainfall, duration of sunlight, winds, nature of soil, slope of the land and composition of water bodies. These elements bring about the variations in types of plants and animals.
2. Living Biotic components. The biotic components can be divided into the following major groups :
(i) The producers : The organisms which produce their own food from the physical environment are called producers. These are called autotrophic organisms. Green plants, blue and green algae and some bacteria produce their own food utilising solar energy through the process of photosynthesis. These are called primary producers. In oceans, phytoplanktons are primary producers.
(ii) The consumers : Organisms which depend on other organisms for food are called consumers or heterotrophic organisms. The consumers can be grouped into three groups :
(a) Herbivores : Organisms which feed only on plants are called herbivores or primary consumers like a rabbit.
(b) Carnivores : Organisms which feed on animals only are called carnivores or secondary consumers like a lion.
(c) Omnivores : Organisms which feed on both plants and animals are called omnivores like human beings.
(d) Decomposers : Organisms which feed on dead or decomposed tissues of plants and animals are called decomposers like bacteria, fungi and earthworms.
Q.4. Describe the vegetation of tropical rain forests.
Ans. Vegetation. Plant life is highly diverse reaching up to a framework of 200 species of trees per hectare. The warm, humid, climate supports broad-leaved evergreen plants with distinct stratification into an upper storey and two or three understoreys. The tallest trees form an open canopy but the lower crown levels block most of the available light from the jungle floor.
The jungle edge is a tangle of sun-loving woody climbers, also called lianas. Animal life is abundant and diverse, including grounddwellers and tree-dwellers. The animals include monkeys, snakes, ant-eaters, tropical birds, bats, large carnivores animals and a variety of fish in the rivers. Of all the species of insects known, nearly 70 to 80 per cent occur in the tropical rain forests.
