Chapter 6 Natural Ecosystem

NIOS Class 12 Environmental Science Chapter 6

INTEXT QUESTIONS 6.1

1. What is a natural ecosystem?

Ans: A natural ecosystem is an assemblage of plants and animals that functions as a unit and is capable of maintaining its identity.

2. Which are the main categories of natural ecosystems?

Ans: Terrestrial and Aquatic.

3. Give examples of terrestrial ecosystems.

Ans: Forest, grasslands, deserts, and tundra

4. Give examples of freshwater ecosystems.

Ans: Rivers, lakes, and ponds

INTEXT QUESTIONS 6.2

1. What are deciduous trees?

Ans: The leaves of these trees shed in autumn, and new foliage grows in spring.

2. Explain two common characteristics of the desert.

Ans: Hot and low-rainfall areas, suffering from water shortage (any other).

3. How are the animals and plants of deserts adapted to heat and drought?

Ans: 

• Animals are fast runners, nocturnal, habit conserve water by excreting concentrated urine.
• Plants are mostly shrubs, with leaves absent or reduced in size; leaves and stems are succulent, root system is well developed.

4. Where are the Prairies and Steppes found?

Ans: North America and Eurasia

INTEXT QUESTIONS 6.3

1. What is plankton?

Ans: Microscopic floating organisms such as diatoms, protozoa, and larval forms are called plankton.

2. What is aquatic ecosystem?

Ans: Aquatic ecosystem refers to plant and animal communities occurring in water bodies. Flora and Fauna of the marine ecosystem. 

3. Name two plants and two animals which found in marine ecosystem.

Ans: Vascular plants are completely absent. Diatoms, algae, dinoflagellates, and jellyfish are free-floating forms. Large crustacean mollusks, turtles, and mammals like seals, porpoises, dolphins and whales are free-floating animals. Bottom dwellers are generally sessile (fixed) organisms like sponges, corals, crabs and starfish.

INTEXT QUESTIONS 6.4

1. Name the various zones of the Himalayas.

Ans: The Eastern Himalayas, the Central Himalayas, the Western Himalayas and the North-West Himalayas.

2. Where are deserts found in India?

Ans: From Punjab, Haryana, Rajasthan, to Gujarat state.

3. Give two differences between Western and Eastern Ghats?

Ans: 

• Eastern Ghats: Extended in a north-south-west strike in the Indian peninsula. Rainfall may vary from 60-160 mm from evergreen trees to that of dry savannas. 
• Western Ghats: Extended from the Tapti River to Kanyakumari. Rainfall may vary from 100 to 500 cm. 3500 species of flowering plants have been recorded.

4. Give two Plants and two animals which found in grassland.

Ans: Plants – Sedges, legumes and sunflower (Any two)

Animals – Rat, mice, deer, elephant, dog, tiger (Any two)

5. Name three gulf which are found in India.

Ans: Gulf of Mannar, Gulf of Kutchch and Gulf of Khambhat.

INTEXT QUESTIONS 6.5

1. Name two threatened ecosystems.

Ans: Estuaries, mangroves and islands (any two).

2. Where are mangrove ecosystems found in India?

Ans: East and west coast, and the islands of Andaman and Nicobar.

3. Why is an estuary a more productive ecosystem than an ocean or freshwater?

Ans: Estuaries are very dynamic and productive ecosystems since the river flow, tidal range and sediment distribution are continuously changing in them. They are richer in nutrients than fresh waters or marine waters; therefore, they are highly productive and support abundant fauna.

4. What are islands?

Ans: An Island is a land mass surrounded by seawater from all sides.

INTEXT QUESTIONS 6.6

1. Define ecotone.

Ans: Ecotone is a zone of function between two or more diverse ecosystems. E.g. the mangrove forest.

2. Give four examples of an ecotone.

Ans: Mangrove, grasslands, estuary and river bank.

3. Define edge species.

Ans: The organisms which occur primarily or most abundantly in this zone are known as edge species.

4. Why are there more number of species of song birds in Mangrove forests?

Ans: Because of their mixed habitat of an ecotone between the forest and the desert.

5. What is meant protection of natural ecosystems for an environmentalist?

Ans: Protection of natural ecosystems to an environmentalist means to protect animals and plants in their natural habitat in totality and not the protection of any one species.

TERMINAL EXERCISE

1. What do you understand by natural ecosystem? Give examples.

Ans: A natural ecosystem is an assemblage of plants and animals which functions as a unit and is capable of maintaining its identity, such as a forest, grassland, or an estuary. Human intervention is an example of a natural ecosystem. A natural ecosystem is totally dependent on solar energy.

2. Give the differences between the following:

a. Alpine and arctic tundra

b. Savanna and prairie

c. Tropical and temperate forests

Ans: 

a. Alpine and arctic tundra

• Arctic tundra extends as a continuous belt below the polar ice cap and above the tree line in the northern hemisphere. It occupies the northern fringe of Canada, Alaska, European Russia, Siberia and the island group of the Arctic Ocean. On the south pole Anatarctica tundra in the south pole is very small since most of it is covered by ocean.
• Alpine tundra occurs at high mountains above the tree line. Since mountains are found at all latitudes therefore alpine tundra shows day and night temperature variations. 

b. Savanna and Prairie

• Tropical grasslands are commonly called Savannas. They occur in eastern Africa, South America, Australia and India. Savannas form a complex ecosystem with scattered medium-sized trees in grasslands.
• Grasslands in North America are known as Prairies. 

c. Tropical and Temperate forests

• Tropical rainforests are found in the high rainfall areas on either side of the equator. Such forests are found on the western coast of India, scattered in Southeast Asia, some parts of Africa and South America.
• Temperate deciduous forests occur mostly in the northwest, central and eastern Europe, eastern North America, north China, Korea, Japan, far eastern Russia and Australia. Trees of deciduous forests shed their leaves in autumn, and new foliage grows in spring.

3. What do you understand by biodiversity? Explain its significance.

Ans: Biodiversity is the total of all types of living organisms on earth, which include both flora and fauna. 

4. Give two desert adaptations of plants and animals.

Ans: Desert plants thrive in hot and dry conditions.

• (i) These plants conserve water by following the methods:
  • They are mostly shrubs.
  • Leaves are absent or reduced in size.
  • Leaves and stems are succulent and water-storing.
  • In some plants, even the stem contains chlorophyll for photosynthesis.
  • Root system well well-developed and spread over a large area.
• (ii) The animals are physiologically and behaviorally adapted to desert conditions.
  • They are fast runners.
  • They are nocturnal in habit to avoid the sun’s heat during the day.
  • They conserve water by excreting concentrated urine.
  • Animals and birds usually have long legs to keep their body away from the hot ground.
  • Lizards are mostly insectivorous and can live without drinking water for several days.
  • Herbivorous animals get sufficient water from the seeds which they eat.

5. Describe the various types of forests found in India (in brief).

Ans: Forests in India can be classified in different ways, based on their position, atmosphere, weather conditions, etc. Some of the common characteristics of various types of natural vegetation in India include

• Tropical rainforests: These types of forests include the tropical evergreen forests and tropical semi-evergreen forests, and they are mostly found in places where there is plenty of rainfall and sunshine throughout the year.
• Tropical deciduous forests: Tropical deciduous forests are also known as deciduous (whether it is moist or dry)forests because they cast leaves for about six to eight weeks in summer. They are also called the monsoon forests with all their grandeur and beauty.
• Temperate broad leaf forests: They mainly occur between 1500-2400 m altitudes in the western  Himalayas. The height of the trees may be 25-30 m. The tree’s canopy is dense, the herbaceous layer is least developed, and grasses are generally lacking.
• Temperate needle leaf or coniferous forests: These types of forests are found in the Himalaya over 1700 to 3000 m. The canopy of these trees always remains green. In many species, it is cone-shaped.
• Alpine and tundra forests: The alpine and tundra forests are another kind of natural vegetation in India. Vegetation growing at altitudes above 3600 m is usually known as alpine vegetation, and it can be noticed that with the increment of the altitude, the plants show stunted growth. The tundra biome occurs in the region where the environmental conditions are very severe, and there is very little vegetation below the poles and at high mountain peaks.

6. Explain various zones of the Himalayas.

Ans: The Himalayas are geographically divided into:

• (i) the Eastern Himalayas or the Assam Himalayas: The Eastern Himalaya has a greater diversity of ecosystems, forests, grasslands, marshes, swamps, lakes, streams, and rivers Eastern Himalayas consist of nearly 8000 species of flowering plants. It has many primitive as well as many endemic plant species. The Eastern Himalayas are known as the centre of origin of cultivated plants. Many cereals, fruits, and vegetables are cultivated here. E.g. Orchids, Aster, Acacia, Albizzia, Delbergia species (timber), and many legumes, etc.
• (ii) the Central Himalayas or the Nepal Himalayas
• (iii) the Western Himalayas: The western Himalayas’ cold deserts of Ladakh support drought and cold-resistant varieties of plants and animals, e.g. Yak. 
• (iv) The North-West Himalayas or the Punjab Himalayas, Eastern Himalayas are one of the of the world and have a large number of animals because of its varied ecological conditions, e.g. Pangolins, elephants, macaque, languor, civet.

7. Write a short note on grassland and deserts found in India.

Ans: Grasslands

Grasslands are one of the intermediate stages in ecological succession and cover a part of the land at all altitudes and latitudes at which climatic and soil conditions do not allow the growth of trees. In India, grasslands are found as village grazing grounds (Gauchar) and extensive low pastures of the dry regions of the western part of the country, and also in the Alpine Himalayas. 

• Perennial grasses are the dominant plant community. 
• In some regions, grasslands also support a variety of other herbaceous plants like sedges, legumes, and members of the sunflower family. 
• Grasslands support a large number of herbivores, from minute insects to very large mammals. 
• In north-east India, the horned rhinoceros is amongst the threatened animals of the grassland in this region. 

Deserts

The Thar Desert in Rajasthan is an extension of the Sahara Desert through the Arabian and Persian deserts. They extend from Punjab, Haryana, Rajasthan, to Gujarat state. Indian deserts are divided into four main types:

• Hills,
• Plains with hills,
• Marshes and
• Plains with sand dunes.

The distinct Rann of Kutchch–Bhuj in Gujarat forms a separate zone within in Thar deserts due to its different climatic conditions. It represents vast saline flats. Since heat and light intensity are very high and sand dunes are shifting, these deserts can not support vegetation. There are only some thorn forests and dry open grasslands.

Indian deserts support many threatened species of birds and mammals, such as the Asiatic lion, wild ass, bats, scaly anteater, desert fox, Indian gazelle, four-horned antelope, white browed Bushchat, Great Indian Bustard, Cranes, and Sandgrouse. Gulf of Kuchch is distinguished by the presence of living corals, pearl oyster, sea turtles, and a large number of migratory birds like kingfisher, cranes, ibis, and herons.

8. Explain how deforestation has resulted in ecological imbalance.

Ans: Increasing human population, its increasing needs and greed are the root causes of the destruction of natural ecosystems. Destruction and loss of any of the natural ecosystems will result in an ecological imbalance. 

9. What is an ecotone? Explain its significance for the edge species.

Ans: Ecotone is a zone of junction between two or more diverse ecosystems, e.g. the mangrove forests. They represent an ecotone between the marine and terrestrial ecosystems. 

Sometimes, the number of species and the population density of some of the species are much greater in this zone than in either community. This is called the edge effect. The organisms that occur primarily or most abundantly in this zone are known as edge species. In the terrestrial ecosystems edge effect is especially applicable to birds. For example, the density of songbirds is greater in the mixed habitat of the ecotone

between the forest and the desert.

10. Give two methods of protecting natural ecosystems.

Ans: Protection of natural ecosystems can be achieved by the following methods:-

• Humans should reduce their needs.
• Introduction of the species from other parts of the world and human interference should be reduced to a minimum in natural ecosystems.
• Some of the areas should be earmarked as protected or reserve zones. This can be achieved by making buffer or transitional zones around the protected area. (Buffer zone and transitional zones are where only a few humans are permitted to enter.)

Additional Study Materials

• Chapter 1 Origin of Earth and Evolution of the Environment
• Chapter 2 Environment and Human Society
• Chapter 3 Degradation of Natural Environment
• Chapter 4 Principles of Ecology