NCERT Solutions for Class 11 Geography Chapter 16 - Life on the Earth

Question 1:

Which one of the following is included in biosphere?

  1. only plants
  2. all living and non-living organisms
  3. only animals
  4. all living organism

(d). all living organism

Question 2:

Tropical grasslands are also known as:

  1. the prairies
  2. the savannas
  3. the steppes
  4. none of the above

(b). the savannas

Question 3:

Oxygen combines with iron found in the rocks to form:

  1. iron carbonate
  2. iron nitrites
  3. iron oxides
  4. iron sulphate

(c). iron oxides

Question 4:

During photosynthesis, carbon dioxide combines with water in the presence of sunlight to form:

  1. proteins
  2. amino acids
  3. carbohydrates
  4. vitamins

(c). carbohydrates

Question 5:

What do you understand by the term Ecology?


Ecology is a combination of two Greek words (Oikos) and (Logy) meaning house and science. Ecology is the study of earth as home of plants, humans, animals and bacteria. These are interdependent. German zoologist Ernst Haeckel was the first to use this term in 1869. He is known as the father of ecology. The study of interactions between life forms (Biotic) and (Abiotic) is the science of ecology.

Question 6:

What is an ecological system? Identify the major types of ecosystems.


Structure and function. The structure of an ecosystem involves a description of the available plant and animal species present. It also describes its history, populations and distribution. From a structural point of view all ecosystems consist of abiotic and biotic factors. Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium etc.) and organic substances (proteins, carbohydrates, lipids and amino acids). Biotic factors include the producers, primary consumers, secondary consumers, tertiary consumers and the decomposers. The producers include all green plants, which manufacture their own food through photosynthesis. The primary consumers include the herbivorous animals like deer, goats, mice and all plant-eating animals. The carnivores include all the flesh-eating animals like snakes, tigers and lions. Certain carnivores that feed also on carnivores are known as top carnivores like hawk and mongoose. Decomposers are those that feed on the dead organisms (for example scanvengers like vulture, crow) and further breaking down of the dead matter by other decomposing agents like bacteria and various micro-organisms.
The producers are consumed by the primary consumers ; whereas, the primary consumers are in turn being eaten by the secondary consumers. Further, the secondary consumers are consumed by the tertiary consumers. The decomposers feed on the dead at each and every level. They change them into various substances such as nutrients, organic and inorganic salts essential for soil fertility. Organisms of an ecosystem are linked together through a food chain.

Question 7:

What do you mean by a food chain? Give an example of a grazing food chain identifying the various levels.


Food Chain : The transfer of energy from one organism to another in the ecosystem is known as food chain. For example, the green plants use solar energy for their growth. These plants provide energy in the form of food for the consumers. Thus, the food chain is really an energy flow system. For example, in a grassland, herbivores such as the deer, feed on the grasses. At the next stage, carnivores such as the lion, feed on the deer. The food chain, thus, involves the flow of energy in the form of food from lower to higher levels.
Example. In a grazing food chain, energy is passed from one level to another. When a herbivore feeds on plants only a fraction of the energy is absorbed by the body, the rest of the energy is lost as waste on released by the animal during its movement. Likewise when a carnivore feeds on its prey only a portion of the energy from the prey is stored in its tissues. As such organisms along a food chain pass on much less energy than what they receive, as much of the energy is lost at every level. The pyramid shaped food chain shows many trees and shrubs providing food and energy to giraffes. There are few giraffes than trees and shrubs and even fewer lions than giraffes. In other words, a large mass of living things at the base is required to support a few at the top. This interdependence of the populations within a food chain helps to maintain the balance of plant and animal populations.
Ecological Pyramid :
Each group of organisms occupies a feeding level called a trophic level. The different trophic levels may be represented in the form of a pyramid called ecological pyramid.
Man is at the top of the ecological pyramid. The pyramid has a large base. It represents primary producers. From base to the top, the numbers go on decreasing at each level. All green plants and other producers occupy the first trophic level. Herbivores which feed on plants occupy the second trophic level.
Carnivores that eat herbivores are at the third trophic level. At each level, the flow of energy is reduced ; because only a fraction of energy is transferred from lower to higher level.

Question 8:

What do you understand by Food Web? Give example.


Food Web. The simple food chain does not exist in any ecosystem. Many simple food chains intermingle with one another to form a food web. For example, each organism may eat a variety of food derived from another organisms and in turn may be eaten by number of organisms at a higher level of the food chain. The primary producers use the energy of the sun and provide it to consumers at higher level. But energy is lost during each upward step in the food chain. The relations between different organisms in a food chain are represented by a pyramid of numbers.
Examples. For example, a plant-eating beetle feeding on a paddy stalk is eaten by a frog, which is in turn eaten by a snake, which is then consumed by a hawk. This sequence of eating and being eaten with the resultant transfer of energy from one level to another level is known as food chain. Transfer of energy that occurs during the process of a food chain from one level to another is known as flow of energy. However, food chains are not isolated from one another. For example, a mouse feeding on grain may be eaten by different secondary consumers (carnivores) and these carnivores may be eaten by other different tertiary consumers (top carnivores).
In such situations even each of the carnivores may consume more than one type of prey. As a result, the food chains interlock with one another. This interconnecting network of species is known as food web. Generally two types of food chains are recognized.
1. Grazing food chain and 2. Detritus food chain. In a grazing food chain the first level starts with plants as producers and ends with carnivores as consumers as the last level, with the herbivores being at the intermediate level. There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food chain range between three to five and energy is lost at each level. A detritus food chain involves the decomposition or breaking down of organic wastes and dead matter derived from the grazing food chain.

Question 9:

What is a Biome?


A biome is a plant and animal community that covers a large geographical area. Therefore, a biome is a total assemblage of plant and animal species. There are five major Biomes—forests, deserts, grassland, aquatic and altitudinal.

Question 10:

What are biogeochemical cycles? Explain how Nitrogen is fixed in the atmosphere.


Sun is the basic source of energy on which all life depends. This energy initiates life processes in the biosphere through photosynthesis, the main source of food and energy for the green plants. During photosynthesis carbon dioxide is converted to organic compounds and oxygen. Out of the total solar insolation that reaches the earth surface only a very small fraction (0.1 per cent) is fixed in photosynthesis. More than half is used for plant respiration and the remaining is temporarily stored or is shifted to other portions of the plant.
Life on earth consists of a great variety of living organisms. These living organisms exist in a diversity of associations. The processes and interactions involved within the biosphere are complex in nature. Living organisms survive in multiplicity and diversity. Such survival involves the presence of systemic flows such as flows of energy, water and nutrients. These flows show variations in different parts of the world, in different seasons of the year and under varying local circumstances. Studies have shown that for the last one billion years, the atmosphere and hydrosphere have been composed of approximately the same balance of chemical components. This balance of the chemical elements is maintained by a cyclic passage through the tissues of plants and animals. The cycle starts by absorbing the chemical elements by the organism and returned back to the air, water and soil through decomposition. These cycles are largely energized by solar insolation. These cyclic movements of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles. ‘Bio’ refers to living organisms and ‘geo’ to rocks, soil, air and water of the earth.
There are two types of bio-geochemical cycles, the gaseous and the sedimentary cycle. In the gaseous cycle the main reservoir of nutrients is the atmosphere and the ocean. In sedimentary cycle the main reservoir is the soil and the sedimentary rocks and other rocks of the earth’s crust.
The nitrogen cycle
Nitrogen is a major constituent of the atmosphere comprising of about seventy-nine per cent of the atmospheric gases. It is also an essential constituent of different organic compounds such as amino acids, nucleic acids, proteins, vitamins and pigments. Only few types of organisms like certain species of soil bacteria and blue green algae are capable of utilizing it directly in its gaseous form. Generally nitrogen is usable only after it is fixed. Ninety per cent of fixed nitrogen is biological. The principal source of free nitrogen is action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil. Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation. In the oceans some marine animals can fix it. After atmospheric nitrogen has been fixed into an available form green plants can assimilate it.
Herbivorous animals feeding on plants in turn consume some of it. Dead plants and animals, excretion of nitrogenous wastes are converted into nitrites by the attachment of bacteria present in the soil. Some bacteria can even convert nitrites into nitrates that can be used again by the green plants. There are still other types of bacteria capable of converting nitrates into free nitrogen, a process known as denitrification.

Question 11:

What is an Ecological Balance? Discuss the important measures needed to prevent ecological imbalance?


Ecological balance
Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem. It can happen when the diversity of the living organisms remains relatively stable. Gradual changes do take place but that happen only through natural succession. It can also be explained as a stable balance in the number of each species in an ecosystem. This occurs through competition and cooperation between the different organisms where population remains stable. This balance is brought about by the fact that certain species compete with one another determined by the environment in which they grow. This balance is also attained by the fact that some species depend on others for their food and sustenance.
Example. Such accounts are encountered in vast grasslands where the herbivorous animals (deers, zebra, buffaloes) are found in plenty. On the other hand the carnivorous animals (tigers, lions, coyotes) that are not usually in large numbers hunt and feed on the carnivores, thereby controlling their population. In the plants any disturbance in the native forests such as clearing the forest for shifting cultivation usually brings about a change in the species distribution. This change is due to competition where the secondary forest species such as grasses, bamboos or pines overtake the native species changing the original forest structure. This is called succession.
Causes of Ecological Imbalance.
(1) Ecological balance may be disturbed due to the introduction of new species, natural hazards or man-made causes.
(2) Man’s interference has affected the balance of plant communities leading to disturbances in the ecosystems. Such disturbances bring about numerous secondary successions.
(3) Human pressure on the earth’s resources has put a heavy toll on the ecosystem. This has destroyed its originality and had caused adverse effects to the general environment.
(4) Ecological imbalances have brought many natural calamities like floods, landslides, diseases, erratic climatic occurrences and such other hazards. There is a very close relationship between plant and animal communities within particular habitats. Diversity of life in a particular area can be employed as an indicator of habitat factors. Proper knowledge and understanding of such factors provide a strong base for protecting and conserving ecosystems.