NCERT Solutions - Life on the Earth

1. Multiple choice questions.

(i) Which one of the following is included in biosphere?

(a) only plants
(b) all living and non-living organisms
(c) only animals
(d) all living organisms
► (b) all living and non-living organisms

(ii) Tropical grasslands are also known as :

(a) the prairies
(b) the savannas
(c) the steppes
(d) none of the above
► (b) the savannas

(iii) Oxygen combines with iron found in the rocks to form :

(a) iron carbonate
(b) iron nitrites
(c) iron oxides
(d) iron sulphate
► (c) iron oxides

(iv) During photosynthesis, carbon dioxide combines with water in the presence of
sunlight to form :
(a) proteins
(b) amino acids
(c) carbohydrates
(d) vitamins
► (c) carbohydrates

2. Answer the following questions in about 30 words.

(i) What do you understand by the term ‘ecology’?

Answer
Ecology is a scientific study of the interactions of organisms with their physical environment
and with each other.

(ii) What is an ecological system? Identify the major types of ecosystems in the world.

Answer
The interactions of a particular group of organisms with abiotic factors within a particular
habitat resulting in clearly defined energy flows and material cycles on land, water and air,
are called ecological systems.
Ecosystems are of two major types:
• Terrestrial
• Aquatic

(iii) What is a food-chain? Give one example of a grazing food-chain identifying the various
levels.

Answer
Thes sequence of eating and being eaten and the resultant transfer of energy from one level
to another is known as the food-chain.
Grass (first level) is eaten by deer (intermediate level) is eaten by lion (last level).

(iv) What do you understand by the term ‘food web’? Give examples.

Answer
A network of food chains mixed together to form a food web. 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).

(v) What is a biome?

Answer
A biome is a plant and animal community that covers a large geographical area.

3. Answer the following questions in about 150 words.

(i) What are bio-geochemical cycles? Explain how nitrogen is fixed in the atmosphere.

Answer
The 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 is returned to the air, water and soil through decomposition. These cycles are largely
energised by solar insolation. The 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.
Ninety per cent of fixed nitrogen is biological. The principal source of free nitrogen is the
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.

(ii) What is an ecological balance? Discuss the important measures needed to prevent
ecological imbalances.

Answer
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.
Ecological imbalances: Ecological balance may be disturbed due to the introduction of new
species, natural hazards or human causes.
The important measures to prevent ecological imbalances are:
• By not interfering in nature.
• By controlling population.
• By reusing and recycling things.
• By using natural resources judiciously.
• Afforestation should be encouraged.
Proper knowledge and management are necessary for protecting and conserving the
ecosystems.

EXTRA QUESTION-ANSWERS
SHORT ANSWER QUESTIONS:

Q. 1. Define Biosphere.
Ans. The Biosphere is that part of earth in which life forms exist.
Q. 2. Why is the biosphere important?
Ans. It is important because life of any kind is possible only in this layer.
Q. 3. Name two categories of organisms.
Ans. (i) Plant Kingdom
(ii) Animal Kingdom.
Q. 4. Define a ‘Homosapien’.
Ans. The earliest man on the earth is known as Homosapien.
Q. 5. Define the term ‘Ecology’.
Ans. The study of the interaction between organisms and their environment is called
Ecology.
Q. 6. Name the two categories of components of an Ecosystem.
Ans. (a) Biotic such as plants and animals (living).
(b) Abiotic such as soil and water (non-living).
Q. 7. Name two sources of internal energy of the ecosystem.
Ans. (i) Matter.
(ii) Energy.
Q. 8. Name three most abundant elements found in all living organisms.
Ans. (i) Carbon
(ii) Hydrogen
(iii) Oxygen.
Q. 9. Name the major nutrients found in Biosphere.
Ans. (i) Carbon, Oxygen, Nitrogen from Atmosphere.
(ii) Iron, sulphur, phosphorus, manganese from Lithosphere.
Q. 10. What makes natural cycles operational?
Ans. Energy, through solar radiation.
Q. 11. Divide the organisms into three groups.
Ans. The major groups of all organisms are :
(i) Producers
(ii) Consumers
(iii) Decomposers.
Q. 12. Define the term ‘Photosynthesis.’
Ans. The process of energy conversion is known as photosynthesis. Plants use light energy
to convert carbon dioxide and water to produce carbohydrates to support life. In simple
words, photosynthesis means production of carbohydrates.
Q. 13. Define the term ‘Decomposers’.
Ans. The microscopic organisms and bacteria (Fungi and Earth-worms) who feed on the
decomposed and decayed organic products are called decomposers.
Q. 14. Where is life found on earth?
Ans. Life on earth is found almost everywhere. Living organisms are found from the poles to
the equator, from the bottom of the sea to several kilometres in the air, from freezing
waters to dry valleys, from under the sea to underground water lying thousands of metres
below the earth’s surface.
Q. 15. Where are most of organisms found in Biosphere?
Ans. The biosphere includes all the living components of the earth. It consists of all plants,
animals including all micro-organisms that populate our planet earth and interact with their
surrounding environment.
Most of the organisms exist on the lithosphere and/or the hydrosphere as well as
atmosphere. There are also many organisms that move freely from one realm to another.
Q. 16. What are the effects of components of Biosphere?
Ans. The biosphere and its components are very significant elements of the environment.
These elements interact with other components of the natural landscape such as land,
water and soil.
They are also influenced by atmospheric elements such as temperature, rainfall, moisture
and sunlight. The ineractions of biosphere with land, air and water are important to growth,
development and evolution of the organism.
Q. 17. What is ecological system?
Ans. The interactions of a particular group of organisms with land, water and air, within a
particular habitat results in a clearly defined energy flow and material cycle, is called an
ecological system.
Q. 18. What is meant by Ecological adaptation?
Ans. When various plants and animal species have got adapted through evolution ; it is
called ecological adaptation.
Q. 19. What is meant by water cycle?
Ans. The water cycle. All living organisms, the atmosphere and the lithosphere maintains
between them a circulation of water in solid, liquid or gaseous form referred to as the water
or hydrologic cycle.
Q. 20. What is meant by Photosynthesis?
Ans. Sun is the main source of energy on which all life depends. Photosynthesis is the
process which supplies food and energy to the green plants. During photosynthesis carbon
dioxide is converted to organic compounds and oxygen.
Q. 21. What do you mean by Ecology, Ecological adaptation and Ecological system?
Ans. Ecology. The environment is made up of the abiotic and biotic elements. It would be
interesting to understand how the diversity of life forms is maintained to bring a kind of
equilibrium or balance.
This balance is maintained in a particular proportion so that a healthy interaction between
the biotic and the abiotic elements is found. The term ecology is derived from the Greek
word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of’ or
‘the study of.’
Literally ecology is the study of the earth as a ‘household’, of plants, animals and micro-
organisms. They all live together as interdependent components. A German zoologist Ernst
Haeckel, who used the term as ‘oekologie’ in 1869, first coined the term ecology.
The study of interactions between lifeforms (biotic) and the physical environment (abiotic)
is the science of ecology. Hence, ecology can be defined as a scientific study of the
interactions of organisms with their physical environment and with each other.
Ecology is mainly concerned with the growth, development, distribution, behaviour and
survival of organisms. Ecology is not only concerned with living organisms and their
interactions but also with energy flows and material cycles that occur on land, water and air.
The interactions of a particular group of organisms with land, air and water (abiotic factors)
within a particular habitat or habitats resulting in clearly defined energy flows and material
cycles on land, water and air, are called ecological systems. A habitat in the ecological sense
may be explained to be the totality of the physical and chemical factors that constitutes the
general environment.
Different types of ecosystems exist with varying ranges of environmental conditions where
various plants and animal species have not adapted through evolution. This phenomenon is
known as ecological adaptation.
Q. 22. Describe the major types of Ecosystems.
Ans. Types of ecosystems. Ecosystems are of two major types— terrestrial and aquatic.
Terrestrial ecosystem can further be classified into ‘biomes’. A biome is a plant and animal
community that covers a large geographical area. The boundaries of different biomes on
land are determined mainly by climate and weathering. Therefore a biome can be defined
as the total assemblage of plant and animal species interacting within specific conditions.
These conditions include rainfall, temperature, humidity and soil conditions. Some of the
major biomes of the world are—forest, grassland, desert and tundra biomes. Aquatic
ecosystems can be classed as marine and freshwater ecosystems. Marine ecosystem
includes oceans, coastal estuaries and coral reefs. Freshwater ecosystem includes lakes,
ponds, streams, marshes and bogs.
Q. 23. What do you mean by ‘Ecology’?
Ans. 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.
Q. 24. Describe the different types of Biomes.
Ans. 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.
Q. 25. Describe the carbon cycle.
Ans. The carbon cycle. Carbon is one of the basic elements of all living organisms. It forms
the basic constituent of all organic compounds. The biosphere contains over half a million
carbon compounds in them. The carbon cycle is mainly the conversion of carbon dioxide.
This conversion is initiated by the fixation of carbon dioxide from the atmosphere through
photosynthesis. Such conversion results in the production of carbohydrate, glucose that
may be converted to other organic compounds such as sucrose, starch, cellulose, etc.
Here, some of the carbohydrates are utilised directly by the plant itself. During this process
more carbon dioxide is generated and is released through its leaves or roots during the day.
The remaining carbohydrates not being utilised by the plant become part of the plant tissue.
The plant tissues are either being eaten by the herbivorous animals or get decomposed by
micro-organisms. The herbivores convert some of the consumed carbohydrates into carbon
dioxide for release in to the air through respiration. The micro-organisms decompose the
remaining carbohydrates after the animal dies.
Q. 26. Describe the mineral cycles.
Ans. Mineral cycles. Other than carbon, oxygen, nitrogen and hydrogen being the principal
geochemical components of the biosphere many other minerals also occur as critical
nutrients for plant and animal life. These mineral elements required by living organisms are
obtained initially from inorganic sources such as phosphorus, sulphur, calcium and
potassium. They usually occur as salts dissolved in soil water or lakes, streams and seas.
Mineral salts come directly from the earth’s crust by weathering where the soluble salts
enter the water cycle eventually reaching the sea.
Other salts are returned to the earth’s surface through sedimentation and after weathering
they again enter the cycle. All living organisms fulfil their mineral requirements from
mineral solutions in their environments. Other animals receive their mineral needs from the
plants and animals they consume. After the death of living organisms the minerals are
returned to the soil and water through decomposition and flow.
Q. 27. Describe the oxygen cycle.
Ans. The oxygen cycle. Oxygen is the main byproduct of photosynthesis. It is involved in the
oxidation of carbohydrates with release of energy, carbon dioxide and water. The cycling of
oxygen is a highly complex process.
Oxygen occurs in a number of chemical forms and combinations. It combines with nitrogen
to form nitrates and with many other minerals and elements to form various oxides such as
iron oxide, aluminium oxide and such others.
Much of oxygen is produced from the decomposition of water molecules by sunlight during
photosynthesis and is released to the atmosphere through transpiration and respiration
processes of plants.
Q. 28. Explain the term ‘‘Biosphere’’.
Ans. Biosphere is the realm of all living forms (human beings, plants, animals) that exist in
hydrosphere, lithosphere, and atmosphere. In this way, natural environment includes man
also. It is a thin life bearing layer above the earth’s surface. It extends vertically from the
deep ocean to the higher layers of atmosphere.
The biosphere is the basis of life on the earth. Man tries to modify the environment and
utilizes the resources of earth. Man tries to bring a totality of environment so that
environment operates as a whole.
Q. 29. Examine the importance of Biosphere.
Ans. Biosphere is a thin layer which contains living things above the earth’s surface. It has a
great significance for human life. The earth has a unique place in the solar system due to the
presence of biosphere.
Organisms in the biosphere provide a variety of food for us. Plants provide us raw materials
for clothing and shelter such as cotton and jute. Human existence and survival on the earth
depends upon biosphere. Coal, mineral oil, wool, silk and many industrial raw materials are
obtained from biosphere.
Q. 30. What do you understand by the term ‘‘Ecological Balance’’?
Ans. In nature, each geographical element has a life cycle. These features are born, grow to
maturity and then die. Landforms, plants, and animals pass through this cycle. Landforms
have a longer life cycle, but plants and animals change within short periods. After the final
stage, there is no change in the composition of plants as a community. This stage is known
as ecological balance.

Long Question Answers: Life on the Earth

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.