15. Life on the Earth

NCERT Questions:

1. Multiple choice questions:

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

a) Only plants

b) All living and nonliving organisms

c) Only animals

d) All living organisms

Ans. d) All living organisms

(ii)  Tropical grasslands are also known as:

a) The prairies

b) The savannahs

c) The steppes

d) None of the above

Ans. b) The savannahs

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

a) Iron carbonate

b) Iron nitrites

c) Iron oxides

d) Iron sulphate

Ans. 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

Ans. c) Carbohydrates

2. Answer the following questions in about 30 words.

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

Ans.

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

b) Ecology is the study of organisms and how they interact with the environment around them.

c) An ecologist studies the relationship between living things and their habitats, in addition to examining how ecosystems function.

d) Ecologist also study what happens when ecosystems do not function normally.

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

Ans. The diversity of life forms is maintained to bring a kind of balance. This balance is maintained in a particular proportion so that a healthy interaction between the biotic and the abiotic components goes on.  The interaction of a particular group of Organism with biotic factors within a particular habitat result in clearly defined energy flow and material cycles on land, water and air are called ecological systems.

Ecosystems are of two major types, terrestrial and aquatic.

a) Terrestrial ecosystems can further be classified into biomes.

b) Aquatic ecosystems can be classified as marine and freshwater ecosystems.

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

Ans. The sequence of eating and being eaten and the resultant transfer of energy from one level to another are known as food chain. There are two types of food chain, grazing food chain and detritus food chain:

a) Grazing food chain: In grazing food chain the first level starts with plants as producers and ends with carnivorous as consumers at last level, with the herbivorous being at the intermediate level.

b) Detritus food chain: A capture initiated by grazing detroiters food chain is based on autotrophs. Energy capture initiated by grazing animals and involves the decomposition or breaking down of organic waste and death matter derived from the grazing food chain. For example plant – beetle – paddy – stock – frog – snake – hawk.

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

Ans. The interconnecting network of species is known as food web. 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 each of the carnivores may consume more than one type of pray. As a result, the food chains get interlocked with one another. This is termed as food web.

(v) What is a Biome?

Ans.

a) Biome is a plant and animal community that covers a large geographical area.

b) The boundaries of different biomes on land are determined mainly by climate.

c) Therefore, a Biome can be defined as the total assemblage of plant and animal species interacting within specific conditions.

d) These include rainfall, temperature, humidity and soil conditions.

e) Some of the major biomes of the world are forest, grasslands, desert, and tundra biomes.

3. Answer the following questions in about 150 words:

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

Ans.

a) The Sun is the source of all energy on Earth.

b) This energy initiates life process in the biosphere through photosynthesis, the main source of food and energy for green plants.

c) A very small fraction of about 0.1% of solar energy reaching Earth is fixed in photosynthesis. More than half is used for plant respiration and the remaining part is temporarily stored or is shifted to other portions of the plant.

d) During photosynthesis, carbon dioxide is converted into organic compounds and oxygen.

e) The balance of the chemical elements is maintained by a cyclic passage through the tissues of plants and animals.

f) The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water and soil through decomposition.

g) This cyclic movement of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles.

h) Fixing of nitrogen in the atmosphere action of soil microorganisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil comprise the principal source of free nitrogen.

i) Lightning and cosmic radiation can also fix nitrogen in the atmosphere.

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

Ans.

a) Ecological balance is a state of dynamic equilibrium within a community of organisms in habitat or ecosystem.

b) It can happen when the diversity of the living organisms remains relatively stable.

c) Gradual changes do take place, but that happens only through natural succession.

d) 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 different organisms where population remains stable.

e) This balance is brought about by the fact that certain species compete with one another, determined by the environment in which they grow.

f) This balance is also attained by the fact that some species depend on others for their food and sustenance.

g) Such accounts are encountered in vast grasslands where the herbivorous animal (deer, zebra, buffaloes etc.) are found in plenty.

h) Ecological balance may be disturbed due to the introduction of new species, natural hazards, or human causes.

i) Human interference has affected the balance of plant communities, leading to disturbances in the ecosystems.

j) Such disturbances bring about numerous secondary successions. Human pressures on the Earth’s resources have put a heavy toll on the ecosystem.

k) This has destroyed its originality and has caused adverse effects to the general environment. Ecological balances have brought many natural calamities like floods, landslides, diseases, erratic climatic occurrences etc.

l) There is a very close relationship between the plant and animal communities within particular habitats.

m) Diversity of life in a particular area can be employed as an indicator of the habitat factor.

Proper knowledge and understanding of such factors provide a strong base for protecting and conserving the ecosystems.

Question Bank:

Multiple choice questions:

1. There are two types of by biogeochemical cycles the gaseous and:

a) The primary cycle

b) The sedimentary cycle

c) The tertiary cycle

d) The water cycle

Ans. b) The sedimentary cycle

There are two types of biogeochemical cycles the gaseous and the sedimentary cycles

2. The main byproduct of photosynthesis is:
3. a) Carbon dioxide
4. b) Nitrogen
5. c) Hydrogen
6. d) Oxygen

Ans. d) Oxygen

It occurs in a number of chemical forms and combinations.

3. ________ can be defined as a scientific study of the interactions of organisms with their physical environment and with each other.

a) Ecology

b) Geography

c) Geomorphology

d) Biology

Ans. a) Ecology

Ecology can be defined as a scientific study of the interactions of organisms with their physical environment and with each other.

4. The deserts have:

a) Porous soil with thin layer of humus

b) Swampy soil

c) Acetic, with poor nutrients in the soil

d) Rich nutrients with organic matter in the soil

Ans. d) Rich nutrients with organic matter in the soil

The desert have rich nutrients in little or no organic matter in the soil it has scanty vegetation.

5. Transfer of energy that occurs during the process of food chain from one level to another is known as flow energy

a) Solar energy

b) Weight energy

c) Ocean current

d) Flow of energy

Ans. d) Flow of energy

Transfer of energy that occurs during the process of a food chain from one level to another is known as flow of energy.

6. Abiotic factors include:

a) Decomposers

b) Green plants

c) Consumers

d) Rainfall

Ans. d) Rainfall

Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions etc.

7. The boundaries of different biomes on land are determined mainly by:

a) Climate

b) Temperature

c) Human activity

d) Humidity

Ans. a) Climate

A biome is a plant and animal community that is spread over large geographic area.

8. Mineral salts come directly from:

a) Earth crust

b) Water cycle

c) Industries

d) Atmosphere

Ans. a) Earth crust

It comes from weathering

9. Temperate Steppe is a sub type of _____ biome:

a) Forest

b) Aquatic

c) Desert

d) Grassland

Ans. d) Grassland

These are the parts of Eurasia and North America

1. Food chains are generally of

a) Six types

b) Four types

c) Two types

d) Three types

Ans. c) Two types

Generally two types of food chains are recognised grazing food chain and detritus food chain. In grazing food chain the first level starts with plants as producers and ends with carnivorous as consumers. A detritus food chain is based on autotrophs energy capture initiated by grazing animals it involves the decomposition or breaking down of organic matter from the grazing food chain.

11. Freshwater ecosystem includes:

a) Ponds

b) Estuaries

c) Oceans

d) Lagoons

Ans. a) Ponds

Freshwater ecosystem includes ponds lakes, streams, rivers etc.

12. Conversion of nitrates into free nitrogen is called:

a) Nitrification

b) Denudation

c) Disintegration

d) Deformation

Ans. a) Nitrification

Nitrification is the process done by bacteria.

13. During photosynthesis carbon dioxide with water in the presence of sunlight form:

a) Proteins

b) Carbohydrates

c) Amino acids

d) Vitamins

Ans. b) Carbohydrates

During photosynthesis, carbon dioxide combines with water in the presence of sunlight and form carbohydrates. At the same time oxygen is also released as the by-product.

14. The most important decomposers are:

a) Microorganism

b) Protozoa

c) Mammals

d) Bacteria

Ans. a) Microorganisms

Microorganisms are the most important of all the decomposers.

15. Which one of the following is not a primary consumer?

a) Mice

b) Tiger

c) Goat

d) Dear

Ans. b) Tiger

Tiger is not a primary consumer. Tiger is a carnivorous animal.

16. The terrestrial ecosystem can be divided into:

a) Regions

b) Biomass geo systems

c) Biomes

d) Biomass

Ans. c) Biomes

Terrestrial ecosystem can be divided into biomes.

17. Oxygen combines with iron found in the rocks to form:

a) Iron nitrate

b) Iron sulphate

c) Iron carbonate

d) Iron oxide

Ans. d) Iron oxide

Oxygen combines with iron found in the rocks to form iron oxide.

18. The major types of ecosystems are:

a) Marine and freshwater

b) Terrestrial and aquatic

c) Atmospheric and lithospheric

d) Herbivorous and carnivorous

Ans. b) Terrestrial and aquatic

Terrestrial and aquatic are the two major types of ecosystems.

19. The cyclic movement of chemical element of the biosphere between organs is called:

a) Bio-cycle

b) Biogeochemical cycle

c) Chemical cycle

d) Biochemical cycle

Ans. b) Biogeochemical cycle

Biogeochemical cycle is the cyclic movement of chemical elements of the biosphere between organisms.

20. Tropical grasslands are also known as:

a) Savannahs

b) Prairies

c) Steppes

d) Grasslands

Ans. a) Savannahs

Tropical grasslands are also known as savannah.

21. _____ is included in biosphere:

a) Only plant

b) All living and non-living organism

c) All living organism

d) Only animals

Ans. b) All living organisms are included in biosphere.

22. Which one of the following is not compound of nitrogen?

a) Nucleic acid

b) Proteins

c) Cellulose

d) Amino acid

Ans. c) Cellulose

Cellulose is a carbohydrate it is not a compound of nitrogen.

23. The basic element of all living organism is:

a) Oxygen

b) Carbon dioxide

c) Nitrogen

d) Water

Ans. a) Oxygen

All living things have six basic elements in common: carbon, hydrogen, nitrogen, oxygen, phosphorous and sulphur abbreviated as CHNOPS. Each element has properties that make it crucial to the building of biomolecules, both in their capacities for bonding to other elements and in them.

24. Altitudinal is found in the:

a) Mountains

b) Grasslands

c) Valleys

d) Desserts

Ans. a) Mountains

Altitudinal are found in mountains.

25. Decomposers feed on:

a) Dead organisms

b) Forest

c) Grassland

d) Agricultural fields

Ans. a) Dead organisms

Decomposers feed on dead organisms such as dead plant materials animal carcasses, faeces. They perform a valuable service as earth’s clean-up crew. Without decomposers, dead leaves, dead insects or animals would pile up everywhere.

26. The interconnecting network of the species is known as:

a) Food chains

b) Food web

c) Food hub

d) Food cycle

Ans. b) Food web

The interconnecting network of species is known as food web. It’s a complex network of interconnecting and overlapping food chains showing feeding relationships within a community. A food chain shows how a matter and energy from food are transferred from one organism to another, whereas a food web illustrates how food chains intertwine in an ecosystem.

27. Biotic components of environment are:

a) Decomposers

b) Soil

c) Temperature

d) Rainfall

Ans. a) Decomposers

Decomposers are the biotic components of environment. Decomposers break down dead organisms. It is a process possible by only certain kingdoms, such as fungi, millipede, earth warm etc. Decomposers are also sometimes referred to as detritivores (detritus).

28. An example of freshwater ecosystem is:

a) Ocean

b) Streams

c) Estuaries

d) Atolls

Ans. b) Streams

Streams are the examples of freshwater ecosystem.

29. Type of soil the desert biome has is:

a) Porous within layers of humus

b) Rich in nutrients with little organic matter

c) Acetic, poor in nutrients

d) Fertile alluvial

Ans. b) Rich in nutrients with little organic matter

The desert biome soil is rich in nutrients with little organic matter. Desert is very fragile in many ways because of the scarcity of water and plants. Most plants that live in the desert take a long time to grow. Once plants are destroyed, it will take many years for them to grow back. Since, soil in the desert is held down by plant roots; once plots are destroyed the soil is, too. Consequently the soil quickly erodes away with the strong winds. Soil often has abundant nutrients because they need only water to become very productive and have little or no organic matter.

30. _____ is a marine ecosystem:

a) Lakes

b) Coral reefs

c) Reverse

d) Marshes

Ans. b) Coral reefs

Coral reefs are marine ecosystems. These are underwater organisms made from calcium carbonate. They are colonies of tiny animals, found in marine waters that contain few nutrients.

31. Total assemblage of plant and animals under specific climatic conditions is called:

a) Community

b) Community region

c) Biome

d) Region

Ans. c) Biome

Biome is a total assemblage of plants and animals under specific climatic conditions.

32. Ecosystem is a:

a) System of life.

b) System consisting of biotic and abiotic components

c) System of animals

d) System of plants

Ans. b) System consisting of biotic and abiotic components

System consisting of biotic and abiotic components and their interaction with each other is known as ecosystem. It is of two type terrestrial and aquatic ecosystem.

33. Tropical grasslands are also known as the:

a) Prairies

b) Savannahs

c) Steppes

d) Veldts

Ans. b) Savannahs

Savannahs are tropical grasslands that lie north and south of tropical rainforest that are on the equator. Some areas beyond savannahs are hot deserts. Others savannahs may be lined with mountains, dense forest and seas. South America is a home to several large savannahs.

34. The boundaries of different biomes on land are determined mainly by:

a) Climate

b) Temperature

c) Human activities

d) Vegetation

Ans. a) Climate

Climate determines the boundaries of different biomes on land. A biome is plant and animal community that is spread over large geographical area. Therefore, a biome can be defined as the total assemblage of plant and animal species interacting with specific conditions.

35. The main byproduct of photosynthesis is:

a) Carbon dioxide

b) Hydrogen

c) Oxygen

d) Nitrogen

Ans. c) Oxygen

The main byproduct of photosynthesis is oxygen. During photosynthesis, carbon dioxide is converted into organic compounds and oxygen.

36. A freshwater ecosystem is:

a) Oceans

b) Marshes

c) Coral reefs

d) Deltas

Ans. b) Marshes

Marshes aquatic ecosystems can be classed as marine and freshwater ecosystems. Marine ecosystems include the oceans, coastal estuaries, red coral reefs. Freshwater ecosystem includes lakes, ponds, streams, marshes and bogs/swamps.

37. Mineral salts directly come from:

a) Forest Biome

b) Atmosphere

c) Water cycle

d) Earth crust

Ans. d) Earth crust

Mineral salts come directly from earth’s crust by weathering where the soluble salts enter the water cycle, eventually reaching the sea.

38. Biotic factors include:

a) Decomposers

b) Sunlight

c) Consumers

d) Producers

Ans. a) Decomposers

All ecosystems consist of biotic and abiotic factors.  Biotic factors include the producers, consumers and decomposers and abiotic factors include rainfall temperature sunlight atmospheric humidity soil conditions inorganic substances etc.

39. Atmosphere consist ___% of nitrogen:

a) 22

b) 75

c) 89

d) 79

Ans. d) 79%

Atmosphere consists of 79% of nitrogen, 21% of Oxygen and 1% of other gases. It is the major constituent of atmospheric gases.

40. The two types of ecosystems are:

a) Marine and freshwater

b) Terrestrial and aquatic

c) Forest and grasslands

d) Atmospheric and lithospheric

Ans. b) Terrestrial and aquatic are the major two types of ecosystems.

Terrestrial ecosystem can be further classified into biomes. Aquatic ecosystem can be classified as marine and freshwater ecosystems.

Short answer type questions: 

1. What is a biome?

Ans. A biome is a plant and animal community that covers a large geographical area. This geographical area is usually determined by climate.

2. Which kingdom does bacteria belong to?

Ans. Bacteria belong to monera kingdom. Blue algae – cyanobacteria, cocci shaped bacteria – streptococcus, bacillus shaped bacteria – E coli, vibrio shaped – vibrio cholera (cholera), spiral shaped bacteria – Treponema palladium (syphilis) etc. are some examples of bacteria.

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

Ans. The interaction 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.

The two major types of ecosystems are:

a) Terrestrial ecosystem

b) Aquatic ecosystem

4. Who are decomposers?

Ans. Decomposers are the organs such as the bacteria and fungi who obtain energy from the chemical breakdown of dead organisms or animal or plant waste.

5. Name the part of earth which consist the entire living Organism.

Ans. The biosphere consist entire living organism.

6. Define agro ecosystem.

Agro ecosystem is specially and functionally coherent unit of agricultural activity. There are some common features that mark all crops; they are generally called agro ecosystems.

7. What are nutrients?

Ans. The nutrients are substances required for the nourishment of an organism, providing source of energy or structural component.

8. Who are first order consumers?

Ans. The herbivorous are called first order consumers like cattle deer and goat that derive their food/energy directly from the plants.

9. Define food chain.

Ans. The food chain shows how each living being gets its food from the other. Some animals eat plants and some animals depend on animals i.e., a simple food chain links the trees and shrubs, the giraffes (that eat trees and shrubs), and the lions (that eat the giraffe). Each link in this chain is food for the next. A food chain always starts with plants life and ends with an animal.

10. Define food web.

Ans. A food web is a natural interconnection of food chains. In other words a number of food chains together make food web.

11. Who are homo-sapiens?

Ans. The scientific name for the human beings is homo-sapiens; it’s a Latin word meaning ‘wise human’.

12. Describe the ecosystem of the earth.

Ans. An ecosystem is a geographic area where animals and other organisms, as well as weather and landscape work together to form a bubble of life. Ecosystems contain biotic or living parts as well as abiotic factors or non-living parts.

13. Who are producers in the ecosystem?

Ans. Plants are considered as producers they are the living organisms who are able to produce their own food by the process of photosynthesis.

14. What is biosphere?

Ans. A global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere and atmosphere is known as biosphere.

15. What are the factors which influence the terrestrial ecosystem?

Ans. The type of terrestrial ecosystem found in a particular place is dependent on the temperature range, the average amount of precipitation received, the soil type, and amount of light it receives.

16. What do you understand by the term ecological balance? Discuss the important measures needed to prevent ecological imbalances.

Ans. The state of equilibrium in the ecosystem is called ecological balance. It is a state where there is equality between organisms and their environment in terms of coexistence. It can happen when the diversity of the living organism remains relatively stable.

Ecological imbalance occurs due to the introduction of new species, natural hazards or human causes.

Measures to prevent ecological imbalance are:

a) Manage natural resources carefully

b) Controlling population – reducing human consumption of natural resources

c) Protecting the water

d) Recycling

e) Planting trees

f) Improving farming techniques to avoid land degradation

g) Shifting from fossil fuels to sustainable energy.

17. Define the process of nitrogen cycle.

Ans. All life requires nitrogen compounds, e.g., proteins and nucleic acids.  Air, which is 79% nitrogen gas (N₂), is the major reservoir of nitrogen. However, most organisms cannot use nitrogen in this form. Plants secure their nitrogen in fixed form, i.e., incorporated in compounds, such as

• Nitrate ions (NO₃^–)

(The nitrate ion is a polyatomic ion and the salts that contain this nitrate ion are called nitrates. The nitrate ion is a conjugate base of nitric acid).

• Ammonia (NH₃)

(Ammonia (NH₂) is a compound made of nitrogen and hydrogen molecules. It is a colourless gas with a pungent odour, and is reactive; it forms secondary particulate matter (PM_2.5) when combined with other pollutants in the atmosphere).

• Urea (NH₂) ₂CO

(Urea is produced in the liver and is a metabolite (breakdown product) of amino acids. Ammonium ions are formed in the breakdown of amino acids. Some are used in the biosynthesis of nitrogen compounds, excess ammonium ions are converted to urea).

Animals secure their nitrogen and all other compounds from plants or animals that have fed on plants.

18. Define carbon cycle.

Ans. Carbon is the basic element to all life in the biosphere and forms the basic constituent of organic compounds. The carbon cycle is mainly concerned with the conversion of carbon dioxide which is initiated by fixation of carbon dioxide from the atmosphere through photosynthesis. Such conversions result in the production of carbohydrates glucose that may be converted into other organic compounds such as sucrose, cellulose etc. Some of the carbohydrates are used directly by the plants and the remaining becomes part of plant tissues.

19. Write short note on the ecological pyramids.

Ans. An ecological pyramid is a graphical presentation showing the relationship between different organisms in an ecosystem. It shows the flow of energy at different trophic levels in an ecosystem. Those at the bottom of the food chain are usually the smallest not always and almost inevitably the largest in number.

Those which feed off these primary producers are less in number, usually because they are larger and require more than one primary producer as a means of food in order to survive. This situation continues to the top of the chain, where few secondary consumers are eaten by an even smaller amount of tertiary consumers.

20. Distinguish between tropical grassland and mid latitude grasslands.

Ans.

21. Distinguish between the Taiga Biome and the Tundra Biome.

Ans.

22. What is ecology?

Ans. Ecology is the branch of science that studies habitats and the interactions between living things and the environment. The term was coined in 1866 by Darwin a German biologist. The German zoologist Ernst Hackle who used the term, it’s derived from the Greek world ‘oikos’ meaning ‘house’ and ‘logos’ meaning science. The environment includes both the biotic environment (climate and geology) and the biotic environment (living things like plants and animals) etc.

23. Describe in detail the functions and characteristics of an ecosystem.

Ans. Structure of ecosystem:

The structure of ecosystem involves the description of the available plant and animal species present. From the structure of ecosystem we are generally concerned with the biotic and abiotic component of ecosystem the structure and the function of ecosystem can be easily defined by the following functions of ecosystem:

a) Ecosystems have energy flow

b) Ecosystems cycle material

These two processes are linked, but they are not quite the same. Energy enters the biological system as light energy, or photons, is transformed into chemical energy into organic molecules by cellular processes including photosynthesis and respiration and ultimately is converted into heat energy this energy is dissipated meaning it is lost to the system as heat. Once it is lost it cannot be recycled.

Elements such as carbon, nitrogen, or phosphorus enter living organisms in a variety of ways. Plants obtain elements from the surrounding atmosphere, water, or soil. Animals may also obtain elements directly from the physical environment, but usually they obtain these mainly as a consequence of consuming other organisms. These materials are transformed biochemically within the bodies of organisms, but sooner or later, due to excretion or decomposition they are returned to an inorganic state. Often bacteria complete this process through the process called decomposition or mineralisation. During decomposition these minerals are not destroyed or lost the elements are cycled endlessly between their biotic and abiotic state within ecosystems. Those elements whose supply tends to limit biological activity are called nutrients.

24. Write a short note on biogeochemical cycle.

Ans. The biogeochemical cycle is a circuit or pathway by which a chemical element or molecule moves through both biotic and abiotic components of an ecosystem. In effect, the element is recycled, although in some cycles there may be places (call ‘sinks’) where the elements are accumulated or held for a long period of time.

The bio-geo-chemical cycle refers to the movement of chemicals or the nutrients in the biosphere so the cyclic movement of the nutrients in the biosphere from the biotic to the abiotic phenomenon is called the biogeochemical cycle.

25. Describe the important characteristics of different forest biomes of the World.

Ans. The three major types of forest biomes on the earth are:

a) Tropical biome

b) Temperate Biome

c) Boreal Biome

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