NIOS Class 12 Biology Chapter 25 Principles of Ecology

NIOS Class 12 Biology Chapter 25 Principles of Ecology Solutions to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Biology Chapter 25 Principles of Ecology Notes and select need one. NIOS Class 12 Biology Chapter 25 Principles of Ecology Question Answers Download PDF. NIOS Study Material of Class 12 Biology Notes Paper 314.

NIOS Class 12 Biology Chapter 25 Principles of Ecology

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Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Biology Chapter 25 Principles of Ecology Solutions, NIOS Senior Secondary Course Biology Solutions for All Chapter, You can practice these here.

Principles of Ecology

Chapter: 25




1. Name the various levels of organisation.

Ans: Genes → Cell → Organ → Organism → Population → Community.

2. Define the term ecology.

Ans: Ecology is “the study of animals and in relation to their habit and habitat”.

3. What are the three physical systems that support life on earth?

Ans: (i) Atmosphere.

(ii) lithosphere. and 

(iii) hydrosphere.

4. Name the major components of the environment.

Ans: (i) Abiotic.

(ii) Biotic.

5. Enumerate the various physical factors of the environment.

Ans: (i) Light.

(ii) Temperature.

(iii) Humility.

(iv) Pressure.

(v) Soil profile.

(vi) Precipitation etc.

6. Why is habitat called the address of organisms and its niche ‘the profession’? 

Ans: Since habit is home of organism but niche show home & profession both.

7. What do we mean by ‘fins are an adaptation of fish to aquatic life’? Explain. 

Ans: Since fins developed to live well in water in fish.


1. A population with equal number of births and deaths will show:

(a) Acceleration phase of growth.

(b) Plateau phase.

(c) Exponential growth phase.

(d) Initial phase of growth.

Ans: (b) Plateau phase.

2. When population reaches carrying capacity:

(a) Mortality rate = Birth rate.

(b) Mortality rate > Birth rate.

(c) Mortality rate < Birth rate.

Ans: (c) Mortality rate < Birth rate.

3. Human population shows: 

(a) S-shaped growth curve.

(b) J-shaped growth curve.

(c) Z-shaped growth curve.

Ans: (a) S-shaped growth curve.


1. Define an ecosystem.

Ans: The ecosystem is “a unit to study ecology/functionally independent unit to study.” It is the interrelation between biotic and abiotic components of environment.

2. What are the main components of an ecosystem?


3. Give reason, why are decomposers necessary in an ecosystem?

Ans: They breakdown products of the dead animals and the plants.

4. What is the role of decomposers in nature?

Ans: They help in recycling of Nutrients. 

5. Why are plants called autotroph and animals called heterotrophs?

Ans: Plants make food but animals cannot, consume food made by plants (heterotrophic).

6. Give one example of food chain.

Ans: Grass → Grasshopper → Frog → Snake → Hawkar eagle.

7. Name the trophic level frog belongs to.

Ans: Secondary level consumer.

8. Snake can be both a secondary as well as tertiary consumer Justify.

Ans: A snake can feed on a rat → so it is a secondary consumer; it can feed on a frog and so it is a tertiary consumer also.


1. What can be the maximum number of steps in a food chain?

Ans: Upto five (5).

2. Why is energy flow linear in ecosystem?

Ans: The energy from solar radiation is fixed in form of food by producers. This energy is passed on to consumers of different trophic level. At each trophic level energy is used by the member for metabolism and only left over energy is passed on each trophic level (10%).

3. Define:

(a) Biomass.

Ans: Biomass: It is the food stored by organisms like plants.

(b) Pyramid of number.

Ans: Pyramid of Number: It is the “graphical representation of standing crop expressed as the number.”

4. What is meant by community stratification?

Ans: Vertical and horizontal distribution of plants in the ecosystem.


1. Fill in the blanks:

(a) The relationship between two organisms where one receives benefits at the cost of other is known as _________.

Ans: Symbiosis.

(b) A group of several species living together with mutual tolerance or adjustment and beneficial interactions in a natural area is known as _________.

Ans: Community. 

(c) A force that acts against maximum population growth is _________.

Ans: Carrying capa city (K).

(d) Association between insect polinated flowers and pollinating insect is an association termed is _________.

Ans: Symbiosis.


1. Define alpine tundra ecosystems. 

Ans: Alpine tundra: It is an ecosystem that occurs high mountain peak above the tree line. The environmental conditions are very severe and show day and night temperature variation.

2. Give two examples of plants of tundra.

Ans: (i) Cotton grass.

(ii) willows and birches. 

3. Give two common characteristics of tundra and desert biome.

Ans: Two common features of tundra and desert are:

(a) Both these biomes have very harsh climatic conditions.

(b) The vegetation is scarce.

4. Names of three main types of forests.

Ans: The main types of forests are:

(a) Tropical rain forest.

(b) Deciduous forest, north. and 

(c) Coniferous forest.

5. Where are savannas found?

Ans: South America and Australia. 

6. What are deciduous trees?

Ans: These shed their leaves in autumn season and grow new foliage during spring season.


1. What are plankton?

Ans: The free floating microscopic organisms are called planktons.

2. Name two phytoplanktons and two bottom dwellers in fresh water ecosystem.

Ans: (a) Diatoms, algae.

(b) Prawn, crabs and snail.

3. What is the maximum pressure in ocean.

Ans: About 1000 atmosphere.

4. Give an example of:

(a) Wet Land.

Ans: Wet: Marshes and mangroves.

(b) Lotic type of ecosystem.

Ans: Lotic type of ecosystem: Streams, springs. 


1. What does the following sequence represent:

(a) Ecological succession. 

(b) Genetic drift. 

(c) Phylogenetic trend.

(d) A food pyramid.

Ans: (a) Ecological Succession.

2. A community which starts succession in a habitat is:

(a) Pioneer community.

(b) Social Community. 

(c) Biotic Community.

(d) Ecosere.

Ans: (a) Pioneer Community.

3. In ecological succession, beginning from pioneer and ending in climax community, the biomass shall:

(a) decrease.

(b) increase and then decrease.

(c) decrease and then increase.

(d) Increase continuously.

Ans: (d) Increase continuously.


1. Define nutrient cycle.

Ans: The movement of nutrient elements through the various components of an ecosystem is known as a nutrient cycle.

2. Where are the bulk of nutrients stored in an ecosystem?

Ans: In the reservoirs pool.

3. Name the nutrient cycle where atmosphere acts as the main reservoir. 

Ans: Gaseous cycle.

4. List any two human activities that have led to increase in atmospheric CO₂ . 

Ans: (i) Urbanisation.

(ii) Increased used of automobiles.

5. Name the reservoirs for water cycle. 

Ans: Polar ice caps and water found deep in oceans are two main reservoirs for water cycle.

6. How do humans affect the phosphorus cycle?

Ans: They hasten loss of the rate of Phosphorous in Cycle.

7. How do the sea birds contribute to the phosphorus cycle?

Ans: Sea birds bring back phosphorous to cycle by their guano deposits.


1. What are the three physical life support systems on the planet earth?

Ans: (i) Atmosphere.

(ii) Hydrosphere. and 

(iii) Lithosphere.

All these three make biosphere.

2. Name the various biotic and abiotic components of the environment.

Ans: (i) Biotic (living) Components of Environment: They are producers, consumers and decomposers. Green plants prepare food and are autotrophs. Consumers eat plants directly or in directly. The decompsers decompose dead bodies of living beings.

(ii) Abiotic (non-living) components of environment. They fall into two groups.

(a) Physical components: They are climatic characteristics like pressure, soil profile, humidity, precipitation, light and temperature etc.

(b) Chemical components: The inorganic substances may be macro and micronutrients. The organic substances are carbohydrates, fats, proteins etc.

3. Give differences between natural and human modified ecosystem.

Ans: Difference between human modified and natural ecosystems:

Human modified EcosystemNatural Ecosystem
1. It is manmade or artificial.It occurs in nature due to interaction of forces there.
2. Examples: a city, a village, an aquarium and a cropland, agroecosystems, aquaculture and spaceship etc.Examples: a sea, a pond and a forest. They are of two types:
(a) terrestrial. and 
(b) aquatic.

4. Why is the number of trophic levels restricted to four or five in a food chain?

Ans: The trophic levels in a food chain is limited in number (4 or 5) as the energy decreases successively at each level according to ten percent law of lindemann.

5. Give only two differences between fresh water and marine biome.

Ans: Difference between Fresh Water and Marine Biomes:

Fresh Water BiomeMarine Biome
1. e.g., pond, lake, river, wetlands and ecotones.e.g., sea, ocean and coastal shores.
2. It includes, low salt fresh water, running or stand shell, flora and fauna.It includes salt water, less light, pressure (1 atm – 1000) at depth, tides (low tides/spring), flora and fauna.

6. What will happen if all the floating animals are removed from a lake ecosystem?

Ans: If all the floating animals are removed from a lake, the number of fishes, frogs and tortoises would decreases as they feed on zooplanktons.

7. What are the benefits of natural ecosystems?

Ans: Benefits of Natural Ecosystems: They are beneficial to us as they form habitat for different fauna and flora. They provide many plant products to us. Rainfall occurs due to dense forests.

8. Give two differences between energy flow and biogeochemical cycle in an ecosystem.

Ans: Two differences Between Energy Flow and Biogeochemical Cycle:

Energy FlowBiogeochemical Cycle
1. Flow of energy by various levels of food chain decreasing at successive levels.Cycling of nutrients in biosphere e.g., N₂. O₂, carbon cycle, P, S cycle etc.
2. It is one way/ linear in an ecosystem.They have reservoir pool and cycling pool.

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