Class 10th Science Chapter 15 – Our Environment and Sustainable Management | Food Chain, Food Web and Trophic Levels

Our Environment and Sustainable Management

Food Chain, Food Web and Trophic Levels

खाद्य श्रृंखला, खाद्य जाल एवं पोषी स्तर

Class 10 CBSE Science | Foundation | Competitive Preparation

🌱 Food Chain, Food Web and Trophic Levels

1. Introduction | परिचय

A food chain describes a sequence in which food and energy pass from one organism to another. A food web consists of interconnected food chains, while a trophic level represents the position occupied by an organism in a food chain.

हिंदी: खाद्य श्रृंखला वह क्रम है जिसमें भोजन और ऊर्जा एक जीव से दूसरे जीव तक स्थानांतरित होती है। कई खाद्य श्रृंखलाओं के आपस में जुड़ने से खाद्य जाल बनता है। खाद्य श्रृंखला में किसी जीव की स्थिति को उसका पोषी स्तर (Trophic Level) कहते हैं।

Sun → Producers → Primary Consumers → Secondary Consumers → Higher Consumers

Core Idea: Food chain = linear pathway; Food web = interconnected pathways; Trophic level = feeding position.

2. Food Chain | खाद्य श्रृंखला

A food chain is a linear sequence of organisms through which food and energy are transferred as one organism eats another.

हिंदी: खाद्य श्रृंखला जीवों का एक क्रम है जिसमें एक जीव दूसरे जीव को खाता है और भोजन तथा ऊर्जा का स्थानांतरण होता है।

🌱
Grass
Producer

→

🦗
Grasshopper
Primary Consumer

→

🐸
Frog
Secondary Consumer

→

🐍
Snake
Higher Consumer

→

🦅
Eagle
Top Consumer

Grass → Grasshopper → Frog → Snake → Eagle

3. Meaning of the Arrow in a Food Chain

The arrow in a food chain generally represents the direction of food and energy transfer. It is read as “is eaten by” or “energy passes to”.

Grass → Deer

This means: Deer eats grass and energy stored in grass becomes available to the deer.

Exam Trap: The arrow does not mean that the organism at the tail of the arrow eats the organism at the head. It indicates the direction of transfer: food/energy → eater.

4. Grazing Food Chain

A grazing food chain begins with living green plants or other photosynthetic producers.

🌿
Grass

→

🐇
Rabbit

→

🦊
Fox

Grass → Rabbit → Fox

Most familiar terrestrial food chains are examples of grazing food chains.

5. Aquatic Food Chain

Aquatic food chains commonly begin with microscopic producers such as phytoplankton, followed by zooplankton and larger aquatic animals.

🟢
Phytoplankton

→

🔬
Zooplankton

→

🐟
Small Fish

→

🐟
Large Fish

6. Examples of Food Chains

Environment	Food Chain
Grassland	Grass → Grasshopper → Frog → Snake → Eagle
Forest	Grass → Deer → Tiger
Pond	Phytoplankton → Zooplankton → Small Fish → Large Fish
Crop field	Wheat → Rat → Snake → Eagle
Garden	Leaves → Caterpillar → Bird → Hawk

7. Trophic Level | पोषी स्तर

A trophic level is the position occupied by an organism in a food chain according to its feeding relationship.

हिंदी: खाद्य श्रृंखला में भोजन प्राप्त करने के आधार पर किसी जीव की स्थिति को उसका पोषी स्तर कहते हैं।

🦅 Fourth Trophic Level
Tertiary / Higher Consumer

⬇️

🐸 Third Trophic Level
Secondary Consumer

⬇️

🐇 Second Trophic Level
Primary Consumer

⬇️

🌱 First Trophic Level
Producer

8. First Trophic Level – Producers

The first trophic level is occupied by producers. They manufacture organic food and introduce energy into the food chain.

TL 1 = Producers

Plants

Algae

Phytoplankton

9. Second Trophic Level – Primary Consumers

The second trophic level is occupied by primary consumers, which generally feed directly on producers.

TL 2 = Primary Consumers

Herbivores

Deer

Rabbit

10. Third Trophic Level – Secondary Consumers

The third trophic level is generally occupied by secondary consumers, which feed on primary consumers.

TL 3 = Secondary Consumers

Frog

Lizard

11. Fourth Trophic Level – Tertiary Consumers

The fourth trophic level may be occupied by tertiary consumers that feed on secondary consumers.

TL 4 = Tertiary Consumers

Snake

Large Predators

12. Important Trophic-Level Table

Trophic Level	Organism Type	Example
1st	Producer	Grass
2nd	Primary Consumer	Grasshopper
3rd	Secondary Consumer	Frog
4th	Tertiary Consumer	Snake
Higher level	Top Consumer	Eagle

13. Food Chain and Energy Flow

Energy enters most ecosystems through sunlight and is captured by producers. It then passes from producers to consumers through feeding relationships.

Sun → Producer → Primary Consumer → Secondary Consumer → Higher Consumer

Energy flow through an ecosystem is unidirectional. It is not recycled in the same way as nutrients.

14. 10% Law of Energy Transfer

According to the commonly taught 10% law, approximately 10% of the energy available at one trophic level is transferred to the next trophic level.

🌱 Producers
10,000 J

→

🐇 Primary
1,000 J

→

🐸 Secondary
100 J

→

🐍 Tertiary
10 J

Energy at next trophic level ≈ 10% of energy at previous trophic level

The remaining energy is not simply “destroyed”; much is used in life processes and ultimately dissipated as heat.

15. Why are Food Chains Usually Short?

Only a small fraction of energy is transferred to the next trophic level. Therefore, progressively less energy becomes available at higher trophic levels.

This is one important reason why ecosystems generally have only a limited number of trophic levels in a food chain.

16. Food Web | खाद्य जाल

A food web is a network of interconnected food chains in an ecosystem. It represents multiple feeding relationships.

हिंदी: किसी परितंत्र में कई खाद्य श्रृंखलाएँ जब आपस में जुड़ जाती हैं, तो खाद्य जाल बनता है।

🌱 Grass

🌾 Plants

🌿 Shrubs

🐇 Rabbit

🦗 Grasshopper

🐭 Rat

🐸 Frog

🐍 Snake

🦊 Fox

🦅 Eagle

🐯 Tiger

Multiple arrows between organisms represent interconnected feeding relationships.

17. Example of a Food Web

Consider an ecosystem containing grass, grasshoppers, rabbits, frogs, snakes and eagles. Grass may be eaten by both grasshoppers and rabbits. Grasshoppers may be eaten by frogs and birds. Snakes may eat frogs and rats, while eagles may eat snakes and other animals.

Grass → Grasshopper → Frog → Snake → Eagle

Grass → Rabbit → Snake → Eagle

Grass → Rabbit → Eagle

Grass → Rat → Snake → Eagle

These interconnected chains together form a food web.

18. Food Chain vs Food Web

Food Chain	Food Web
Usually a single linear feeding pathway.	Contains several interconnected feeding pathways.
Shows one main route of energy transfer.	Shows multiple routes of energy transfer.
Simple representation.	More complex representation.
Less representative of the complete feeding relationships of many ecosystems.	Represents greater complexity of actual ecosystems.

19. Why is a Food Web More Stable?

A food web can provide alternative food pathways. If one food source becomes scarce, a consumer may sometimes use another available food source.

Therefore, interconnected feeding relationships can contribute to ecosystem stability.

However, a food web is not completely immune to disturbance. Major environmental changes can affect many connected populations simultaneously.

20. Difference Between Food Chain and Trophic Level

Food Chain	Trophic Level
A sequence showing feeding relationships.	The position of an organism in that sequence.
Example: Grass → Deer → Tiger.	Grass = TL1, Deer = TL2, Tiger = TL3.

21. Difference Between Food Web and Trophic Level

A food web describes the network of feeding relationships, whereas trophic level identifies the feeding position of an organism within a particular food pathway.

22. Organism Can Have Different Trophic Positions

An organism can occupy different trophic positions in different food chains because its position depends on what it eats.

Plants → Human

Human acts as a primary consumer in this pathway.

Plants → Goat → Human

Human occupies a higher trophic position in this pathway.

This is particularly important for omnivores, which may eat both plants and animals.

23. Food Chain and Decomposers

Decomposers do not normally appear as a simple successive trophic level in the same way as producers and consumers. They act on dead organisms and wastes from different trophic levels.

Dead Producers + Dead Consumers + Organic Waste → Decomposers → Simpler Substances + Nutrients

24. Food Chain, Food Web and Nutrient Cycling

🌱
Producers

→

🐇
Consumers

→

🦅
Higher Consumers

↓

🍄 🦠
Decomposers

↓

♻️
Nutrients

↓

🌱
Producers

25. Important Examples for CBSE

Food Chain	Producer	Primary Consumer	Secondary Consumer
Grass → Grasshopper → Frog → Snake	Grass	Grasshopper	Frog
Grass → Rabbit → Fox	Grass	Rabbit	Fox
Phytoplankton → Zooplankton → Fish	Phytoplankton	Zooplankton	Fish
Wheat → Rat → Snake → Eagle	Wheat	Rat	Snake

26. Important Exam Concepts

✔ Producer: First trophic level.

✔ Primary consumer: Usually herbivore; second trophic level.

✔ Secondary consumer: Usually feeds on primary consumers; third trophic level.

✔ Tertiary consumer: Feeds on secondary consumers in a given chain.

✔ Food chain: Linear feeding pathway.

✔ Food web: Interconnected food chains.

✔ Arrow: Direction of food/energy transfer.

✔ Energy: Flows in one direction and decreases at successive trophic levels.

✔ Nutrients: Can be recycled through ecosystem processes.

27. 30 MCQs with Answers

1. What is a food chain?

A. A linear sequence of feeding relationships

B. A list of abiotic factors

C. A group of decomposers only

D. A chemical cycle

Answer: A

2. Which organism occupies the first trophic level?

A. Frog

B. Producer

C. Snake

D. Eagle

Answer: B

3. In Grass → Deer → Tiger, deer is a:

A. Producer

B. Secondary consumer

C. Primary consumer

D. Decomposer

Answer: C

4. In Grass → Grasshopper → Frog, frog is a:

A. Producer

B. Primary consumer

C. Decomposer

D. Secondary consumer

Answer: D

5. The arrow in a food chain generally shows:

A. Direction of food and energy transfer

B. Direction of animal movement

C. Direction of reproduction

D. Direction of rainfall

Answer: A

6. Which is the correct food chain?

A. Eagle → Snake → Grass → Frog

B. Grass → Grasshopper → Frog → Snake

C. Frog → Grass → Snake → Grasshopper

D. Snake → Grass → Frog → Eagle

Answer: B

7. A food web consists of:

A. Only producers

B. Only one food chain

C. Interconnected food chains

D. Only decomposers

Answer: C

8. Which is generally an aquatic producer?

A. Eagle

B. Snake

C. Large fish

D. Phytoplankton

Answer: D

9. In a grazing food chain, the first organism is generally:

A. A living producer

B. A carnivore

C. A decomposer

D. A top predator

Answer: A

10. The second trophic level is generally occupied by:

A. Producers

B. Primary consumers

C. Decomposers

D. Top consumers

Answer: B

11. The third trophic level is generally occupied by:

A. Producers

B. Primary consumers

C. Secondary consumers

D. Decomposers

Answer: C

12. In Grass → Rabbit → Fox, fox is:

A. Producer

B. Primary consumer

C. Decomposer

D. Secondary consumer

Answer: D

13. Approximately what percentage of energy is transferred to the next trophic level according to the 10% law?

A. 10%

B. 25%

C. 50%

D. 90%

Answer: A

14. If producers contain 10,000 J, approximately how much may reach the next trophic level?

A. 10 J

B. 100 J

C. 1,000 J

D. 9,000 J

Answer: C

15. Energy flow in an ecosystem is generally:

A. Circular

B. Unidirectional

C. Random only

D. Completely reversible

Answer: B

16. Which statement is correct?

A. Food webs have only one feeding pathway

B. Food chains are always circular

C. Food webs contain interconnected feeding pathways

D. Trophic levels are abiotic factors

Answer: C

17. Which organism can occupy different trophic positions depending on its diet?

A. Omnivore

B. Producer only

C. Decomposer only

D. Sun

Answer: A

18. In Phytoplankton → Zooplankton → Fish, zooplankton is:

A. Producer

B. Primary consumer

C. Secondary consumer

D. Decomposer

Answer: B

19. Which organisms act on dead matter from different trophic levels?

A. Producers

B. Herbivores

C. Decomposers

D. Top predators

Answer: C

20. Why does energy decrease at higher trophic levels?

A. Energy is created at every level

B. All energy is stored permanently

C. Producers disappear

D. Much energy is used and eventually dissipated as heat

Answer: D

21. Which sequence represents increasing trophic level?

A. Producer → Primary → Secondary → Tertiary

B. Tertiary → Producer → Primary → Secondary

C. Secondary → Producer → Tertiary → Primary

D. Primary → Producer → Secondary → Tertiary

Answer: A

22. Which is NOT a food chain?

A. Grass → Rabbit → Fox

B. Grass → Deer → Tiger

C. Phytoplankton → Fish

D. Grass, rabbit, fox, snake as unrelated organisms

Answer: D

23. A food web is generally more complex because:

A. It has multiple interconnected food chains

B. It contains only producers

C. It excludes consumers

D. It contains no energy transfer

Answer: A

24. Which trophic level contains producers?

A. First

B. Second

C. Third

D. Fourth

Answer: A

25. If grass has 20,000 J, approximately how much may reach the primary consumers?

A. 2,000 J

B. 200 J

C. 20 J

D. 18,000 J

Answer: A

26. If 1,000 J reaches a primary consumer, approximately how much may reach the secondary consumer?

A. 1 J

B. 10 J

C. 100 J

D. 900 J

Answer: C

27. Which statement about nutrients is correct?

A. Nutrients can be recycled through ecosystem processes

B. Nutrients are always destroyed

C. Nutrients flow only from animals to sunlight

D. Nutrients are not required by producers

Answer: A

28. Which is an example of a food web relationship?

A. One animal eating only one food forever

B. Several animals sharing multiple food sources

C. Only sunlight reaching a plant

D. Only decomposition

Answer: B

29. Which factor helps explain why food chains usually contain limited trophic levels?

A. Energy transfer is inefficient

B. Producers eat top predators

C. Energy increases at every level

D. Decomposers stop all energy flow

Answer: A

30. Which statement is most accurate?

A. Food chain and food web mean exactly the same thing

B. Trophic level describes an organism's feeding position

C. Energy is completely recycled

D. Producers occupy the highest trophic level

Answer: B

28. Subjective Questions with Answers

2 Marks 1. Define food chain.

A food chain is a linear sequence of organisms through which food and energy are transferred as one organism eats another.

2 Marks 2. What is a trophic level?

A trophic level is the feeding position occupied by an organism in a food chain.

2 Marks 3. What is a food web?

A food web is a network of interconnected food chains in an ecosystem.

2 Marks 4. What does an arrow in a food chain represent?

It represents the direction of food and energy transfer from the organism being eaten to the organism that eats it.

2 Marks 5. Name the first trophic level.

The first trophic level is occupied by producers.

3 Marks 6. Give one example of a food chain and identify its trophic levels.

Grass → Grasshopper → Frog → Snake. Grass is TL1, grasshopper TL2, frog TL3 and snake TL4.

3 Marks 7. Differentiate between food chain and food web.

A food chain is generally a single linear pathway, whereas a food web consists of several interconnected food chains and represents multiple feeding pathways.

3 Marks 8. What are primary consumers?

Primary consumers are organisms that feed directly on producers. They generally occupy the second trophic level and are usually herbivores.

3 Marks 9. Why is energy flow in an ecosystem unidirectional?

Energy enters mainly as sunlight, passes through producers and consumers, and is ultimately dissipated as heat. It is not recycled back in the same usable form.

4 Marks 10. Explain the different trophic levels.

The first trophic level consists of producers. The second consists generally of primary consumers. The third consists generally of secondary consumers. Higher trophic levels may contain tertiary or top consumers.

4 Marks 11. Explain the significance of the 10% law.

Approximately 10% of energy at one trophic level is transferred to the next. Consequently, energy decreases sharply at successive levels, limiting the number of trophic levels in many food chains.

4 Marks 12. Explain a grazing food chain with an example.

A grazing food chain begins with a living producer. Example: Grass → Grasshopper → Frog → Snake. Grass is the producer and the other organisms occupy successive consumer levels.

4 Marks 13. Why are food webs important?

Food webs show multiple feeding relationships. They provide alternative pathways for energy transfer and can contribute to stability because a consumer may have more than one food source.

5 Marks 14. Explain food chain with a suitable diagram.

A food chain represents a linear sequence of feeding relationships. Example: Grass → Grasshopper → Frog → Snake → Eagle. Grass is the producer, followed by primary, secondary and higher consumers. Arrows show the direction of food and energy transfer.

5 Marks 15. Explain food web with an example.

A food web consists of interconnected food chains. For example, grass may be eaten by rabbit, grasshopper and rat; these animals may be eaten by frogs, snakes, foxes and eagles. The interconnections form a food web.

5 Marks 16. Explain how energy decreases at successive trophic levels.

Only a fraction of the energy available at one trophic level is transferred to the next. According to the commonly taught 10% law, about 10% may be transferred. Much of the remaining energy is used in life processes and eventually dissipated as heat.

5 Marks 17. Explain the relationship between food chain and trophic levels.

A food chain shows the sequence of feeding relationships. Each position in that sequence represents a trophic level. Producers occupy TL1, primary consumers TL2, secondary consumers TL3 and higher consumers occupy subsequent levels.

5 Marks 18. Explain why a food web is more realistic than a single food chain for many ecosystems.

Most organisms eat more than one type of food and may themselves be eaten by several organisms. Therefore, actual feeding relationships form interconnected networks rather than a single simple pathway.

6 Marks 19. Explain food chain, food web and trophic levels together.

A food chain is a linear pathway of feeding. A food web is formed when several food chains become interconnected. Trophic level indicates an organism's feeding position. Producers are at TL1, primary consumers at TL2 and higher consumers occupy successive trophic levels.

6 Marks 20. Describe energy flow through a food chain.

Solar energy is captured by producers and converted into chemical energy. Primary consumers obtain energy by eating producers. Secondary and higher consumers obtain energy by eating other consumers. At each transfer, much energy is used and ultimately dissipated as heat, so available energy decreases.

6 Marks 21. Explain the 10% law using a numerical example.

If producers contain 10,000 J, approximately 1,000 J may reach primary consumers. About 100 J may reach secondary consumers and about 10 J may reach tertiary consumers. This illustrates the progressive decrease in available energy.

6 Marks 22. Explain why food chains generally have limited length.

Energy transfer between trophic levels is inefficient. Since only a small fraction is transferred to the next level, progressively less energy is available to support organisms at higher trophic levels.

6 Marks 23. How can a change in one species affect a food web?

Because organisms are interconnected, a change in one population can affect its prey, predators and competitors. For example, removal of a predator may allow some prey populations to increase, which can then affect their food resources.

6 Marks 24. Explain the importance of producers in a food chain.

Producers form the first trophic level and capture energy, mainly from sunlight. They convert it into chemical energy stored in organic food. This energy supports primary consumers and indirectly all higher trophic levels.

6 Marks 25. Explain the role of decomposers in relation to food chains.

Decomposers act on dead organisms and wastes from different trophic levels. They break down organic matter and help return nutrients to the environment, which can again become available to producers.

6 Marks 26. Explain the difference between energy flow and nutrient cycling.

Energy enters the ecosystem, flows through trophic levels and is eventually dissipated as heat. Nutrients, in contrast, can move between organisms and the environment and be recycled through processes such as decomposition.

6 Marks 27. Explain with an example how an omnivore can occupy different trophic positions.

If a human eats plants directly, the human acts as a primary consumer in that pathway. If the human eats an animal that feeds on plants, the human occupies a higher trophic position. Thus trophic position depends on the feeding pathway.

6 Marks 28. What happens to higher consumers if producers are severely reduced?

A reduction in producers reduces food and energy available to primary consumers. This can reduce populations of primary consumers and subsequently affect secondary and higher consumers through the interconnected food web.

6 Marks 29. Explain why food webs can contribute to ecosystem stability.

A food web provides several feeding pathways. If one food source becomes scarce, some consumers may use alternative sources. This flexibility can reduce the effect of a single disturbance, although severe disturbances can still affect the whole web.

6 Marks 30. Explain the complete sequence of energy transfer and nutrient recycling.

Sunlight is captured by producers and stored as chemical energy. Consumers obtain this energy through feeding. When organisms die or produce wastes, decomposers break down the organic matter and return nutrients to the environment. Producers use these nutrients again, while energy continues to flow and is eventually dissipated as heat.

29. Assertion–Reason Questions

1. Assertion: Producers occupy the first trophic level.
Reason: Producers capture energy and manufacture organic food.

Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

2. Assertion: A food web is generally more complex than a food chain.
Reason: A food web contains interconnected food chains.

Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

3. Assertion: Energy decreases at successive trophic levels.
Reason: Only a fraction of energy is transferred to the next trophic level.

Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

4. Assertion: Energy is completely recycled in an ecosystem.
Reason: Energy is eventually dissipated as heat.

Answer: Assertion is false, but Reason is true.

5. Assertion: Producers form the base of most food chains.
Reason: They introduce captured energy into the food chain.

Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

30. HOTS Questions

HOTS 1: Why does a food web generally represent an ecosystem better than one food chain?

Because organisms commonly have multiple food sources and multiple predators. A food web captures these interconnected relationships.

HOTS 2: If all frogs in a food web disappeared, what could happen?

Insect populations eaten by frogs might increase, while predators that depend on frogs might lose a food source. The exact effect depends on the whole food web.

HOTS 3: Why is energy available to an eagle less than energy available to grass in a food chain?

Energy is lost from the system as heat and used in life processes at each transfer. Therefore, progressively less energy is available at higher trophic levels.

HOTS 4: Why can the same organism occupy different trophic levels?

Its trophic position depends on what it eats and therefore on the particular food pathway being considered.

HOTS 5: Why would removal of producers have a larger ecosystem effect than removal of one individual consumer?

Producers form the base of energy input into most ecosystems. Their reduction can affect many consumers across multiple food chains and therefore the wider food web.

31. Quick Revision Table

Concept	Key Point
Food Chain	Linear feeding pathway.
Food Web	Interconnected food chains.
Trophic Level	Feeding position of an organism.
TL 1	Producers.
TL 2	Primary consumers.
TL 3	Secondary consumers.
TL 4	Tertiary consumers.
Energy Flow	Unidirectional.
10% Law	Approximately 10% transfer to next trophic level.
Decomposers	Break down dead matter and support nutrient recycling.

32. One-Minute Revision

🌱 Food Chain
Linear pathway of food and energy transfer.

🕸️ Food Web
Network of interconnected food chains.

1️⃣ First Trophic Level
Producers.

2️⃣ Second Trophic Level
Primary consumers.

3️⃣ Third Trophic Level
Secondary consumers.

4️⃣ Fourth Trophic Level
Tertiary/higher consumers in a suitable chain.

➡️ Arrow
Shows direction of food and energy transfer.

⚡ Energy
Flows in one direction and decreases at successive trophic levels.

♻️ Nutrients
Can be recycled through decomposition.

33. Golden Points for CBSE Exam

1. Food chain is generally a linear feeding pathway.

2. Food web consists of interconnected food chains.

3. Producers occupy the first trophic level.

4. Primary consumers generally occupy the second trophic level.

5. Secondary consumers generally occupy the third trophic level.

6. Tertiary consumers may occupy the fourth trophic level.

7. The arrow shows the direction of food/energy transfer.

8. Energy flow is unidirectional.

9. Approximately 10% energy transfer is used as the standard school-level 10% law.

10. Energy decreases at successive trophic levels.

11. Food webs provide multiple feeding pathways.

12. Decomposers act on dead organisms and wastes from different trophic levels.

13. Nutrients can be recycled.

14. A food web is more complex than a simple food chain.

15. Trophic position depends on the feeding relationship being considered.

34. MCQ Answer Key

Q	Ans	Q	Ans	Q	Ans
1	A	11	C	21	A
2	B	12	D	22	D
3	C	13	A	23	A
4	D	14	C	24	A
5	A	15	B	25	A
6	B	16	C	26	C
7	C	17	A	27	A
8	D	18	B	28	B
9	A	19	C	29	A
10	B	20	D	30	B

Our Environment and Sustainable Management
Food Chain • Food Web • Trophic Levels
Class 10 CBSE Science | Foundation | Competitive Preparation