🌍 Our Environment
10% Law of Energy Transfer | Class 10 Science | CBSE + Foundation + Competitive
🌍 Our Environment | 10% Law of Energy Transfer
1. Introduction | परिचय
The 10% Law of Energy Transfer explains how energy decreases as it moves from one trophic level to the next in a food chain.
According to this law, approximately 10% of the energy available at one trophic level is transferred to the next trophic level.
हिंदी: 10% ऊर्जा स्थानांतरण का नियम बताता है कि खाद्य श्रृंखला में एक पोषण स्तर से अगले पोषण स्तर तक लगभग 10% ऊर्जा ही स्थानांतरित होती है।
हिंदी: 10% ऊर्जा स्थानांतरण का नियम बताता है कि खाद्य श्रृंखला में एक पोषण स्तर से अगले पोषण स्तर तक लगभग 10% ऊर्जा ही स्थानांतरित होती है।
Energy at Next Trophic Level ≈ 10% × Energy at Previous Trophic Level
Exam Line: Only about 10% of the energy available at one trophic level is transferred to the next trophic level.
2. Why is the 10% Law Important?
The law helps us understand:
✔ Why energy decreases along a food chain.
✔ Why energy pyramids are upright.
✔ Why food chains usually contain only a few trophic levels.
✔ Why top consumers receive very little energy.
✔ Why large amounts of energy are lost from one trophic level before reaching the next.
✔ Why energy decreases along a food chain.
✔ Why energy pyramids are upright.
✔ Why food chains usually contain only a few trophic levels.
✔ Why top consumers receive very little energy.
✔ Why large amounts of energy are lost from one trophic level before reaching the next.
3. Basic Energy Flow
☀ Sun
↓
🌱 Producers
↓
🐇 Primary Consumers
↓
🐸 Secondary Consumers
↓
🐍 Higher Consumers
↓
🔥 Heat Dissipation
↓
🌱 Producers
↓
🐇 Primary Consumers
↓
🐸 Secondary Consumers
↓
🐍 Higher Consumers
↓
🔥 Heat Dissipation
4. The 10% Rule with a Simple Example
Suppose producers have 10,000 J of available energy.
According to the 10% law:
Primary consumers receive: 1,000 J
Secondary consumers receive: 100 J
Tertiary consumers receive: 10 J
Primary consumers receive: 1,000 J
Secondary consumers receive: 100 J
Tertiary consumers receive: 10 J
10,000 J → 1,000 J → 100 J → 10 J
5. Mathematical Expression
Enext = 10/100 × Eprevious
Enext = Eprevious / 10
Enext = Eprevious / 10
Important: The 10% rule is an approximate ecological rule used to describe energy transfer between trophic levels. Actual transfer efficiencies can vary in real ecosystems.
6. Step-by-Step Energy Transfer
| Trophic Level | Example | Energy Available |
|---|---|---|
| 1st | Producers | 10,000 J |
| 2nd | Primary Consumers | 1,000 J |
| 3rd | Secondary Consumers | 100 J |
| 4th | Tertiary Consumers | 10 J |
7. Animated Energy Transfer Diagram
8. Where Does the Remaining Energy Go?
The energy not transferred to the next trophic level is not simply “destroyed”.
Organisms use energy for:
✔ Respiration
✔ Movement
✔ Growth
✔ Reproduction
✔ Repair
✔ Maintenance
✔ Other metabolic activities
A large part of the energy used in metabolism is ultimately released as heat.
✔ Respiration
✔ Movement
✔ Growth
✔ Reproduction
✔ Repair
✔ Maintenance
✔ Other metabolic activities
A large part of the energy used in metabolism is ultimately released as heat.
Energy is transformed and dissipated as heat; it is not destroyed in violation of the law of conservation of energy.
9. Why Does Only a Small Fraction Reach the Next Level?
A consumer does not convert all the food energy it consumes into new biomass.
Some energy is used for metabolism, some is lost in waste and some is released as heat.
Therefore, only a fraction of the energy becomes available to organisms at the next trophic level.
10. 10% Law and Energy Pyramid
The 10% law explains the typical upright shape of an energy pyramid.
The producer level contains the greatest available energy.
As we move upward:
Producer → Primary Consumer → Secondary Consumer → Higher Consumer
the available energy becomes progressively smaller.
Producer → Primary Consumer → Secondary Consumer → Higher Consumer
the available energy becomes progressively smaller.
10,000 J → 1,000 J → 100 J → 10 J
Maximum → Less → Much Less → Least
Maximum → Less → Much Less → Least
11. Why Are Food Chains Short?
Since only about 10% of the available energy is transferred to the next trophic level, energy decreases rapidly as we move upward.
After several trophic transfers, very little energy remains to support another level.
Therefore, food chains are generally short.
12. Numerical Problem – Basic
Q. If producers have 5,000 J of energy, how much energy will reach primary consumers?
10% of 5,000 J
= 10/100 × 5,000
= 500 J
= 10/100 × 5,000
= 500 J
13. Numerical Problem – Two Transfers
Q. Producers contain 20,000 J. Calculate energy available at the secondary consumer level.
Producer = 20,000 J
Primary consumers = 10% × 20,000 = 2,000 J
Secondary consumers = 10% × 2,000 = 200 J
Answer: 200 J
Primary consumers = 10% × 20,000 = 2,000 J
Secondary consumers = 10% × 2,000 = 200 J
Answer: 200 J
14. Numerical Problem – Three Transfers
Q. If producers contain 40,000 J, calculate the approximate energy available to tertiary consumers.
40,000 J
↓ 10%
4,000 J
↓ 10%
400 J
↓ 10%
40 J
Answer = 40 J
↓ 10%
4,000 J
↓ 10%
400 J
↓ 10%
40 J
Answer = 40 J
15. Shortcut Formula for Multiple Trophic Transfers
En = E0 × (0.1)n
Where:
E0 = initial energy
En = energy after n transfers
n = number of trophic transfers
E0 = initial energy
En = energy after n transfers
n = number of trophic transfers
For Class 10 calculations, count the number of times energy moves from one trophic level to the next.
16. Example Using the Shortcut
Question: Producers contain 50,000 J. What energy is expected after three trophic transfers?
En = E0 × (0.1)n
= 50,000 × (0.1)3
= 50,000 × 0.001
= 50 J
= 50,000 × (0.1)3
= 50,000 × 0.001
= 50 J
17. Reverse Calculation
Question: If approximately 10 J is available at the tertiary consumer level after three transfers, estimate the producer energy.
10 J = Producer energy × (0.1)3
Producer energy = 10 / 0.001
= 10,000 J
Producer energy = 10 / 0.001
= 10,000 J
18. Energy Transfer vs Energy Loss
| Concept | Meaning |
|---|---|
| Energy transferred | Approximately 10% is available to the next trophic level under the textbook rule. |
| Energy not transferred | Used in life processes and eventually largely dissipated as heat. |
| Energy flow | Moves through trophic levels in one direction. |
| Energy recycling | Energy is not continuously recycled as usable energy in the ecosystem. |
19. Energy Flow and Nutrient Cycling
Energy: Flows through the ecosystem and is ultimately dissipated as heat.
Nutrients: Move between organisms and the environment and can be recycled.
Nutrients: Move between organisms and the environment and can be recycled.
Energy → Flow
Nutrients → Cycle
Nutrients → Cycle
20. Important Exam Facts
✔ 10% law concerns energy transfer between trophic levels.
✔ It is an approximate rule.
✔ Producers form the first trophic level.
✔ Primary consumers form the second trophic level.
✔ Secondary consumers form the third trophic level.
✔ Higher consumers occupy subsequent levels.
✔ Energy decreases at successive trophic levels.
✔ Energy pyramid is upright.
✔ Energy flow is unidirectional.
✔ Nutrients are recycled.
✔ It is an approximate rule.
✔ Producers form the first trophic level.
✔ Primary consumers form the second trophic level.
✔ Secondary consumers form the third trophic level.
✔ Higher consumers occupy subsequent levels.
✔ Energy decreases at successive trophic levels.
✔ Energy pyramid is upright.
✔ Energy flow is unidirectional.
✔ Nutrients are recycled.
21. 30 MCQs | Multiple Choice Questions
1. The 10% law is related to:
A. Energy transfer between trophic levels
B. Water cycle
C. Population growth
D. Soil formation
Answer: A
2. According to the 10% law, approximately how much energy reaches the next trophic level?
A. 1%
B. 10%
C. 50%
D. 90%
Answer: B
3. If producers have 1,000 J, primary consumers receive approximately:
A. 10 J
B. 100 J
C. 500 J
D. 900 J
Answer: B
4. If producers have 10,000 J, secondary consumers may receive approximately:
A. 10 J
B. 1,000 J
C. 100 J
D. 5,000 J
Answer: C
5. The 10% law helps explain why:
A. Energy increases upward
B. Energy decreases at successive trophic levels
C. Producers disappear
D. Nutrients disappear
Answer: B
6. If 500 J is present at one trophic level, the next may receive:
A. 50 J
B. 5 J
C. 250 J
D. 450 J
Answer: A
7. Energy not transferred is largely:
A. Converted into sunlight
B. Used in life processes and dissipated as heat
C. Stored forever
D. Destroyed
Answer: B
8. The energy pyramid is generally:
A. Upright
B. Always inverted
C. Circular
D. Horizontal
Answer: A
9. Which level generally contains maximum energy?
A. Producer
B. Secondary consumer
C. Tertiary consumer
D. Top predator
Answer: A
10. If 2,000 J reaches primary consumers, secondary consumers may receive:
A. 20 J
B. 200 J
C. 1,000 J
D. 1,800 J
Answer: B
11. The 10% law is a:
A. Mathematical approximation used in ecology
B. Law of gravity
C. Law of reflection
D. Gas law
Answer: A
12. Which statement is correct?
A. All consumed energy becomes biomass
B. Only a fraction becomes available to the next level
C. Energy increases at each level
D. Energy is fully recycled
Answer: B
13. If producers contain 30,000 J, primary consumers may receive:
A. 3,000 J
B. 300 J
C. 15,000 J
D. 27,000 J
Answer: A
14. If producers contain 30,000 J, secondary consumers may receive:
A. 3,000 J
B. 300 J
C. 30 J
D. 15,000 J
Answer: B
15. If producers contain 30,000 J, tertiary consumers may receive:
A. 30 J
B. 3 J
C. 300 J
D. 3,000 J
Answer: A
16. Energy is mainly lost from trophic transfer through:
A. Metabolic activities and heat dissipation
B. Photosynthesis only
C. Rainfall
D. Soil erosion only
Answer: A
17. A major consequence of the 10% law is:
A. Short food chains
B. Infinite food chains
C. Increasing energy upward
D. No energy loss
Answer: A
18. Energy flow in an ecosystem is:
A. Unidirectional
B. Completely cyclic
C. Random
D. Reversible
Answer: A
19. Which is recycled in ecosystems?
A. Nutrients
B. Heat
C. Usable energy
D. Sunlight
Answer: A
20. If 100 J is available at one level, approximately how much reaches the next?
A. 1 J
B. 10 J
C. 50 J
D. 90 J
Answer: B
21. If 1,000 J is available at one level, energy at the next is:
A. 100 J
B. 10 J
C. 500 J
D. 900 J
Answer: A
22. The 10% rule applies to transfer between:
A. Successive trophic levels
B. Different planets
C. Soil layers
D. Atmospheric layers
Answer: A
23. If energy at producers is 80,000 J, primary consumers may receive:
A. 8,000 J
B. 800 J
C. 40,000 J
D. 72,000 J
Answer: A
24. If 8,000 J reaches primary consumers, secondary consumers may receive:
A. 800 J
B. 80 J
C. 4,000 J
D. 7,200 J
Answer: A
25. The 10% law demonstrates that:
A. Available energy decreases upward
B. Energy increases upward
C. Producers get no energy
D. Consumers create energy
Answer: A
26. What happens to much of the energy used by organisms?
A. It is ultimately dissipated as heat
B. It becomes sunlight
C. It becomes a new planet
D. It is stored forever
Answer: A
27. The 10% law helps explain the shape of:
A. Energy pyramid
B. Water cycle
C. Carbon atom
D. Food web only
Answer: A
28. If energy at producers is 100,000 J, after four transfers it is approximately:
A. 10,000 J
B. 1,000 J
C. 100 J
D. 10 J
Answer: D
29. The 10% law is useful for understanding:
A. Energy distribution in food chains
B. Only rainfall
C. Only reproduction
D. Only soil texture
Answer: A
30. Which is the correct sequence?
A. 10,000 → 1,000 → 100 → 10 J
B. 10 → 100 → 1,000 → 10,000 J
C. 10,000 → 5,000 → 2,500 → 1,250 J
D. 10,000 → 9,000 → 8,000 → 7,000 J
Answer: A
22. 30 Subjective Questions with Answers
2 Marks
Q1. State the 10% law of energy transfer.
Approximately 10% of the energy available at one trophic level is transferred to the next trophic level.
2 Marks
Q2. What happens to energy at successive trophic levels?
The available energy decreases at successive trophic levels because organisms use energy for life processes and much is dissipated as heat.
2 Marks
Q3. What is meant by trophic transfer?
Trophic transfer is the movement of energy from one trophic level to the next through feeding.
2 Marks
Q4. If producers have 1,000 J, how much reaches primary consumers?
Approximately 100 J.
2 Marks
Q5. Why is the 10% law called an approximate rule?
Actual energy-transfer efficiency varies among organisms and ecosystems, so 10% is a useful simplified approximation.
3 Marks
Q6. Explain the 10% law with an example.
If producers have 10,000 J, approximately 1,000 J reaches primary consumers, 100 J reaches secondary consumers and 10 J reaches tertiary consumers.
3 Marks
Q7. Why does energy decrease along a food chain?
Energy is used for respiration, movement, growth and other metabolic activities. Much is dissipated as heat, so less remains for the next trophic level.
3 Marks
Q8. How does the 10% law explain an upright energy pyramid?
Only a small fraction of energy passes to each next level. Thus producers have maximum energy and higher trophic levels have progressively less energy.
3 Marks
Q9. Why are food chains generally short?
Because energy decreases greatly at every trophic transfer, very little energy remains after several transfers to support additional trophic levels.
3 Marks
Q10. Distinguish energy flow from nutrient cycling.
Energy flows through an ecosystem and is eventually dissipated as heat. Nutrients are matter and can be recycled between organisms and the environment.
4 Marks
Q11. Explain the importance of the 10% law.
It explains the decrease of available energy at successive trophic levels, the upright energy pyramid, the limited number of trophic levels and the small amount of energy available to top consumers.
4 Marks
Q12. Calculate energy at the secondary consumer level if producers contain 50,000 J.
Primary consumers = 5,000 J
Secondary consumers = 500 J
Answer: 500 J
Secondary consumers = 500 J
Answer: 500 J
4 Marks
Q13. Calculate energy at tertiary consumers if producers contain 80,000 J.
80,000 → 8,000 → 800 → 80 J
4 Marks
Q14. Why cannot energy be continuously recycled like nutrients?
Energy is transformed during metabolic processes and much is dissipated as heat. Nutrients, being matter, can return to the environment and be reused.
4 Marks
Q15. What is the relationship between the 10% law and higher consumers?
Because only about 10% passes upward at each step, higher consumers receive progressively smaller amounts of energy.
5 Marks
Q16. Explain energy transfer through four trophic levels.
Suppose producers have 10,000 J. Primary consumers receive about 1,000 J, secondary consumers about 100 J and tertiary consumers about 10 J. This progressive decrease illustrates the 10% law.
5 Marks
Q17. Explain where the remaining 90% of energy goes.
The “remaining 90%” is not simply a single lost fraction. Much of the consumed energy is used in respiration, movement, growth, reproduction and maintenance, and much is ultimately dissipated as heat. Some energy may also remain in material not consumed or in waste.
5 Marks
Q18. Explain why energy available to top consumers is small.
At every transfer only a small fraction becomes available to the next level. Repeated transfers therefore reduce the available energy rapidly, leaving little energy for top consumers.
5 Marks
Q19. Explain the importance of producers in energy transfer.
Producers capture solar energy and convert it into chemical energy. This energy enters food chains and becomes available to primary consumers and higher trophic levels.
5 Marks
Q20. What would happen if energy transfer were 100% efficient?
In a hypothetical 100% efficient system, there would be no energy loss between trophic levels, producing a very different energy distribution. Real ecosystems are not 100% efficient because organisms use energy for metabolism and other processes.
6 Marks
Q21. Explain the 10% law with a suitable diagram.
The 10% law states that approximately 10% of energy at one trophic level becomes available to the next. Example: 10,000 J → 1,000 J → 100 J → 10 J. The diagram shows the progressive decrease in energy.
6 Marks
Q22. Explain how the 10% law affects food-chain length.
Only a small fraction of energy is transferred at each trophic level. Repeated transfers cause a rapid reduction in available energy. Eventually, the energy remaining is insufficient to support another higher trophic level effectively. Hence food chains usually contain only a few trophic levels.
6 Marks
Q23. Explain energy flow and the 10% law together.
Energy enters most ecosystems through sunlight and is captured by producers. It passes to consumers through feeding. At each trophic transfer, approximately 10% is transferred under the textbook rule, while much energy is used in life processes and dissipated as heat. Therefore energy flow is unidirectional.
6 Marks
Q24. A producer contains 60,000 J. Calculate energy at the fourth trophic level.
Producer = 60,000 J
Primary consumer = 6,000 J
Secondary consumer = 600 J
Tertiary consumer = 60 J
Primary consumer = 6,000 J
Secondary consumer = 600 J
Tertiary consumer = 60 J
6 Marks
Q25. If tertiary consumers contain 20 J after three transfers, calculate producer energy.
Producer energy = 20 ÷ (0.1)3
= 20 ÷ 0.001
= 20,000 J
= 20 ÷ 0.001
= 20,000 J
6 Marks
Q26. Explain why the 10% law is important in ecology.
It provides a simple way to understand energy distribution in food chains. It explains decreasing energy at higher trophic levels, the upright energy pyramid, short food chains and the limited energy available to top consumers.
6 Marks
Q27. Explain energy loss without saying that energy is destroyed.
Energy is not destroyed. It is transformed into different forms during life processes. Much of the chemical energy is eventually dissipated as heat, making it unavailable as usable chemical energy for the next trophic transfer.
6 Marks
Q28. Explain why actual energy-transfer efficiency may differ from exactly 10%.
The proportion transferred depends on the organisms, food quality, metabolism, ecosystem conditions and how much consumed material becomes new biomass. Therefore 10% is a simplified rule rather than a universal exact percentage.
6 Marks
Q29. Explain the difference between energy transfer and nutrient recycling.
Energy passes through trophic levels and is eventually dissipated as heat. Nutrients such as carbon and nitrogen move between organisms and the environment and can be reused. Thus energy flows while matter cycles.
6 Marks
Q30. Write a complete note on the 10% law.
The 10% law states that approximately 10% of the energy available at one trophic level is transferred to the next. It explains why energy decreases at successive trophic levels, why energy pyramids are upright and why food chains are usually short. Much of the remaining energy is used for life processes and ultimately dissipated as heat. The rule is an approximate ecological generalisation, not an exact universal percentage.
23. Assertion–Reason
Assertion (A): Energy decreases at successive trophic levels.
Reason (R): Only a small fraction of available energy is transferred to the next level.
Reason (R): Only a small fraction of available energy is transferred to the next level.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): The energy pyramid is generally upright.
Reason (R): Available energy decreases at each successive trophic level.
Reason (R): Available energy decreases at each successive trophic level.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): Energy is recycled continuously in an ecosystem.
Reason (R): Energy eventually dissipates as heat.
Reason (R): Energy eventually dissipates as heat.
Answer: Assertion is false, but Reason is true.
Assertion (A): Food chains usually have only a few trophic levels.
Reason (R): Energy decreases rapidly at successive trophic levels.
Reason (R): Energy decreases rapidly at successive trophic levels.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): Nutrients and energy are both recycled in exactly the same manner.
Reason (R): Nutrients can be recycled but energy flows through the ecosystem and is ultimately dissipated as heat.
Reason (R): Nutrients can be recycled but energy flows through the ecosystem and is ultimately dissipated as heat.
Answer: Assertion is false, but Reason is true.
24. HOTS | Higher Order Thinking
HOTS 1: Producers contain 90,000 J. How much energy is expected at the third trophic level?
90,000 → 9,000 → 900 J.
HOTS 2: If producers decline sharply, why will top consumers also be affected?
Less producer biomass means less energy enters the food chain. This reduces energy available to primary consumers and subsequently to all higher trophic levels.
HOTS 3: Why is the 10% law important for understanding ecosystem stability?
It shows that higher trophic levels depend on progressively smaller energy supplies. Changes at lower trophic levels can therefore affect organisms throughout the food chain.
HOTS 4: A food chain has producer energy of 1,000,000 J. Estimate the energy after five transfers.
1,000,000 × (0.1)5 = 10 J.
HOTS 5: Why should “90% energy is lost” not be interpreted as “90% energy is destroyed”?
Energy is conserved. Much of it is transformed during metabolic processes and ultimately dissipated as heat, making it unavailable as usable chemical energy for the next trophic level.
25. Important Formulae
10% Transfer:
Enext = 0.1 × Eprevious
Multiple Transfers:
En = E0(0.1)n
Enext = 0.1 × Eprevious
Multiple Transfers:
En = E0(0.1)n
26. Golden Points | परीक्षा के लिए
✔ 10% law describes approximate energy transfer.
✔ About 10% reaches the next trophic level.
✔ Energy decreases upward through a food chain.
✔ Producers have the maximum available energy.
✔ Higher consumers have much less available energy.
✔ Energy pyramid is upright.
✔ Energy flow is unidirectional.
✔ Energy is ultimately dissipated as heat.
✔ Nutrients are recycled.
✔ 10% law is an approximation, not an exact universal percentage.
✔ About 10% reaches the next trophic level.
✔ Energy decreases upward through a food chain.
✔ Producers have the maximum available energy.
✔ Higher consumers have much less available energy.
✔ Energy pyramid is upright.
✔ Energy flow is unidirectional.
✔ Energy is ultimately dissipated as heat.
✔ Nutrients are recycled.
✔ 10% law is an approximation, not an exact universal percentage.
27. One-Minute Revision
🌱 Producer = Starting trophic level
⬇
10% energy transfer
⬇
🐇 Primary Consumer
⬇
10% transfer again
⬇
🐸 Secondary Consumer
⬇
🐍 Higher Consumer
Remember:
10,000 J → 1,000 J → 100 J → 10 J
Energy flows; nutrients cycle.
⬇
10% energy transfer
⬇
🐇 Primary Consumer
⬇
10% transfer again
⬇
🐸 Secondary Consumer
⬇
🐍 Higher Consumer
Remember:
10,000 J → 1,000 J → 100 J → 10 J
Energy flows; nutrients cycle.
28. Concept Map
29. Final Summary
The 10% Law of Energy Transfer states that approximately 10% of the energy available at one trophic level is transferred to the next trophic level.
For example:
10,000 J → 1,000 J → 100 J → 10 J
Energy is used by organisms for respiration, growth, movement, reproduction and other life processes, and much is ultimately dissipated as heat.
The decreasing energy explains the upright energy pyramid and why food chains generally contain only a few trophic levels.
Most important line:
🌍 Energy flows through an ecosystem, while nutrients are recycled.
The 10% figure is a useful approximate ecological rule; actual transfer efficiency varies among ecosystems and organisms.
For example:
10,000 J → 1,000 J → 100 J → 10 J
Energy is used by organisms for respiration, growth, movement, reproduction and other life processes, and much is ultimately dissipated as heat.
The decreasing energy explains the upright energy pyramid and why food chains generally contain only a few trophic levels.
Most important line:
🌍 Energy flows through an ecosystem, while nutrients are recycled.
The 10% figure is a useful approximate ecological rule; actual transfer efficiency varies among ecosystems and organisms.
🌍 Class 10 Science | Our Environment
10% Law • Trophic Levels • Energy Transfer • Energy Pyramid • Food Chain • Energy Flow
CBSE + Foundation + Competitive Preparation
10% Law • Trophic Levels • Energy Transfer • Energy Pyramid • Food Chain • Energy Flow
CBSE + Foundation + Competitive Preparation
