1 markVery Short AnswerSection A

In a food chain, if 10,000 joules of energy is available to the producer, how much energy will be available to the secondary consumer to transfer it to the tertiary consumer ?

Our Environment

Flow of Energy in an Ecosystem

Official Answer

According to the 10% law of energy transfer in a food chain, only 10% of the energy available at one trophic level is transferred to the next trophic level.

Producer level: $10,000\text{ J}$
Primary Consumer level: $10\% \text{ of } 10,000\text{ J} = 1,000\text{ J}$
Secondary Consumer level: $10\% \text{ of } 1,000\text{ J} = 100\text{ J}$

Therefore, the energy available at the secondary consumer level is $100\text{ J}$ . Out of this, the energy that can be transferred to the tertiary consumer (which is 10% of the secondary consumer's energy) is $10\text{ J}$ .

10% lawLindeman's law10,000 J1,000 J100 J10 Jtrophic level

Marking Scheme

1Calculating energy at primary consumer level ( $1,000\text{ J}$ ). (0.25 marks)
2Calculating energy at secondary consumer level ( $100\text{ J}$ ). (0.25 marks)
3Calculating energy transferred to tertiary consumer ( $10\text{ J}$ ). (0.5 marks)

Hint

Apply the 10% law step-by-step starting from the producer ( $10,000\text{ J}$ ) to the primary consumer, then to the secondary consumer, and finally calculate the 10% of that which goes to the tertiary consumer.

Quick Oral Answer

According to the 10% law, if the producer has $10,000\text{ J}$ , the primary consumer gets $1,000\text{ J}$ , the secondary consumer gets $100\text{ J}$ , and only $10\text{ J}$ is transferred to the tertiary consumer.

Analysis & Explanation

The 10% law states that during the transfer of organic food energy from one trophic level to the next higher level, only about 10% of the transferred energy is stored as flesh/organic matter. The remaining 90% is lost during transfer, broken down in respiration, or lost as heat to the environment. This progressive loss of energy limits the length of food chains to 3 or 4 steps.

Common Mistakes

1Skipping a trophic level and directly calculating 10% of $10,000\text{ J}$ as $1,000\text{ J}$ for the secondary consumer.
2Confusing the energy present at the secondary consumer level ( $100\text{ J}$ ) with the energy actually transferred to the tertiary consumer ( $10\text{ J}$ ).

Interesting Facts

Because of this drastic 90% energy loss at each step, top predators (like tigers or eagles) require a massive territory of producers to support their energy needs.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2012?

This question carries 1 mark in the CBSE Class 10 Science 2012 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Our Environment" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Flow of Energy in an Ecosystem" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2012 paper?

This is a Very Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.