1 markVery Short AnswerSection A

In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes ?

Plants $\rightarrow$ Rats $\rightarrow$ Snakes $\rightarrow$ Hawks

Chemical Reactions and Equations

Energy Flow in Ecosystem

Official Answer

The energy available to hawks from snakes will be $5 \text{ J}$ .

10\%

Law

50 \text{ J}

5 \text{ J}

trophic levelenergy transfer

Marking Scheme

10.5 marks for calculating energy for snakes ( $50 \text{ J}$ )
20.5 marks for calculating energy for hawks ( $5 \text{ J}$ )

Hint

Apply the $10\%$ law for each step in the food chain: Rats $\rightarrow$ Snakes $\rightarrow$ Hawks.

Quick Oral Answer

Using the $10\%$ law, if rats have $500 \text{ J}$ , snakes get $50 \text{ J}$ , and hawks finally receive $5 \text{ J}$ .

Analysis & Explanation

The NCERT text (Section 1.2.1) notes that we need energy to stay alive and obtain it from food. In an ecosystem, this energy transfer follows the $10\%$ rule. As energy moves from rats to snakes and then to hawks, $90\%$ is lost (largely as heat during respiration, which is an exothermic process as per Eq. 1.18) and only $10\%$ is passed to the next level.

Common Mistakes

1Applying the $10\%$ law starting from the wrong level.
2Calculating $10\%$ of the total plant energy instead of the energy provided to rats.
3Incorrect decimal placement.

Interesting Facts

Because energy decreases so rapidly at each level, food chains rarely exceed four or five trophic levels.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2017?

This question carries 1 mark in the CBSE Class 10 Science 2017 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

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

What type of question is this in the CBSE Class 10 Science 2017 paper?

This is a Very Short Answer question from Section A in the CBSE Class 10 Science 2017 paper.