How do harmful chemicals get accumulated progressively at each trophic level in a food chain?
How do harmful chemicals get accumulated progressively at each trophic level in a food chain?
Harmful chemical pesticides and crop-protection chemicals enter and accumulate progressively in a food chain through the following steps:
- Entry into the Food Chain: Pesticides and chemicals sprayed on crops are washed down into the soil or water bodies. From the soil, they are absorbed by plants along with water and minerals. From water bodies, they are taken up by aquatic plants and animals.
- Progressive Accumulation: Since these synthetic chemicals are non-biodegradable, they cannot be broken down, metabolized, or excreted by the organisms. Consequently, they get accumulated progressively at each successive trophic level.
- Maximum Concentration at the Top: Because human beings (or top predators) occupy the top level in any food chain, the maximum concentration of these toxic chemicals gets accumulated in our bodies. This phenomenon is known as biological magnification.
Marking Scheme
- 11 Mark: Explaining how chemicals enter the food chain (absorbed by plants/producers from soil or water).
- 21 Mark: Explaining that because these chemicals are non-biodegradable, they cannot be broken down and thus accumulate progressively at each trophic level, reaching maximum concentration at the top level (biological magnification).
Hint
Think about why pesticides sprayed on crops cannot be digested or excreted by organisms, and what happens to their concentration as they move up from plants to herbivores and carnivores.
Quick Oral Answer
Harmful chemicals like pesticides enter the food chain through soil or water. Because they are non-biodegradable, they cannot be metabolized or excreted, so their concentration increases at each successive trophic level. This is called biological magnification.
Analysis & Explanation
The question asks for the mechanism of progressive accumulation of harmful chemicals in a food chain. The explanation must highlight:
- The source and entry of chemicals (absorption by producers from soil/water).
- Their non-biodegradable nature, which prevents excretion or breakdown.
- The progressive increase in concentration at each successive trophic level (biological magnification), reaching the highest concentration at the top trophic level (usually occupied by humans).
Common Mistakes
- 1Confusing biological magnification with energy flow (thinking chemical concentration decreases at higher levels).
- 2Stating that chemicals are biodegradable or can be easily washed off from inside the plant tissues.
Interesting Facts
Biological magnification was first widely noticed when DDT caused bald eagle populations to crash in the mid-20th century because it made their eggshells extremely thin and fragile.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2023?
This question carries 2 marks in the CBSE Class 10 Science 2023 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 "Biological Magnification" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2023 paper?
This is a Very Short Answer question from Section B in the CBSE Class 10 Science 2023 paper.