medium importancemedium difficulty6 min

Biological Magnification

Biological magnification is the gradual increase in the concentration of harmful, non-biodegradable substances at higher trophic levels in a food chain.

In one line: More eating up the chain means more toxin up the chain.

Practice This Concept

Understand it

When a toxic substance like DDT enters an ecosystem, it may not break down easily. Small organisms absorb it in small amounts, and larger organisms eat many smaller ones, so the concentration increases at each step. The top consumer therefore receives the highest concentration.

Example

In a water body, tiny plankton may have a little pesticide, small fish may have more, bigger fish may have still more, and birds that eat fish may receive the highest amount.

Rule to remember

Biological magnification = concentration of a persistent toxin increases at successive trophic levels.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1If water contains a very small amount of pesticide, plankton absorb it first.
2Small fish eat many plankton, large fish eat many small fish, and the concentration becomes highest in the bird that eats the fish.

Method you can reuse

1Identify the persistent toxin.
2Trace its entry into the food chain.
3Show how it accumulates in each level.
4Conclude that top consumers receive the highest concentration.

Sketch it in your answer

Draw an upward pyramid showing toxin concentration increasing from water to plankton to fish to bird.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why do top consumers suffer more from biological magnification?

Think first, then show answer

Top consumers suffer more because harmful non-biodegradable substances become more concentrated at each trophic level. By the time the toxin reaches the top consumer, its amount is highest.

Common wrong answer

A common wrong answer is to say digestion removes the toxin completely at each step.

Why it loses marks: The toxin is not broken down easily.

Don't mix this up

Students often think the toxin amount stays the same at every level. The correct idea is that concentration increases as we move up the food chain.

Exam tip

In answers, write the words non-biodegradable and higher trophic levels to show full understanding.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Explain why top predators are most affected by pesticides, or describe the movement of a toxin through a food chain.

1
Enough for 1 mark
Biological magnification is the gradual increase in the concentration of harmful, non-biodegradable substances at higher trophic levels in a food chain.
2
Add for 2 marks
Example: In a water body, tiny plankton may have a little pesticide, small fish may have more, bigger fish may have still more, and birds that eat fish may receive the highest amount.
3
Add for 3 marks
When a toxic substance like DDT enters an ecosystem, it may not break down easily.

MCQ Quiz

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