Biological magnification
A tiny bit of a chemical falls on every leaf. Which animal ends up with the most?
- Grass carries the chemical, in tiny amounts.
- A deer eats a lot of grass over its life. The amount in the deer is higher.
- A lion eats many deer over its life. The amount in the lion is higher still.
- Made-up units: 1 at grass, 4 at deer, 16 at lion. Each level holds more than the one below it.
Step up the chain. Watch the units grow.
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Suppose the chemical cannot break down. Then the top animal holds the most.
New word
Biological magnification — a chemical that cannot break down stays in the body. It builds up more at each higher trophic level.
The rule
An animal at a higher level eats many animals below it. A chemical that cannot break down stays in its body. It builds up more at every higher level. The top of the chain holds the most.
| Level | Who | Made-up units |
|---|---|---|
| 1 | Grass | 1 |
| 2 | Deer | 4 |
| 3 | Lion | 16 |
Farmers spray pesticides, chemicals that kill pests, on crops. Some pesticides do not break down easily. Rain can wash them into soil and water. Plants absorb them from there. Then they enter a food chain and build up. People are at the top of many chains. Some foods can carry small amounts of pesticide.