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5.4Unit 4: Ecosystems

Bioaccumulation — Cambridge Checkpoint Biology 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 4 1 quiz

📚 Cambridge Checkpoint Biology 0893 Hub / Topical Revision
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Lesson summary

5.4 Bioaccumulation — CHECKPOINT BIOLOGY 0893 notes: Explain why DDT builds up in organisms and why animals at the top of a food chain have the highest concentrations.DDT is an insecticide, a chemical that kills insects.It was first produced in the 1940s.It killed insects that tr…

  • Biomagnification
  • Limitation
  • Persistent
  • Biodegradable
  • It killed insects that transmit diseases, especially mosquitoes that transmit malaria and fleas that transmit typhus
  • It also killed insects that eat crops

Part 1 of 7DDT

1
DDT is an insecticide, a chemical that kills insects.
2
It was first produced in the 1940s.
3
It killed insects that transmit diseases, especially mosquitoes that transmit malaria and fleas that transmit typhus.
4
It also killed insects that eat crops.
5
No one thought at first that DDT could harm organisms other than insects.
6
In 1962 Rachel Carson wrote the book Silent Spring, which described how DDT was killing birds as well as mosquitoes.

Part 2 of 7Why DDT harms ecosystems

1
DDT is a persistent chemical, which means it does not break down.
  • It stays in the environment for many years.
  • Decomposers cannot break it down.
2
Sprayed DDT is carried high into the air and blown very long distances from where it was used.
3
DDT that gets into an animal's body stays there for the animal's whole life.
4
DDT is toxic (poisonous) to many animals.
  • It makes the shells of birds' eggs very thin and easy to break, so eggs fail to hatch.

Part 3 of 7Bioaccumulation

Bioaccumulation
Bioaccumulation the build-up of a substance in an organism's body over its lifetime.
All the DDT in all the food that an animal eats over its lifetime builds up in its body.
The longer the organism lives and the more DDT it takes in, the more DDT it has in its body.
Substances that bioaccumulate are persistent and are not broken down or excreted.

Part 4 of 7Biomagnification

Biomagnification
Biomagnification the increase in the concentration of a substance along a food chain.
In the example food chain algae → shrimps → fish → cormorants:
  • Algae take up DDT from the water.
  • Shrimps eat many algae, so all the DDT in them builds up in the shrimps.
  • Fish eat many shrimps, so they have a higher concentration.
  • Cormorants eat many fish, so they have the highest concentration.
Concentration is measured in parts per million (ppm), which is the grams of DDT in one million grams of the organism.
Animals at the top of a food chain have the highest concentration because each consumer eats many organisms from the level below.

Part 5 of 7Modelling DDT in a food chain

A model uses tokens as the DDT and people as insects, small birds and an eagle.
  • The insects collect tokens by feeding in an area.
  • The small birds feed on the insects and take their tokens.
  • The eagle feeds on the small birds.
The mean number of tokens each animal has increases along the chain.
The model shows that the amount of DDT in the body increases up the food chain.
Limitation
  • Limitation in a real ecosystem the amounts and feeding patterns are not so simple.

Part 6 of 7Biodegradable insecticides

Biodegradable insecticides
Biodegradable insecticides can be broken down by microorganisms in the environment or inside an animal's body.
They do not show biomagnification because they do not stay in the body.
Not everyone has stopped using DDT because it is very effective, cheap and kills the insects that carry disease.

Part 7 of 7Reducing the problem

Reducing the problem
Ban persistent pesticides.
Use biodegradable insecticides.
Use biological control and treat industrial waste.

Key terms

TermMeaning
DDTA persistent insecticide that is toxic to many animals.
PersistentNot broken down in the environment.
BioaccumulationThe build-up of a substance in an organism's body over time.
BiomagnificationThe increase in concentration of a substance along a food chain.
InsecticideA chemical that kills insects.
BiodegradableAble to be broken down by microorganisms.
ToxicPoisonous.

Avoid these mistakes

1
Confusing bioaccumulation with biomagnification — bioaccumulation is build-up in one organism, and biomagnification is the increase along the food chain.
2
Saying DDT is broken down by decomposers — it is persistent.
3
Saying top predators eat the most DDT only because they are bigger — each consumer eats many contaminated organisms from the level below.
4
Saying DDT only harms insects — it harms birds and other animals.
5
Thinking DDT stays where it was sprayed — it can be blown far away by the wind.

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