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3.4Unit 7: Microorganisms and food webs

Microorganisms in food webs — Cambridge Checkpoint Biology 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 4 of 4 2 quizzes

📚 Cambridge Checkpoint Biology 0893 Hub / Topical Revision
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Lesson summary

3.4 Microorganisms in food webs — CHECKPOINT BIOLOGY 0893 notes: Explain the role of decomposers in food webs and nutrient recycling, and draw food chains that include microorganisms.Almost all decomposers are microorganisms, and fungi and bacteria are the most important.Decompos…

  • Recycling of nutrients
  • Phytoplankton
  • Decomposers break down dead bodies and animal waste (dung)
  • Decay is mostly useful, although decay of an apple spoils the food
  • Without decomposers, dead plants, dead animals and dung would build up everywhere
  • Decomposers return the nutrients to the soil when they decay organic matter

Section 1 of 8Roles of decomposers

1
Almost all decomposers are microorganisms, and fungi and bacteria are the most important.
2
Decomposers break down dead bodies and animal waste (dung).
3
Decay is mostly useful, although decay of an apple spoils the food.
4
Without decomposers, dead plants, dead animals and dung would build up everywhere.

Section 2 of 8Nutrient recycling

1
Dead bodies and waste contain substances that living organisms can use for energy or to help them grow.
  • These substances are called nutrients.
2
Decomposers return the nutrients to the soil when they decay organic matter.
3
Plants use the nutrients to grow, and animals benefit because there are more plants to eat.
4
Recycling of nutrients:
1
Plants take up nutrients from the soil and are eaten by animals.
2
Plants and animals die or produce waste.
3
Bacteria and fungi release enzymes to digest the dead material.
4
Decomposers respire and release carbon dioxide.
5
Nutrients are returned to the soil and absorbed by plant roots.

Section 3 of 8Decomposers in food webs

1
Decomposers feed on almost every organism after it dies and on animal waste.
2
Energy from dead organisms and waste is transferred to the decomposers.
3
A food web can show this by adding an arrow from every organism to the decomposers.
4
It is not usually done because the arrows make the web look very complicated.
5
A decomposer is a consumer and not a producer, because it gets its energy from dead organisms.

Section 4 of 8Decomposers that are not microorganisms

1
Some fungi, such as toadstools, are large and can be seen without a microscope.
2
A fungus growing on a log is a decomposer, because it breaks down the log.
  • Most of the fungus is inside the log and cannot be seen.
3
A slug that eats the fungus gets energy that came originally from the Sun, through the plant that made the log.
4
Other microorganisms that act as decomposers are bacteria.

Section 5 of 8Other microorganisms in food webs

Other microorganisms in food webs
Microscopic algae (phytoplankton) are producers at the start of ocean food chains.
Protozoa can be consumers, feeding on bacteria and algae.
Some microorganisms cause disease.
  • Malaria is caused by a microscopic protozoan that is spread by mosquitoes.

Section 6 of 8Without decomposers

1
Dead material would pile up.
2
Nutrients would not be recycled.
3
Plants would lack minerals.
4
Animals would have less to eat.

Section 7 of 8Key terms

TermMeaning
DecomposerA microorganism or fungus that breaks down dead material and waste.
NutrientA substance that living organisms use for energy or to help them grow.
DungThe waste of animals.
Recycling of nutrientsThe return of nutrients from dead material to the soil.
PhytoplanktonMicroscopic algae that act as producers in oceans.
MouldA fungus that grows on organic matter and decays it.

Section 8 of 8Exam technique

1
Saying decomposers are producers — they are consumers that feed on dead material.
2
Saying all decomposers are microorganisms — some fungi, such as toadstools, are large.
3
Forgetting that decomposers return nutrients to the soil.
4
Drawing arrows from the decomposers to the dead organism — arrows point from the dead organism to the decomposer.
5
Saying decay makes energy disappear — energy is transferred to the decomposers.

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