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Unit 7: Microorganisms and food webs

Microorganisms in food webs — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 10 parts Lesson 5 of 6 Unit quiz

📚 HIA International - Grade 6 Hub / Topical Revision
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Lesson summary

7.4 Microorganisms in food webs — HIA INTERNATIONAL notes: Explain the roles of decomposers in food webs and how they recycle nutrients.Decomposers — almost all are microorganisms, with fungi and bacteria the most important.Dead bodies and waste — decomposers break down dead plan…

  • Without decomposers
  • Energy source
  • Food chain with decomposer
  • Toadstools
  • Hidden threads
  • Still decomposers

Section 1 of 10Roles of decomposers

Decomposers
  • Decomposers almost all are microorganisms, with fungi and bacteria the most important.
Dead bodies and waste
  • Dead bodies and waste decomposers break down dead plants, dead animals and dung.
Without decomposers
  • Without decomposers dead material and dung would pile up everywhere.
Nutrients
Nutrients substances in dead bodies and waste that living organisms use for energy or growth.
Soil
  • Soil decomposers return nutrients to the soil, plants use them to grow, and animals benefit because there are more plants to eat.

Section 2 of 10Decomposers in food chains and webs

Energy source
  • Energy source decomposers feed on almost every organism after it dies and on animal waste, so energy is transferred to them.
Arrows
  • Arrows an arrow is drawn from each organism to the decomposers, which is why decomposers are often left out of diagrams.
Consumers
  • Consumers decomposers are consumers, because they feed on ready-made organic matter.
Food chain with decomposer
  • Food chain with decomposer grass, rabbit, fox, then microorganisms that decompose the dead fox.

Section 3 of 10Fungi as decomposers

Toadstools
  • Toadstools they are the visible part of a fungus and are not microorganisms.
Hidden threads
  • Hidden threads the rest of the fungus is inside the log or soil, breaking down the dead material.
Still decomposers
  • Still decomposers a large fungus is a decomposer even though it is not a microorganism.
Energy for a slug
  • Energy for a slug when a slug eats a fungus, the energy originally came from the Sun, via a plant, then into the dead material, then into the fungus.

Section 4 of 10Recycling 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, releasing carbon dioxide.
5
Nutrients are returned to the soil and absorbed by plant roots.
  • Energy and nutrients
    • energy flows one way from the Sun, but nutrients are recycled.

Section 5 of 10Decomposing fruit

Decomposing fruit
Place a piece of fruit on a labelled dish and leave it uncovered in a warm place.
Look at the fruit every two or three days.
Record changes with photographs or drawings.
  • Observation
    • the fruit becomes soft and brown and is covered in mould as fungi decompose it.

Section 6 of 10Microorganisms and disease

Most microorganisms are not harmful, but some cause disease.
Malaria
  • Malaria a serious disease caused by a microscopic protozoan and spread by mosquitoes.
Where malaria occurs
  • Where malaria occurs only in tropical and subtropical countries where the mosquitoes live.

Section 7 of 10DDT and food chains

DDT
  • DDT a chemical used to kill the mosquitoes that spread malaria.
Persistence
  • DDT does not break down completely, so over half of it can still be present in a lake or river 150 years later.
Passing on
  • Passing on an animal that eats another animal containing DDT also takes in the DDT.
Birds of prey
  • DDT makes their eggshells very thin, so eggs break before hatching, and bald eagle numbers fell until DDT was banned in the USA in 1972.
Other animals
  • DDT is very poisonous to fish and quite poisonous to frogs.

Section 8 of 10Controlling malaria

Indoor spraying
  • DDT sprayed on house walls kills mosquitoes for up to 6 months and needs much less DDT than outdoor spraying.
Other chemicals
  • Other chemicals they also kill mosquitoes but are usually much more expensive.
Bed nets
  • Bed nets sleeping under a bed net reduces the risk of being bitten.
Vaccine
  • Vaccine the best malaria vaccine so far needs four injections and only halves the risk.
Global warming
  • Global warming a warmer climate may let the mosquitoes spread to new areas.

Section 9 of 10Key terms

TermMeaning
DecomposerAn organism that breaks down dead material and waste.
NutrientsSubstances that living organisms use for energy or growth.
DungAnimal waste.
Nutrient recyclingReturning nutrients from dead matter to the soil.
Food webLinked food chains in a habitat.
ProducerAn organism that makes its own food.
PersistentLasting a long time without breaking down.
MalariaA disease caused by a protozoan spread by mosquitoes.

Section 10 of 10Exam technique

1
Leaving decomposers out of the nutrient cycle — they return minerals to the soil.
2
Saying all decomposers are microorganisms — large fungi such as toadstools are decomposers but not microorganisms.
3
Saying decomposers are producers — they feed on dead matter, so they are consumers.
4
Saying energy is recycled like nutrients — energy flows one way and is lost as heat.

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