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Unit 7: Genes and inheritance

Microorganisms and decay — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 12 parts Lesson 4 of 9 2 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

Microorganisms and decay — HIA INTERNATIONAL notes: Explain how decomposers break down dead material, which conditions speed up decay and how decay recycles nutrients.Microorganisms are everywhere — they live in the air, in soil, in water, on skin and inside bodies.Decay — the br…

  • Organic matter
  • Decomposers release enzymes onto dead material
  • They respire
  • Decomposers are not usually drawn in food webs
  • Not useful
  • Mineral ions such as nitrates

Part 1 of 9Decomposers and decay

Decomposers and decay
Microorganisms are everywhere
  • Microorganisms are everywhere they live in the air, in soil, in water, on skin and inside bodies.
Decay
  • Decay the breakdown of dead material, which makes it go soft, brown and rotten.
Decomposer
Decomposer an organism that makes dead material decay; the main decomposers are bacteria and microscopic fungi.
Organic matter
Organic matter any substance made by a living organism, such as fruit, wood, leather, bread and waste.
Mould on an apple is a colony of millions of microscopic fungus cells.
  • The fungi feed on the apple, break it down and make it brown and soft.

Part 2 of 9How decomposers work

1Decomposers release enzymes onto dead material
  • Decomposers release enzymes onto dead material the enzymes digest it into small soluble molecules.
2
The decomposers absorb these molecules and use them as food.
3They respire
  • They respire this releases carbon dioxide into the air.
4Decomposers are not usually drawn in food webs
  • Decomposers are not usually drawn in food webs but they feed on almost every organism after it dies and on animal waste.

Part 3 of 9Why decay is useful and why it is not

Useful
  • Useful dead bodies and waste are broken down, so they do not build up in heaps.
Useful
  • Useful nutrients in dead material are returned to the soil, so plants can use them to grow.
Useful
  • Useful more plants means more food for animals.
Not useful
  • Not useful decay spoils food, which is why food is preserved.

Part 4 of 9Recycling of nutrients

Recycling of nutrients
Mineral ions such as nitrates
  • Mineral ions such as nitrates return to the soil and are absorbed by plant roots.
Carbon returns to the air
  • Carbon returns to the air as carbon dioxide, which plants use for photosynthesis.
Cycle: dead leaf → decomposers feed → nutrients released into soil → absorbed by roots → new plant.

Part 5 of 9Conditions that affect the rate of decay

Warmth
  • Warmth decay is fastest when it is warm because enzymes work best at warm temperatures.
Moisture
  • Moisture microorganisms need water to grow, so decay is slow in dry conditions.
Oxygen
  • Oxygen most decomposers respire aerobically, so decay is slow without air.
Small pieces
  • Small pieces chopped material has a larger surface area, so it decays faster.
Cold slows decay
  • Cold slows decay and very high temperatures kill microorganisms or denature their enzymes.

Part 6 of 9Investigating how temperature affects decay

1
Put two similar pieces of bread on two paper plates.
2
Add the same small amount of water to both pieces, without making them too wet.
3
Leave the bread open to the air for about 30 minutes, then cover each plate with a plastic bag or food wrap.
4
Put one plate in a warm place and the other in a refrigerator.
5
Record the appearance of each piece of bread every day for several days.
6
Compare the results and make a conclusion from the actual results; the warm bread grows more mould.

Part 7 of 9Helpers in decay and decay in use

Detritivores
  • Detritivores earthworms, woodlice and millipedes eat dead material and break it into smaller pieces, which speeds up decay.
Composting
  • Composting turns garden and food waste into fertiliser using decay.
A compost heap is kept warm and moist and is turned to let air in.

Part 8 of 9Preventing decay

Preventing decay
Food preservation
  • Food preservation removes at least one condition microorganisms need.
Cold
  • Cold refrigerating or freezing slows growth.
Drying, salting or adding sugar
  • Drying, salting or adding sugar removes water that microorganisms need.
Heating or canning
  • Heating or canning kills the microorganisms.
Pickling in vinegar
  • Pickling in vinegar the acid prevents growth.

Part 9 of 9More from the specification

Microbial decomposition by bacteria and yeast
  • Microbial decomposition by bacteria and yeast decaying organic substrates support rapid proliferation of cellular bacteria and yeast, accelerating biological recycling.
Decomposers
  • Decomposers bacteria and fungi break down dead plants and animals, returning nutrients to the soil.
Food chain
  • Food chain energy moves from producers to consumers, and decomposers feed on dead material at every level.
Environmental conditions
  • Environmental conditions warmth, moisture and oxygen speed up decay, while cold or dry conditions slow it.
Model and group
  • Model and group a model such as a compost bin can be used to investigate decay, comparing groups with controlled variables.
Decomposers
  • Decomposers bacteria and fungi break down dead plants and animals, returning nutrients to the soil.
Food chain
  • Food chain energy moves from producers to consumers, and decomposers feed on dead material at every level.
Environmental conditions
  • Environmental conditions warmth, moisture and oxygen speed up decay, while cold or dry conditions slow it.
Model and group
  • Model and group a model such as a compost bin can be used to investigate decay, comparing groups with controlled variables.
Solar eclipse
  • The Moon blocks light from the Sun to Earth.
Lunar eclipse
  • The Earth blocks light from the Sun to the Moon.
Eclipse
  • When one body blocks light and casts a shadow on another.

Key terms

TermMeaning
MicroorganismA living organism too small to be seen clearly without a microscope.
DecayThe breakdown of dead organic matter by microorganisms.
DecomposerAn organism, mainly a bacterium or fungus, that makes dead material decay.
Organic matterAny substance made by a living organism.
NutrientsSubstances that organisms use for energy or growth, returned to the soil by decay.
MouldA microscopic fungus that grows as a furry colony on food.
DetritivoreAn animal that feeds on dead material and breaks it into smaller pieces.
CompostRotted plant material used to feed soil.

Avoid these mistakes

1
Thinking decay happens only to plants — all dead organisms and waste are broken down.
2
Saying decomposers eat dead material with a mouth — they release enzymes onto it and absorb the digested molecules.
3
Saying very hot conditions speed decay — very high temperatures kill microorganisms or denature their enzymes.
4
Forgetting that decay recycles nutrients — minerals return to the soil and carbon returns to the air.

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