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Unit 7: Microorganisms and food webs

Microorganisms and decay — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 10 parts Lesson 4 of 6 3 quizzes

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

7.3 Microorganisms and decay — HIA INTERNATIONAL notes: Explain how decomposers make organic matter decay and how temperature and moisture affect the rate of decay.Where found — microorganisms live in the air, soil, water, on our skin and inside our bodies.Mould = a visible patch…

  • Not organic
  • Respiration
  • Detritivores
  • Composting
  • Expected result
  • Hypothesis

Section 1 of 10Microorganisms everywhere

Where found
  • Where found microorganisms live in the air, soil, water, on our skin and inside our bodies.
Mould
Mould a visible patch of microscopic fungi; each spot on a mouldy apple is a colony of millions of fungal cells.

Section 2 of 10Decay and decomposers

Decay
Decay the breakdown of dead organic matter into simpler substances; it makes food soft, brown and rotten.
Decomposer
Decomposer an organism, mainly bacteria and fungi, that makes things decay.
Organic matter
Organic matter any substance made by a living organism, such as fruit, bread, wood and leather.
Not organic
  • Not organic water and rock are not made by living organisms, so decomposers do not break them down.

Section 3 of 10How decomposers break down material

Enzymes
  • Enzymes decomposers release enzymes onto dead material to digest it into small soluble molecules.
Feeding
  • Feeding they absorb these molecules as food.
Respiration
  • Respiration they respire and release carbon dioxide into the air.
Recycling
  • Recycling mineral ions such as nitrates return to the soil for plants, and carbon returns to the air as carbon dioxide.

Section 4 of 10Conditions that affect the rate of decay

ConditionFast decaySlow or no decayReason
TemperatureWarm (about 25 to 35 °C)Cold, or very hotEnzymes work best when warm; high heat kills microorganisms
MoistureMoistDryMicroorganisms need water
OxygenPlenty of airNo airMost decomposers respire aerobically
Piece sizeMany small piecesLarge piecesGreater surface area for microorganisms

Section 5 of 10Helpful and unhelpful decay

Unhelpful
  • Unhelpful decay spoils food, so nobody wants to eat a rotten apple.
Helpful
  • Helpful decay removes dead plants and animals and recycles their nutrients.
Detritivores
  • Detritivores earthworms, woodlice and millipedes feed on dead material and break it into smaller pieces, which speeds up decay.
Composting
  • Composting decay turns garden and food waste into fertiliser in a compost heap that is kept warm, moist and aerated.

Section 6 of 10Investigating how temperature affects decay

1
Place two similar pieces of bread on two paper plates.
2
Add the same small amount of water to each piece of bread without making it 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 based on your actual results.
Expected result
  • Expected result the warm bread grows mould faster than the cold bread because warmth speeds up the growth of the microorganisms.
Safety
  • Safety keep the bags sealed and do not open them or touch the mould.

Section 7 of 10Planning a moisture investigation

Planning a moisture investigation
Hypothesis
  • Hypothesis moist bread decays more quickly than dry bread.
Variable to change
  • Variable to change the moisture of the bread, for example moist and dry.
Variable to measure
  • Variable to measure the amount of mould on the bread or its appearance each day.
Variables to keep the same
  • Variables to keep the same type and size of bread, temperature, time and amount of air.
Prediction if the hypothesis is correct
  • Prediction if the hypothesis is correct the moist bread shows mould sooner and covers more area.

Section 8 of 10Preventing decay in food

Preventing decay in food
Principle
  • Principle preservation removes a condition that decomposers need.
Cooling
  • Cooling refrigerating or freezing slows or stops growth.
Drying, salting or adding sugar
  • Drying, salting or adding sugar removes water.
Heating or canning
  • Heating or canning kills the microorganisms.
Pickling
  • Pickling vinegar is acidic and prevents growth.

Section 9 of 10Key terms

TermMeaning
DecayThe breakdown of dead organic matter.
DecomposerAn organism, mainly bacteria or fungi, that makes dead matter decay.
Organic matterAny substance made by a living organism.
MouldVisible colonies of microscopic fungi.
RotTo become soft and brown through decay.
DetritivoreAn animal that feeds on dead material and breaks it into smaller pieces.
EnzymeA protein that speeds up reactions such as digestion.
CompostDecayed plant waste used to feed soil.

Section 10 of 10Exam technique

1
Saying microorganisms cannot break down all matter — they only decay organic matter.
2
Thinking decay is always harmful — it recycles nutrients and removes dead material.
3
Saying cold kills decomposers — cold only slows them.
4
Comparing bread samples that differ in more than one way — only one variable may change.

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