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9.3Unit 7: Microorganisms and food webs

Microorganisms and decay — Cambridge Checkpoint Biology 0893 Revision Notes & Topical Questions

5 min read 10 parts Lesson 3 of 4 1 quiz

📚 Cambridge Checkpoint Biology 0893 Hub / Topical Revision
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Lesson summary

9.3 Microorganisms and decay — CHECKPOINT BIOLOGY 0893 notes: Explain how microorganisms make organic matter decay and how temperature and moisture affect decay.Habitats — microorganisms live in the air, in soil, in water, on our skin and inside our bodiesAbsent from simple webs …

  • Decomposer
  • Organic examples
  • Not organic
  • Not useful
  • Fuller role
  • Variable changed

Part 1 of 8Where microorganisms live

Habitats
  • Habitats microorganisms live in the air, in soil, in water, on our skin and inside our bodies
Absent from simple webs
  • Absent from simple webs food chains and webs often leave them out even though they are everywhere

Part 2 of 8Decay and decomposers

Decay and decomposers
Decay
  • Decay microorganisms growing on food change it, so a mouldy apple becomes brown and soft
  • Each spot on the apple is a colony made of millions of microscopic fungus cells, called mould.
Decomposer
Decomposer an organism that makes things decay by breaking down organic matter
Kinds
  • Kinds many bacteria and microscopic fungi are decomposers
Feeding
  • Feeding decomposers break down organic matter when they feed on it, which makes it rot

Part 3 of 8Organic matter

Organic matter
Organic matter any substance made by a living organism, plant or animal
Organic examples
  • Organic examples apples, bread, wood, leather and fruit are organic matter
Not organic
  • Not organic water and rock are not made by living organisms, so microorganisms cannot decay them

Part 4 of 8Usefulness of decay

Not useful
  • Not useful decay spoils food and makes it rot
Useful
  • Useful microorganisms break down dead bodies and waste so they do not pile up
Fuller role
  • Fuller role the nutrients from the dead material are returned for living organisms to use

Part 5 of 8Investigating temperature and decay

1
Put two similar pieces of bread on two paper plates.
2
Add the same small amount of water to each piece, taking care not to make them too wet.
3
Leave both pieces open to the air for about 30 minutes so microorganisms land on them.
4
Cover each plate with a plastic bag or transparent food wrap.
5
Put one plate in a warm place and the other in a refrigerator.
6
Record the appearance of each piece of bread every day for several days.
7
Compare the results and make a conclusion using the actual results.

Part 6 of 8Variables in the investigation

Variable changed
  • Variable changed the temperature, warm place compared with refrigerator
Variable observed
  • Variable observed the appearance of the bread and the amount of mould that grows
Variables kept the same
  • Variables kept the same the type and size of bread, the amount of water and the time left open to the air
Result
  • Result more mould grows and the bread decays faster in the warm place than in the cold place
Reliability
  • Reliability comparing results with other groups helps to explain any differences

Part 7 of 8Planning a moisture investigation

Hypothesis
  • Hypothesis moist bread decays more quickly than dry bread
Variable changed
  • Variable changed the amount of water added to the bread
Variable measured
  • Variable measured the appearance and amount of mould on each piece
Variables kept the same
  • Variables kept the same type of bread, temperature and time exposed to the air
Prediction
  • Prediction if the hypothesis is correct the moist bread shows mould sooner than the dry bread

Part 8 of 8More from the specification

1Biological decomposition
  • Saprotrophic bacteria and fungi secrete extracellular enzymes to break down complex organic polymers in dead matter into simple soluble nutrients.
2Environmental factors affecting decay
  • Temperature, moisture availability, and oxygen concentration directly influence microbial enzyme kinetics and decomposition rates.
3Investigating decay rates
  • Measuring mass loss or carbon dioxide evolution from decomposing organic substrates under varying temperature conditions.
4Nutrient recycling
  • Decay processes release locked-up carbon dioxide, nitrates, and phosphates back into the soil and atmosphere for plant uptake.

Key terms

TermMeaning
DecayBreakdown of organic matter by microorganisms.
DecomposerOrganism that makes organic matter decay.
MouldMicroscopic fungus that grows in colonies on food.
Organic matterSubstance made by a living organism.
RotTo become soft and brown through decay.
HypothesisIdea that can be tested by an experiment.

Avoid these mistakes

1
Thinking decay happens by itself — decay is caused by living decomposers such as bacteria and fungi.
2
Thinking all matter can decay — only organic matter is broken down by microorganisms.
3
Believing decay is always harmful — it spoils food but also removes dead material and returns nutrients.
4
Changing several variables in the bread experiment — only the temperature or moisture should change.

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