C
CraftExam
medium difficulty7 min

Decomposition

Decomposition is the breakdown of complex dead organic matter into simpler inorganic substances by decomposers such as bacteria and fungi.

In one line: F-L-C-H-M keeps the order: fragmentation, leaching, catabolism, humification, mineralisation.

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Understand it

  • Decomposition returns nutrients locked in dead plants, animals and wastes back to the ecosystem.
  • The raw material is detritus, which includes leaf litter, dead remains and animal waste.
  • Detritivores first fragment the material into smaller particles.
  • Soluble nutrients may be removed by leaching.
  • Microbes then carry out catabolism by secreting enzymes that break complex organic substances.
  • Humification forms dark, resistant humus, while mineralisation releases inorganic nutrients into soil.
  • Warm, moist and oxygen-rich conditions generally increase decomposition, while low temperature, dryness and anaerobic conditions slow it down.
  • Exams test both the correct sequence and the role of decomposers.

Example

In a forest, fallen leaves are broken into smaller pieces by soil organisms, acted upon by fungi and bacteria, converted partly into humus, and finally release mineral nutrients used again by plants.

Rule to remember

Key sequence: detritus undergoes fragmentation, leaching, catabolism, humification and mineralisation.

Rate rule: warm, moist and aerobic conditions generally favour faster decomposition.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

If fallen leaves become small particles, soluble nutrients move into soil water, microbes digest organic compounds, humus forms and minerals are released, the complete process is decomposition with both humification and mineralisation.

Method you can reuse

  1. 1Identify detritus as dead organic matter.
  2. 2State fragmentation by detritivores.
  3. 3Add leaching of soluble substances.
  4. 4Explain microbial catabolism by enzymes.
  5. 5Distinguish humification from mineralisation.
  6. 6Mention factors such as temperature, moisture and oxygen.

Sketch it in your answer

Use a decomposition flow chart. Labels should include detritus, detritivores, fragmentation, leaching, microbial enzymes, catabolism, humus, mineral nutrients and decomposers.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why are decomposers essential in an ecosystem?

Think first, then show answer
Decomposers break down detritus and release nutrients back into the soil or surroundings. Without them, dead organic matter would accumulate and nutrient cycling would slow down.

Common wrong answer

Writing that decomposition is only rotting is too vague and misses the named steps and nutrient release.

Don't mix this up

Students often confuse humification with mineralisation. Humification forms humus, while mineralisation releases inorganic nutrients.

Exam tip

For decomposition questions, write the steps in order: fragmentation, leaching, catabolism, humification and mineralisation.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Asked as a long answer on steps of decomposition, a diagram-based flow chart, short notes on humification and mineralisation, or assertion-reason on environmental factors affecting decomposition rate.

Answer plan

Define decomposition. Mention detritus as raw material. Write the ordered steps with one line for each: fragmentation, leaching, catabolism, humification and mineralisation. Add the role of decomposers and one factor affecting rate.
  1. 1

    Enough for 1 mark

    Decomposition is the breakdown of complex dead organic matter into simpler inorganic substances by decomposers such as bacteria and fungi.

  2. 2

    Add for 2 marks

    Example: In a forest, fallen leaves are broken into smaller pieces by soil organisms, acted upon by fungi and bacteria, converted partly into humus, and finally release mineral nutrients used again by plants.

  3. 3

    Add for 3 marks

    Decomposition returns nutrients locked in dead plants, animals and wastes back to the ecosystem.

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