Decomposition & Decay (OCR Gateway GCSE Biology)

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Factors Affecting Decomposition

Rate of decay

  • Decomposition (also known as decay or rotting) is the breaking down and digestion of biological material (waste products and dead organisms) by organisms called decomposers
  • Decomposers include microorganisms (bacteria and fungi) and detritus feeders
    • Detritus is a catch-all term for dead organic matter eg. leaf mulch, animal remains, fallen trees, other organic debris. etc
  • Decomposition is a crucial process as it ensures that materials such as carbon and mineral ions are recycled and returned to the environment
    • Remember, there is a finite (fixed) amount of all the elements on Earth, new atoms cannot be created out of nothing!
  • The rate of decay is the speed that decomposers break down biological material and is affected by three key factors:
    • Temperaturewater and availability of oxygen

Factors Affecting Rate of Decay Table

Factors affecting rate of decay table, downloadable IGCSE & GCSE Biology revision notes

Calculating Rate of Decay

  • When studying rates of decay, you should be able to:
    • Calculate rate changes in the decay of biological material
    • Calculate percentages of mass
    • Translate information between numerical and graphical form
    • Plot and draw appropriate graphs, selecting appropriate scales for the axes

Worked example rate of change in pH of milk_1, downloadable IGCSE & GCSE Biology revision notesWorked example rate of change in pH of milk_2, downloadable IGCSE & GCSE Biology revision notesworked-example-rate-of-change-in-ph-of-milk_3-downloadable-igcse--gcse-biology-revision-notes

Examiner Tip

Always look out for the word 'rate' in exam questions that relate to practical investigations. Rate means 'speed' so like a calculation of the speed of a car, the change in the dependent variable has to be divided by a suitable time value (hours, minutes, seconds etc). In this experiment the time value is a day (24 hours).
  • kilometres per hour (speed of a car)
  • pH change per hour(decay investigation)

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Phil

Author: Phil

Expertise: Biology

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.