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RespirationEdexcel GCSE Biology: Revision notes

Section 1

What Is Respiration?

Cellular respiration is an exothermic reaction releasing energy continuously in living cells for metabolism. Two types: aerobic (needs oxygen) and anaerobic (no oxygen).

Key termscellular respirationexothermic reaction
Common mistake

Respiration ≠ breathing (gas exchange).

Section 2

Aerobic Respiration

Uses oxygen in mitochondria: glucose + oxygen → carbon dioxide + water. Releases large amount of energy.

Key termsaerobic respirationmitochondria

Section 3

Anaerobic Respiration

No oxygen, less energy, incomplete glucose breakdown. Muscles: glucose → lactic acid. Plants/yeast: glucose → ethanol + CO2 (fermentation).

Key termsanaerobic respirationlactic acidfermentation
Common mistake

Muscle anaerobic = lactic acid, NOT ethanol/CO2.

Section 4

Aerobic vs Anaerobic

FeatureAerobicAnaerobic
OxygenYesNo
EnergyLargeSmall
Products (muscle)CO2+waterLactic acid
LocationMitochondriaCytoplasm
Key termsoxygen debt
Example

After a sprint, heavy breathing repays oxygen debt by breaking down lactic acid.

Section 5

Core Practical: Rate of Respiration

Measure gas volume change (respirometer/manometer) with a control (soda lime/glass beads). Vary temperature, calculate rate = volume ÷ time.

Key termsrespirometerrate of reaction
Exam tip

Soda lime absorbs CO2 so change reflects oxygen use alone.

Must Know

  • Respiration = exothermic, continuous energy release.
  • Aerobic: glucose+O2→CO2+water, large energy.
  • Anaerobic (muscle): glucose→lactic acid. (Plants/yeast): glucose→ethanol+CO2.
  • Oxygen debt repaid after exercise.
  • Practical uses control + rate=volume/time.

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