Aerobic and anaerobic respiration

Aerobic respiration

Respiration using oxygen to break down food molecules is called . 'Aero' means air, which contains oxygen, leading to the name aerobic respiration. Glucose is the molecule normally used for respiration - it is the main . Glucose is to release its energy, which is then stored in ATP molecules.

The word equation for aerobic respiration is:

glucose + oxygen → carbon dioxide + water (+ ATP made)

You need to be able to recognise the chemical formulas:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Respiration is a series of chemical reactions, but this equation summarises the overall process. Aerobic respiration breaks down glucose and combines the broken down products with oxygen, making water and carbon dioxide. The carbon dioxide is a waste product of aerobic respiration because cells do not need it.

The first stages of respiration occur in the cytoplasm of plant and animal cells, but most of the stages of respiration that release energy happen in the . Microorganisms do not have mitochondria - they carry out respiration only in the .

Anaerobic respiration

Most organisms cannot respire without oxygen but some organisms and tissues can continue to respire if the oxygen runs out. In conditions of low or no oxygen the process of occurs. The 'an' in 'anaerobic' means without.

During anaerobic respiration, the oxidation of glucose is incomplete - not all of the energy can be released from the glucose molecule as it is only partially broken down. The reaction therefore releases much less energy than aerobic respiration - around only a nineteenth of the energy released during aerobic respiration. This means that fewer molecules of ATP can be made.

Glucose in human muscle cells is converted to during anaerobic respiration:

glucose → lactic acid (+ ATP made)

The lactic acid is a waste product.

Some plants, and such as yeast can respire anaerobically - it's preferable to release less energy and make less ATP but remain alive.

Glucose in yeast cells is converted to carbon dioxide and , which we refer to simply as 'alcohol':

glucose → ethanol + carbon dioxide (+ ATP made)

This reaction is also called .

This table compares aerobic and anaerobic respiration:

	Aerobic respiration	Anaerobic respiration
Oxygen	Present	Absent or in short supply.
Oxidation of glucose	Complete	Incomplete. All of the energy available from glucose is not released.
Reactants of respiration	Glucose and oxygen	Glucose.
Products of respiration	Carbon dioxide and water (and ATP)	Mammalian muscle - lactic acid (and ATP). Yeast - ethanol and carbon dioxide (and ATP). Some plants - ethanol and carbon dioxide (and ATP).
Amount of ATP made	Large amount	Smaller amount, but produced more quickly.

Oxygen
Aerobic respiration	Present
Anaerobic respiration	Absent or in short supply.

Oxidation of glucose
Aerobic respiration	Complete
Anaerobic respiration	Incomplete. All of the energy available from glucose is not released.

Reactants of respiration
Aerobic respiration	Glucose and oxygen
Anaerobic respiration	Glucose.

Products of respiration
Aerobic respiration	Carbon dioxide and water (and ATP)
Anaerobic respiration	Mammalian muscle - lactic acid (and ATP). Yeast - ethanol and carbon dioxide (and ATP). Some plants - ethanol and carbon dioxide (and ATP).

Amount of ATP made
Aerobic respiration	Large amount
Anaerobic respiration	Smaller amount, but produced more quickly.

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What happens during cellular respiration? - OCR 21st CenturyAerobic and anaerobic respiration