Aerobic and anaerobic respiration: glucose ethanol + carbon dioxide

Q: How do I revise Aerobic and anaerobic respiration: glucose ethanol + carbon dioxide for GCSE?

Read the notes on Aerobic and anaerobic respiration: glucose ethanol + carbon dioxide, then test yourself without looking. Answering questions and checking what you missed builds recall faster than re-reading.

Q: Is this Aerobic and anaerobic respiration: glucose ethanol + carbon dioxide guide aligned to the AQA specification?

Yes. This guide is linked to the Aerobic and anaerobic respiration: glucose ethanol + carbon dioxide topic in the AQA GCSE specification.

This word equation summarises fermentation, the anaerobic respiration carried out by yeast.

Study notes

From the checked teaching notes for this specification point.

The idea

This word equation summarises fermentation, the anaerobic respiration carried out by yeast. Glucose is broken down without oxygen to produce ethanol and carbon dioxide. In words: glucose → ethanol + carbon dioxide. The reaction releases a relatively small amount of energy compared with aerobic respiration because the glucose is not fully oxidised. A useful method is to compare the two equations: aerobic respiration gives carbon dioxide and water, whereas fermentation gives ethanol and carbon dioxide. Yeast cells use this pathway when oxygen is absent, for example in brewing and bread-making. The carbon dioxide makes dough rise, while the ethanol produced is the alcohol in alcoholic drinks.

What earns the marks

State the correct word equation: glucose → ethanol + carbon dioxide.
Identify the reactants and products: glucose is the reactant; ethanol and carbon dioxide are the products.
Recognise that this process is anaerobic, so oxygen is not a reactant and does not appear in the equation.
Link the equation to yeast cells and to fermentation.
Explain that less energy is released than in aerobic respiration because glucose is not fully broken down.
Apply the equation to bread-making (carbon dioxide raises dough) and alcoholic drinks (ethanol is the alcohol).

Common mistakes and how to put them right

Writing water as a product instead of ethanol.
Put it right by remembering that fermentation produces ethanol and carbon dioxide, while aerobic respiration produces water and carbon dioxide.
Including oxygen as a reactant.
Put it right by noting that fermentation is anaerobic, so oxygen must not appear in the equation.
Reversing the products, for example writing carbon dioxide + ethanol → glucose.
Put it right by checking that glucose is the starting substance and the two products are formed from it.

Exam tips

Write the equation with a clear arrow and use the correct names, not formulae, unless the question asks for symbols.
If asked to compare, set out aerobic respiration and fermentation side by side so the products and energy release are easy to contrast.
When explaining an application, name the product responsible: carbon dioxide for raising bread, ethanol for alcoholic drinks.

Try the lesson

The start of the Aerobic and anaerobic respiration: glucose ethanol + carbon dioxide lesson, made from checked teaching notes for this specification point.

Have a go first

Which two products are formed when glucose is broken down by anaerobic respiration in yeast cells?

Tip: press 1 to 4 to choose

See it

A left-to-right flowchart with three nodes. The node on the left is labelled Glucose. Two arrows lead from Glucose to two nodes on the right: one labelled Ethanol and one labelled Carbon dioxide. This shows that glucose is broken down to produce ethanol and carbon dioxide. — The word equation for fermentation in yeast, showing glucose as the reactant producing ethanol and carbon dioxide.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 2 boxes numbered instead of named. A left-to-right flowchart with three nodes. The node on the left is labelled Glucose. Two arrows lead from Glucose to two nodes on the right: one labelled Ethanol and one labelled Carbon dioxide. This shows that glucose is broken down to produce ethanol and carbon dioxide.

1Box 1
2Box 2

0 of 2 labelled

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