Biological catalysts, food tests and energy in food — Edexcel GCSE Combined Science
Why enzymes are important for building up and breaking down carbohydrates, proteins and lipids in the body.
Revision notes
1 short note, in the order of the specification. Each one in short:
Enzymes are biological catalysts that speed up reactions in cells, which would otherwise be far too slow to keep us alive. They are needed to build and break down large molecules: carbohydrates are made from and broken into sugars, proteins into amino acids, and lipids into fatty acids and glycerol. Different enzymes catalyse each reaction, because enzymes are specific.
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Quick check questions
What are proteins broken down into?
Show answer
Amino acids.
What does a catalyst do?
Show answer
It speeds up a reaction and is not used up.
Which reagent turns purple when protein is present?
Show answer
Biuret reagent (Triple only).
How can the energy in food be measured?
Show answer
By burning it to heat water and using the temperature change (calorimetry) (Triple only).
Frequently asked questions
Why are enzymes important in the body?
Enzymes are important because chemical reactions in living things would be far too slow to keep us alive without them. As biological catalysts, they speed up reactions in cells. They are needed both to break down large molecules such as proteins, carbohydrates and lipids, and to build them up from smaller molecules.
What are carbohydrates, proteins and lipids broken down into?
Carbohydrates are broken down into sugars, proteins into amino acids, and lipids into fatty acids and glycerol. Each reaction is catalysed by a different enzyme, because enzymes are specific. The same small molecules are also used to synthesise the large carbohydrates, proteins and lipids that the body needs.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026