IMO Practice Test — Biomolecules
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
Per gram, fats store more energy than carbohydrates, which is why the body uses fat for:
Long-term energy storage
Immediate quick energy
Genetic information
Catalysing reactions
Explanation: Energy-dense fats are ideal for compact, long-term energy storage; carbohydrates give quick energy.
Question 2 of 6
An enzyme acts only on one specific substrate because:
Only that substrate fits its active site (lock-and-key)
It has no active site
All substrates fit
It is a carbohydrate
Explanation: Specificity comes from the unique shape of the active site, which fits only its substrate.
Question 3 of 6
Boiling a solution of the enzyme amylase stops it digesting starch because heat:
Denatures the enzyme, destroying its active site
Adds more substrate
Lowers the pH
Makes more enzyme
Explanation: High heat denatures the protein enzyme, so the active site no longer works.
Question 4 of 6
Pepsin works best in the stomach and trypsin in the intestine. This shows that enzymes have an optimum:
pH
Colour
Mass
Size
Explanation: Pepsin's optimum is acidic, trypsin's is alkaline — each enzyme has an optimum pH.
Question 5 of 6
Increasing substrate concentration speeds up an enzyme reaction up to a point, after which the rate levels off because:
All the enzyme active sites become occupied (saturated)
The enzyme is used up
The substrate disappears
The temperature falls
Explanation: Once every active site is busy, adding more substrate cannot increase the rate further.
Question 6 of 6
Many B-complex vitamins are needed in tiny amounts because they act as:
Coenzymes that help enzymes function
Main energy fuels
Structural proteins
Genetic material
Explanation: Several vitamins serve as coenzymes, assisting enzyme-catalysed reactions, so only small amounts are needed.