A student adds yeast to a sugar solution and keeps it warm. Over several days, the sugar is changed into ethanol and carbon dioxide.
Which statement describes the role of the yeast?
It contains enzymes that act as catalysts for the reaction.
It is the main reactant that is changed into ethanol.
It provides the heat energy needed for the reaction.
It absorbs the carbon dioxide, so the reaction goes faster.
56 exam-style questions on OCR GCSE Chemistry 5.2 Controlling reactions, covering 5.2.1 Measuring and interpreting rate of reaction, 5.2.2 Factors affecting rate and collision theory, and 5.2.3 Catalysts, activation energy and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.