OCR GCSE Biology A B1.3 Respiration Exam Questions

About OCR GCSE Biology A B1.3 Respiration

B1.3 covers respiration, the process that releases energy from glucose in every living cell. On the OCR Gateway Biology A course you compare aerobic and anaerobic respiration in animals, plants and microorganisms such as yeast, and learn how large biological molecules are built up and broken down. It is part of Topic B1, assessed in Paper 1 (Foundation) or Paper 3 (Higher), and links to exercise and the circulatory system in B2, and to photosynthesis in B1.4. Examiners often ask for equations, comparisons of the two types of respiration, explanations of oxygen debt and interpretation of yeast fermentation experiments.

What you need to know

• Purpose of respiration Respiration is a series of enzyme-controlled, exothermic reactions that release energy from glucose. The energy is used to make ATP, which cells use for muscle contraction, active transport, protein synthesis and keeping warm in mammals and birds.
• Aerobic respiration Aerobic respiration uses oxygen and takes place mainly in the mitochondria: glucose + oxygen -> carbon dioxide + water. It releases much more energy per glucose molecule than anaerobic respiration.
• Anaerobic respiration in animals When oxygen is in short supply, muscle cells respire anaerobically in the cytoplasm: glucose -> lactic acid. Less energy is released and lactic acid must later be broken down using oxygen.
• Anaerobic respiration in plants and yeast Plants and yeast respire anaerobically to produce ethanol and carbon dioxide: glucose -> ethanol + carbon dioxide. In yeast this is called fermentation and is used in bread making and brewing.
• Synthesis and breakdown of molecules Carbohydrates are polymers of sugars, proteins are polymers of amino acids, and lipids are made from fatty acids and glycerol. Enzymes break these down for respiration or use the smaller units to build new molecules.
• Investigating respiration The rate of respiration in yeast can be measured by counting bubbles or measuring the volume of carbon dioxide produced in a set time at different temperatures or sugar concentrations.

Common mistakes in B1.3 Respiration

• Saying respiration produces energy. Energy cannot be made; respiration releases energy (transferred to ATP).
• Confusing respiration with breathing. Respiration is a chemical reaction in cells; breathing is the movement of air in and out of the lungs.
• Writing that anaerobic respiration in humans produces carbon dioxide or ethanol. In humans it produces only lactic acid.
• Stating that plants only photosynthesise and do not respire. Plant cells respire all the time, day and night.
• Forgetting that aerobic respiration takes place in mitochondria while anaerobic respiration takes place in the cytoplasm.

Try three B1.3 Respiration exam-style questions