Edexcel GCSE Biology Topic 8: Exchange and Transport in Animals Exam Questions

About Edexcel GCSE Biology Topic 8: Exchange and Transport in Animals

Topic 8 of Edexcel GCSE Biology is assessed on Paper 2. It explains why multicellular animals need specialised exchange surfaces and transport systems, how the alveoli are adapted for gas exchange, and how blood, blood vessels and the heart deliver oxygen and glucose to respiring cells. It also covers aerobic and anaerobic respiration and the core practical measuring the rate of respiration in small organisms. It links to diffusion in Topic 1 and plant transport in Topic 6. Examiners often set surface area to volume ratio, cardiac output and Fick's law calculations, and ask you to label the heart.

What you need to know

• Exchange and surface area Substances such as oxygen, carbon dioxide, water, dissolved food molecules, mineral ions and urea must be exchanged. Larger organisms have a smaller surface area to volume ratio, so they need specialised exchange surfaces and a transport system.
• Alveoli Alveoli are adapted for gas exchange by having a large surface area, a moist lining, walls one cell thick for a short diffusion distance, and a rich capillary network that maintains a steep concentration gradient.
• Fick's law (Biology only) Rate of diffusion is proportional to (surface area x concentration difference) / thickness of membrane. Use it to explain why each adaptation of an exchange surface increases the rate of diffusion.
• Blood Red blood cells contain haemoglobin, have no nucleus and are biconcave to carry oxygen. White blood cells (phagocytes and lymphocytes) defend against pathogens. Platelets help clotting. Plasma transports carbon dioxide, digested food, urea, hormones and heat.
• Blood vessels and the heart Arteries have thick muscular, elastic walls for high pressure; veins have valves and a large lumen; capillaries are one cell thick. The heart has four chambers: the right side pumps deoxygenated blood to the lungs through the pulmonary artery, the left side pumps oxygenated blood to the body through the aorta. Valves prevent backflow.
• Cardiac output Cardiac output = stroke volume x heart rate. Learn to rearrange the equation and use the correct units (cm3 per minute or dm3 per minute).
• Respiration and the core practical Aerobic respiration: glucose + oxygen -> carbon dioxide + water. Anaerobic respiration in animals produces lactic acid and causes an oxygen debt; in plants and fungi it produces ethanol and carbon dioxide. Core practical: use a respirometer with soda lime to absorb carbon dioxide and measure oxygen uptake by small organisms such as woodlice or germinating seeds.

Common mistakes in Topic 8: Exchange and Transport in Animals

• Saying red blood cells have a nucleus. Red blood cells have no nucleus, leaving more space for haemoglobin.
• Saying the pulmonary artery carries oxygenated blood. It carries deoxygenated blood from the right ventricle to the lungs.
• Saying the left ventricle wall is thicker because it pumps more blood. It is thicker because it pumps blood at higher pressure around the whole body.
• Saying the respirometer measures carbon dioxide produced. Soda lime absorbs carbon dioxide, so movement of the liquid shows oxygen uptake.
• Confusing respiration with breathing. Respiration is a chemical reaction in cells that transfers energy.

Try three Topic 8: Exchange and Transport in Animals exam-style questions