OCR GCSE Biology B B5.1 How do substances get into out of and around our bodies? Exam Questions

About OCR GCSE Biology B B5.1 How do substances get into out of and around our bodies?

B5.1 opens chapter B5, The Human Body, Staying Alive, with how materials are exchanged and transported. You need to explain why large organisms need specialised exchange surfaces and a transport system, using surface area to volume ratio. The adaptations of the alveoli and small intestine villi, the structure of the heart, the double circulatory system, and the structure of arteries, veins and capillaries are all tested, along with the components of blood. This builds on diffusion and osmosis from B3.2 and links to respiration in B4.1. Examiners commonly ask for SA:V calculations and structure to function explanations.

What you need to know

• Surface area to volume ratio As organisms get bigger, SA:V decreases, so diffusion across the surface is too slow to supply all cells. A 1 cm cube has SA:V of 6 : 1; a 2 cm cube has 24 : 8, which is 3 : 1.
• Exchange surfaces Good exchange surfaces have a large surface area, a thin barrier for a short diffusion distance, and a good blood supply or ventilation to keep a steep concentration gradient.
• Alveoli and villi Alveoli are tiny air sacs with walls one cell thick surrounded by capillaries. Villi in the small intestine have microvilli, thin walls and capillaries to absorb digested food by diffusion and active transport.
• Double circulation Blood passes through the heart twice in each circuit: the right side pumps deoxygenated blood to the lungs; the left side pumps oxygenated blood to the body at higher pressure.
• The heart Four chambers: atria receive blood, ventricles pump it out. The left ventricle has a thicker muscular wall. Valves prevent backflow. Coronary arteries supply the heart muscle.
• Blood vessels Arteries have thick, elastic, muscular walls for high pressure; veins have thinner walls, a wide lumen and valves; capillaries are one cell thick for exchange.
• Blood Plasma carries dissolved substances; red blood cells contain haemoglobin to carry oxygen and have no nucleus; white blood cells defend against pathogens; platelets help clotting.

Common mistakes in B5.1 How do substances get into out of and around our bodies?

• Saying larger organisms have a larger SA:V. Larger organisms have a smaller SA:V ratio.
• Stating that capillary walls are one cell thin. Say one cell thick, giving a short diffusion distance.
• Mixing up the sides of the heart. The right side receives blood from the body and pumps to the lungs; diagrams are drawn as if facing you, so the right side appears on the left.
• Writing that arteries carry oxygenated blood and veins deoxygenated. Arteries carry blood away from the heart; the pulmonary artery carries deoxygenated blood.
• Saying the left ventricle is thicker to pump more blood. It is thicker to pump blood at higher pressure around the whole body.

Try three B5.1 How do substances get into out of and around our bodies? exam-style questions