Edexcel International GCSE Biology Section 2: Structure and Functions in Living Organisms Exam Questions

About Edexcel International GCSE Biology Section 2: Structure and Functions in Living Organisms

Section 2 is the largest part of Edexcel International GCSE Biology and is examined across Paper 1 and Paper 2. It covers levels of organisation, cell structure, biological molecules and enzymes, diffusion, osmosis and active transport, nutrition in plants and humans, respiration, gas exchange, transport, excretion and coordination. Many of the specification's practicals sit here, including food tests, enzyme investigations, osmosis, photosynthesis, the energy content of food and gas exchange with hydrogencarbonate indicator. Examiners frequently ask about enzyme graphs, leaf and alveolus adaptations, the heart and circulation, the nephron, reflex arcs and homeostasis.

What you need to know

• Cells and molecules Know organelles in animal and plant cells and the levels of organisation: organelles, cells, tissues, organs and organ systems. Carbohydrates, proteins and lipids are made from simple sugars, amino acids, and fatty acids and glycerol. Enzymes are biological catalysts affected by temperature and pH. Tests: iodine, Benedict's, biuret and ethanol emulsion.
• Movement of substances Diffusion, osmosis and active transport move substances into and out of cells. Rate is affected by surface area to volume ratio, distance, temperature and concentration gradient.
• Nutrition in plants Photosynthesis: carbon dioxide + water -> glucose + oxygen (6CO2 + 6H2O -> C6H12O6 + 6O2), limited by light, carbon dioxide and temperature. Leaves are adapted for photosynthesis; nitrate and magnesium ions are needed for protein and chlorophyll.
• Nutrition in humans A balanced diet includes carbohydrates, proteins, lipids, vitamins A, C and D, calcium, iron, fibre and water. Food is digested by amylase, maltase, protease and lipase; bile neutralises acid and emulsifies fat; villi absorb products. Energy content of food can be estimated by burning it under water.
• Respiration and gas exchange Aerobic: glucose + oxygen -> carbon dioxide + water. Anaerobic in animals gives lactic acid; in plants and yeast gives ethanol and carbon dioxide. Gas exchange happens through stomata in plants and in the alveoli in humans; smoking damages the lungs and circulation.
• Transport Plants use xylem (water and mineral ions) and phloem (sucrose and amino acids); transpiration rate depends on light, temperature, humidity and wind. In humans, blood contains plasma, red cells, white cells (phagocytes and lymphocytes) and platelets; the heart pumps blood through arteries, veins and capillaries. Exercise increases heart rate.
• Excretion Plants excrete oxygen and carbon dioxide. Humans excrete through the lungs, kidneys and skin. In the nephron, ultrafiltration in the glomerulus and selective reabsorption of glucose and water produce urine; ADH controls water reabsorption in the collecting duct.
• Coordination and response Plants respond to light and gravity (phototropism, geotropism) using auxin. Humans use the nervous system (reflex arcs, synapses, the eye) and hormones such as adrenaline, insulin, testosterone, progesterone, oestrogen, ADH, FSH and LH. Homeostasis controls water content and body temperature (sweating, vasodilation, vasoconstriction, shivering).

Common mistakes in Section 2: Structure and Functions in Living Organisms

• Saying enzymes are killed above the optimum temperature. They are denatured because the active site changes shape.
• Saying bile is an enzyme. Bile emulsifies fats and neutralises stomach acid; lipase digests the fats.
• Saying plants only respire at night. Plants respire all the time; in bright light photosynthesis is faster, so there is a net uptake of carbon dioxide.
• Saying glucose is filtered and then lost in urine in healthy people. All glucose is selectively reabsorbed in the proximal convoluted tubule.
• Saying shoots grow towards light because light pulls them. Auxin collects on the shaded side and stimulates cell elongation there.

Try three Section 2: Structure and Functions in Living Organisms exam-style questions