GCSE Biology: Bioenergetics — Topic Revision Workbook

Inside GCSE Biology: Bioenergetics — Topic Revision Workbook

nail the photosynthesis word and symbol equations and where it happens, interpret rate graphs and limiting factors including the inverse-square light idea, master aerobic respiration in the mitochondria, then compare anaerobic respiration in muscle and yeast, oxygen debt and metabolism. About 30 minutes.

Learning objectives

• photosynthesis — the word and balanced symbol equations, chloroplasts and chlorophyll, and why the reaction is endothermic;
• limiting factors — light intensity, carbon dioxide and temperature, reading rate graphs, calculating rate, the inverse-square light idea and the uses of glucose (starch, proteins);
• aerobic respiration — the equation, the role of the mitochondria and why respiration is exothermic;
• anaerobic respiration — lactic acid in muscle versus fermentation (ethanol + carbon dioxide) in yeast and plants, oxygen debt, response to exercise and metabolism.

Activities in this book

1. Task 1 — Photosynthesis & Its Equations

   photosynthesis happens in chloroplasts, which contain the green pigment chlorophyll to absorb light. It is endothermic — energy is transferred from the environment (light) to the plant. Word equation: carbon dioxide + water → glucose + oxygen. Symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

2. Task 2 — Limiting Factors, Rate & Uses of Glucose

   a limiting factor is the one in shortest supply that holds back the rate. The three limiting factors of photosynthesis are light intensity, carbon dioxide concentration and temperature. Light intensity follows the inverse-square law: it is proportional to 1 ÷ distance², so doubling the distance from a lamp quarters the light.

3. Task 3 — Aerobic Respiration

   respiration happens in every living cell, all the time, to transfer energy from glucose. Aerobic respiration uses oxygen and mostly takes place in the mitochondria. It is exothermic — it transfers energy to the surroundings. Word equation: glucose + oxygen → carbon dioxide + water.

4. Task 4 — Anaerobic Respiration, Oxygen Debt & Metabolism

   anaerobic respiration releases energy without oxygen, but incompletely, so it transfers less energy. In muscle: glucose → lactic acid. In yeast and plants (fermentation): glucose → ethanol + carbon dioxide. After hard exercise the body needs extra oxygen — the oxygen debt — to break down the lactic acid.

5. Task 5 — Exam-Style 6-Marker

   a 6-mark answer needs organised, detailed biology, not a list. Plan two or three clear points, use the correct terms (limiting factor, mitochondria, endothermic, oxygen debt) and, where you can, link cause to effect.

Suggestions for teaching

• Drill the equations. Get both the photosynthesis and aerobic respiration word equations automatic before touching the symbol equations.
• Read graphs actively. Practise spotting where a rate line rises, then plateaus, and naming which factor is limiting in each region.
• Calculate rate. Rate = amount ÷ time; keep units consistent and show the working.
• Compare respiration types. Build a two-column table: aerobic (oxygen, mitochondria, more energy) versus anaerobic (no oxygen, lactic acid or fermentation, less energy).