You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
This lesson consolidates everything you have learned in the Bioenergetics topic and prepares you for the AQA GCSE Biology exam. It covers key definitions, common question types, mark scheme expectations, and strategies for maximising your marks. Use this lesson as a revision resource and a checklist to ensure you have covered all the required content.
The following definitions appear repeatedly in exam questions. You should be able to write each one accurately from memory.
| Term | Definition |
|---|---|
| Photosynthesis | An endothermic reaction in which light energy is used to convert carbon dioxide and water into glucose and oxygen |
| Aerobic respiration | An exothermic reaction in which glucose is broken down using oxygen to release energy, producing carbon dioxide and water |
| Anaerobic respiration | Respiration without oxygen; in animals it produces lactic acid; in plants and yeast it produces ethanol and carbon dioxide |
| Limiting factor | The factor in shortest supply that directly controls the rate of a reaction |
| Metabolism | The sum of all chemical reactions in a cell or the body |
| Oxygen debt | The amount of extra oxygen needed after exercise to break down lactic acid |
| Endothermic | A reaction that takes in energy from the surroundings |
| Exothermic | A reaction that releases energy to the surroundings |
| Denature | When an enzyme's active site permanently changes shape due to high temperature or extreme pH, so the substrate can no longer fit |
| Fermentation | Anaerobic respiration in yeast, producing ethanol and carbon dioxide |
| Compensation point [H] | The light intensity at which the rate of photosynthesis equals the rate of respiration |
Exam Tip: Definitions are often worth 1-2 marks and appear at the start of longer questions. If you can nail the definition, you set yourself up to access the higher marks in the rest of the question. Practise writing definitions under timed conditions.
You must know these equations and be able to reproduce them accurately:
graph TD
A[Key Equations] --> B[Photosynthesis]
A --> C[Aerobic Respiration]
A --> D[Anaerobic — Animals]
A --> E[Anaerobic — Plants/Yeast]
B --> B1[CO2 + water --light--> glucose + O2]
C --> C1[glucose + O2 --> CO2 + water + energy]
D --> D1[glucose --> lactic acid + energy]
E --> E1[glucose --> ethanol + CO2 + energy]
Exam Tip: Examiners report that many students lose marks by writing incorrect or unbalanced symbol equations. Double-check the numbers of each atom on both sides. For photosynthesis and aerobic respiration, the coefficient is 6 for CO2, H2O and O2.
These ask you to state facts. Be precise and use scientific terminology.
Example: "Describe the process of aerobic respiration." (2 marks)
Model answer: Aerobic respiration is a chemical reaction that takes place in the mitochondria of cells. Glucose reacts with oxygen to produce carbon dioxide and water, releasing energy for life processes.
These ask you to give reasons. Always use "because" or "this means that" to show chains of reasoning.
Example: "Explain why the rate of photosynthesis levels off at high light intensities." (3 marks)
Model answer: At high light intensities, the rate of photosynthesis reaches a plateau because light is no longer the limiting factor. Another factor, such as carbon dioxide concentration or temperature, is now in shortest supply and is limiting the rate. Increasing light intensity further has no effect because there is not enough CO2 for the reaction, or the enzymes have reached their maximum rate at that temperature.
These ask you to identify similarities and/or differences. Use a clear, parallel structure.
Example: "Compare aerobic and anaerobic respiration." (4 marks)
Model answer: Both aerobic and anaerobic respiration break down glucose to release energy. However, aerobic respiration requires oxygen, while anaerobic respiration does not. Aerobic respiration produces carbon dioxide and water, while anaerobic respiration in animals produces lactic acid. Aerobic respiration releases much more energy per glucose molecule because the glucose is completely broken down, whereas in anaerobic respiration the glucose is only partially broken down.
These give you a graph and ask you to describe trends or identify limiting factors.
Strategy:
These test your knowledge of the pondweed practical.
Key points to include:
These require a well-structured, detailed answer. Use paragraphs, key terms, and logical flow.
Example: "Describe and explain how a plant uses the glucose produced by photosynthesis." (6 marks)
Model answer structure:
| Use of Glucose | Product | Purpose |
|---|---|---|
| Respiration | Energy (+ CO2 + water) | Powers all life processes |
| Storage | Starch | Insoluble energy reserve |
| Cell walls | Cellulose | Structural support |
| Growth | Amino acids/proteins | Enzymes, cell structures (needs nitrates) |
| Seed reserves | Lipids (fats/oils) | High-energy storage for germination |
| Transport | Sucrose | Moved through phloem to other parts of the plant |
Exam Tip: For 6-mark questions, aim for at least three well-developed points. Each point should include a fact AND an explanation. Use scientific terminology correctly and write in full sentences. The quality of your written communication matters — spelling, grammar and the use of technical terms are all assessed.
If you are sitting the Higher tier paper, make sure you also know:
| Topic | Key Knowledge |
|---|---|
| Inverse square law | Light intensity is proportional to 1/d squared |
| Compensation point | When rate of photosynthesis = rate of respiration; no net gas exchange |
| Net vs gross photosynthesis | Net = gross photosynthesis minus respiration |
| Oxygen debt | Extra oxygen needed to break down lactic acid in the liver after exercise |
| Deamination | Excess amino acids broken down in the liver; amino group removed; ammonia converted to urea; excreted by kidneys |
| Metabolism | Sum of all reactions; anabolic (building up) vs catabolic (breaking down) |
Use this checklist to ensure you have covered every part of the Bioenergetics topic:
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.