Energy
Cambridge A-Level Biology (9700) · Unit 12: Energy and respiration · 8 flashcards
Energy is topic 12.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 12 — Energy and respiration , alongside Respiration. In one line: 1. Cytoplasm: Substrate-linked reactions. 2. Mitochondria/Chloroplasts: Chemiosmosis in membranes.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 2 definitions, 5 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Two cellular locations where ATP is synthesized
1. Cytoplasm: Substrate-linked reactions. 2. Mitochondria/Chloroplasts: Chemiosmosis in membranes.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Outline why living organisms need energy, illustrated by movement, active transport and anabolic reactions (for example, those in protein synthesis and DNA replication).
- Describe the features that suit ATP to being the universal energy currency.
- State the two ways ATP is synthesised: phosphate transfer in substrate-linked reactions, and chemiosmosis across the membranes of chloroplasts and mitochondria.
- Explain why carbohydrates, lipids and proteins release different relative amounts of energy when used as respiratory substrates.
- State that the respiratory quotient (RQ) equals the number of CO₂ molecules given out divided by the number of O₂ molecules used up in respiration.
- Calculate the RQ of various respiratory substrates using their respiration equations.
- Carry out and describe investigations that use simple respirometers to find the RQ of small invertebrates such as blowfly larvae, or of germinating seeds.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Energy
- › Always state that 'energy is released' or 'energy is transferred'; energy cannot be created or destroyed.
- › Use 'ATP synthase' (or synthetase) for the enzyme that synthesizes ATP; 'ATPase' typically refers to the enzyme that breaks it down.
- › When discussing chemiosmosis, always mention the 'proton gradient' and the movement of protons through 'ATP synthase' specifically.
- › When contrasting chemiosmosis, focus on the final electron acceptor: oxygen in mitochondria (forming water) and NADP in chloroplasts in non-cyclic photophosphorylation (forming reduced NADP).
Outline three energy-requiring processes in living organisms.
1. Active Transport: Moving substances against their concentration gradient. 2. Movement: Muscle contraction requires ATP. 3. Anabolic Reactions: Synthesis of complex molecules like DNA replication and protein synthesis.
Describe three features of ATP that make it suitable as the universal energy currency.
1. Small, manageable energy packets: Releases energy in small, usable amounts. 2. Readily Hydrolyzed: Phosphate bonds are easily broken to release energy. 3. Renewable: Quickly regenerated from ADP and Pi using energy from respiration or photosynthesis.
State two cellular locations where ATP is synthesized.
1. Cytoplasm: Substrate-linked reactions. 2. Mitochondria/Chloroplasts: Chemiosmosis in membranes.
Explain the relative energy values of carbohydrates, lipids, and proteins as respiratory substrates.
Lipids have the highest energy value due to their higher proportion of C-H bonds, which release more energy upon oxidation. Proteins have a variable energy value, while carbohydrates have the lowest energy value per unit mass.
Define the Respiratory Quotient (RQ).
The Respiratory Quotient (RQ) is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen consumed during respiration. RQ = CO₂ produced / O₂ consumed.
Calculate the RQ value for the complete oxidation of glucose (C₆H₁₂O₆).
The equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. RQ = CO₂ produced / O₂ consumed = 6/6 = 1.0
Describe the purpose of using KOH or soda lime in a respirometer experiment.
KOH or soda lime is used to absorb the carbon dioxide produced by the respiring organism (
Explain how a respirometer measures the rate of respiration.
As the organism respires and consumes oxygen, the volume of gas in the respirometer decreases. This decrease in volume causes the fluid in the manometer to move. The distance the fluid moves in a given time is a measure of the rate of oxygen consumption, and thus, the rate of respiration.
Review the material
Read full revision notes on Energy — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 12 — Energy and respiration
Energy sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Energy deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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