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
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- outline the need for energy in living organisms, as illustrated by active transport, movement and anabolic reactions, such as those occurring in DNA replication and protein synthesis
- describe the features of ATP that make it suitable as the universal energy currency
- state that ATP is synthesised by: • transfer of phosphate in substrate-linked reactions • chemiosmosis in membranes of mitochondria and chloroplasts
- explain the relative energy values of carbohydrates, lipids and proteins as respiratory substrates
- state that the respiratory quotient (RQ) is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen taken in, as a result of respiration
- calculate RQ values of different respiratory substrates from equations for respiration
- describe and carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae)
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
- › Only draw a line of best fit through or between the data points provided; do not extrapolate unless specifically told to do so.
- › Always state that 'energy is released' or 'energy is transferred'; energy cannot be created or destroyed.
- › Always mention the 'proton gradient' and that the movement is from the intermembrane space back into the matrix through ATP synthase.
- › 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.
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.
More 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.
How to study this Energy deck
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