Respiration
Cambridge A-Level Biology (9700) · Unit 12: Energy and respiration · 16 flashcards
Respiration is topic 12.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 12 — Energy and respiration , alongside Energy. In one line: Glycolysis occurs in the cytoplasm of eukaryotic cells. It's the first stage of both aerobic and anaerobic respiration, breaking down glucose into pyruvate.
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 16 flashcards — 5 definitions and 11 key concepts — covering the precise wording mark schemes reward. Use the 5 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.
Where does glycolysis occur in eukaryotic cells
Glycolysis occurs in the cytoplasm of eukaryotic cells. It's the first stage of both aerobic and anaerobic respiration, breaking down glucose into pyruvate.
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.
- explain why the energy yield from respiration in aerobic conditions is much greater than the energy yield from respiration in anaerobic conditions (a detailed account of the total yield of ATP from the aerobic respiration of glucose is not expected)
- explain how rice is adapted to grow with its roots submerged in water, limited to the development of aerenchyma in roots, ethanol fermentation in roots and faster growth of stems
- describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast
- describe and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration
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 Respiration
- › 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.
- › Energy is not produced; it is transferred. ATP is 'synthesized' from ADP and inorganic phosphate (Pi).
- › State that energy is 'released' as electrons move along the chain and that reduced NAD/FAD release hydrogen atoms which then split into protons and electrons.
Where does glycolysis occur in eukaryotic cells?
Glycolysis occurs in the cytoplasm of eukaryotic cells. It's the first stage of both aerobic and anaerobic respiration, breaking down glucose into pyruvate.
Outline the process of glycolysis.
Glycolysis involves the phosphorylation of glucose, followed by the splitting of fructose 1,6-bisphosphate (6C) into two triose phosphate molecules (3C). These are then oxidized to pyruvate (3C), producing ATP and reduced NAD.
What is the role of coenzyme A in the link reaction?
Coenzyme A combines with the 2-carbon acetyl group formed from pyruvate, creating acetyl coenzyme A. This transports the acetyl group to the Krebs cycle.
Describe the key events of the Krebs cycle, including decarboxylation and dehydrogenation.
The Krebs cycle involves oxaloacetate (4C) accepting a 2C fragment from acetyl coenzyme A to form citrate (6C). Through a series of steps, citrate is converted back to oxaloacetate. Decarboxylation removes carbon dioxide, and dehydrogenation removes hydrogen (reducing NAD and FAD).
What is the role of NAD and FAD in respiration?
NAD and FAD are coenzymes that accept hydrogen atoms (and electrons) during glycolysis, the link reaction, and the Krebs cycle. They then transport these hydrogen atoms to the electron transport chain on the inner mitochondrial membrane.
Outline the process of oxidative phosphorylation.
Hydrogen atoms split into protons and electrons. Electrons release energy as they pass through the electron transport chain. This energy pumps protons across the inner mitochondrial membrane, creating a gradient. Protons then diffuse back through ATP synthase, driving ATP synthesis. Oxygen is the final electron acceptor, forming water.
Explain how the structure of the mitochondria relates to its function in respiration.
The highly folded inner membrane (cristae) increases surface area for electron transport and ATP synthesis. The matrix contains enzymes for the Krebs cycle and link reaction. The intermembrane space accumulates protons for chemiosmosis.
Describe ethanol fermentation in yeast cells under anaerobic conditions.
In ethanol fermentation, pyruvate is decarboxylated to acetaldehyde, which is then reduced by reduced NAD to ethanol, regenerating NAD+ so glycolysis can continue. This process allows yeast to produce ATP in the absence of oxygen.
Describe lactate fermentation in mammalian cells under anaerobic conditions.
In lactate fermentation, pyruvate is reduced by reduced NAD to lactate, regenerating NAD+ so glycolysis can continue. This process allows muscle cells to produce ATP in the absence of sufficient oxygen, but lactate accumulation causes muscle fatigue.
Explain why aerobic respiration yields significantly more energy than anaerobic respiration.
Aerobic respiration uses oxygen to fully oxidize glucose, extracting all available energy. Anaerobic respiration only partially breaks down glucose, resulting in a much lower ATP yield as the Krebs cycle and oxidative phosphorylation are not utilized.
Describe two adaptations of rice plants that allow them to survive in submerged conditions.
Rice plants develop aerenchyma in their roots, creating air spaces for oxygen diffusion to submerged tissues. They also undergo ethanol fermentation in roots to produce ATP in the absence of oxygen, and exhibit faster stem growth to reach above the water surface for gas exchange.
What is the role of DCPIP in investigations of respiration?
DCPIP is a redox indicator that acts as an electron acceptor. As it accepts electrons during respiration, it becomes reduced and changes color (
How does increasing temperature generally affect the rate of respiration in yeast, up to a certain point?
Increasing temperature generally increases the rate of respiration in yeast, as enzyme activity increases with temperature, leading to faster metabolic reactions. However, beyond an optimal temperature, enzymes denature and the rate decreases.
Describe how a simple respirometer can be used to measure the rate of respiration.
A respirometer measures the rate of oxygen consumption. The organism is placed in a sealed chamber, and the decrease in oxygen volume (often indicated by a change in fluid level in a connected manometer) is measured over time. This change reflects the rate of respiration.
Explain the purpose of using a control in an experiment investigating the effect of temperature on yeast respiration.
The control establishes a baseline for comparison. It contains all components of the experimental setup *except* the variable being tested (temperature). This allows you to isolate and determine the specific effect of temperature on the rate of respiration, excluding other potential factors.
What is the role of methylene blue in investigating respiration?
Methylene blue functions as a redox indicator, accepting electrons during respiration and becoming colorless when reduced. The time taken for methylene blue to decolorize is inversely proportional to the rate of respiration.
More topics in Unit 12 — Energy and respiration
Respiration 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 Respiration deck
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