12.1

Respiration

Cambridge IGCSE Biology (0610)  · Unit 12: Respiration  · 16 flashcards

Respiration is topic 12.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 12 — Respiration , alongside Aerobic respiration and Anaerobic respiration.  In one line: Respiration is the chemical process that releases energy from glucose. In aerobic respiration, glucose reacts with oxygen to produce carbon dioxide, water, and energy.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 confirm this is a high-yield topic: Cambridge has set 35 questions worth 506 marks here (about 7.6% of all Biology marks across those years).

The deck below contains 16 flashcards — 5 definitions, 7 key concepts, 2 process cards, 1 application card and 1 study tip — 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 application cards to handle explain, describe and compare questions.

Watch out: one common mark-loser flagged on this topic — read the study-tip card below before attempting past-paper questions.

Key definition

Respiration

Respiration is the chemical process that releases energy from glucose. In aerobic respiration, glucose reacts with oxygen to produce carbon dioxide, water, and energy.

Example: muscle cells respire aerobically during exercise; yeast can respire anaerobically.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. State State the uses of energy in living organisms, including: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature
  2. Investigate Investigate and describe the effect of temperature on respiration in yeast

Common mark-losers in Respiration

Explain why respiration is not the same as breathing.

Breathing (ventilation) is the physical process of moving air in and out of the lungs. It is a mechanical process involving the ribs and diaphragm.

Respiration is a chemical reaction that occurs in every living cell, releasing energy from glucose. It happens continuously in all organisms, not just those with lungs.

Breathing provides the oxygen for aerobic respiration and removes the CO₂ produced, but they are separate processes.

Key Concept Flip

List seven uses of energy in living organisms.

Answer Flip

Energy is used for: 1) muscle contraction (

Example: movement of limbs), 2) protein synthesis (. enzyme production), 3) cell division (. growth), 4) active transport (. nutrient uptake in roots), 5) growth (. increase in height), 6) nerve impulse transmission (. relaying sensory information), and 7) maintaining body temperature (. endothermic mammals).
Definition Flip

What is respiration?

Answer Flip

Respiration is the chemical process that releases energy from glucose. In aerobic respiration, glucose reacts with oxygen to produce carbon dioxide, water, and energy.

Example: muscle cells respire aerobically during exercise; yeast can respire anaerobically.
Definition Flip

What is the equation for aerobic respiration?

Answer Flip

Glucose + Oxygen → Carbon Dioxide + Water + Energy. This process occurs in the mitochondria of cells, such as muscle cells during physical activity.

Definition Flip

What is the equation for anaerobic respiration in muscles?

Answer Flip

Glucose → Lactic Acid + Energy. This occurs during strenuous exercise when oxygen supply is limited, leading to muscle fatigue,

Example: in a sprinter.
Definition Flip

What is the equation for anaerobic respiration in yeast?

Answer Flip

Glucose → Ethanol + Carbon Dioxide + Energy. This process is used in brewing beer (ethanol production) and baking bread (carbon dioxide makes the dough rise).

Key Concept Flip

How does temperature affect the rate of respiration in yeast?

Answer Flip

As temperature increases up to an optimum, the rate of respiration in yeast increases due to increased enzyme activity. Above the optimum temperature, the enzymes denature and the rate decreases.

Example: at very high temperatures, yeast will no longer ferment sugar.
Definition Flip

What is oxygen debt?

Answer Flip

Oxygen debt is the amount of oxygen needed to oxidize the lactic acid that builds up during anaerobic respiration. After intense exercise, deep breathing helps repay the oxygen debt. The liver converts lactic acid back to glucose.

Key Concept Flip

What is the role of enzymes in respiration?

Answer Flip

Enzymes are biological catalysts that speed up the rate of respiration. Different enzymes are involved in each step of both aerobic and anaerobic respiration.

Example: enzymes are used to break down glucose into pyruvate.
Key Concept Flip

Explain how muscle contraction requires energy from respiration.

Answer Flip

Muscle contraction is an active process that requires ATP (adenosine triphosphate), which is produced during respiration. The energy from ATP is used to power the sliding of actin and myosin filaments within muscle cells. For instance, moving your arm uses ATP from respiration in the arm muscles.

Key Concept Flip

Describe how a respirometer can be used to measure the rate of respiration.

Answer Flip

A respirometer measures oxygen consumption by an organism. It typically involves a sealed container with the organism, a means to absorb carbon dioxide (

Example: soda lime), and a manometer to measure the decrease in volume due to oxygen uptake. The rate of respiration is calculated based on the oxygen consumed over time.
Key Concept Flip

What is the difference between aerobic and anaerobic respiration in humans?

Answer Flip

Aerobic respiration uses oxygen:
glucose + oxygen → carbon dioxide + water (+ energy)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Releases a large amount of energy.

Anaerobic respiration occurs without oxygen:
glucose → lactic acid (+ less energy)
Releases much less energy. Occurs during vigorous exercise when oxygen supply is insufficient.

Key Concept Flip

Why does anaerobic respiration in yeast produce different products from anaerobic respiration in humans?

Answer Flip

In yeast (fermentation): glucose → ethanol + carbon dioxide
In humans: glucose → lactic acid

These are different metabolic pathways with different enzymes. Yeast produces ethanol (used in brewing and baking), while human muscles produce lactic acid (which causes muscle fatigue and cramps). Both release less energy than aerobic respiration.

Key Concept Flip

What is oxygen debt and how is it repaid?

Answer Flip

Oxygen debt is the extra oxygen needed after vigorous exercise to break down the lactic acid that accumulated during anaerobic respiration.

After exercise:
• Breathing rate and heart rate remain high to deliver extra oxygen
• Lactic acid is transported in the blood to the liver
• In the liver, lactic acid is broken down using oxygen (or converted back to glucose)

This is why you continue to breathe heavily after stopping exercise.

Key Concept Flip

List seven uses of energy from respiration in living organisms.

Answer Flip

1. Muscle contraction (movement)
2. Protein synthesis (building new proteins from amino acids)
3. Cell division (mitosis for growth and repair)
4. Active transport (moving substances against a concentration gradient)
5. Growth (producing new cells and tissues)
6. Maintaining body temperature (in mammals and birds)
7. Transmitting nerve impulses

All living cells respire continuously — respiration is not the same as breathing.

Key Concept Flip

Describe an experiment to investigate the effect of temperature on respiration rate in yeast.

Answer Flip

1. Mix yeast with glucose solution in a flask
2. Connect the flask to a delivery tube leading into a measuring cylinder filled with water (to collect CO₂ gas)
3. Place the flask in a water bath at a set temperature (

Example: 20°C)<br>4. Measure the volume of CO₂ produced in 10 minutes<br>5. Repeat at different temperatures (. 25°C, 30°C, 35°C, 40°C)<br>6. Use a control with boiled (dead) yeast<br><br>Expected result: rate increases up to an optimum (~35-40°C), then decreases sharply as enzymes denature.
Study Tip Flip

Explain why respiration is not the same as breathing.

Answer Flip

Breathing (ventilation) is the physical process of moving air in and out of the lungs. It is a mechanical process involving the ribs and diaphragm.

Respiration is a chemical reaction that occurs in every living cell, releasing energy from glucose. It happens continuously in all organisms, not just those with lungs.

Breathing provides the oxygen for aerobic respiration and removes the CO₂ produced, but they are separate processes.

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11.1 Gas exchange in humans 12.2 Aerobic respiration

Key Questions: Respiration

What is respiration?

Respiration is the chemical process that releases energy from glucose. In aerobic respiration, glucose reacts with oxygen to produce carbon dioxide, water, and energy.

Example: muscle cells respire aerobically during exercise; yeast can respire anaerobically.
What is the equation for aerobic respiration?

Glucose + Oxygen → Carbon Dioxide + Water + Energy. This process occurs in the mitochondria of cells, such as muscle cells during physical activity.

What is the equation for anaerobic respiration in muscles?

Glucose → Lactic Acid + Energy. This occurs during strenuous exercise when oxygen supply is limited, leading to muscle fatigue,

Example: in a sprinter.
What is the equation for anaerobic respiration in yeast?

Glucose → Ethanol + Carbon Dioxide + Energy. This process is used in brewing beer (ethanol production) and baking bread (carbon dioxide makes the dough rise).

What is oxygen debt?

Oxygen debt is the amount of oxygen needed to oxidize the lactic acid that builds up during anaerobic respiration. After intense exercise, deep breathing helps repay the oxygen debt. The liver converts lactic acid back to glucose.

Tips to avoid common mistakes in Respiration

More topics in Unit 12 — Respiration

Respiration sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

12.2 Aerobic respiration

11 flashcards
12.3 Anaerobic respiration

10 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

respiration aerobic respiration anaerobic respiration glucose oxygen carbon dioxide water energy ATP mitochondria lactic acid ethanol fermentation oxygen debt yeast exercise

Key terms covered in this Respiration 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.

Respiration
The equation for aerobic respiration
The equation for anaerobic respiration in muscles
The equation for anaerobic respiration in yeast
Oxygen debt

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How to study this Respiration deck

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