Transport of oxygen and carbon dioxide
Cambridge A-Level Biology (9700) · Unit 8: Transport in mammals · 9 flashcards
Transport of oxygen and carbon dioxide is topic 8.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 8 — Transport in mammals , alongside The circulatory system and The heart. In one line: Carbonic anhydrase catalyses the reversible reaction between carbon dioxide and water, forming carbonic acid. This increases the rate of carbon dioxide conversion, facilitating its transport in the blood.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 9 flashcards — 2 definitions and 7 key concepts — 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.
The role of carbonic anhydrase in red blood cells
Carbonic anhydrase catalyses the reversible reaction between carbon dioxide and water, forming carbonic acid. This increases the rate of carbon dioxide conversion, facilitating its transport in the blood.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · AS 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).
- Describe how red blood cells carry oxygen and carbon dioxide, referring to haemoglobin, carbonic anhydrase, and the formation of carbaminohaemoglobin and of haemoglobinic acid.
- Describe what the chloride shift is and explain why it is important.
- Describe the part plasma plays in carrying carbon dioxide.
- Describe and explain the shape of the oxygen dissociation curve for adult haemoglobin.
- Explain why the oxygen dissociation curve matters at the partial pressures of oxygen found in respiring tissues and in the lungs.
- Describe what the Bohr shift is and explain why it is important.
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 Transport of oxygen and carbon dioxide
- › Use 'carbaminohaemoglobin' for carbon dioxide bound to the globin part of haemoglobin.
- › Always specify 'chloride ions' (Cl-) when describing the chloride shift; 'chlorine' refers to the toxic gas molecule (Cl2).
Describe the role of haemoglobin in oxygen transport.
Haemoglobin, found in red blood cells, has a high affinity for oxygen. It binds oxygen in the lungs, forming oxyhaemoglobin, and transports it to tissues where oxygen is released due to lower partial pressures and higher carbon dioxide concentrations.
What is the role of carbonic anhydrase in red blood cells?
Carbonic anhydrase catalyses the reversible reaction between carbon dioxide and water, forming carbonic acid. This increases the rate of carbon dioxide conversion, facilitating its transport in the blood.
Explain how haemoglobinic acid is formed and its significance.
Haemoglobinic acid (HHb) is formed when haemoglobin accepts hydrogen ions (H⁺). This buffering action helps maintain a stable pH in the blood by binding excess H⁺ released during carbon dioxide transport and metabolic processes.
Describe the formation of carbaminohaemoglobin.
Carbaminohaemoglobin is formed when carbon dioxide directly binds to haemoglobin. This binding reduces haemoglobin's affinity for oxygen, promoting oxygen release in tissues with high carbon dioxide concentrations.
Outline the chloride shift and its importance.
The chloride shift is the movement of chloride ions (Cl⁻) into red blood cells as hydrogencarbonate ions (HCO₃⁻) diffuse out into the plasma (reversed in the lungs). It keeps the red blood cell electrically neutral, so HCO₃⁻ can keep leaving and more carbon dioxide can be converted and carried in the plasma.
How does blood plasma contribute to carbon dioxide transport?
Plasma transports carbon dioxide dissolved directly in it (small amount). More significantly, carbon dioxide is transported as bicarbonate ions (HCO₃⁻) within the plasma after being formed in red blood cells.
Describe the shape of the adult haemoglobin oxygen dissociation curve and explain its significance.
The oxygen dissociation curve for adult haemoglobin is sigmoidal (S-shaped). The shape reflects the cooperative binding of oxygen; initial binding is difficult, but subsequent binding is easier due to conformational changes in the haemoglobin molecule.
Explain the importance of the oxygen dissociation curve at low partial pressures of oxygen (e.g., in respiring tissues).
At low partial pressures of oxygen, the oxygen dissociation curve shows that haemoglobin readily releases oxygen. This ensures efficient oxygen delivery to respiring tissues where metabolic activity has lowered the pO₂.
Explain the Bohr shift and its significance for oxygen delivery.
The Bohr shift describes the decreased affinity of haemoglobin for oxygen at lower pH (higher H⁺ concentration) or higher carbon dioxide concentration. This shift promotes oxygen unloading in active tissues where carbon dioxide production and lactic acid (lowering pH) are elevated.
Review the material
Read full revision notes on Transport of oxygen and carbon dioxide — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 8 — Transport in mammals
Transport of oxygen and carbon dioxide 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 Transport of oxygen and carbon dioxide deck
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