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
Official 2025-2027 spec · AS 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.
- describe the role of red blood cells in transporting oxygen and carbon dioxide with reference to the roles of: • haemoglobin • carbonic anhydrase • the formation of haemoglobinic acid • the formation of carbaminohaemoglobin
- describe the chloride shift and explain the importance of the chloride shift
- describe the role of plasma in the transport of carbon dioxide
- describe and explain the oxygen dissociation curve of adult haemoglobin
- explain the importance of the oxygen dissociation curve at partial pressures of oxygen in the lungs and in respiring tissues
- describe the Bohr shift and explain the importance of the Bohr shift
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
- › Define double circulation as blood passing through the heart twice for every complete circuit of the body, or mention pulmonary and systemic circuits.
- › Use 'carboxyhaemoglobin' for carbon monoxide binding and 'carbaminohaemoglobin' for carbon dioxide binding to the globin part of haemoglobin.
- › Use 'stretch' and 'recoil' for elastic fibres; 'contract' and 'relax' should only be applied to smooth muscle tissue.
- › Always use comparative adjectives like 'wider lumen', 'thicker wall', or 'more smooth muscle' when the question asks to compare structures.
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 bicarbonate ions (HCO₃⁻) leave, and vice versa. This maintains the electrochemical gradient and prevents the buildup of negative charge within the red blood cell during carbon dioxide transport.
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.
More 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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