The gas exchange system
Cambridge A-Level Biology (9700) · Unit 9: Gas exchange · 8 flashcards
The gas exchange system is topic 9.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 9 — Gas exchange . In one line: Cartilage provides support to the trachea and bronchi, preventing them from collapsing during inhalation due to pressure changes. This ensures a clear airway for efficient gas exchange.
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 8 flashcards — 4 definitions and 4 key concepts — covering the precise wording mark schemes reward. Use the 4 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 cartilage in the trachea and bronchi
Cartilage provides support to the trachea and bronchi, preventing them from collapsing during inhalation due to pressure changes. This ensures a clear airway for efficient gas exchange.
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 the human gas exchange system is structured, covering only the trachea, bronchi, bronchioles, alveoli and capillary network, plus the lungs.
- Describe where goblet cells, cartilage, ciliated epithelium, smooth muscle, capillaries and alveolar squamous epithelium are found in the gas exchange system.
- Recognise smooth muscle, capillaries, goblet cells, cartilage, ciliated epithelium and alveolar squamous epithelium on microscope slides, in photomicrographs and in electron micrographs.
- Recognise the alveoli, bronchioles, bronchi and trachea in electron micrographs, photomicrographs and on microscope slides, and draw plan diagrams of the trachea wall and bronchus wall in transverse section.
- Describe how goblet cells, mucous glands and ciliated epithelial cells keep the gas exchange system healthy.
- Describe the function of each of the following in the gas exchange system: squamous epithelium, elastic fibres, smooth muscle and cartilage.
- Describe how gases are exchanged between the blood in capillaries and the air in alveoli.
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 The gas exchange system
- › Only use 'endothelium' when referring to the lining of blood vessels. Bronchioles contain ciliated epithelium, smooth muscle, and elastic fibres.
- › Elastic fibres stretch when you breathe in and recoil when you breathe out, helping push air out; do not say they 'contract'.
Describe the structure of the human gas exchange system.
The human gas exchange system consists of the lungs, trachea, bronchi, bronchioles, alveoli, and a capillary network. The trachea branches into two bronchi, which further divide into bronchioles, terminating in alveoli, where gas exchange occurs with surrounding capillaries.
What is the role of cartilage in the trachea and bronchi?
Cartilage provides support to the trachea and bronchi, preventing them from collapsing during inhalation due to pressure changes. This ensures a clear airway for efficient gas exchange.
Describe the function of goblet cells and mucous glands in the gas exchange system.
Goblet cells and mucous glands secrete mucus, which traps pathogens and particulate matter. This prevents harmful substances from reaching the delicate alveoli and damaging the gas exchange process.
What is the function of ciliated epithelial cells in the trachea and bronchi?
Ciliated epithelial cells have cilia that beat in a coordinated manner to move mucus, along with trapped particles and pathogens, up the trachea and towards the throat, where it can be swallowed or expelled. This is known as the mucociliary escalator.
Describe the structure and function of alveoli in gas exchange.
Alveoli are tiny air sacs with thin walls composed of squamous epithelium, surrounded by a dense capillary network. This structure facilitates efficient gas exchange: oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.
What is the role of elastic fibers in the alveoli?
Elastic fibers in the alveolar walls allow the alveoli to stretch during inhalation and recoil during exhalation. This elastic recoil helps to expel air from the lungs and maintain alveolar structure.
Explain how gas exchange occurs between the alveoli and the blood capillaries.
Gas exchange occurs via diffusion down a concentration gradient. Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration), while carbon dioxide diffuses from the blood (high concentration) into the alveoli (low concentration).
Describe the function of smooth muscle in the bronchioles.
Smooth muscle in the walls of the bronchioles can contract or relax to control the diameter of the airways. This helps to regulate airflow to the alveoli, ensuring efficient gas exchange based on the body's needs.
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