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
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 structure of the human gas exchange system, limited to: • lungs • trachea • bronchi • bronchioles • alveoli • capillary network
- describe the distribution in the gas exchange system of cartilage, ciliated epithelium, goblet cells, squamous epithelium of alveoli, smooth muscle and capillaries
- recognise cartilage, ciliated epithelium, goblet cells, squamous epithelium of alveoli, smooth muscle and capillaries in microscope slides, photomicrographs and electron micrographs
- recognise trachea, bronchi, bronchioles and alveoli in microscope slides, photomicrographs and electron micrographs and make plan diagrams of transverse sections of the walls of the trachea and bronchus
- describe the functions of ciliated epithelial cells, goblet cells and mucous glands in maintaining the health of the gas exchange system
- describe the functions in the gas exchange system of cartilage, smooth muscle, elastic fibres and squamous epithelium
- describe gas exchange between air in the alveoli and blood in the capillaries
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.
- › Recall that elastic fibres allow for recoil; it is the surfactant and transpulmonary pressure that prevent alveolar collapse.
- › Use 'endothelium' or 'endothelial cells' specifically for the lining of blood vessels and 'epithelium' for other surfaces like the alveoli.
- › Always specify 'chloride ions' (Cl-) when describing the chloride shift; 'chlorine' refers to the toxic gas molecule (Cl2).
- › Remember that every cell surface membrane is a phospholipid bilayer; therefore, a molecule must pass through two phospholipid layers for every membrane it crosses.
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.
Key terms covered in this The gas exchange system deck
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