The circulatory system
Cambridge A-Level Biology (9700) · Unit 8: Transport in mammals · 9 flashcards
The circulatory system is topic 8.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 8 — Transport in mammals , alongside Transport of oxygen and carbon dioxide and The heart. In one line: Tissue fluid provides nutrients and oxygen to cells and removes waste products like carbon dioxide and urea. It acts as an intermediary between blood capillaries and cells.
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 primary functions of tissue fluid
Tissue fluid provides nutrients and oxygen to cells and removes waste products like carbon dioxide and urea. It acts as an intermediary between blood capillaries and cells.
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).
- State that mammals have a closed double circulation made up of the heart, the blood and blood vessels: arteries and arterioles, capillaries, venules and veins.
- Describe what the main blood vessels of the systemic and pulmonary circulations do, covering only the aorta, vena cava, pulmonary artery and pulmonary vein.
- Recognise capillaries, arteries and veins in electron micrographs, photomicrographs and on microscope slides, and draw plan diagrams of artery and vein structure in both longitudinal section (LS) and transverse section (TS).
- Explain how the structures of elastic arteries, muscular arteries, capillaries and veins relate to their functions.
- Recognise and draw lymphocytes, monocytes, neutrophils and red blood cells as seen on microscope slides, in photomicrographs and in electron micrographs.
- State that blood and tissue fluid are mostly water, and relate water's properties to its transport role in mammals, limited to its high specific heat capacity and its solvent action.
- State what tissue fluid does, and describe how it forms in a network of 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 circulatory system
- › Define double circulation as blood passing through the heart twice for every complete circuit of the body, or mention pulmonary and systemic circuits.
- › 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 key structural feature that differentiates arteries from veins in transverse section.
Arteries have a thicker tunica media (middle layer) containing more smooth muscle and elastic fibers compared to veins. This allows arteries to withstand higher blood pressure.
Outline the pathway of blood in the pulmonary circulation.
Deoxygenated blood is carried from the right ventricle to the lungs via the pulmonary artery. In the lungs, blood becomes oxygenated and returns to the left atrium via the pulmonary vein.
What are the primary functions of tissue fluid?
Tissue fluid provides nutrients and oxygen to cells and removes waste products like carbon dioxide and urea. It acts as an intermediary between blood capillaries and cells.
Explain how the high specific heat capacity of water is beneficial in mammalian blood.
Water's high specific heat capacity means it can absorb or release a large amount of heat without significantly changing temperature. This helps maintain a stable body temperature in mammals and prevents drastic temperature fluctuations in blood.
Describe the structure of a capillary and how it relates to its function.
Capillaries have a single-celled layer of endothelium, creating a short diffusion pathway. This thin wall allows for efficient exchange of substances like oxygen, carbon dioxide, and nutrients between the blood and tissue fluid.
Identify two differences between elastic and muscular arteries, relating the structural differences to their specific functions.
Elastic arteries have a higher proportion of elastin in their tunica media, allowing them to stretch and recoil to maintain blood pressure. Muscular arteries have more smooth muscle, allowing them to control blood flow to different organs through vasoconstriction and vasodilation.
Describe the formation of tissue fluid from blood plasma in a capillary network.
Blood pressure at the arteriole end of capillaries forces fluid out through gaps in the capillary walls, forming tissue fluid. Most of the fluid returns to the capillary at the venule end due to oncotic pressure created by plasma proteins, while the rest drains into the lymphatic system.
State two key differences between monocytes and lymphocytes when observed under a microscope.
Monocytes are typically larger than lymphocytes and have a kidney-shaped nucleus. Lymphocytes have a large, round nucleus that occupies most of the cell, leaving only a small amount of cytoplasm visible.
Explain how the structure of veins facilitates the return of blood to the heart, particularly against gravity in the limbs.
Veins have thinner walls and wider lumens compared to arteries, reducing resistance to blood flow. They also contain valves that prevent backflow of blood, ensuring it moves towards the heart even against gravity.
Review the material
Read full revision notes on The circulatory system — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 8 — Transport in mammals
The circulatory system 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 The circulatory system deck
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