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
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.
- state that the mammalian circulatory system is a closed double circulation consisting of a heart, blood and blood vessels including arteries, arterioles, capillaries, venules and veins
- describe the functions of the main blood vessels of the pulmonary and systemic circulations, limited to pulmonary artery, pulmonary vein, aorta and vena cava
- recognise arteries, veins and capillaries from microscope slides, photomicrographs and electron micrographs and make plan diagrams showing the structure of arteries and veins in transverse section (TS) and longitudinal section (LS)
- explain how the structure of muscular arteries, elastic arteries, veins and capillaries are each related to their functions
- recognise and draw red blood cells, monocytes, neutrophils and lymphocytes from microscope slides, photomicrographs and electron micrographs
- state that water is the main component of blood and tissue fluid and relate the properties of water to its role in transport in mammals, limited to solvent action and high specific heat capacity
- state the functions of tissue fluid and describe the formation of tissue fluid in a capillary network
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 '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.
- › Recall that the right atrium has the lowest pressure as it fills from the vena cava and only moves blood into the ventricle.
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.
More 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
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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