The circulatory system
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of the need for transport systems in multicellular organisms (from GCSE). You can test your knowledge on these below.
Why do large, multicellular organisms require a transport system?
Large organisms have a low surface area to volume ratio, meaning diffusion alone is insufficient to transport substances efficiently to all body cells
How does size affect surface area to volume ratio?
As organisms increase in size, their surface area to volume ratio decreases.
What are the different types of blood vessels and their functions?
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Arteries: Carry blood away from the heart under high pressure, with thick muscular walls.
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Veins: Carry blood towards the heart, containing valves to prevent backflow.
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Capillaries: Microscopic vessels that facilitate the exchange of gases, nutrients, and waste between blood and tissues.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains the circulatory system or read the full notes below. Once you've gone through the whole note, try out the practice questions!
The Importance of a Circulatory System
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Transports oxygen and nutrients to cells for respiration and metabolism.
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Removes metabolic waste products like carbon dioxide and urea.
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Helps regulate body temperature and immune responses.
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Supports the transport of hormones and cell-signalling molecules.
Types of Circulatory Systems
Open vs. Closed Circulatory Systems
Open System: Found in insects and molluscs.
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Blood (haemolymph) is pumped into a cavity, bathing organs directly.
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Low pressure, less efficient oxygen transport.
Closed System: Found in vertebrates (e.g., mammals, fish, birds).
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Blood is confined within vessels, creating higher pressure.
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More efficient transport of oxygen and nutrients.
Single vs. Double Circulatory Systems
Single Circulatory System: Found in fish.
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Blood passes through the heart once per circuit.
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Less efficient as oxygenated and deoxygenated blood mix.
Double Circulatory System: Found in mammals and birds.
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Blood passes through the heart twice per circuit.
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Pulmonary circulation: Blood pumped to the lungs from the right ventricle for oxygenation.
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Systemic circulation: Oxygenated blood pumped to body tissues from the left ventricle.
Returning to the heart after travelling to the lungs helps to increase the blood pressure. This leads to more efficient transport of oxygen and nutrients in the blood.
The Structure of the Human Circulatory System
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Heart: A muscular pump with four chambers (right atrium, right ventricle, left atrium, left ventricle).
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Blood vessels:
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Arteries: Carry blood away from the heart (thick, muscular walls).
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Veins: Carry blood towards the heart (contain valves to prevent backflow).
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Capillaries: Microscopic vessels where gas and nutrient exchange occurs.
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Blood: Consists of red blood cells (oxygen transport), white blood cells (immune function), platelets (clotting), and plasma (fluid carrying nutrients, hormones, and waste products).
Key Terms
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Double Circulatory System: Blood passes through the heart twice per circuit.
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Pulmonary circulation: Movement of blood between the heart and lungs.
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Systemic circulation: Movement of blood between the heart and the rest of the body.
No answer provided.
Explain why horses require a closed, double circulatory system. (3 marks)
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Horses are large animals with a low surface area to volume ratio, requiring an efficient transport system (1 mark).
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A closed circulatory system maintains high pressure, allowing rapid oxygen and nutrient transport to muscles (1 mark).
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A double circulatory system separates oxygenated and deoxygenated blood, ensuring sufficient oxygen is carried to respiring cells (1 mark).
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!