Biology › Section P · Breathing, circulation, and excretion › Topic P.4
Circulatory systems and blood
Diffusion works over a fraction of a millimetre, but many of your cells sit more than a metre from your lungs and gut. Circulatory systems bridge that gap, and blood is the fluid that carries gases, nutrients, wastes, heat and defenders to every tissue.
In this topic
- When diffusion is not enough
- Open and closed systems
- Vertebrate hearts: from two chambers to four
- Worked example: single versus double circulation
- What blood is made of
- Worked example: reading a centrifuge tube
- Erythrocytes: built to carry
- White blood cells and platelets
- How blood clots
- Blood groups
- Common mistakes to avoid
- Key takeaways
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