Knowledge Organiser
Part of Blood Components and Vessels · GCSE GCSE Biology revision
This topic summary covers Knowledge Organiser within Blood Components and Vessels for GCSE Biology. Blood composition, red and white blood cells, platelets, plasma, blood vessel structure and function, adaptations for transport It is section 15 of 16 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 15 of 16
Practice
18 questions
Recall
24 flashcards
Knowledge Organiser
Key Terms
- Plasma — liquid component (90% water)
- Erythrocyte — red blood cell
- Leucocyte — white blood cell
- Haemoglobin — oxygen-carrying protein
- Phagocytosis — engulfing pathogens
- Platelet — clotting cell fragment
- Fibrinogen — clotting protein in plasma
- Fibrin — insoluble clot mesh
- Lumen — central space inside a vessel
Must-Know Facts
- Blood is 55% plasma, 45% cells
- Red cells: biconcave, no nucleus, packed with haemoglobin
- Phagocytes engulf pathogens; lymphocytes produce antibodies and antitoxins
- Platelets are cell fragments, not whole cells
- Arteries: thick wall, small lumen, no valves
- Veins: thin wall, large lumen, valves present
- Capillaries: one cell thick, tiny lumen, branching network
- Clotting sequence: damage → platelet plug → fibrin mesh
Common Mistakes
- Saying deoxygenated blood is blue: Blood is always red — oxygenated blood is bright red, deoxygenated blood is dark red. The blue colour in diagrams is only a convention. Writing "blue blood" in an exam answer is never awarded a mark.
- Confusing artery/vein in the pulmonary circulation: The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs; the pulmonary veins carry oxygenated blood back to the left atrium. This is the opposite of every other artery-vein pair — learn it as the exception.
- Describing phagocytosis without using the correct term: Writing "white blood cells eat/absorb the pathogen" is not awarded the mark — you must use the term "phagocytosis" or "engulf." The mark scheme requires biological vocabulary.
- Saying platelets are cells: Platelets are fragments of larger cells (megakaryocytes) — they have no nucleus. Calling them "cells" is incorrect. AQA mark schemes specifically award marks for stating they are cell fragments.
- Describing red blood cell adaptations without linking to function: Stating "biconcave disc shape" alone scores 0 at explanation level. You must add the function: "increases surface area to volume ratio, so oxygen diffuses in and out more quickly." Every adaptation needs a reason.
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Practice Questions for Blood Components and Vessels
What is the main function of red blood cells?
Explain how red blood cells are adapted for their function of transporting oxygen.
Quick Recall Flashcards
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