AQA GCSE Biology Foundation (8461), Foundation tier · Organisation › Animal tissues, organs and organ systems
Practise Blood. 8 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Blood is a tissue made of plasma, red blood cells, white blood cells and platelets. You need to know what each part does, recognise the cells in a photograph or diagram, and explain how they are adapted to their functions.
Key facts
Blood = a tissue: plasma + red blood cells + white blood cells + platelets
Plasma transports CO2, urea, glucose, amino acids, hormones and antibodies
Red blood cell: haemoglobin carries oxygen; biconcave disc; no nucleus
Biconcave → large surface area → fast diffusion of oxygen
White blood cell: has a nucleus; phagocytosis, antibodies, antitoxins
Platelets: fragments of cells, no nucleus; help the blood to clot
Notes
What blood is made of
Blood is a tissue. It is made of a liquid called plasma, in which red blood cells, white blood cells and platelets are suspended.
Plasma is a pale yellow liquid that transports dissolved substances: carbon dioxide from the organs to the lungs, urea from the liver to the kidneys, soluble products of digestion (e.g. glucose, amino acids) from the small intestine to the cells, hormones and antibodies.
Red blood cells
Red blood cells carry oxygen from the lungs to the body cells.
They contain haemoglobin, a red protein that binds to oxygen in the lungs and releases it in the tissues.
They are biconcave discs: this shape gives a large surface area to volume ratio, so oxygen diffuses in and out quickly.
They have no nucleus, which leaves more space for haemoglobin, so each cell carries more oxygen.
They are small and flexible, so they can squeeze through narrow capillaries.
White blood cells and platelets
diagram
White blood cells are part of the immune system and defend the body against pathogens. They are larger than red blood cells, far fewer, and have a nucleus.
Some white blood cells engulf and digest pathogens (phagocytosis). Others produce antibodies or antitoxins.
Platelets are small fragments of cells with no nucleus. They help the blood to clot at a wound. The clot stops blood loss and stops pathogens getting in.
In a stained blood photo, red blood cells are the most numerous and look paler in the middle, white blood cells have a darkly stained nucleus, and platelets are tiny specks between them.
Red blood cells, a white blood cell and platelets (not to scale)
How to answer each type of question
Recall the function of a blood component
1 mark eachGrade 4
Match each part to one job: transport (plasma), oxygen (red cells), defence (white cells), clotting (platelets).
Be specific: red blood cells carry oxygen, not just 'gases' or 'blood'.
Example. Give the function of: (a) platelets (b) plasma (c) red blood cells
Show the model answerHide the model answer
(a) help the blood to clot (1) (b) transports dissolved substances, e.g. glucose / carbon dioxide / urea (1) (c) carry oxygen (1)
Identify blood cells in a photo or diagram
1 to 2 marksGrade 5
Red blood cells: the most numerous, no nucleus, paler in the middle.
White blood cells: larger and fewer, with a clearly stained nucleus (often lobed).
Platelets: tiny fragments between the cells.
Example. A student looks at a stained blood smear under a microscope. Cell X is larger than most of the other cells and has a dark purple, lobed nucleus. (a) Identify cell X. (b) Give one way cell X protects the body.
Saying plasma carries oxygen. Red blood cells carry oxygen; plasma carries dissolved substances such as carbon dioxide, urea and glucose.
Calling platelets cells. They are fragments of cells.
Saying white blood cells 'eat germs' instead of using the scientific words: engulf, phagocytosis, pathogens, antibodies, antitoxins.
Saying red blood cells have a large surface area without linking it to faster diffusion of oxygen.
Calling blood an organ. Blood is a tissue.
More tips
Memory tricks
Red = oxygen; White = war on pathogens; Platelets = plug the wound; Plasma = the transport liquid.
Neither red blood cells nor platelets have a nucleus, but for different reasons: red cells make room for haemoglobin; platelets are only bits of cells.
Photo check: red blood cells hugely outnumber white blood cells.
Exam technique
Use the word haemoglobin in any answer about red blood cells carrying oxygen.
For 'explain how it is adapted' questions, give feature + effect for each pair of marks.
If a photo or drawing is given, justify your identification with what you can see: size, nucleus and shape.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Name the four components of bloodPlasma, red blood cells, white blood cells and platelets.
Grade 4
State the function of each componentPlasma transports dissolved substances, red blood cells carry oxygen, white blood cells defend against pathogens and platelets help the blood clot.
Grade 5
Identify blood cells in a photo or diagramRed blood cells are biconcave discs with no nucleus, white blood cells are larger with a nucleus, and platelets are tiny fragments.
Grade 5
List substances transported by the plasmaCarbon dioxide, urea, soluble products of digestion such as glucose and amino acids, hormones and antibodies.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Blood is a tissue. Name the liquid part of the blood.
plasma
Urea is transported in the plasma. Complete the sentence. Urea is carried from the ____________ to the ____________ .
liver; kidneys
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Blood is a tissue.
(a) Name the liquid part of the blood.[1]
(b) Which part of the blood helps the blood to clot at a wound? Tick (✓) one box.[1]
Plasma
Platelets
Red blood cells
White blood cells
(c) Name the substance in red blood cells that combines with oxygen.[1]
(d) Give one function of white blood cells.[1]
Show the answer and mark scheme
(a)Answer: plasma
plasma
(b)Answer: Platelets
(c)Answer: haemoglobin
haemoglobin
(d)
to protect the body against pathogens / infection (e.g. by ingesting pathogens or producing antibodies)
Question 2Medium5 marks
Red blood cells are adapted to carry oxygen.
(a) Red blood cells have no nucleus. Explain how this helps them to carry out their function.[2]
(b) Red blood cells are shaped like biconcave discs. Explain the advantage of this shape.[2]
(c) Red blood cells are small and flexible. Suggest why this is important.[1]
Show the answer and mark scheme
(a)
there is more space for haemoglobin
so more oxygen can be carried
(b)
it gives a large surface area (to volume ratio)
so oxygen diffuses into and out of the cell faster