Blood and Blood Components — AQA GCSE Biology
Blood is a tissue made of a liquid (plasma) carrying three types of cell fragment and cells.
Plasma
Plasma is the straw-coloured liquid that transports dissolved substances:
- carbon dioxide (from cells to the lungs),
- urea (from the liver to the kidneys),
- digested food (e.g. glucose and amino acids), hormones, antibodies and heat.
Red blood cells
- Carry oxygen from the lungs to the body's cells.
- Contain the red pigment haemoglobin, which binds oxygen to form oxyhaemoglobin.
- Adaptations: a biconcave disc shape (large surface area), no nucleus (more room for haemoglobin), and they are small and flexible.
White blood cells
Part of the immune system; they defend against pathogens by:
- phagocytosis (engulfing pathogens),
- producing antibodies, and
- producing antitoxins. Unlike red cells, they have a nucleus.
Platelets
Small cell fragments (no nucleus) that help the blood to clot at a wound, forming a scab that prevents blood loss and stops pathogens entering.
Exam tips
- Learn what plasma transports.
- Explain red blood cell adaptations (biconcave, no nucleus, haemoglobin) and link to oxygen transport.
- White blood cells defend the body (phagocytosis, antibodies, antitoxins).
- Platelets are for clotting.