Edexcel IGCSE Biology

Revision Notes

2.8.6 Human Transport Systems: Red Blood Cells & Plasma

Red Blood Cells

  • Red blood cells are specialised cells which carry oxygen to respiring cells
  • They are adapted for this function in 3 key ways
    • They are full of haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin
    • They have no nucleus which allows more space for haemoglobin to be packed in
    • The shape of a red blood cell is described as being a ‘biconcave disk’  this shape gives them a large surface area to volume ratio to maximise diffusion of oxygen in and out

Red Blood Cells, IGCSE & GCSE Biology revision notes

Red blood cells


  • Plasma is a straw coloured liquid which the other components of the blood are suspended within
  • Plasma is important for the transport of many substances including:
    • Carbon dioxide – the waste product of respiration, dissolved in the plasma as hydrogencarbonate ions and transported from respiring cells to the lungs
    • Digested food and mineral ions – dissolved particles absorbed from the small intestine and delivered to requiring cells around the body
    • Urea – the waste substance produced in the breakdown of proteins by the liver. Urea is dissolved in the plasma and transported to the kidneys
    • Hormones – chemical messengers released into the blood from the endocrine organs (glands) and delivered to target tissues/organs of the body
    • Heat energy – created in respiration (an exothermic reaction), heat energy is transferred to cooler parts of the body or to the skin where heat can be lost

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.

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