Blood Composition (OCR Gateway GCSE Biology: Combined Science)

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Red Blood Cells

Blood as a transport system

  • The role of blood in the body is to act as a transport system carrying useful substances to every cell of the body, and carrying harmful waste substances to other organs for processing and/or excretion
    • It also plays a vital role in transferring heat from “active” organs to cooler parts of the body (such as the extremities – hands and feet)
      • Blood consists predominantly of red blood cells and plasma
        • Over half of the volume of the blood is made up of plasma
        • The majority of the other half is made up of red blood cells
      • Less than 1% of blood contains white blood cells and platelets

Blood micrograph, IGCSE & GCSE Biology revision notes

Blood micrograph

The components of the blood 1, downloadable IGCSE & GCSE Biology revision notes

Composition of human blood

Red blood cells carry oxygen

  • Red blood cells are specialised cells that carry oxygen from the lungs to cells throughout the body
  • The structure of red blood cells are adapted for this function in 3 key ways
    • Red blood cells are small with a 'biconcave disk' shape which gives them a large surface area to volume ratio to maximise diffusion of oxygen in and out
    • 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
    • Their small size and flexibility allows them to pass through capillaries

Red Blood Cells, IGCSE & GCSE Biology revision notes

Red blood cells

Blood Plasma

  • 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:
    • Red blood cellswhite blood cells and platelets
    • Water
    • Carbon dioxide - the waste product of cellular respiration
    • Digested food and mineral ions - absorbed from the small intestine and delivered to 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
    • Antibodies - which are special proteins to help fight infection
    • 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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Author: Phil

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.