Edexcel IGCSE Biology: Double Science 复习笔记 2.8.4 Human Transport Systems: Red Blood Cells & Plasma

• 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

• 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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