The Blood (Edexcel IGCSE Biology)

Components of Blood

Spec point — 2.59 · describe the composition of the blood: red blood cells, white blood cells, platelets and plasma

• Blood consists of red blood cells, white blood cells, platelets 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
• The remaining fraction consists of white blood cells and platelets

Blood micrograph

Composition of human blood

Components of the Blood Table

Plasma

Spec point — 2.60 · understand the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy

• 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 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- urea is a waste substance 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 - heat energy (created in respiration) is transferred to cooler parts of the body or to the skin where heat can be lost

Red Blood Cells

Spec point — 2.61 · understand how adaptations of red blood cells make them suitable for the transport of oxygen, including shape, the absence of a nucleus and the presence of haemoglobin

• Red blood cells are specialised cells which carry oxygen to respiring cells

• They are adapted for this function in three key ways:

  • Red blood cells are packed with haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin
  • They have no nucleus which allows more space for haemoglobin to be packed in
  • Red blood cells have a biconcave disc shape, which means they are thinner in the middle than at the edges. This shape gives them a larger surface area to volume ratio, allowing oxygen to diffuse in and out quickly and efficiently.

Red blood cells