The Role of Water in Circulation (Cambridge International A-Level Biology)

The Role of Water in Blood & Tissue Fluid

Spec point — 8.1.6 · state that water is the main component of blood and tissue fluid and relate the properties of water to its role in transport in mammals, limited to solvent action and high specific heat capacity

Solvent action

• Water is the main component of blood (where it constitutes 95% of plasma, a straw-coloured liquid) and tissue fluid

  • Tissue fluid is formed when plasma passes through capillaries and some of it leaks out, through gaps between the cells in the capillary walls, into the spaces between the body cells
  • Tissue fluid is therefore mainly water

• Water’s properties as a solvent make it ideal for transport in mammals

• For example:

  • Glucose is transported in solution from the small intestine to every cell of the body for respiration
  • Urea is transported in solution from the liver to the kidneys

Specific heat capacity

• Specific heat capacity is a measure of the energy required to raise the temperature of 1 kg of a substance by 1°C

• Water has a high specific heat capacity of 4200 J / Kg °C

  • This means a relatively large amount of energy is required to raise its temperature

• This means that water is able to absorb a lot of heat without big temperature fluctuations

  • This is vital in maintaining temperatures that are optimal for enzyme activity

• Water in blood plasma is also vital in transferring heat around the body, helping to maintain a fairly constant temperature

  • As blood passes through more active (‘warmer’) regions of the body, heat energy is absorbed but the temperature remains fairly constant
  • Water in tissue fluid also plays an important regulatory role in maintaining a constant temperature