The Role of Water in Circulation (Cambridge (CIE) AS Biology): Revision Note

The role of water in blood & tissue fluid

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 into the spaces between the cells in the walls of the capillary

  • 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