4.1 - Water

Properties of Water

• Polarity of water
  • Water is an inorganic compound consisting of hydrogen (H) and oxygen (O).
  • A water molecule is polar because the shared electrons between oxygen and hydrogen are attracted towards the more electronegative oxygen atom.
  • This polarity produces hydrogen bonds between water molecules and allows water to act as a universal solvent.
  • Solutes such as glucose and electrolytes can therefore be transported across plasma membranes into cells for biochemical reactions.
• Cohesive and adhesive forces of water
  • Cohesive force: Water molecules attach to one another.
  • Adhesive force: Water molecules attach to other surfaces.
  • Both forces produce capillary action, allowing water to enter and move along narrow spaces such as xylem vessels.
• Specific heat capacity of water
  • Water has a high specific heat capacity of $4.2{\text{ kJ kg}}^{-1}{}^{\circ }{\text{C}}^{-1}$.
  • $4.2\text{ kJ}$ of heat energy is required to raise the temperature of $1\text{ kg}$ of water by $1{}^{\circ }\text{C}$.
  • Water absorbs a large amount of heat energy with only a small rise in temperature; this helps maintain the body temperature of organisms.

Importance of Water in a Cell

• Acts as a universal solvent.
• Enables solutes such as glucose and electrolytes to be transported across plasma membranes into cells for biochemical reactions.
• Produces capillary action through cohesive and adhesive forces.
• Helps maintain the body temperature of organisms through its high specific heat capacity.