Water

Question 1

How do hydrogen bonds form between water molecules?

Answer 1

Water is polar

• O is more electronegative than H, so attracts electron density in covalent bond more strongly
• forms O slightly negative charged
• forms H slightly positive charged

The intermolecular forces of attraction between a lone pair on the O(-) of one molecule and the H(+) on the adjacent molecule

Question 2

7 biologically important properties of water

Answer 2

Reaches maximum density at 4°c
High surface tension
Incompressible 
Metabolite/ solvent for chemicals reactions in the body
High specific heat capacity 
High latent heat of vaporisation
Cohesion between molecules

Question 3

Why is the incompressible nature of water important for organisms

Answer 3

Provides turgidity to plant cells
Provides hyrdostatic skeleton for some small animals
EG earthworms

Question 4

Explain why ice floats on water. Why is this important for organisms?

Answer 4

Ice is less dense than water because H-bonds hold molecules in fixed positions further away from each other.

Insulates water in artic climates so aquatic organisms can survive. Water act as a habitat.

Question 5

Why is high surface tension of water important for organisms?

Answer 5

Slows water loss due to transpiration in plants.

Water rises unusually high narrow tubes, lowering demand on root pressure.

Some insects can ‘skim’ across the surface of water.

Question 6

Why is water an important solvent for organisms?

Answer 6

Polar universal solvent dissolves & transports charged particles involved in intra & extracellular reactions

Question 7

Why are the high specific heat capacity and latent of vaporisation of water important for organisms?

Answer 7

Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity

Cooling effect when water evaporates from skin surface such as sweat/ from mouth when panting