Water

Question 1

Hydrogen Bonding

Answer 1

> Water molecules are polar
Electrons are not shared equally between atoms
Oxygen atom - negative charge
Hydrogen atoms - positive charge
The oxygen atom of one molecule is attracted to the hydrogen atoms in a neighbouring molecule - forming a hydrogen bond.

Question 2

Properties of water

Answer 2

> Hydrogen bonds are relatively weak, but occur in large numbers, making them stronger in comparison to other intermolecular forces
Unique properties of water are due to hydrogen bonding
These properties make water essential for life.

Question 3

1. Good Solvent

Answer 3

> Polar water molecules attract and dissolve the polar molecules and ions
Water can then transport dissolved solutes (e.g. in blood or phloem)
Chemical reactions can also occur between these molecules as water is a metabolite.

Question 4

2. High specific heat capacity

Answer 4

> A relatively large amount of energy is required to increase water temperature
This allows for thermal stability inside of organisms and in aquatic environments - (habitats + enzyme activity).

Question 5

3. Large latent heat of vaporisation

Answer 5

> A relatively large amount of energy is needed to change water from a liquid to a gas
This allows for thermoregulation of organisms - sweating and panting cools down organisms when water on the body is evaporated.

Question 6

4. Strong Cohesion

Answer 6

> Hydrogen bonds cause water molecules to be attracted to each other and therefore ‘stick’ and flow together
This allows for water to move in columns up xylem for efficiency
This also provides surface tension so small invertebrates can move on the water surface.

Question 7

5. Low density solid

Answer 7

> When water freezes to become ice, hydrogen bonds become fixed, but further apart
This produces a giant rigid, but open structure that is less dense than water, so ice floats
This provides an insulating layer for aquatic habitats during cold climates
The ice surface also provides habitats for other organisms (e.g. polar bears).

Question 8

Water for life: Transport Medium

Answer 8

> Strong cohesion of molecules allows for capillary action (movement of water in columns against gravity)
So water can move efficiently up xylem and in blood so dissolved molecules and ions can be transported quicker.

Question 9

Water for life: Temperature Stability

Answer 9

> High specific heat capacity + latent heat of vaporisation helps to buffer temperature changes due to chemical reactions
So temperatures are relatively constant in cellular environments and enzymes don’t denature.