water

Question 1

what is water? (2)

Answer 1

water is the main constituent of all organisms. we, like all mammals, are around 65% water.

Question 2

why is water important?

Answer 2

life on earth arose from water and is still where a large amount of that life lives today

Question 3

what are two basic characteristics of water?

Answer 3

• it can produce turgor pressure in plant cells as it’s not easily compressed
• it is transparent allowing light to travel through water to aquatic plants or through the eye to reach the retina

Question 4

what are 6 characteristics of water and explanations of them?

Answer 4

DIPOLAR PROPERTIES OF WATER (3)
- a water molecule consists of two atoms of hydrogen and one oxygen.
- the molecule has no overall charge but the hydrogen has a slight positive charge whilst the oxygen has a slight negative one, therefore is dipolar (two poles).
- as opposite poles attract, weak hydrogen bonds form between water molecules.

WATER IN METABOLISM (3)
- water is essential in the hydrolysis and condensation reactions that take place eg protein hydrolysis to amino acids.
- many chemical reactions take place in an aqueous solution eg the cytoplasm of the cell.
- water is a raw material for photosynthesis.

HIGH SPECIFIC HEAT CAPACITY OF WATER (2)
- as the molecules are bonded together, it takes more heat to separate them. if the molecules weren’t attached, they’d exist as a gas (water vapour) on earth.
- due to the high specific heat capacity of water, it acts as a good buffer against sudden temperature changes. this means that an aquatic environment is a temperature stable one. as organisms are largely water, they are buffered against changes in temperature.

LATENT HEAT VAPORISATION OF WATER (1)
- hydrogen bonding between water results in the need for a high amount of energy to evaporate it. this energy is called the latent heat vaporisation of water. this is important in animals as it results in the removal of body heat when sweating.

COHESION AND SURFACE TENSION (2)
- the hydrogen bonding between water molecules is a cohesive force. this cohesion allows water to be pulled through a tube such as the xylem of a plant.
- when water meets air this cohesive force pulls the water molecules towards the body of water creating surface tension. this is important to support small organisms such as pond skaters.

WATER AS A SOLVENT (3)
water dissolves other substances :
- gases eg oxygen and carbon dioxide
- wastes such as ammonia and urea
- inorganic ions and hydrophilic molecules eg amino acids, ATP.