water

Question 1

name several properties of water

Answer 1

is an important solvent in which metabolic reactions occur
* is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
* has a relatively high (specific) heat capacity, buffering changes in temperature
* has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
* has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air

Question 2

water is a dipole molecule

Answer 2

has a delta negative on the oxygen
has a delta positive on the hydrogen

Question 3

water as a solvent

Answer 3

As a result, polar (charged) molecules dissolve in water.
In fact more molecules dissolve in water compared to any other liquid, so we call water the “universal solvent”.
It’s one of the major components of the cytoplasm, because it allows chemicals and enzymes to dissolve and so essential chemical reactions can occur.

Question 4

hydrogen bonds

Answer 4

Because water is a dipole, the d- Oxygen of one water molecule is attracted to the d+ Hydrogen of another water molecule, forming a hydrogen bond.

This is known as cohesion (when H bonds form between water molecules).

H bonds allow surface tension to be created, insects like pond-skaters walk on water because they are light enough not to break the H bonds between water molecules.

Water also shows adhesion (when H bonds form between water and another other types of molecule)
Cohesion and adhesion allows water to form continuous colums, in the xylem vessels of plants.

Although individually Hydrogen bonds are weak compared with a covalent bond, they form in large numbers in water causing important forces that give water its unusual properties.

Question 5

water as metabolite

Answer 5

• Hydrolysis reactions and photosynthesis use water
• Condensation reactions and respiration produce water
• Break down of large molecules –hydrolysis
• Making polymers – condensation
• Water used in photosynthesis (to make oxygen)
• Chemical reactions take place in an aqueous (containing water) medium
• Enzymes and substrates dissolve and so can react

Question 6

specific heat capacity

Answer 6

• Water requires a lot of heat energy to heat it up, because it has a lot of H bonds.
• Water has a higher specific heat capacity than air. So it takes more energy to heat water than air.
• Habitats in water (lakes, ponds etc) can resist temperature fluctuations (stabilises external temperatures)
• So the organisms enzymes always have their optimum temperature to work
• As organisms cells are mostly (70%) water, it protects them against sudden temperature change too

Question 7

latent heat of vapouristion of water

Answer 7

• Takes a lot of heat energy to break H bonds in water
• Hydrogen bonds increase the energy required to evaporate water
• Lots of body heat is required to evaporate a small volume of sweat/water, which therfore lowers the internal temperature of the organism

Question 8

cohesion and surface tension of water

Answer 8

• Water molecules stick together in a process known as cohesion due to weak hydrogen bonding
• This surface tension can be enough to support small organisms
• This can allow water to be pulled up a thin tube e.g. xylem vessels in plants
• Also water will be pulled back into a body of water rather than escaping it

Question 9

Water as a solvent

Answer 9

• Water can dissolve other substances:

o Gases e.g. oxygen and carbon dioxide – so oxygen can be transported from the lungs to the respiring tissues, and carbon dioxide can be transported from the respiring tissues to the lungs
o Waste such as ammonia and urea – made in the cells to be transported to the kidneys and excreted (urine formation)
o Inorganic ions, amino acids, monosaccharides and ATP (link to osmosis)
o Enzymes (globular proteins) dissolve in water

Question 10

other properties of water

Answer 10

• When water freezes, it becomes less dense.
• It has the same mass (Kg) but it takes up a bigger
  volume (3D space) because the water molecules form crystalline structures (density = mass / volume).

This is good because ice forms:
* Habitats for animals
* Insulates the water below and stops is freezing
(allowing nutrients to still be cycled)

• Not easily compressed can so provide support
  o Support (turgor) in plants
  o Hydroskeleton in worms
• Transparent so light can penetrate through it
  o Plants underwater can photosynthesise
  o Light can pass through the eye ball