1.7 Water

Question 1

How hydrogen bonding occurs between water molecules

Answer 1

• water is polar
• slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules
• so hydrogen bonds form between water molecules

Question 2

Properties of water

Answer 2

High specific heat capacity

High latent heat of evaporation

Cohesive

Solvent

Metabolite

Important solvent in which metabolic reactions occur

Question 3

High specific heat capacity

Answer 3

Polar so many H bonds form between water molecules

These allow water to absorb a relatively large amount of heat energy before its temperature changes

Buffers changes in temperature

Question 4

High latent heat of evaporation

Answer 4

Polar so many H bonds form between water molecules

These can absorb a lot of energy before breaking, when water evaporates

So, helps organisms maintain a constant body temperature through cooling mechanisms

Question 5

Cohesive

Answer 5

Polar so many H bonds form between water molecules

So water molecules tend to stick together

So, column of water doesn’t break when pulled up a narrow tube e.g. xylem during transpiration

Question 6

Solvent

Answer 6

Polar (has slightly positive and negative ends)

Can dissolve ionic compounds e.g. NaCl as + end attracted to - ion (Cl-) and negative end attracted to positive ion (Na+)

So, acts as a medium for metabolic reactions & acts as transport medium e.g. in xylem to transport nitrates which are needed to make amino acids

Question 7

Metabolite

Answer 7

Water is reactive

So, condensation releases H2O and forms a chemical bond; hydrolysis requires H2O to break a chemical bond, e.g. amino acids joined by condensation reactions to form polypeptides