Water and inorganic ions

Question 1

Water is cohesive

Answer 1

Polar so hydrogen bonds form between water molecules, so water molecules tend to stick together.

Column of water doesn’t break when pulled up a narrow tube eg xylem during transpiration

Produces surface tension at an air-water surface so invertebrates can walk on water.

Question 2

Water as a solvent

Answer 2

Polar so it can separate (dissolve) ionic compounds as +ve end attracted to -ve ion and negative end attracted to positive ion

Can dissolve other substances so it:
- acts as a medium for metabolic reactions (which can happen in water)
- acts as a transport medium eg in xylem to transport nitrates which are needed to make amino acids

Question 3

Water as a metabolite

Answer 3

Water is reactive

Condensation releases water and forms a chemical bond; hydrolysis requires water to break a bond

Question 4

Inorganic ions

Answer 4

Occur in the solution of cytoplasm and the body fluids of organisms, differing concentrations and roles

Question 5

Phosphate ion role in organisms PO4 3-

Answer 5

Attached to other molecules as a phosphate group, for example:
- in DNA nucleotides, enabling nucleotides to join together forming phosphodiester bonds
- in ATP: bonds between these store/release lots of energy

Question 6

Hydrogen ion role in organisms H+

Answer 6

Maintain pH levels in the body
- too much H+ acidic
- too little H+ alkaline

Affects rate of enzyme-controlled reactions as it can cause enzymes to denature

Question 7

Iron ion role in organisms Fe2+

Answer 7

Component of (haem group of) haemoglobin which is contained in red blood cells

Transports oxygen around the body. Oxygen temporarily binds to it, so it becomes Fe3+

Question 8

High latent heat of vaporisation of water

Answer 8

Due to the many hydrogen bonds (polar molecule) between water molecules, it can absorb a large amount of energy before breaking when water evaporates

Effective cooling mechanism, helps organisms maintain body temperature

Question 9

High specific heat capacity of water

Answer 9

Due to the many hydrogen bonds (polar molecule) between water molecules, it can absorb a large amount of energy before its temperature changes.

Good habitat for aquatic organisms eg lakes as temperature is more stable

Organisms mainly made of water so helps maintain a constant internal body temperature - important as temperature affects enzyme activity

Question 10

Water polarity

Answer 10

Water is a polar molecule

Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules

So hydrogen bonds form between water molecules