Water and its functions

Question 1

Describe the polarity of a water molecule

Answer 1

• It is dipolar as it has both positive and negative poles.
• The oxygen atom has a slightly negative charge whilst the hydrogens have a slight positive charge.

Question 2

Describe the bonding between water molecules

Answer 2

The negative pole of one water molecule attracts the positive pole of another and forms a hydrogen bond. Although these bonds are weak individually, together they from important forces that help water molecules stick together.

Question 3

Why does water have a high specific heat capacity

Answer 3

Because the hydrogen bonding holds the molecules together

Question 4

Why is heat capacity an important property of water

Answer 4

• Water has a high specific heat capacity
• this means it can act as a buffer against sudden temperature variations, making the aquatic environment a temperature stable one.
• As organisms are mostly water is also buffers them against sudden temperature changes.

Question 5

Why is waters latent heat of vaporisation an important property

Answer 5

• Hydrogen bonding between water molecules means that it requires a lot of energy to evaporate.
• Evaporation of water such as sweat in mammals is a very effective method of cooling because body heat is used to evaporate the water.

Question 6

Describe how the cohesion and surface tension of water is an important property

Answer 6

• With it’s hydrogen bonding, water has strong cohesive forces and these allow it to be pulled through a tube such as the xylem vessels in plants.
• Similarly, when water molecules meet the air they are pulled back towards the body of water (surface tension) and this means that the water surface acts like a skin and is strong enough to support small organisms such as pond skaters.

Question 7

List the key properties of water

Answer 7

1) Its polarity
2) Specific heat capacity
3) latent heat of vaporisation
4) cohesion and surface tension
5) it is a metabolite

Question 8

How is water important in metabolism

Answer 8

• It is involved in hydrolysis and condensation reactions
• Chemical reactions take place in an aqueous medium
• water is a major raw material in photosynthesis

Question 9

Why is water a useful solvent

Answer 9

It readily dissolves in many other substances such as:
- gases such as oxygen and carbon dioxide
- wastes such as ammonia and urea
- inorganic ions and small hydrophilic molecules such as amino acids,monosachharides and ATP
- enzymes, whose reactions take place in solutions

Question 10

What are some other key features of water

Answer 10

• Its evaporations cools organisms and allows them to controls their temperature
• It is not easily compressed and therefore provides support for example the hydrostatic skeleton of animals such as the earthworm and turgid pressure in herbaceous plants.
• It is transparent and therefore aquatic plants can photosynthesise and light rays can penetrate the jelly-like fluid that fills the eyes and so can reach the retina

Question 11

How are inorganic ions found in organisms

Answer 11

The occur in solution in the cytoplasm of cells, and in bodily fluids as well as as part of larger molecules. They can be found in high and low concentrations.

Question 12

List some examples of inorganic ions and their functions

Answer 12

• Iron ions in haemoglobin which help to transport oxygen
• Phosphate ions that have a structural role in DNA molecules
• Sodium ions in the co-transport of glucose
• Hydrogen ions in determining the PH of a solution