Water

Question 1

What type of molecule is water?

Answer 1

• DIPOLAR

(A polar molecule)

Question 2

How is one Water MOLECULE attracted to another Water Molecule?

(What type of bond?)

Answer 2

• HYDROGEN bonds

-opposites attract: Hydrogen (of one molecule) - Oxygen (another molecule)

Question 3

Define COHESION.

What type of bonding in water causes this? What does this allow?

Give an example.

Answer 3

Cohesion is the tendency of molecules to stick together.

H bonding in H2O = large cohesive forces = allows it to be pulled up through a tube;

E.g xylem vessel in plants

Question 4

What is the reason for the boiling point of water to be so high?

Answer 4

BC water molecules stick together, it takes more energy (heat) to separate them than would be needed if they did not bond to one another.

For this reason the boiling point of water is higher than expected.

Question 5

If water didn’t have H bonds, what state of matter would it be at room temp?

Answer 5

Without its hydrogen bonding, water would be a gas (water vapour) at the temperatures commonly found on Earth and life as we know it would not exist.

Question 6

Why does water have a high specific heat capacity?

And what effect does it cause in animals?

Answer 6

High specific heat capacity bc H bonds = more energy to heat a given mass of water.

= H2O acts as a buffer against sudden temperature variations, making the aquatic environment a temperature-stable one.

As organisms are mostly water, it also buffers them against sudden temperature changes especially in terrestrial environments.

Question 7

What is latent heat of vaporisation? And of water?

Give an example of this in mammals.

Answer 7

H bonding between water molecules = a lot of energy to evaporate 1 gram of water require.

This energy is called the latent heat of vaporisation.

Evaporation of water such as sweat in mammals is therefore a very effective means of cooling because body heat is used to evaporate the water.

Question 8

What is surface tension?

Answer 8

Where water molecules meet in air
to be pulled back into the body of water rather than escaping from it.

E.g the water surface can act as skin and strong enough to support small organisms like pond skaters

Question 9

Give 4 ways water is used in METABOLISM.

Answer 9

• Water is used to break down many complex molecules by hydrolysis, for example, proteins to amino acids.
• Water is also produced in condensation reactions.
• Chemical reactions take place in an aqueous medium.
• Water is a major raw material in photosynthesis.

Question 10

List 4 things/ways that water acts as a SOLVENT.

Answer 10

• gases such as oxygen and carbon dioxide
• wastes such as ammonia and urea
• inorganic ions and small hydrophilic molecules such as amino acids, monosaccharides and ATP
• enzymes, whose reactions take place in solution.

Question 11

List 4 other important features of Water.

Answer 11

• Its evaporation cools organisms and allows them to control their temperature.

-Not easily compressed ∴ provides support, for e.g. the hydrostatic skeleton of animals such as the earthworm and turgor pressure in herbaceous plants.

• Transparent =

1. aquatic plants can photosynthesise
2. light rays can penetrate the jelly-like fluid that fills the eye and so reach the retina.

Question 12

Where are inorganic ions found? (3 places)

Answer 12

• Found in organisms, where they occur in:

1. the solution in the cytoplasm of cells
2. body fluids
3. part of larger molecules.

They may be in concentrations that range from very high to very low.

Question 13

Name some inorganic ions found in our body and explain their functions. (4)

Answer 13

• Iron ions: in haemoglobin —> transport of oxygen.
• Phosphate ions –> that forms a structural role in DNA molecules and a role in storing energy in ATP molecules
• Hydrogen ions = important in determining the pH of solutions and ∴ the functioning of enzymes.
• Sodium ions = important in the transport of glucose and amino acids across plasma membranes.

Question 14

Describe 5 key features of Water

Answer 14

• is a metabolite in many metabolic reactions e.g. condensation and hydrolysis reactions
• is an important solvent in which metabolic reactions occur
• has a relatively high 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.