Module 2: lipids, oils & water

Question 1

Describe the structure of a triglyceride ( include details of saturated and unsaturated fats)

Answer 1

One glycerol molecule.
Three fatty acid tails.
The fatty acids can be saturated or unsaturated.
Saturated fatty acids only contain single bonds between the carbon atoms.
Unsaturated fatty acids have at least one double bond between the carbon atoms.

Question 2

Describe how triglycerides are formed

Answer 2

A condensation reaction occurs between the glycerol molecule and the fatty acids.
A hydrogen atom is removed from the glycerol.
An OH group is removed from the fatty acids to form three molecules of water.
An ester bond is formed.

Question 3

Describe the functions of triglycerides and explain how their structure aids the function

Answer 3

Energy storage molecules.
They are insoluble.
Therefore don’t affect the water potential of the cell.
The fatty acid tails contain a lot of chemical energy.
This energy is released when the bonds are broken.

Question 4

Describe the structure of a phospholipid

Answer 4

One glycerol molecule.
One phosphate group.
Two fatty acid tails.
The phosphate group is hydrophilic and the fatty acids are hydrophobic.

Question 5

Describe the functions of phospholipids and explain how their structure aids the function

Answer 5

Form the bilayer in membranes.
The phosphate heads are hydrophilic and the fatty acid tails are hydrophobic.
Therefore the phosphate heads face outwards and the tails face inwards, away from the water.
The fatty acid tails act as a barrier to water soluble substances.

Question 6

Describe the functions of cholesterol and explain how its structure aids the function

Answer 6

Strengthen the plasma membrane.
Small, flat shape.
Therefore it can fit in between the tails of the fatty acids in the membrane.
The cholesterol can bind to the tails of the phospholipids.
Therefore making the membrane less fluid and more rigid.

Question 7

Describe the biological test for lipids

Answer 7

Shake the sample with ethanol.
Pour the solution into water.
If lipid is present the solution turns white.
If no lipid is present the solution stays clear.

Question 8

Draw a diagram of 3 water molecules (include the partial charges, a covalent bond and a hydrogen bond)

Answer 8

Draw it in ur mind

Question 9

Describe properties of water. For each one, explain how it aids living organisms

Answer 9

1. Ice is less dense than water.
   Ice will float and insulate the water underneath.
   The whole body of water does not freeze, meaning aquatic mammals can survive.
2. Water has a high specific heat capacity.
   Because the hydrogen bonds can absorb a lot of energy.
   Therefore it is thermally stable, making it a good habitat, particularly for ectotherms.
3. Water has a high latent heat of evaporation.
   Because it takes a lot of energy to break the hydrogen bonds.
   Therefore, can be used to cool organisms down via sweating.
4. Water has high cohesion.
   Because it is a polar molecule.
   Therefore it flows by mass flow through the xylem and phloem by cohesion tension.
5. Water is a good solvent.
   Because it is a polar molecule.
   Therefore ions and glucose easily dissolve and can be transported.