Topic 1.3 - Lipids

Question 1

Name 2 groups of lipids

Answer 1

1) Triglycerides

2) Phospholipids

Question 2

Describe the structure of a fatty acid (2)

Answer 2

1) Variable R group - hydrocarbon chain

2) COOH = Carboxyl group

Question 3

Describe the difference between saturated and unsaturated fatty acids

Answer 3

Saturated - no double carbon bonds in hydrocarbon chain, all carbons fully saturated with hydrogen

Unsaturated - One or more double carbon bond in hydrocarbon chain

Question 4

Describe how triglycerides form (4)

Answer 4

1) 1 glycerol molecule and 3 fatty acids

2) Condensation reaction

3) Removing 4 water molecules

4) Forming 3 ester bonds

Question 5

What is the function of triglycerides?

Answer 5

Energy storage

Question 6

How are the properties of triglycerides related to their structure (2)

Answer 6

1) High ratio of C-H bonds to carbon atoms in hydrocarbon chain
- So used in respiration to release more energy than same mass of carbohydrates

2) Hydrophobic / non polar fatty acids so insoluble in water
- So no effect on water potential of cell

Question 7

Describe the difference between the structure of triglycerides and phospholipids

Answer 7

One of the fatty acids of a triglyceride is substituted by a phosphate containing group

Question 8

What is the function of phospholipids?

Answer 8

To form a bilayer in the cell membrane, allowing diffusion of lipid soluble (non-polar) or very small substances and restricting movement of water soluble (polar) or larger substances

Question 9

Describe how the properties of phospholipids relate to their structure (2)

Answer 9

1) Phosphate heads are hydrophilic
- Attracted to water so point to water either side of membrane

2) Fatty acid tails are hydrophobic
- Repelled by water so point away from water / to interior of membrane

Question 10

Describe the test for lipids (2)

Answer 10

1) Add ethanol, shake then add water

2) Positive result = milky white emulsion