1.3 Lipids

Question 1

(Lipids) Describe how to test for in a sample. (3)

Answer 1

1) Dissolve solid samples in ethanol.
2) Add an equal volume of water and shake.
3) Positive result: milky white emulsion forms.

Question 2

(Lipids) How do triglycerides form?

Answer 2

Condensation reaction between 1 molecule of glycerol & 3 fatty acids, forms ester bonds.

Question 3

(Lipids) Describe the features of saturated fatty acids. (4)

Answer 3

• Contain only single bonds
• Straight-chain molecules have many contact points
• Higher melting point = solid at room temperature.
• Found in animal fats.

Question 4

(Lipids) Describe the features of unsaturated fatty acids. (4)

Answer 4

• Contain C=C double bonds.
• ‘Kinked’ molecules have fewer contact points.
• Lower melting point = liquid at room temperature
• Found in plant oils.

Question 5

(Lipids) Relate the structure of triglycerides to their functions. (4)

Answer 5

• High energy: mass ratio = high calorific value from oxidation (energy storage).
• Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing.
• Slow conductor of heat = thermal insulation.
• Less dense than water = buoyancy of aquatic animals.

Question 6

(Lipids) Describe the structure and function of phospholipids.

Answer 6

Glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head.
- Forms phospholipid bilayer in water = component of membranes.
- Tails can splay outwards = waterproofing.

Question 7

(Lipids) State 4 similarities of phospholipids and triglycerides.

Answer 7

• Both have a glycerol backbone.
• Both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids.
• Both contain the elements C, H, and O.
• Both are formed by condensation reactions.

Question 8

(Lipids) State 3 differences of phospholipids and triglycerides.

Answer 8

(P) 2 fatty acids & 1 phosphate group attached.
(T) 3 fatty acids attached.

(P) Hydrophilic head & hydrophobic tail.
(T) The entire molecule Is hydrophobic.

(P) Used primarily in membrane formation.
(T) Used primarily as a storage molecule (oxidation releases energy).

Question 9

(Lipids) Are phospholipids and triglycerides polymers?

Answer 9

No, they are not made from a small repeating unit. They are macromolecules.