1.4

Question 1

What characteristics do lipids have? (5)

Answer 1

(1) they’re a LARGE GROUP of molecules
(2) they contain Oxygen, Carbon & Hydrogen
(3) Proportion of O to C & H is smaller than in carbs
(4) they’re INSOLUBLE in WATER
(5) they’re SOLUBLE in ORGANIC solvents

Question 2

What are the 3 main groups of lipids? (3)

Answer 2

(1) Triglycerides
(2) Phospholipids
(3) Waxes

Question 3

What are the main roles of lipids? (5)

Answer 3

(1) they make up PLASMA MEMBRANES
(2) they’re an ENERGY SOURCE
(3) they help in WATERPROOFING materials
(4) they act as INSULATORS
(5) they PROTECT ORGANS externally

Question 4

How are triglycerides formed? Include the structure of its constituent units. (6)

Answer 4

(1) each fatty acid has a CARBOXYL group (-COOH)
(2) each glycerol molecule has 3 carbon atoms
(3) 3 fatty acids & a glycerol molecule…
(4) undergo CONDENSATION…
(5) which means that an OH from the fatty acid binds to the H from glycerol…
(6) to form an ESTER BOND

Question 5

Which reaction breaks down triglycerides? (1)

Answer 5

Hydrolysis

Question 6

Since all glycerol molecules are the same, how do triglycerides differ from each other? (3)

Answer 6

(1) there are 70 different fatty acids
(2)… which have the formula of R-COOH
(3) every fatty acid has a different R group/ hydrocarbon chain.

Question 7

What are the 3 different types of fatty acids? Explain each. (6)

Answer 7

(1) Saturated —> (4) NO C-C double bonds
(2) Mono-unsaturated —> (5) 1 C-C double bond
(3) Poly-unsaturated —> (6) More than 1 C-C double bond

Question 8

Why are unsaturated fatty acids oils/liquids at room temp.? (2)

Answer 8

(1) double bonds = causes the molecule to BEND
(2) so they CANT PACK CLOSELY together

Question 9

Explain the components of phospholipids. (5)

Answer 9

(1) it’s made of glycerol, 2 fatty acids and a phosphate group
(2) the 2 fatty acids are HYDROPHOBIC (non-polar),
(3) so they REPEL WATER
(4) the phosphate group is HYDROPHILIC (polar),
(5) so they ATTRACT WATER

Question 10

How do you test for lipids? (8)

Answer 10

(1) take a dry & grease-free test tube
(2) Add 2cm of the sample
(3) Add 5cm of ethanol
(4) SHAKE the tube thoroughly
(5) Add 5cm of water
(6) SHAKE gently
(7) a cloudy/milky/white solution = lipid present
(8) CONTROL = repeat the procedures using water instead of the sample

Question 11

Why does the solution appear cloudy? (3)

Answer 11

(1) lipids in the sample are FINELY DISPERSED in the water…
(2) forming an EMULSION
(3) any LIGHT that passes through the emulsion is REFRACTED, making it cloudy.