3.1.3 Lipids

Question 1

(Lipids) What are lipids made from?

Answer 1

A variety of different components but they all contain hydrocarbons.

Question 2

(Lipids) What do the components the lipid is made from relate to?

Answer 2

The lipid’s role.

Question 3

(Lipids) Name two types of lipid.

Answer 3

Triglycerides and phospholipids

Question 4

(Lipids) What do triglycerides consist of?

Answer 4

One molecule of glycerol with three fatty acids attached to it.

Question 5

(Lipids) State a feature of fatty acid molecules?

Answer 5

Long ‘tails’ made of hydrocarbons which are hydrophobic

Question 6

(Lipids) What does hydrophobic mean?

Answer 6

The substance repels water molecules.

Question 7

(Lipids) What do the fatty acid molecule ‘tails’ make lipids?

Answer 7

Insoluble in water

Question 8

(Lipids) Describe saturated fatty acids.

Answer 8

Don’t have any double bonds between their carbon atoms. ‘Saturated’ with hydrogen.

Question 9

(Lipids) Describe unsaturated fatty acids.

Answer 9

Have double bonds between carbon atoms, which cause the chain to kink.

Question 10

(Lipids) What are triglycerides formed by?

Answer 10

Condensation

Question 11

(Lipids) During a condensation reaction, what bond forms between glycerol and a fatty acid?

Answer 11

Ester bond.

Question 12

(Lipids) Describe fatty acids (4)

Answer 12

• Long chain carboxylic acids
• Typically 12-18 carbon atoms in a hydrocarbon chain
• Immiscible in water (won’t mix)
• Some contain carbon double bonds and other don’t

Question 13

(Lipids) Properties of saturated fatty acids (5).

Answer 13

• Strong attraction between fatty acid chains
• High melting point
• Solid at room temperature
• Only have C-C so form linear hydrocarbon chains
• Fit closely in a regular pattern

Question 14

(Lipids) Properties of unsaturated fatty acids (5).

Answer 14

• Fewer (so weaker) interactions between fatty acid chains
• Low melting points
• Liquid at room temperature
• 1+ C=C which causes hydrocarbon chain to bend
• Push each other apart forming irregular patterns

Question 15

(Lipids) Describe condensation in lipids. (4)

Answer 15

• Produces a triglyceride
• Formed from a glycerol + 3 fatty acids
• 3 water molecules are released
• Formation of an ester bond

Question 16

(Lipids) Describe the food/emulsion test for lipids. (4)

Answer 16

If the sample is solid then grind it.
Add 2cm3 of ethanol / alcohol and shake.
THEN add 2cm3 of water and shake.
Colour change from clear to white / milky emulsion.

Question 17

(Lipids) What is a phospholipid made up of?

Answer 17

A glycerol molecule, 2 fatty acids and a phosphate group.

Question 18

(Lipids) What are the two parts that a phospholipid is made up of?

Answer 18

• A hydrophilic head
• A hydrophobic tail

Question 19

(Lipids) Describe the properties of a hydrophilic head.

Answer 19

Is attracted to water and faces “outwards”.

Question 20

(Lipids) Describe the properties of a hydrophobic tail.

Answer 20

Repels water, tails turn “inward”.

Question 21

(Lipids) What do phospholipids do in aqueous environments?

Answer 21

Form a bilayer due to their bipolar nature, e.g. in cell membranes, which produces a hydrophobic barrier between the inside and outside of cells.

Question 22

(Lipids) What do hydrophilic head in phospholipids help?

Answer 22

To hold cell membranes together.

Question 23

(Lipids) What can phospholipids form?

Answer 23

Glycolipids.

Question 24

(Lipids) What are triglycerides mainly used as?

Answer 24

Energy storage molecules.

Question 25

(Lipids) Describe the features that make triglycerides good at being energy storage molecules. (2)

Answer 25

• Long hydrocarbon tails which contain lots of chemical energy, which can be realised when broken down.
• Insoluble in water, so they don’t affect water potential, therefore water cannot enter the cell by osmosis.

Question 26

(Lipids) What do the long hydrocarbon tails of fatty acids in triglycerides mean lipids contain?

Answer 26

About twice as much energy per gram as carbohydrates because they contain a lot of chemical energy.

Question 27

(Lipids) Describe how triglycerides are insoluble in water.

Answer 27

They bundle together as insoluble droplets in cells because fatty acid tails are hydrophobic.