1.5- Lipids

Question 1

what characteristics to lipids have? (4)

Answer 1

1. contain carbon, hydrogen and oxygen
2. proportion of carbon and hydrogen smaller than carbohydrates
3. insoluble in water
4. soluble in organic solvents e.g alcohols, acetone

Question 2

Name the 2 main types of lipids

Answer 2

1. triglycerides
2. phospholipids

Question 3

Name the 5 roles of lipids

Answer 3

1. flexibility of membranes/ transfer lipid-soluble substances across them
2. source of energy- lots when oxidised
3. waterproofing
4. insulation
5. protection

Question 4

Structure of triglycerides

Answer 4

3 fatty acids
1 glycerol

Question 5

how many types of fatty acids are there ?

Answer 5

over 70

Question 6

bonding of a triglyceride molecule

Answer 6

each fatty acid forms an ester bond with glycerol in a condensation reaction (water produced)

Question 7

saturated lipids

Answer 7

saturated
lipids don’t contain any carbon-carbon double bonds.

Question 8

Unsaturated lipids (found in plants)

Answer 8

unsaturated
lipids contain carbon-carbon double bonds. The presence of a
double bond means that the molecule is able to bend. As a
result unsaturated fats cannot pack together as tightly and are
therefore liquid at room temperature

Question 9

properties of triglycerides (4)

Answer 9

1. high ratio of energy storing carbon-hydrogen bonds to carbon atoms= excellent store of energy
   2.low mass to energy ratio=good storage molecule,lots of energy small volume
2. storage does not affect water potential of cells= as they are large and non- polar + insoluable in water
   4.high ratio of hydrogen to oxygen atoms= triglycerides release water when oxidised, provide important source of water for organisms in dry environments

Question 10

How is a low mass to energy ratio, a property of triglycerides beneficial to animals?

Answer 10

energy can be stored in small volumes, this means the mass they have to carry as they move around is reduced

Question 11

Phospholipid structure

Answer 11

1 phosphate molecule
2 fatty acids
glycerol

Question 12

are fatty acid molecules hydrophobic or hydrophilic?

Answer 12

fatty acid molecules are hydrophobic (repel water)

Question 13

are phosphate molecules hydrophobic or hydrophilic?

Answer 13

phosphate molecules are hydrophilic (attract water)

Question 14

What are the 2 parts to a Phospholipid?

Answer 14

hydrophilic ‘head’- interacts with water but not fat
hydrophobic ‘tail’- away from water but mixes readily with fat

Question 15

Are Phospholipids polar or non polar?

Answer 15

polar- poles act differently

Question 16

What happens when Phospholipid molecules are placed in water?

Answer 16

position themselves so hydrophilic heads are as close to water as possible and hydrophobic tails are as far away from water as possible

Question 17

phospholipid properties (3)

Answer 17

1. polar molecules- in aqueous environment form bilayer within cell surface membranes
2. ‘heads’ help to hold at the surface of cell surface membrane
3. form glycolipids by combining carbs within cell surface membrane- important in cell recognition

Question 18

test for lipids name

Answer 18

emulsion test

Question 19

describe emulsion test

Answer 19

1. Take a completely grease free test tube and add 2cm3 of the sample to be tested and
   5cm3 of ethanol.
2. Shake the test tube thoroughly to dissolve all the lipid in the solution.
3. Add 5cm3 of water and shake gently.
4. A cloudy-white colour indicates the presence of a lipid.
5. As a control repeat the experiment using water as the sample, the final solution
   should remain clear