Lipids, triglycerides and emulsion test

Question 1

what do all lipids have

Answer 1

contain carbon hydrogen and oxygen

soluble in acetone and alcohol

Question 2

what are the main groups of lipids

Answer 2

triglycerides and phospholipids

Question 3

what are the roles of lipids

Answer 3

insulation
protection
cell membranes
source of energy
waterproofing

Question 4

how do lipids provide a source of energy

Answer 4

when oxidised lipids provide more than twice the energy of the same carbohydrate and release valuable water

Question 5

how do lipids provide waterproof

Answer 5

they are insoluble in water, therefore they are valuable in waterproofing

Question 6

how do lipids provide insualtion

Answer 6

fats are slow conductors of heat and when stored beneath the surface of the body they help to retain heat

Question 7

how do lipids contribute to cell membranes

Answer 7

phospholipids contribute to flexibility of cell membrane and transfer of lipid soluble substances across them

Question 8

what are triglycerides made of

Answer 8

3 fatty acids and one glycerol molecule

Question 9

how are triglycerides formed

Answer 9

fatty acids form esther bonds with glycerol to make triglycerides via a condensation reaction

Question 10

what does hydrolysis of triglycerides produce

Answer 10

glycerol and three fatty acid molecules

Question 11

what do all fatty acid chains contain

Answer 11

COOH group and OH attached

Question 12

what is a saturated molecule

Answer 12

when there is no double carbon bond

Question 13

what is the shape and state of a saturated fat at room temperature

Answer 13

straight chain and solid

Question 14

what is an unsaturated molecule

Answer 14

double carbon bond present

Question 15

what is the shape and state of unsaturated molecules

Answer 15

double bond causes kinks in structure. kinks mean fatty acids unable to closely pack together so it is liquid at room temp

Question 16

how does the structure of triglycerides mean that it is a good source of water

Answer 16

high ratio of hydrogen to oxygen atoms means triglycerides release water when oxidised

Question 17

how does the structure of triglycerides make it a good storage molecule

Answer 17

low mass to energy ratio means alot of energy can be stored in a small volume

Question 18

how does the structure of triglycerides make it an excellent source of energy

Answer 18

high ratio of energy storing carbon-hydrogen bonds to carbon atoms

Question 19

how are phospholipids different to triglycerides

Answer 19

one fatty acid is replaced with a phosphate molecule

Question 20

what are phospholipids made of

Answer 20

hydrophobic head

hydrophillic tail

Question 21

how does the hydrophobic head behave

Answer 21

attracted to water so interacts with it

Question 22

how do the hydrophillic tails behave

Answer 22

repels water so orientates itself readily away from water but mixes with fat

Question 23

how does the structure of phospholipids relate to its function

Answer 23

hydrophillic head helps to hold at the surface of the cell membrane

phospholipid structure allows them to form glycolipids by combining with carbohydrates at the cell surface membrane. Glycolipids are important in cell recogniition.

polar molecule of hydrophillic head and two fatty acid tails means when in an aqueous environment phospholipids form a bilayer within cell surface membrane and therefore hydrophobic barrier is formed inside and outside of cell

Question 24

describe the emulsion test

Answer 24

1. take a completely dry and grease free tube
2. to 2cm^3 of sample being tested add 5cm^3 of ethanol
3. shake the tube thoroughly to dissolve any lipid in sample
4. add 5cm^3 of water and shake gently
5. A milky white solution indicates the presence of a lipid
6. as a control repeat the procedure with water instead of sample and the final solution should remain clear

Question 25

why does solution turn cloudy when lipids are present

Answer 25

cloudy colour due to lipids being finely dispersed in solution to form an emulsion. light passing through this is refracted from water droplets to oil droplets making the solution appear cloudy