lipids

Question 1

test for lipids

Answer 1

2cm3 sample 5cm3 ethanol
shake thoroughly to dissolve any lipid in the sample
5cm3 water shake gently
milky white emulsion indicates presence
as a control repeat with water instead of sample - remains clear

Question 2

how do triglycerides form

Answer 2

condensation reaction between 3 fatty acids and 1 glycerol forms ester bonds

Question 3

contrast saturated and unsaturated fatty acids

Answer 3

saturated - no C=C bonds, straight chain compact
many contact points
higher melting point, solid at room temp
found in animal fats
unsaturated - 1 or more C=C bonds, bends so cannot be tightly packed
few contact points
lower melting point, liquid at room temp
fount in plant oils

Question 4

relate triglyceride structure to its functions

Answer 4

1) high ratio of high energy storing C-H bonds to C atoms - excellent energy source
2) low mass:energy, much energy stored in small vol - high calorific value from oxidation
3) large, non polar, insoluble, their storage doesn’t have any osmotic effect on cells, insoluble - waterproofing
4) high ratio of H:O atoms, release water when oxidised, provides important source of water for animals
5) slow conductor of heat - thermal insulation
6) less dense than water - buoyancy of aquatic animals

Question 5

benefit of low mass:energy in triglycerides

Answer 5

much energy can be stored in a small volume, reduces mass animals have to carry around

Question 6

benefit of high H:O atoms in triglycerides

Answer 6

releases water when oxidised - important water source for animals esp those living in dry climates eg camels store fat in their hump

Question 7

describe the structure and function of phospholipids

Answer 7

2 fatty acids + phosphate group bonded to glycerol molecule
1) hydrophilic phosphate head
2) hydrophobic fatty acid tail
3) forms phospholipid bilayer in aqueous environment eg at cell surface membranes - waterproof barrier between inside/outside cell
4) hydrophobic tails can splay outside for waterproofing

Question 8

similarities of triglycerides and phospholipids (4)

Answer 8

1) both have glycerol backbone
2) both may be attached to a mixture of (un)saturated fatty acids
3) both contain C H O atoms
4) both formed by condensation

Question 9

contrast triglycerides and phospholipids

Answer 9

1) phospholipids have 1 phosphate group instead of a fatty acid
2) p - hydrophilic head and hydrophobic tail. t - hydrophobic
3) p - primarily used in membrane formation. t - storage molecule (oxidation releases energy)

Question 10

are triglycerides and phospholipids polymers?

Answer 10

no, they are not made of repeating subunits. they are macromolecules