Exam specific answers

Question 1

explain 1 way in which starch molecules are adapted for their function in plant cells (storage substance)? (2)

Answer 1

insoluble so they don’t affect water potential
helical structure so compact
large molecule so cannot leave cell

Question 2

explain how cellulose molecules are adapted for their function in plant cells? (3)

Answer 2

they are made up of long and straight chains which become linked by many hydrogen bonds to form fibrils, so they provide strength to the cell wall

Question 3

in what ways is the structure of cellulose different to the structure of starch? (5)

Answer 3

starch/cellulose
alpha glucose/beta glucose
branched/unbranched
helical/straight
no microfibrils/has microfibrils
all glucoses same way up/alternate glucoses are upside down

Question 4

state two differences between the structure of cellulose and starch? (2)

Answer 4

cellulose is made up of β-glucose and glycogen is made up of α-glucose
cellulose molecule has straight chain and glycogen is branched
glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds

Question 5

why do red blood cells have a higher percentage by mass of cholesterol than ileum cells? (1)

Answer 5

red blood cells are not supported by other cells, so the cholesterol helps them to maintain their shape

Question 6

describe a test to show that raffinose solution contains a non-reducing sugar? (3)

Answer 6

1. heat with acid and neutralise
2. heat with Benedict’s solution
3. red precipitate/colour will form

Question 7

explain how a peptide bond forms in a protein? (2)

Answer 7

forms in a condensation reaction between an amine group and a carboxyl group

Question 8

explain how enzymes increase rate of reaction? (3)

Answer 8

lower activation energy
induced fit causes active site of enzyme to change shape
enzyme-substrate complex causes bonds to break

Question 9

the secondary structure of a polypeptide is produced by bonds between amino acids - describe how.
(2 marks)

Answer 9

hydrogen bonds form between NH and C=O group, forming alpha helix or beta pleated sheet

Question 10

describe the induced fit model of enzyme action. (2)

Answer 10

before the reaction, the active site is not complementary to the substrate
as the substrate binds to the active site, the shape of the active site changes

Question 11

give two ways in which the hydrolysis of ATP is used in cells. (2)

Answer 11

1. to provide energy for other reactions
2. add phosphate to other substances to make them more reactive

Question 12

give two ways in which ATP is a suitable energy source for cells to use. (2)

Answer 12

1. it releases energy instantaneously
2. it can be rapidly resynthesised

Question 13

explain five properties that make water important for organisms. (5)

Answer 13

1. metabolite in condensation and hydrolysis reactions
2. solvent so reactions can occur
3. high specific heat capacity so buffers changes in temperature
4. large latent heat of vaporisation so provides cooling effect
5. cohesion so produces surface tension which supports small organisms

Question 14

explain how a competitive inhibitor decreases the rate of an enzyme-controlled reaction. (3)

Answer 14

1. the inhibitor has a similar shape to the substrate
2. the inhibitor binds to the active site
3. this reduces the formation of enzyme-substrate complexes

Question 15

describe how the structure of a protein depends on the amino acids it contains. (5)

Answer 15

1. structure is determined by position of amino acids
2. primary structure is the sequence of amino acids
3. secondary structure forms by hydrogen bonding between amino acids
4. tertiary structure forms by interactions between R groups
5. quaternary structure is formed by interactions between polypeptides

Question 16

describe two ways in which all dipeptides are similar and one way in which they might differ (3)

Answer 16

similar - both contain NH2 group at end, both contain COOH group at end
different - have variable R group

Question 17

describe how a non-competitive inhibitor decreases the rate of an enzyme-controlled reaction (3)

Answer 17

1. attaches to enzyme at site other than active site
2. changes tertiary structure of enzyme
3. active site no longer complementary fewer substrates can bind