June 22 Paper 1

Question 1

Define the quaternary structure of a protein

Answer 1

-more than one polypeptide

Question 2

Explain how two enzymes with different amino acid sequences can catalyse the
same reaction.

Answer 2

-1. (Both) active sites have similar/identical tertiary
structures
-2. (So) form enzyme-substrate complexes (with the
same substrate);

Question 3

Describe the transport of carbohydrate in plants

Answer 3

1. Sucrose actively transported into phloem
2. (By) companion/transfer cells;
3. Lowers water potential (in phloem) and water
   enters (from xylem) by osmosis;
4. ((Produces) high(er) (hydrostatic) pressure;
5. Mass flow to respiring cells
6. Unloaded/removed (from phloem) by active
   transport;

Question 4

Describe the complete digestion of starch by a mammal.

Answer 4

-1. Hydrolysis;
2. (Of) glycosidic bonds;
3. (Starch) to maltose by amylase;
4. (Maltose) to glucose by disaccharidase/maltase;
5. Membrane-bound (disaccharidase/maltase)