exam questions

Question 1

using your knowledge of the formation of structural polysaccharides, describe the formation of the chitin
molecule from its monomer and predict its structure. (4)

Answer 1

glycosidic bond formed via condensation (1)
releases a molecule of water (1)
alternate monomers rotated (1)
similar to cellulose structure (1)
forms a straight, unbranched chain (1)

Question 2

state two ways in which the molecular structure of cholesterol is similar to the molecular structure of
glucose. (2)

Answer 2

contain a hydroxyl group (1)
both contain O atom (1)
both contain H and C atoms (1)

Question 3

explain why mammals store glycogen instead of glucose (3)

Answer 3

insoluble so does not affect water potential of cell (1)
metabolically inactive (1)
compact, lots in a small space (1)
highly branched, rapid release of glucose when needed (1)

Question 4

another disaccharide is maltose. maltose and lactose both contain the same number of atoms of each element,
C, H and O.

state two other structural similarities between lactose and maltose. (2)

Answer 4

made from two hexoses (1)
1-4 glycosidic bond (1)

Question 5

complete the table below to identify differences between the structures of lactose and maltose. (4)

Answer 5

lactose: one glucose monomer and one galactose monomer
maltose: both glucose monomer

lactose: beta glucose
maltose: alpha glucose

lactose: b-glycosidic bond
maltose: a-glycosidic bond

lactose: suggars flipped
maltose: both in same direction

Question 6

explain how the structure of galactose allows it to be used as a respiratory substrate. (3)

Answer 6

hydroxyl group gives polarity which makes it soluble so can be moved in the cell (1)
bonds contain lots of energy which can be broken by enzymes (1)
hydroxyl group can form hydrogen bonds with water to be transported (1)

Question 7

suggest and explain why lactose is unable to cross membranes (2)

Answer 7

lactose is too big (1)
unable to pass between the phospholipid bilayer (1)
requires a carrier protein (1)

Question 8

in order for lactose to enter the cytoplasm of E. coli a protein is required.

the E. coli living in the digestive system of young mammals are more likely to contain this protein than E. coli living in the digestive system of old mammals.

suggest an explanation for this observation. (2)

Answer 8

mammal diet high in milk especially at young ages so high lactose concentration (1)

lactose present so structural gene for lactose permease is transcribed (1)

lactose permease (protein) is produced (1)

Question 9

give three properties of cellulose that make it suitable as the basis of plant cell walls (3)

Answer 9

insoluble (1)
flexible (1)
unreactive (1)
high tensile strength (1)