Biological molecules exam Qs

Question 1

In mammals, in the early stages of pregnancy, a developing embryo exchanges
substances with its mother via cells in the lining of the uterus. At this stage, there
is a high concentration of glycogen in cells lining the uterus.

(a) Describe the structure of glycogen. (2)

Answer 1

1. Polysaccharide of α-glucose;
   OR
   polymer of α-glucose;
2. (Joined by) glycosidic bonds
   OR
   Branched structure;

Question 2

(b) During early pregnancy, the glycogen in the cells lining the uterus is an
important energy source for the embryo.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer (2)

Answer 2

1. Hydrolysed (to glucose);
2. Glucose used in respiration;

Question 3

(a) Name the monomers from which a maltose molecule is made. (1)

Answer 3

Glucose (and glucose)

Question 4

(b) Name the type of chemical bond that joins the two monomers to form
maltose (1)

Answer 4

(α1,4) Glycosidic;

Question 5

Explain the difference in the structure of the starch molecule and the
cellulose molecule (2)

Answer 5

1. Starch formed from α-glucose but cellulose formed from β-glucose;
2. Position of hydrogen and hydroxyl groups on carbon atom 1
   inverted.

Question 6

Starch molecules and cellulose molecules have different functions in plant
cells. Each molecule is adapted for its function.
Explain one way in which starch molecules are adapted for their function in
plant cells. (2)

Answer 6

1. Insoluble;
2. Don’t affect water potential;
   OR
3. Helical;
   Accept form spirals
4. Compact;
   OR
5. Large molecule;
6. Cannot leave cell.

Question 7

Explain how cellulose molecules are adapted for their function in plant
cells. (3)

Answer 7

1. Long and straight chains;
2. Become linked together by many hydrogen bonds to form
   fibrils;
3. Provide strength (to cell wall)

Question 8

A biochemical test for reducing sugar produces a negative result with
raffinose solution.
Describe a biochemical test to show that raffinose solution contains a
non-reducing sugar. (3)

Answer 8

1. Heat with acid and neutralise;
   Accept boil/water bath for heat
   Accept named alkali for neutralise
   Accept named examples, eg HCl, NaHCO3
2. Heat with Benedict’s (solution);
3. Red precipitate/colour;
   Accept other colours eg orange/ brown/green