Exam style questions

Question 1

Scientists have investigated the effects of competitive and non-competitive
inhibitors of the enzyme maltase.
Describe competitive and non-competitive inhibition of an enzyme

Answer 1

1. Inhibitors prevent formation of
   ES complex;
2. Inhibitor similar shape (idea) to substrate;
3. (Binds) in to active site (of enzyme);
4. (Inhibition) can be overcome by more substrate;
   (Non-competitive inhibition),
5. Inhibitor binds to site on enzyme other than active site;
6. Prevents formation of active site / changes (shape of) active site;
7. Cannot be overcome by adding more substrate;

Question 2

In humans, the enzyme maltase breaks down maltose to glucose.
This takes place at normal body temperature.
Explain why maltase:
* only breaks down maltose
* allows this reaction to take place at normal body temperature.

Answer 2

1. Tertiary structure / 3D shape of enzyme (means);
2. Active site complementary to maltose
3. Description of induced fit;
4. Enzyme is a catalyst / lowers activation energy
5. By forming enzyme-substrate complex;

Question 3

Explain the difference in the structure of the starch molecule and the cellulose
molecule

Answer 3

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 4

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

Answer 4

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 5

Give two ways in which the structure of starch is similar to cellulose

Answer 5

(Both)
1. Are polymers / polysaccharides / are made of monomers / of
monosaccharides;
2. Contain glucose / carbon, hydrogen and oxygen;
3. Contain glycosidic bonds;
4. Have 1−4 links;
5. Hydrogen bonding (within structure).

Question 6

Give two ways in which the structure of starch is different from cellulose

Answer 6

(Starch)
1. Contains α / alpha glucose;
Assume ‘it’ refers to starch
Accept: forms α glycosidic bonds
2. Helical / coiled / compact / branched / not straight;
3. 1,6 bonds / 1,6 branching;
4. Glucoses / monomers same way up;
5. No H-bonds between molecules;
6. No (micro / macro) fibres / fibrils

Question 7

Explain how cellulose molecules are adapted for their function in plant cells

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

Before starting their experiments, the scientists confirmed that, like human breast
milk, cat’s milk also contained bile-activated lipase.
To do this, they added bile to cat’s milk and monitored the pH of the mixture.
Explain why monitoring the pH of the mixture could show whether the cat’s milk
contained lipase

Answer 8

1. Hydrolysis of lipids produces fatty acids;
2. Which lower pH of mixture

Question 9

The structure of a phospholipid molecule is different from that of a triglyceride.
Describe how a phospholipid is different

Answer 9

1. Phosphate / PO4;
   “It” refers to phospholipid.
2. Instead of one of the fatty acids / and two fatty acids;

Question 10

Hydrogen bonds are important in cellulose molecules. Explain why.

Answer 10

1. Holds chains / cellulose molecules together / forms cross links
   between chains / cellulose molecules / forms microfibrils, providing
   strength / rigidity (to cellulose / cell wall);
2. Hydrogen bonds strong in large numbers;

Question 11

A starch molecule has a spiral shape. Explain why this shape is important to
its function in cells

Answer 11

Compact / occupies small space / tightly packed

Question 12

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

Answer 12

1. BOIL with acid and neutralise;
2. Heat with Benedict’s (solution);
3. Red precipitate/colour;

Question 13

A student carried out the Benedict’s test. Suggest a method, other than
using a colorimeter, that this student could use to measure the quantity of
reducing sugar in a solution.

Answer 13

1. Filter and dry (the precipitate);
2. Find mass/weight;

Question 14

What is a monomer?

Answer 14

(a monomer is a smaller / repeating) unit / molecule from which larger
molecules / polymers are made;

Question 15

Lactulose is a disaccharide formed from one molecule of galactose and
one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference
between the structures of lactulose and lactose.

Answer 15

Both contain glycosidic bonds
Lactulose contains fructose whereas lactose conntains glucose

Question 16

Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule
and a glycogen molecule.

Answer 16

Cellulose is made up from beta glucose monomers whereas glycogen is made up from alpha glucose monomers
Cellulose has a straight chain and glycogen is highly branched

Question 17

Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage
molecule.

Answer 17

Insoluble in water so dosen’t effect the water potential of the cell
Coiled so makes molecue compact

Question 18

Describe the structure of glycogen

Answer 18

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

Question 19

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.

Answer 19

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