lipids

Question 1

The diagram shows the structure of a fat substitute.

(d) This fat substitute cannot be digested in the gut by lipase.

Suggest why.

Answer 1

Fat substitute) is a different/wrong shape/not complementary;

OR

Bond between glycerol/fatty acid and propylene glycol different
(to that between glycerol and fatty acid)/no ester bond;

2. Unable to fit/bind to (active site of) lipase/no ES complex formed;

Question 2

This fat substitute is a lipid. Despite being a lipid, it cannot cross the cell-surface membranes of cells lining the gut.

Suggest why it cannot cross cell-surface membranes.

what should you think about before answering

Answer 2

properties of lipids non polar

what can cross a membrane (non polar small)

so must be big hydrophilic or polar

Question 3

A student investigated the effect of lipase concentration on the hydrolysis of lipids.

He took a beaker containing a suspension of lipids. He placed a pH probe attached to a data logger into the beaker. After 5 minutes, he added the lipase solution. The data logger recorded the pH. The apparatus used is shown in the diagram below

The student did not add a buffer to the lipase solution.

Explain why.

___________________________________________________________________

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(1)

(b) Give two variables the student would have controlled in this investigation.

1. _________________________________________________________________
2. _________________________________________________________________

(2)

(c) Give the suitable control for this investigation.

Answer 3

Student was measuring change in pH

OR

Buffer would maintain a constant pH.

1 max

(b) 1. Volume of suspension of lipids;

2. Concentration of suspension of lipids;
3. Volume of lipase solution;
4. Temperature;

2 max

(c) Boiled lipase solution;

1

Question 4

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 4

Hydrolysis of lipids produces fatty acids;

2. Which lower pH of mixture.