HKDSE Biology Exercise Vol1

HKDSE Biology Sample Question

Page 5

Question 4:

Read the paragraph below and answer the questions that follow.

Lactose Intolerance

Lactose is a sugar that is naturally present in milk. It can be digested by the enzyme lactase, which is adequately secreted in newborn babies. However, in some adult humans, levels of lactase decline and become too low to digest lactose adequately. As a result, lactose passes through the alimentary canal undigested, causing cramps and diarrhea. This condition is known as lactose intolerance.

(a)

Write a word equation to show how lactose is digested by lactase.

(b)

Based on your biological knowledge, explain why people with lactose intolerance often have diarrhea after they consume milk products.

(c)

(2 marks)

(4 marks)

A person received a diagnostic test for lactose intolerance. He was first fed with lactose and then his blood glucose level was measured to monitor any changes. Sketch two curves on the graph below to show how the blood glucose levels change, (

B b o

a lo r it d r a

g r

lu y c u o n s it e ) le v e l

Time (minutes) Intake of lactose

(i)

if he has lactose intolerance; and

(ii)

if he does not have lactose intolerance.

(3 marks)

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(d)

Page 6

A student wants to build up the size of his muscles by working out at the gym. In order to get the desired results quickly, his personal trainer advises him to drink milk every day, in additional to doing weight bearing exercise. (i)

Explain why drinking milk helps build up muscle.

(2 marks)

(ii)

As the student suffers from lactose intolerance, he feels uncomfortable after consuming milk. What drink will you recommend to him instead?

(e)

(1 mark)

Whether lactose intolerance should be regarded as "abnormal" is still under debate. From a dietary point of view, argue why it can als o be considered as "normal" in human. (3 marks)



Page 7

Question 5:

In 1855, a French scientist named Claude Bernard conducted a series of experiments to study the role of liver in glucose metabolism. Below is the outline of his design and the results: Experimental conditions

Results

Treatment 1

a fasting dog with its liver intact

blood glucose level remained normal

Treatment 2

a fasting dog with its liver removed

blood glucose level fell rapidly

Treatment 3

a fasting dog with its liver intact;

blood glucose level in hepatic vein

blood sample was taken from its

was higher than that in hepatic portal

hepatic vein and hepatic portal vein

vein

A liver was removed from a dog, which



Treatment 4 (a)

had been fed normally for a few days.

and the emerging blood

It was then washed with cold water

contained glucose;

through the portal vein and the blood came out through the hepatic vein. The liver was washed in this way continuously for 40 minutes.

Treatment 4 (b)

at the beginning, both the liver



at the end of the washing, both the liver and the emerging blood did not contain glucose

The sugar-free liver from 4 (a) was left

a high level of glucose was found in

in a closed jar for 24 hours;

the liver

then its glucose level was measured again

(a) Based on the results of treatment 1 and 2, what conclusion can you draw?

(1 mark)

(b) Based on present day knowledge of glucose metabolism, explain the result of treatment 3. (4 marks) (c) In Bernard's time, people believed that the liver caused the formation of glucose directly in the blood passing through it. Is this belief supported by the results of this experiment? Explain your answer.

(2 marks)

(d) To account for the result in treatment 4 (b), someone hypothesized that an enzyme's action may be involved (i)

Suggest what further experiment can be done in order to prove his hypothesis. (1 mark)

(ii) What is the expected result if this hypothesis is correct?

(1 mark)



HKDSE Biology Exercise Vol1

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