An experiment was carried out to study the uptake of

An experiment was carried out to study the uptake of substances A and B by amoeba . It
is known that amoeba takes up these two substances by different mechanisms. Amoebae
were placed in a solution with equal concentrations of substances A and B. The
experimental set-up was kept at 15 ºC. The concentrations of substances A and B in the
cytoplasm of the amoeba were measured at 30-minute intervals over a period of six
hours. The following graph shows the results.
(a) Compare the uptake rate of substances A and B by the amoeba during the
six hours. (4 marks)
0 1 2 3 4 5 6
Time
(hours)
Concentration in
cytoplasm (pg cm -3 )
0
2
4
6
8
10
12
14
Substance A
Substance B
Note: 1 pg = 10 –12 g
© 2019 Aristo Educational Press Ltd. 14

HKDSE BIOLOGY: Connecting Concepts Chapter 4
Question bank Structured questions
(b) According to the graph, state and explain the mechanism by which amoeba takes
up substance B. (4 marks)
(c) If the temperature is increased to 25 ºC, what would you expect the uptake rate of
substance B to change? Explain your answer. (3 marks)
(d) By what mechanism does amoeba take up substance A? (1 mark)
##
_________
(12 marks)
##
Skills assessed Marks
(a) Analysing data 4
© 2019 Aristo Educational Press Ltd. 15

HKDSE BIOLOGY: Connecting Concepts Chapter 4
Question bank Structured questions
(b) Analysing data 1
Applying concepts 3
(c) Applying concepts 3
(d) Analysing data 1
|!|BCELB0040000009|!|
The water potentials of four plant root cells are shown in the table below. (kPa is a unit
of pressure.)
Cell
Water potential
(kPa)
A – 1800
B – 2100
C – 530
D – 200
The cells were placed in sucrose solution with a water potential of –530 kPa.
(a) Which cell(s) would have a net uptake of water? (1 mark)
(b) Which cell would initially take in water at the highest rate? Explain your answer.

(3 marks)