Ch 4 Enzymes and metabolism
Exercise
Multiple-choice questions (p. 4-25)
1
A
2
B
5
B
6
C
3
A
4
A
Short questions (p. 4-27)
7
HKCEE Biology 2011 I Q2
8
a
9
As the temperature increases, the time for the milk to clot decreases and
then increases again.
1
b
40 °C
1
c
The enzyme denatured / changed shape at 70 °C.
1
a
All the starch had been broken down.
1
b
At 25 °C, more collisions occurred between the amylase and the starch
molecules / molecules moved faster / molecules had more kinetic energy /
enzymes worked faster.
1
Enzymes work on specific substrate only. / Only starch fits into the active
site of amylase.
1
c
Structured questions (p. 4-28)
10 a
b
Insoluble proteins are broken down into products, which dissolve in the
solution.
i
1
The activity of trypsin increases between pH 5 and 8. /
Trypsin is most active at pH 8. /
The activity drops between pH 8 and 10. (any 2)
ii
c
1x2
Unsuitable pH breaks some bonds in the enzyme molecules,
1
causing a change in shape of the active sites.
1
Thus, substrates / protein molecules cannot bind to the active site.
1
This is to keep the temperature of the reaction constant.
1
45 °C is the optimum temperature of trypsin. The reaction rate is higher at
this temperature.
1
11
HKDSE Biology Sample Paper IB Q9
Essay (p. 4-28)
12 Enzymes are catalysts / speed up / lower the activation energy of chemical
reactions. 1
Enzymes have an optimum temperature.
1
At low temperatures, the enzymes are inactive.
1
High temperatures may cause conformational change in the active site. /
Enzymes may denature at high temperatures.
1
All enzymes have an optimum pH.
1
Unsuitable pH may cause conformational change in the active site. / Enzymes
may denature at unsuitable pH.
1
Inhibitors decrease enzyme activity.
1
Communication
3
Reading to learn (p. 4-29)
1
It causes less environmental problems
1
and gives products of higher quality because it does not involve the use of
alkaline solution.
2
3
1
The activity of pectinase is higher at 30 °C.
1
Incubation allows time for pectinase to act on.
1
The action of pectinase is specific.
1
Cellulose and pectin have different structure. Cellulose cannot fit into the active
site of pectinase, thus pectinase cannot catalyse the breakdown of cellulose.
1