1. C
2. C
3. B
4. E
5. A
6. B
7. C
8. C
9. D
10. A
(c)
Outline how enzymes catalyse reactions.
1.
2.
3.
4.
5.
6.
Enzymes increase rate of (chemical) reaction;
Enzymes remains unused/unchanged at the end of the reaction;
Enzymelower activation energy of the chemical ;
The activation energy of a chemcial is energy needed to overcome energy barrier that
prevents reaction;
The substrate/ chemical reactant joins with enzyme at active site;
When the substrate bonds with the active site of the enzyme they form enzyme-substrate
complex;
7. The active site/enzyme (usually) specific for a particular substrate/ chemical reactant as described by the
lock and key model;
8. Enzyme binding with substrate brings reactants closer together to
facilitate chemical reactions (such as
electron transfer);
High level
Stuff
9. The induced fit model shows how the substrate initiates a change in enzyme conformation
(when
enzyme-substrate/ES complex forms);
10. This change in enzyme conformation makes the substrate more reactive
11. Students may have an annotated graph showing reaction with and without enzyme;
IB Questionbank Biology
1
(a) The activity of enzymes determines the rate at which chemical reactions occur in
living organisms. Outline the effects of two factors that can both increase and decrease
enzyme activity.
Award marks only for the first two factors outlined.
(a) temperature; -- 3 Points Max.
1. Rate of reaction increases as temperature increases / rate of reaction decreases as
temperature decreases.
2. When temperatures are higher molecules have more kinetic energy / faster movement
of molecules means more collisions between enzyme / active site and substrate;
3.
Optimum temperature is temperature at which rate of enzyme-catalyzed reaction is
fastest;
4. At high temperatures above the optimum temperature for a given enzymes, enzyme
will be denatured and stop working;
5. Denatured means change of structure in enzyme / protein resulting in loss of its biological
properties / no longer can carry out its function;
6. High temperatures denature an enzyme because too much kinetic energy / vibrations
breaks bonds that give enzyme specific shape which change the shape of the active site
and therefore decrease the rate of reaction.
pH; -- 3 points max
1.
2.
3.
4.
enzyme activity is highest at the optimum pH / graph to show this;
different optimum pH with different enzymes;
Optimum pH is the pH where enzyme activity/ reaction rate is the highest
Denaturation of enzymes by high and low pH / extreme pHs because bonds are made and
IB Questionbank Biology
2
broken which change the shape of the active site and therefore decrease the rate of
reaction.
substrate concentration – 3 points max;
1. at low substrate concentrations, an increase in substrate concentration causes an
increase in rate of reaction (point a to b on graph -- See below);
2. Higher substrate concentration results in more chance of collision between substrate
and enzyme / active site;
3. at a certain level of high substrate concentration, there is no change in rate as the
substrate continues to increase in concentration, that is, the reaction rate reaches a plateau
on the graph (point c on graph—See below);
4. At the levels of concentration of substrate where the reaction rate plateaus, all of the
active sites on the enzymes are occupied/ saturated with substrate;
(a)
(i)
15.2 mg 3 hrs–1 (allow answers in the range of 15.0 to 15.4)
(ii)
1.93 NAG units 3 hrs–1 (allow answers in the range of 1.92 to 1.95)
1
1
(b) You are asked to compare the correlation between men and women, and so you should make
comparison about positive, negative or no relationships, and you should also compare strength of
relationship (stronger, weaker), and you should compare steepness of the slope of the best fit line
1. Both men and women have a positive relationship;
2. Bothe men and women’s values are very scattered for both;
3. There is a more positive correlation/steeper gradient for men than for women;
IB Questionbank Biology
3
4. The data is more scattered in women/greater range in hepatic activity / more scattered/
greater
range in men in renal activity;
2 max
Evaluate a hypotheses base on data = Clearly state if the data support the hypothesis or not? The
explain/ discuss how data supports hypothesis or does not support hypothesis.
1. The hypothesis is supported because there is a positive correlation between both increased
hepatic activity and
renal damage/ people with more renal damage have more cytochrome activity
( hepatic activity is meant to be an indirect measurement of cadmium exposure/ toxicity).
2. The data shows a difference in the effect between men and women, for example: there
is a greater hepatic (liver) effect in women than in men / there is a greater renal (kidney) effect in
men
than women;
3. While there is a positive relationship between renal damage and hepatic activity, this
positive trend does not necessarily prove a direct causal relationship between
hepatic and renal function with cadmium toxicity, and thus the hypothesis is not
supported by this data
4. There are problems with the data, for example, there is a very wide range of data, which
makes it very difficult to evaluate and it is possibly
not statistically significant relationship (i.e. no
R-Value/ correlation coefficient is reported) ;
5. From this data it is impossible to establish a causal relationship because there is no
control group /
other factors may be involved/ hepatic activity might not be a good measurement of cadmium
toxicity;;
IB Questionbank Biology
4