METABOLIC REACTIONS
Anabolic reactions, also called endergonic reactions, include
A. glycolysis.
B. Kreb’s cycle.
C. photosynthesis.
D. protein digestion.
RESPIRATION
1. 2,4-dinitrophenol is a chemical that is toxic to mitochondria. When added to mitochondria this
chemical allows electron transport to occur but prevents the phosphorylation of ADP to ATP.
The chemical achieves this by breaking the essential link between electron transport and ATP
synthesis. This toxin causes mitochondria to produce heat instead of ATP. The greater the
amount of toxin added, the quicker is its action.
a. If mitochondria are poisoned with 2,4-dinitrophenol by what process could a plant cell
produce more ATP?
b. Where in the mitochondria does electron transport and ATP production occur?
A researcher wanted to study cellular respiration in insect cells. She cultured some muscle cells
from the common fi eld cricket, Teleogryllus oceanicus, then studied the effects of adding 2,4dinitrophenol to these cells. An agricultural company may want to fund this research.
c. Give one reason why an agricultural company might want to fund research on the effects of
this toxin on field crickets.
The experiment is summarised in the table below. Temperature observations in each trial were
made at equal time intervals
d. In terms of energy production, why did the temperature go up in trial 1 and not in the control?
e. Explain why the temperature went down after the fi fth observation in trial 1.
f. Trial 2 had twice the concentration of 2,4-dinitrophenol added. Complete the table by writing
in temperatures in the spaces provided to predict the trend.
Another researcher suggested adding pyruvate to the cells to cancel out the effects of this toxin.
g. Explain what effect adding pyruvate would have on cancelling out the effect of this toxin.
Springhares are large nocturnally active rodents that live in arid regions of southern and eastern
Africa. They spend much of the day sheltering in burrows. Biologists studied the characteristics
of springhares that enable them to cope with the scarcity of water and extremes of temperature in
their habitat. Eighteen adult springhares were caught and brought to the laboratory for study.
Each springhare was placed in an experimental chamber and the rate at which it used up oxygen
was measured. The measurements were repeated for each springhare at a range of chamber
temperatures.
a. Explain why studying oxygen usage for each springhare enabled the scientists to calculate the
metabolic rate of each animal.
1 mark
The average results are shown in the following graph.
The thermoneutral zone (TNZ) for an animal is that range of temperatures at which their energy
expenditure is the lowest.
b. What is the thermoneutral zone for these springhares during the experiment?
The biologists observed the springhares as the temperature of the experimental chamber was
changed.
c. Explain how each of the observations listed below (i., ii. and iii.) would contribute to regulation of
body temperature.
i. As the chamber temperature decreased below 15°C, the springhares curled up with their heads between
their hind legs and their tails wrapped around their backs.
ii. As the chamber temperature decreased below 15°C, shivering became increasingly apparent.
iii. At 35°C, blood vessels in the ears and legs were visibly dilated and the springhares spread saliva over
their faces and throats.
After the experiment, the springhares were kept for a week in the laboratory animal house which
was maintained at 20°C. Dry food and drinking water were provided; however, there was no
evidence that the animals ever drank.
d. What would be the water source for these animals if they do not normally drink when the
environmental temperature is 20°C?
The biologists returned to the region in which the springhares had been caught to investigate the
temperatures in their burrows. They found that although outside day and night temperatures
varied significantly between 33°C and 3°C, temperatures within burrows remained stable at
about 12°C.
e. Explain how spending most of the daytime in burrows helps springhares maintain their water
balance.
POTOSYNTHESIS
The chloroplast is the organelle responsible for photosynthesis in eukaryotic cells.
In chloroplasts
A. the light independent reactions require water as the initial reactant.
B. the light independent reactions occur in the inner membrane area.
C. the fi nal product of the light reaction is glucose.
D. the light reactions occur in the grana.
The following image shows a portion of an electron photomicrograph of a chloroplast.
Light-dependent reactions occur in region P and the Calvin cycle reactions occur in region Q.
Considering events that occur in a chloroplast during photosynthesis it is reasonable to claim that
A. oxygen is an input to reactions at P.
B. carbon dioxide is an input to reactions at Q.
C. chlorophyll is essential for reactions that occur at Q.
D. ADP produced during the events at P is used by events at Q.
Pieces of leaf epidermis were peeled from the plant Commelina communis. The pieces were then
placed in a solution of a dye that binds to potassium ions.
You would expect that most of the dye would be concentrated in the
A. guard cells when the stomata are open.
B. stomatal pore when the stomata are closed.
C. epidermal cells when the stomata are open.
D. intercellular spaces of the leaf when the stomata are closed.
The production of organic molecules in a crop is reduced when leaves begin to wilt because
A. stomata close preventing the entry of CO2.
B. the chlorophyll of wilting leaves decomposes.
C. ß accid mesophyll cells of a leaf are not capable of photosynthesis.
D. accumulation of CO2 in the leaf inhibits the enzymes required for photosynthesis.
Although photosynthesis is often summarised by a single equation, in fact the process occurs in
two distinct phases; the light phase and another phase called the carbon fixation phase or the
light independent phase. These two phases can be summarised in diagrammatic form as follows.
The diagram shows outputs X and Y.
a. i. What is output X?
ii. How is output X produced?
b. What is output Y?
Cellular respiration provides energy for cells. It may be aerobic or anaerobic.
c. Aerobic respiration in plants and animals ultimately depends on photosynthesis. Explain this
dependence.
d. What is an advantage of aerobic over anaerobic respiration?
The following drawing shows a portion of the undersurface of a leaf at two different times of
day.
In this drawing, the arrows indicated by
A. label V, point to non-respiring cells.
B. label W, point to photosynthetic cells.
C. label X, show the direction of movement of potassium ions.
D. label Y, show the direction of movement of starch molecules.
The following figure shows a drawing of a Chlamydomonas cell with some features labelled.
Chlamydomonas are classified into Kingdom Protista, Phylum Chlorophyta. Each cell has a cell
wall made of a complex molecule called a glycoprotein.
A Chlamydomonas cell has a single large chloroplast containing a green pigment.
Photosynthesis and cellular respiration are two biochemical processes that are crucial for the
maintenance of life on earth.
Photosynthesis takes place in two phases – a light-dependent phase and a light-independent
phase.
One of the products of the reactions of the light-dependent phase takes no further part in the
overall process and is sometimes referred to as a ‘waste’ product of photosynthesis.
e. What is this waste product of photosynthesis?
1 mark
During the light-independent phase of photosynthesis, sugars are formed which are later used in
respiration.
f. Name the high-energy compound produced during cellular respiration of glucose.
1 mark
During cellular respiration, cells vary in the amount of usable energy they produce per molecule
of glucose used.
g. i. Name the condition that determines how much of this high-energy compound is produced.
ii. Compare the relative amounts of high-energy compound produced under the altered condition.
c. In what way is this cell wall not typical of a true plant cell?
Transpiration
Transpiration rate was measured in the bean, Phaseolus vulgaris. Three identical groups were
tested. In group X the soil moisture was high, in group Y it was medium and in group Z it was
low.
The graph below shows the results of the experiment.
It is reasonable to conclude that
A. stomata were closed between 8.00 am and 4.00 pm in group Z.
B. no water was lost between 8.00 pm and midnight in group Z.
C. the rate of water loss through stomata was greatest in group X.
D. at 12.00 noon, water loss in group X was four times greater than water loss in group Y.
ENZYMES
1. Bacteria such as Thermus aquaticus live in hot springs where temperatures are around 90°C.
The most likely reason that the bacteria are able to carry out their metabolic functions in this
environment is that the bacteria
A. have enzymes with a high optimal temperature.
B. can lower the temperature of the cellular environment.
C. use compounds other than enzymes to catalyse reactions.
D. have enzymes other than proteins that do not respond to changes in temperature.
2. In the production of isoleucine from threonine in bacteria (Biochemical Pathway 1 [BP 1]),
the end product acts as an inhibitor of the fi rst enzyme in the pathway. In the production of
arginine (Biochemical Pathway 2 [BP 2]), the end product has no infl uence on other enzymes in
the pathway.
It is reasonable to conclude that in
A. BP 1, if the production of enzyme 3 stops there would be continuous production of isoleucine.
B. BP 2, if the production of enzyme 3 stops there would be continuous production of arginine.
C. BP 1, providing all enzymes are present, the production of isoleucine would be continuous if
there was a continuous supply of threonine.
D. BP 2, providing all enzymes are present, the production of arginine would be continuous if
there was a continuous supply of substrate.
Yeast cells divide rapidly provided they are mixed with warm water to form a suspension and
sucrose is added. Sucrose is unable to cross the yeast cell membrane and is digested into glucose
and fructose by the enzyme sucrase. Sucrase is synthesised within the yeast cell but acts in the
water surrounding the yeast cells.
Question 21
Warming the yeast suspension increases the rate at which sucrose is broken down to glucose and
fructose because warming
A. increases the concentration of the products.
B. increases the frequency of collisions between molecules.
C. improves the .Þ t. between active site of the enzyme and substrate.
D. ensures the pH is optimal for formation of enzyme-substrate complex.
Question 22
The graph that shows the effect of adding more sucrose to the yeast suspension is
The enzyme activity of these microorganisms was investigated over a range of temperatures. The
results obtained were plotted and are shown in the following graph.
The temperature at point X is most likely to be
A. 10°C.
B. 37°C.
C. 57°C.
D. 100°C.
A graph with the same shape would be obtained if the variable plotted on the horizontal axis was
A. pH.
B. amount of light.
C. concentration of substrate.
D. concentration of product.