SECTION B
1.
The graph below shows the results of an experiment to determine the effect of salt (NaCl)
concentration on photosynthesis of the freshwater green alga Chlorella vulgaris. The
experiment attempted to determine the effect of salt concentration on the light-dependent
reactions overall and separately on photosystem I and photosystem II.
[Source: M M El-Sheekh, “Inhibition of the water splitting system by sodium chloride stress in the green alga
Chlorella vulgaris”, Brazilian Journal of Plant Physiology, Volume 16, Issue 1, Figure 1, (2004)]
(a)
Describe the effect of salt concentration on the activity of the light-dependent reactions
overall.
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(1)
(b)
Compare the effect of increasing salt concentration on photosystem I with the effect on
photosystem II.
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(1)
IB Questionbank Biology
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SECTION B
(c)
When salt concentration is increased, some algal cells increase their rates of cyclic
photophosphorylation. Deduce the reasons for this.
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(2)
(d)
Using the graph, predict the effect of high salt concentration on the growth of Chlorella
vulgaris. Give a reason for your answer.
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(2)
(Total 6 marks)
IB Questionbank Biology
2
SECTION B
1.
Global atmospheric carbon dioxide levels are rising. A study was carried out to test if the
temperature dependence of photosynthesis was altered by elevated atmospheric CO2.
Maize plants were grown in natural sunlight in controlled environmental chambers at different
temperatures using current atmospheric and doubled CO2 levels.
The graph below shows daily patterns of CO2 exchange at three different temperatures.
Open shapes (○, Δ, □) represent current atmospheric CO2 levels and closed shapes (●, ▲, ■)
represent elevated CO2 levels.
[Reprinted from: Kim, S H et al. 2007. “Temperature dependence of growth, development, and photosynthesis in
maize under elevated CO2”. Environmental and Experimental Botany. Vol 61. Pp 224–236.]
(a)
(i)
State the time at which carbon dioxide exchange rate is maximal.
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(1)
(ii)
Explain the reasons for maximum carbon dioxide exchange rate at this time.
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(2)
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SECTION B
(b)
State the temperature that resulted in the highest rate of photosynthesis under current
atmospheric conditions.
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(1)
(c)
Using the data in the graph, discuss whether rising carbon dioxide levels in the
atmosphere will increase growth rates in maize.
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(2)
(Total 6 marks)
IB Questionbank Biology
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SECTION B
2. During aerobic cell respiration, oxygen is consumed and carbon dioxide is produced inside
cells. This generates concentration gradients between respiring cells and the environment, which
cause diffusion of oxygen and carbon dioxide. Both oxygen and carbon dioxide are soluble in
water. As the temperature rises, water becomes saturated at a lower concentration of the gas.
Laternula elliptica is a mollusc that lives on the sea bed in Antarctica. Its body temperature is
always similar to that of the environment around it. To investigate the effect of temperature on
Laternula elliptica, specimens were kept in temperature-controlled aquaria. The oxygen
concentrations of water near the gills and in the body fluids were measured, at a range of
temperatures from 0°C to 9°C. The graph below shows the mean results.
[With kind permission from Springer Science+Business Media and the author.]
(a)
(i)
Outline the relationship between temperature and oxygen concentration in the body
fluids in Laternula elliptica.
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(2)
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SECTION B
(ii)
Suggest two reasons for the relationship.
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(2)
(b)
In its natural environment, Laternula elliptica buries itself in the mud on the sea bed.
In this investigation, it was found that above 6°C it is unable to bury itself. Suggest a
reason for this.
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(1)
IB Questionbank Biology
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SECTION B
IB Questionbank Biology
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SECTION B
ANSWERS
HL1. (a)
overall photosynthesis rates go down with increasing salt concentration
1
(b)
decline in activity for photosystem II but not for photosystem I
1
(c)
cyclic photophosphorylation dependent on photosystem I;
photosystem I is not affected by increasing salt concentration;
2
reduced growth;
due to reduction in rates of photosynthesis/energy fixation;
2
(d)
[6]
SL1. (a)
(i)
12:00 (Accept 12:00 to 13:00)
(ii)
photosynthesis in maize requires uptake of CO2 and light
as energy source;
sunlight intensity strongest at midday therefore rate of
photosynthesis is highest at this time;
light is limiting factor for photosynthesis so increased
intensity increases photosynthesis;
high rate of photosynthesis means high exchange rate of CO2;
(b)
31ºC
(c)
data does not support idea that rising CO2 levels will increase
growth rates in maize;
(at all temperatures) there appears to be no difference between
exchange rate at current or elevated CO2 levels;
temperature has larger effect on growth of maize;
so if rising CO2 levels causes more of a greenhouse effect/larger
temperature increase, this will affect growth of maize;
1
2 max
1
2 max
[6]
HL/SL2.
(b)
(a)
(i)
oxygen concentration falls as temperature rises / negative correlation/
inverse relationship;
steady decline below 4.2/4.3/4.4°C / vice versa:
rapid decrease between 4.2/4.3/4.4°C and 5°C;
zero oxygen concentration at/above 9 °C;
2 max
(ii)
warmer water can hold less oxygen / lower oxygen solubility as
temperature rises;
lower oxygen concentration of water reaching gills / less oxygen
available from the water to diffuse into the gills;
higher metabolic rate / faster rates of respiration / more oxygen
consumption as temperature rises;
2 max
not enough energy/ATP/aerobic respiration (for muscle contraction/movement)
IB Questionbank Biology
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