DBQ on p. 107 – January 16th 2013
1) Describe the relationship between wavelength of light and oxygen yield, when
there was no supplementary light. Up to a wavelength of approximately 670 nm, the
oxygen yield remained constant at around 0.12 oxygen molecules per photon of light.
After that point, oxygen yield decreases with increasing wavelengths of light.
2) Describe the effect of the supplementary light. The effect of the supplementary light
is that it provided smaller wavelengths of 650 nm that contained enough energy to
keep the oxygen yield constant throughout the experiment.
3) Explain how the error bars help in drawing conclusions from this experiment. The
error bars help in drawing conclusions from this experiment because if they overlap it
means that the data points aren’t significantly different. The overlapping error bars
for oxygen yield with supplementary light show that the yield did remain constant,
and any fluctuations were not signficant. On the other hand, the non-overlapping
error bars for oxygen yield without supplementary light show that the yield did
decrease as the wavelength increased.
4) The probable maximum yield of oxygen was 0.125 molecules per photon of light.
Calculate how many photons are needed to produce on oxygen molecule in
photosynthesis. 8 photons.
5) Oxygen production by photolysis involves this reactions:
4H2O  O2 + 2H2O + 4H+ + 4eEach photon of light is used to excite an electron (raise it to a higher energy level).
Calculate how many times each electron produced by photolysis must be excited
during the reactions of photosynthesis. Two times – once for each of the two
photosystems.
DBQ on p. 112 – January 14th 2013
1) Explain the evidence from the graph that convinced Calvin that glycerate
3-phosphate is the first product of carbon dioxide fixation.
2) Explain the evidence from the graph for the conversion of glycerate-3-phosphate to
triose phosphate and other sugar phosphates. In the graph, it shows that as the
percent radioactivity for glycerate-3-phosphate increases, it decreases for triosphate
and other sugar phosphates. This continues after the radioactivities intersect and the
percent radioactivity for triose phosphate and other sugar phosphates peaks, and then
decreases. This could be explained by the conversion of glycerate-3-phosphate to
triose phosphate and other sugar phosphates – because this conversion occurs, the
percent radioactivity decreases for glycerate-3-phosphate and increases for triose
phosphate and other sugar phosphates.
3) Using the data in the graph, estimate how rapidly carbon dioxide can diffuse into
cells and be converted with RuBP to glycerate-3-phosphate.
DBQ on p. 110 – January 10th, 2013
1)
a) Describe the relationship between pH of ADP solution and ATP yield,
when acid incubation was at pH 3.8.
b) Explain why the pH of the ADP solution affects the ATP yield.
2) Explain the effect of changing the pH of acid incubation on the yield of ATP.
3) Explain why there was only a short burst of ATP production.
4) Explain the reason for performing the experiment in darkness.
Performing the experiment in light triggers light-dependent reactions, one of which
produces ATP. Because the point of this experiment was to support the theory that
chemiosmosis produces ATP, all other sources off ATP needed to be cut off.
DBQ on p. 105 – January 9th, 2013
1) Why was pH monitored during this experiment?
The pH was monitored during this experiment to show the change in oxygen
concentration. Carbon dioxide is an acid, so as the pondweed uses it up to produce
oxygen, the pH of the water increases (because it becomes less acidic).
2) Identify the independent and the dependent variable.
The independent variable is temperature and the dependent variable is the pH.
3) Deduce which variable should go on the x-axis and which variable on the y-axis if a
graph of the results is plotted.
Time should go on the x-asis and pH should go on the y-axis.
4) Discuss what conclusions can be drawn about the optimum temperature for
photosynthesis in the green alga Chlorella.
The optimum temperature for photosynthesis in the green alga Chlorella is the
temperature at which the change in pH is the greatest. Water at 22.5˚C had a change in
pH of 0.25, at 25.0˚C it had a change in pH of 0.28, at 27.5˚C it had a change in pH of
0.26, at 30.0˚C it had a change in pH of 0.19, at 32.5˚C it had a change in pH of 0.13.
Therefore, the optimum temperature around 25.0˚C because the change in pH was
greatest. However, when taking the ±0.05 uncertainty into consideration, the actual
optimum temperature could be different because change in pH for most of the
temperatures were very close to each other. Thus it can be concluded that the
optimum temperature is around 25.0˚C.
5) If this experiment is repeated using a different alga, the results may not be the
same. Suggest reasons for differences in the results.
Results could be different for different alga because the optimum temperature for
photosynthesis could be different, or because the concentration of the alga is different.
6) Evaluate the methods used in the experiment and suggest improvements.
The experiment controls the initial concentration of carbon dioxide and the
temperature, which is good because they affect the rate of photosynthesis (and thus
would affect the change in pH). However, the experiment doesn’t control some factors
that could affect the change in pH such as light intensity and the concentration of the
alga. Therefore, a certain light intensity should be set and maintained throughout the
duration of the experiment and a certain alga concentration should be set for all trials
of the experiment.