DBQ on p. 114 – January 14th 2013
1) Identify structures I to XI.
2)
a) Calculate the width of the chloroplasts. Approximately 1.2 µm.
b) Estimate the total length of the chloroplast. Approximately 4.3 µm.
3) Deduce, with reasons, whether the chloroplast had been in the dark or in the light.
Lipid droplets, which indicate that the chloroplast has been photosynthesizing rapidly,
are visible in the electron micrograph. Because a plant would photosynthesize more
rapidly in the light than in the dark, it can be deduced that this chloroplast had been in
light.
4) State three membrane-bound organelles that are likely to have been in the parts of
this cell that are not visible in the electron micrograph.
Mitochondria, vesicles, and lysosomes.
Question 2 on p. 22 (SG) – January 9th 2013
2)
a) State the relationship shown in the graph between
(i) light intensity and CO2 concentration
Inverse relationship – as light intensity increases, CO2
concentration decreases.
(ii) temperature and CO2 concentration
Inverse relationship – as temperature increases, CO2 concentration
decreases.
b) Deduce, from the data in the graph, whether the effect of light intensity or
temperature on carbon dioxide concentration is greater.
The effect of temperature is greater than the effect of light intensity.
c) The graph shows both rises and falls in CO2 concentration. Explain the
causes of
(i) rises in CO2 concentration
The light intensity was at 0 lux and the temperature was low –
photosynthesis was not carried out, so the CO2 concentration increased.
(ii) falls in CO2 concentration
Both the light intensity and the temperature were high – the rate of
photosynthesis was fast, so the CO2 concentration decreased.
DBQ on p. 104 – January 9th, 2013
1) Why are the following procedures necessary?
a) Boiling and then cooling the water before the experiment.
This removes the carbon dioxide and other dissolved gases (that were in the
water) so that the concentration of carbon dioxide can be controlled.
b) Keeping the water at 25˚C and brightly illuminating it.
The temperature affects the rate of photosynthesis because it affects the
enzymes that carry out carbon dioxide fixation – converting carbon dioxide into
sugars. Light also affects the rate of photosynthesis because as the light intensity
increases, the carbon dioxide uptake increases (at a decelerating rate). Controlling
these two variable ensures that the change in the rate of photosynthesis is caused
solely by the change in the concentration of carbon dioxide.
c) Repeating bubble counts until several consistent counts have been
obtained.
This ensures that if there are anomalies, they can be identified. If several
consisten counts aren’t obtained, you wouldn’t be able to discern which results are
anomalies and which are valid.
2) What other factor could be investigated using bubble counts with pondweed and
how would you design the experiment?
Another factor that could be investigated is the effect of temperature on the
rate of photosynthesis. Instead of changing the concentration of carbon dioxide, you
could change the temperature of the water (e.g. increasing it by intervals of 5˚C).
3) How could you make the measurement of the rate of oxygen production more
accurate?
You could make the measurement of the rate of oxygen production more
accurate by carrying out at least five trials and finding the average of the five bubble
counts (if there is an anomaly it should be disregarded). Also, distilled water could be
used from the beginning so that removing carbon dioxide/other dissolved gases is
unnecessary.