(b) The least malate in a CAM plant would be found at the end of the day.
(c) CAM plants close their stomata during the day to prevent water loss, as they live in dry environments.
(d) The gas that is preferentially absorbed during the cool evening is CO2.
(e) During the dark, CAM plants take in CO2 and incorporate it into C4 organic acids using PEP carboxylase. These are stored in vacuoles until morning.
Applying Inquiry Skills
7. (a) Students should focus on the carboxylation reactions of rubisco and the generation of chemical potential energy, …show more content…
C3 plant numbers are expected to increase relative to C4 plants, as rubisco is reduced inefficiently in C3 plants because of higher atmospheric CO2 concentrations. 3.5 PHOTOSYNTHESIS AND THE ENVIRONMENT
Section 3.5 Questions
Irradiance limits the overall rate of photosynthesis under low light conditions. As irradiance increases, photosynthesis begins. C4 plants generally exhibit higher rates of photosynthesis when compared with C3 plants because of the fact that although photorespiration rates increase with increasing temperatures in C3 plants, the loss of CO2 by photorespiration in C4 plants is almost nonexistent. C4 plants spatially separate the light reactions and the Calvin cycle. This separation means that the concentration of CO2 is much higher than the concentration of O2 in the bundle sheath cells, which means that the rate of
CO2 fixation does not go down because of increase in photorespiration.
Applying Inquiry Skills
The amount of oxygen evolved over time (mmol O2/m2/s) is not a good indicator of the rate of photosynthesis of a plant, because photorespiration and cellular respiration use oxygen as a final electron …show more content…
The student who measured water absorption would not obtain reliable results because the water absorbed by a plant can be required to replace that lost by transpiration, not just photosynthesis. Plants require most of the water they absorb to replace water lost by transpiration, not metabolism.
5. (a) Light compensation point (CO2 uptake = CO2 evolution).
(b) Point A represents the light intensity at which the rate that CO2 is fixed into a carbohydrate is equal to the CO2 produced by photorespiration and cellular respiration.
(c) Light-saturation point.
(d) The light-saturation point occurs when carbon fixation reactions are supplying the Calvin cycle with more ATP and
NADPH than it can use.
Students’ answers will depend on whether they are concerned with highest activity or greatest activity with lowest irradiance. For example, curve A has the highest photosynthetic activity at high irradiance levels; however, curve B has the highest photosynthetic activity at low irradiance levels.
8. (a) C3 plants have a higher CO2 compensation point than C4 plants, because they require higher CO2 concentrations to outcompete O2 for the active site of rubisco. In contrast, C4 plants spatially separate their rubisco enzymes to ensure