Part A:
Plant A is conducting C4 photosynthesis. In C4 photosynthesis, carbon dioxide is fixed into a 4-carbon compound in the mesophyll cells before being transported to bundle sheath cells where the Calvin cycle occurs. This process allows for efficient carbon fixation in hot and dry conditions. The high levels of glucose and starch in Plant A suggest that it is able to efficiently carry out photosynthesis.
Plant B is conducting C3 photosynthesis. In C3 photosynthesis, carbon dioxide is fixed into a 3-carbon compound in the mesophyll cells, which then enters the Calvin cycle. This type of photosynthesis is less efficient in hot and dry conditions compared to C4 photosynthesis. The low levels of glucose and starch in Plant B suggest that it may be less efficient in photosynthesis compared to Plant A.
Plant C is a CAM plant. CAM plants open their stomata at night to take in carbon dioxide and fix it into organic acids, which are stored in the vacuole. During the day, the stomata are closed and the organic acids are broken down to release the carbon dioxide for the Calvin cycle. CAM plants are well adapted to dry conditions. The low levels of glucose and starch in Plant C suggest that it may be conserving resources during the day.
Part B:
Plant B is biochemically defective after the light-independent reactions. This can be deciphered by looking at the levels of glucose and starch in each plant. Since Plant B has extremely low levels of glucose and starch compared to Plant A and Plant C, it indicates that there is a defect in the conversion of photosynthetic products into glucose and starch after the light-independent reactions. This suggests that Plant B may have a deficiency in enzymes or metabolic pathways involved in this process.
Three plants grow side by side in a pond. Glucose and starch are measured for each and shown in relative units below, along with the pH of the vacuole at dawn and at noon.
Plant Glucose Starch Vacuolar pH, dawn Vacuolar pH, noon
A
100
50
100
10
B
C
1,000
2
1
4
4
4
4
4
Part A:
Explain what kind of photosynthesis is being done by each plant with some details about how each works. Justify your answer.
Part B:
Decipher which plant is biochemically defective after the light-independent reactions and explain how you deciphered
this.
1 answer