Question

questions 2 and 3 refer to the following

figure 1 effect of light intensity (\\( \mu \mathrm { mol } \cdot \mathrm { m } ^ { - 2 } \cdot \mathrm { s } ^ { - 1 } \\) ) on the ph of a solution containing algae
students investigated the effect of light intensity on the rate of photosynthesis and cellular
respiration in algae. they placed equal numbers of algal cells into test tubes containing a
solution at ph 7.40. the test tubes were divided into four treatment groups, and each treatment

2
which of the following claims is best supported by the data?
a algae only carry out photosynthesis when exposed to
\\( 200 \mu \mathrm { mol } \cdot \mathrm { m } ^ { - 2 } \cdot \mathrm { s } ^ { - 1 } \\)
b algae double the rate of photosynthesis when the light intensity

c algae that are exposed to \\( 50 \mu \mathrm { mol } \cdot \mathrm { m } ^ { - 2 } \cdot \mathrm { s } ^ { - 1 } \\) of light perform
photosynthesis instead of cellular respiration
d algae that are exposed to \\( 100 \mu \mathrm { mol } \cdot \mathrm { m } ^ { - 2 } \cdot \mathrm { s } ^ { - 1 } \\) of light have a greater
rate of photosynthesis than of cellular respiration over time

Explanation:

The graph shows light intensity on the x-axis and pH on the y-axis. Algae perform photosynthesis (absorbing CO₂, raising pH) and cellular respiration (releasing CO₂, lowering pH). At low light intensities (e.g., 100 μmol m⁻² s⁻¹), the pH of the algae group is lower than the control (no algae), meaning net CO₂ release (respiration > photosynthesis). At 200 μmol m⁻² s⁻¹, algae pH exceeds the control, indicating net CO₂ absorption (photosynthesis > respiration). Option A incorrectly claims algae only do photosynthesis at 200; they do both but net photosynthesis starts there. Option B has no data for doubling rate. Option C: 300 μmol m⁻² s⁻¹ shows algae pH higher than control, so net photosynthesis, not respiration. Option D: 100 μmol m⁻² s⁻¹ algae pH is lower than control, meaning higher CO₂ (respiration > photosynthesis).

Answer:

D. Algae that are exposed to 100 μmol m⁻² s⁻¹ of light have a greater rate of photosynthesis than of cellular respiration over time