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Following are some of the Statements regarding the effect of CO2 concentration on photosynthesis in plants.
P. With elevated CO2 levels, C3 plants are much more responsive than C4 plants under well watered conditions.
Q. In C3 plants, increasing intracellular CO2 partial pressure can stimulate photosynthesis only over a narrow range.
R. In C4 plants, the CO2 compensation point is nearly zero.
Which one of the following combinations of above statements is/are correct?
P and Q
Q and R
Pand R
R only
Answers (1)
in C3 plants, increasing intracellular carbon dioxide (CO2) partial pressure can indeed stimulate photosynthesis, but only over a relatively narrow range. This phenomenon is known as the CO2 compensation point.
C3 plants, which include the majority of plant species, initially benefit from increasing intracellular CO2 levels as it enhances photosynthesis. This is because CO2 is an essential substrate for the carbon-fixing enzyme, RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase). At low intracellular CO2 concentrations, RuBisCO can bind with oxygen instead of CO2, leading to a process called photorespiration that reduces the efficiency of photosynthesis.
When intracellular CO2 partial pressure increases, the likelihood of RuBisCO binding with CO2 instead of oxygen also increases. This leads to enhanced carbon fixation, resulting in higher photosynthetic rates.
However, beyond a certain point, further increases in intracellular CO2 partial pressure have diminishing returns on photosynthesis in C3 plants. This is because other factors, such as the availability of light and other nutrients, can become limiting. Additionally, excessive CO2 concentrations can lead to stomatal closure, reducing the entry of CO2 into the leaf, which can negatively impact photosynthesis.
Therefore, Statement Q is wrong. Hence, the correct answer is option 3.
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