Final answer:
The maximum rate of CO2 utilization in plants often reaches a plateau due to enzymatic saturation, particularly of the enzyme rubisco. Additional factors such as temperature and water availability can further limit CO2 uptake, showing that increasing CO2 levels alone will not indefinitely increase photosynthesis.
Step-by-step explanation:
The maximum CO2 utilization rate in plants such as the tomato and oxalis is reached due to saturation points in their physiological processes. One of the main reasons higher intensities do not cause an increase in the rate of CO2 use once the maximum rate has been reached is saturation of the enzymes involved in CO2 utilization, such as rubisco. Rubisco is an enzyme that fixes CO2 during photosynthesis, but it operates efficiently only within a certain concentration range of CO2. Once the concentration of CO2 is high enough that all the enzyme active sites are occupied, additional CO2 cannot be processed any faster.
Furthermore, increasing the availability of CO2 does not necessarily increase photosynthesis indefinitely due to other limiting factors such as light intensity, temperature, and water availability. Temperature affects enzyme activity, and extremely high temperatures can lead to a decrease in enzyme efficiency. Alongside this, water scarcity can lead to the closure of stomata to conserve water, limiting CO2 intake regardless of the external CO2 concentration.
The other options provided, such as limited availability of sunlight, lack of water supply, and mutation in plant genes, could also affect the rate of CO2 utilization under specific circumstances, but in the context of maximum CO2 utilization rate capacity, the primary factor is usually enzymatic saturation.