Question

What is the fixation rate of ${ CO }_{ 2 }$ under the high light conditions in ${ C }_{ 3 }$ and ${ C }_{ 4 }$ plants?

Answer 1

Hint: ${ C }_{ 4 }$ plants are different from ${ C }_{ 3 }$ plants in having physically separated mechanisms of light reaction and Calvin-cycle. This specialized mechanism of these plants makes them perfect for hot and temperate climates.

Complete answer:
The ${ C }_{ 3 }$ plants are the normal plants that we see in our surroundings which don't have photosynthetic adaptations to reduce photorespiration. The standard mechanism of these plants is the fixation of carbon dioxide by rubisco which is the first step of the Calvin cycle as well. As they don't show any adaptations to reduce photorespiration, the ${ CO }_{ 2 }$ fixation rate under high light conditions than their normal environment will show deviation and will be lower than its normal fixation rate. It occurs due to an increase in transpiration and a decrease in carbon dioxide intake.
On the other hand, the ${ C }_{ 4 }$ plants show adaptation to living in areas where there are high temperatures and scarcity of water i.e. mainly tropical climate. In these plants, the light dependent reactions and the Calvin cycle are separated to minimize photorespiration. This kind of mechanism is used by $3\%$ of all vascular plants, mainly that grows in hot conditions. As they are already adapted to high light and temperate conditions, therefore the fixation rate of ${ CO }_{ 2 }$of these plants doesn't show any deviations even in high light density conditions.

Note: ${ C }_{ 4 }$ plants have certain adaptations to live in conditions where there is a high density and temperate climate. Some examples of ${ C }_{ 4 }$ plants are maize, sorghum, and sugarcane. Their main lead is identified by their typical anatomy which is different from ${ C }_{ 3 }$ plants. They maintain low oxygen levels in their leaves by keeping the stomata closed and by modifying the Calvin Benson cycle to prevent water loss and photorespiration.