(10) Why are most plants on Earth C3 plants? Explain the difference between a C3 and CAM plant in terms of the photosynthetic process. If a plant is a facultative CAM plant, in what conditions would it undergo C3 photosynthesis rather than CAM?

A. C3 plants are likely to appear in areas with moderate temperature, moderate sunlight intensity and plentiful water. And these areas are dominant on Earth.
In C3 plants, stomata are open during daytime; when in CAM plants, nighttime is when they are open.
CAM plants take up CO2 and convert it to malic acid using PEP, then during daytime, they reconvert this acid to CO2, which it then fixes using the C3 cycle. Instead of using PEP, C3 plants have the light reactions to convert solar energy to the chemical energy of ATP and NADPH.
Since it takes more energy for the CAM pathway to photosynthesize, a facultative CAM plant would undergo C3 photosynthesis when their living environments become less arid. It might happen after having a good amount of precipitation.

B.C3 plants, accounting for more than 95% of earth's plant species, use rubisco to make a three-carbon compound as the first stable product of carbon fixation. C3 plants flourish in cool, wet, and cloudy climates, where light levels may be low, because the metabolic pathway is more energy efficient, and if water is plentiful, the stomata can stay open and let in more carbon dioxide. More CO2 equal more photosynthesis.
C3 plants involve direct carbon fixation of CO2. That is, the initial steps involve the CO2 being bound to ribulose bisphosphate to produce two molecules of three-carbon compound (i.e. 3-phosphogylycerate). The key enzyme that catalyzes carbon fixation is rubisco.
C3 plants must however be in areas where CO2 concentration is high, temperature and light intensity are moderate, and ground water is abundant. This is because in hot areas, the stomata are closed to prevent water loss. However, it results in the rise of O2 level. When this occurs, rubisco reacts with O2 instead of CO2, and leads to photorespiration, which in turn, causes wasteful loss of CO2 in C3 plants.
CAM plants often show xerophytic features, such as thick, reduced leaves with a low surface-area-to-volume ratio, thick cuticle, and stomata sunken into pits.
Cam plants utilize an elaborate carbon fixation pathway in a way that the stomata are open at night to permit entry of CO2 to be fixed and stored as a four-carbon acid(i.e. malate).Then, during the day the CO2 is released for use in the Calvin cycle. In this way, the rubisco is provided with high concentration of CO2 while the stomataare closed during the hottest and driest part of the day to prevent the excessive loss of water. CAM plants are therefore highly adapted to arid conditions.

C.C3 plants make the most energy but they also use the most water. Since water is fairly abundant on earth plants want to get the most energy for their water intake. Both C3 photosynthesis and CAM photosynthesis take place in the same part of the leaf. the difference is that CAM plants only open their stomata at night to take up CO2 and stores it for the day to make sugar out of it but, C3 plants leave their stomata open during photosynthesis and everything takes place at the same time. CAM plants can save water this way, but it cost more energy. If the plant is a facultative CAM plant, meaning it can be either CAM or C3 plant, then it would much rather use C3 photosynthesis because more energy is made but it will only be able to when there is water around.

D.The C3 plants, the capture the light energy and transformation of CO2 into sugars occur in the mesophyll cells. CAM plants oopen their stomata at night, taking up CO2, and converting it to malic acid using PEP, which accumulates in large quantities in the mesophyll cells. During the day, the plant closes its stomata and reconcerts the malic acid into CO2, which it then fixes using the C3 cycle. CAMplants dramatically reduce water loss through transpiration and increase water-use efficiency.