When it gets hot what happens? C3 plants: first organic acid made in the process has 3 carbons During photosynthesis there are light and dark reactions. One takes place in the light and one doesn’t need light. In the case of C3 plants, both light and dark reactions take place in the same cells. This can be both good and bad. The good thing is that it allows for the easy transport of Hydrogen atoms. However, when it’s hot and sunny there begins to be excess Oxygen created in the plant’s cells. This is a problem because RuBisCO (enzyme), which is responsible for grabbing CO₂ to work toward producing glucose, will grab Oxygen instead. When this happens, you do not get glucose but rather a process called photorespiration. When a plant is in photorespiration mode, its production is going to be capped. It will utilize far less sunlight than it is capable of and may lose biomass or stop growing. This is especially true if the plant does not have access to good amounts of water. Without water, the plant is unable to cool itself via transpiration. C4 plants: first organic acid made in the process has 4 carbons These plants are productive in hot, summer months because they have a workaround for photorespiration. Unlike the C3 plants above, light and dark reactions take place in separate cells. The light reactions can be found nearest to sunlight (leaf surface). The dark reactions take place closer to the plant’s transportation system (vascular system). This arrangement makes it easier for light reaction cells to release excess Oxygen and for dark reaction cells to move glucose more rapidly throughout the plant. The other reason C4 plants are productive in the heat is that CO₂ is pushed from the leaf to the dark reaction cells. All of this allows for C4 plants to avoid photorespiration. Not only that but C4 plants can use more sunlight than C3 plants and can put on a lot more daily biomass (up to 3x) than C3 plants.