Final answer:
Option 1 is correct, C3 photosynthesis occurs in all plants while C4 photosynthesis occurs only in certain plants, particularly in hot, dry locations to reduce water loss and minimize photorespiration.
Step-by-step explanation:
C3 and C4 Photosynthesis
The correct statement regarding C3 and C4 photosynthesis is that C3 photosynthesis occurs in all plants, while C4 photosynthesis occurs only in certain plants. Therefore, the valid statement is option 1. C3 photosynthesis represents the most common form of photosynthesis in which carbon dioxide is fixed into a three-carbon compound, and it takes place in the stroma of chloroplasts, where the Calvin cycle occurs. C4 photosynthesis is an adapted form that primarily occurs in plants living in hot and dry conditions. The C4 pathway involves an additional set of steps that help the plant reduce photorespiration, which can be a wasteful process that occurs in C3 plants. While C4 photosynthesis requires more ATP energy, it is more efficient in terms of water use, making it advantageous in arid environments and at higher temperatures.
Moreover, both photosynthesis and cellular respiration occur at the same time in plants. However, it's important to understand that the light-dependent reactions of photosynthesis, which produce ATP and NADPH, only occur during daylight when sunlight is available. These light reactions happen in the thylakoid membranes, and the generated ATP and NADPH are then used in the Calvin cycle for the synthesis of glucose. On the other hand, cellular respiration is a continuous process that can occur both day and night in the mitochondria, converting glucose and oxygen into ATP, with carbon dioxide and water as by-products.