These questions tend to focus on leaf structure in relation to photosynthesis, limiting factors, or levels of the gases carbon dioxide and oxygen in the day and night - ie they want to assess whether you appreciate the close relationship between photosynthesis and respiration. Main Lesson Photosynthesis Green plants use light energy to make their own food. They obtain the raw materials they need to make the food from the air and the soil. The carbon dioxide is obtained from the air surrounding the leaves and enters by diffusion through the stomata. The water is absorbed from the soil by the roots of the plant and transported to the leaf through the xylem vessels in the stem and leaf vein.
Light energy is absorbed by a green substance called chlorophyll which is found in plant cells.
The rate of photosynthesis depends on three main factors. Light energy is needed to perform the reaction and so the more light is provided, the faster the reaction can proceed. In reality photosynthesis does not proceed indefinitely in a linear fashion. In other words the plant does not make more and more product. Similarly you could give a plant lots of carbon dioxide but if there is not enough light then the rate of photosynthesis will be limited by the amount of light.