Photosynthesis is the process through which plants make their food. The process requires the presence of light, carbon dioxide and water. The plants should also have chlorophyll, which is the green colouring matter that helps in absorbing light energy from sunlight. The light energy breaks down water into hydrogen and oxygen atoms which combine with carbon dioxide to make starch and oxygen. There are various experiments you can conduct to prove photosynthesis in a plant.
Put two plants in two buckets or plant pots with soil. Place one of the plants outdoors where there is adequate sunlight and the other plant in a dark place such as a cupboard. Give the two plants equal amounts of water and observe them for 48 hours. The plant in the cupboard will start to wither after 48 hours while the one outdoors will remain healthy. This proves that sunlight is essential for photosynthesis to take place.
Put two leaves from a healthy plant in different glass flasks. Put sodium hydrogen carbonate solution in one flask and potassium hydroxide solution in the other. (Purchase these chemical from any laboratory equipment manufacturer in your area.) Seal the flasks with masking tape to ensure that no air can get in. Water the plant and keep it outdoors. Observe the two leaves for several days. The leaf in the flask with sodium hydrogen carbonate solution will be stronger because of the presence of carbon dioxide. The leaf with sodium hydroxide will be weak because the chemical will have absorbed all the carbon dioxide in the flask, hampering photosynthesis.
Put two plants outdoors where there is sunlight. Give one of the plants adequate water and leave the other one without water. Observe the plants for a week. The plant that has received water will be healthy and the one without water will die. This proves that water is necessary for photosynthesis to take place.