Photosynthesis is the process by which plants and other organisms use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. The three things necessary for photosynthesis to happen are:

* Light: Light energy is the driving force behind photosynthesis. It is absorbed by chlorophyll, a green pigment found in the leaves of plants.

* Carbon dioxide: Carbon dioxide is a gas that is present in the atmosphere. It is taken in by plants through their leaves.

* Water: Water is essential for photosynthesis. It is taken in by plants through their roots.

These three things are all necessary for photosynthesis to happen. If any one of these things is missing, photosynthesis cannot occur.