This means that they have to eat other things to get the carbohydrates, fats, proteins, vitamins and minerals which they need. When plants are in the sunlight they can make a sugar called glucose. All the carbon needed for photosynthesis comes from carbon dioxide. All the hydrogen comes from water. When plants use carbon dioxide and water to make glucose there is a lot of oxygen left over.
Light energy is trapped by a green chemical called chlorophyll.
In photosynthesis, light energy is converted into chemical energy. When animals and plants respire, the chemical energy in glucose can be converted into other forms of energy e.g. kinetic energy. Plants can make enough glucose on a sunny day to last them through the night and through lots of cloudy dark days, but they cannot store up lots of glucose. What they do is convert the extra glucose into starch. When they need to use the energy, they can turn the starch back into glucose.