Photosynthesis occurs in their Chloroplasts, which only plants have. This means that plants undergo photosynthesis to create their own energy. Water(from the ground) + CO2(Carbon Dioxide) + Light(Energy) = glucose(sugar or energy) + oxygen. The glucose is the energy that all organisms need to function. Plants just use photosynthesis to make it. Photosynthesis occurs in their Chloroplasts, which only plants have.