Plants carry out photosynthesis and respiration as well.
Respiration is carried out all the time by plants but photosynthesis takes place all the time in day time , but does not take place at night as sunlight is necessary for photosynthesis
Plants make their own food by photosynthesis. Carbon dioxide and water react together in the presence of light and chlorophyll to make glucose and oxygen. The glucose is converted into starch, fats and oils for storage. But photosynthesis takes palce only in presence of sunlight.
Plants respire all the time because their cells need energy to stay alive, but plants can only photosynthesise when they are in the light.