for the same reason you do
by resperation
Yes, they do. In Biology, respiration is the process in which atmospherical gases, like oxygen or carbon dioxide, exchange with inner organisms gases; for most us, respiration is the process of inhaling and exhaling. The most common gas exchange in nature is oxygen forcarbon dioxyde and viceversa.
photosynthesis
to store energy
Plants need water, carbon dioxide and the right amount of sunlight to be healthy. Those are the main things that I can think of. Water and CO2 are needed for photosynthesis - a process a bit like resperation. Resperation in humans is O2+C6H12O6=CO2+H2O, whereas photosynthesis is CO2+H2O=C6H12O6+O2 (these are not balanced equasions) and if weeds are there pull them out they drank the water of the plants
Plants use the energy from sunlight to carry out photosynthesis.
Plants need sunlight, water, and carbon dioxide to carry out photosynthesis effectively.
Plants need sunshine to carry out photosynthesis.
the chloroplast
plants that's it.
In order to carry out vital activities, plants need to release energy from their foods.
resperation resperation