The leaves of plants make all the food that most plants need. They contain a substance called chlorophyll, which makes the leaves look green and which aids in photosynthesis.
Photosynthesis is the process plants use to make food. The chlorophyll in the leaves absorbs light, either sunlight or artificial. This is combined with carbon dioxide, which also is absorbed through the leaves, and water taken in by the roots.
Xylem are specialized cells that carry the water from the roots of the plants up through the stems and into the leaves.
Stomates are little holes in a leaf that allow the carbon dioxide into the plant and also let the oxygen, a byproduct of photosynthesis, escape back into the air.
The leaves of marine plants do not have to worry about drying out, so they are able to take in carbon dioxide without the need of stomates. They still use photosynthesis to produce their food.
Carnivorous plants, such as the Venus Fly Trap or the sundews, supplement their diet by catching insects. They do this by enticing their victims with sweet nectar; once the treat is sampled, the insect is trapped.