What is special about the structure of a plant that allows it to produce its own food?
Plants have specialized organelles within their cells known as chloroplasts. These contain photosynthetic pigments including chlorophyll a and b. Any area of the plant that is green in color is capable of producing food by photosynthesis. This can includes its leaves and stems. Plants require light, carbon dioxide and water to carry out photosynthesis.
Inside a chloroplast are stacks of thylakoids called grana. These contain chlorophyll along with enzymes to aid in the chemical reaction of photosynthesis. Chlorophyll can absorb visible light energy which is used to split water into hydrogen and oxygen. Plants can combine the carbon dioxide and hydrogen atoms to produce carbohydrates like glucose along with ATP which cells use to perform work. They release oxygen gas as their main waste product.
Plants contain special vascular (conducting) tissue in their veins. Water, which is needed for photosynthesis as a reactant, is transported up the xylem tubes (conducting tissue) against gravity to the leaves in a continuous column. One reason it can do this is because water is a polar molecule with an attraction for other water molecules. They tend to stick together (this is known as cohesion). They also tend to stick to the walls of the conducting xylem tubes (this is known as adhesion). As water evaporates by transpiration out of the leaves, it creates a sort of suction allowing water brought in from the root system to move up the column toward the leaves.
Another reactant needed for photosynthesis is carbon dioxide. Plants are adapted to absorb this gas from the atmosphere by diffusion through pores in their leaves known as stomata. The carbon dioxide enters air spaces inside the pores and can diffuse into cells where photosynthesis is taking place.
Because of chloroplasts, chlorophyll, stomata, and conducting tissue, plants are capable of making their own food and are known as autotrophs.