Plants differ from most organisms on Earth in that they can produce their own food by synthesising sugar from water and carbon dioxide using energy from the sun. Chlorophyll, found in a plant's cells, helps accomplish this process.
You can find chlorophyll inside cellular structures called chloroplasts, the tiny pill-shaped organelles responsible for photosynthesis. All green parts of the plant contain chloroplasts. Within the chloroplast, stacks of round structures called thylakoids contain the chlorophyll. Within these thylakoids, the process of photosynthesis begins.
Photosynthesis begins with light absorption. Chlorophyll absorbs all colours of light except for green -- plants appear green because chlorophyll reflects back the green wavelengths that strike it. This light energises electrons inside the chlorophyll, giving the plant energy to power sugar synthesis.
Plants contain vast numbers of chloroplasts and, therefore, large amounts of chlorophyll as well. One square millimetre of plant tissue can contain 500,000 chloroplasts, according to Florida State University's Molecular Expressions website. The plant parts primarily responsible for photosynthesis, such as leaves, contain more chloroplasts and chlorophyll.