Grass and most other plants are green because they contain a pigment
known as chlorophyll. The chlorophyll is used in the process of
photosynthesis where a plant produces sugar in the presence of
sunlight. In fact the word 'photosynthesis' means literally to
synthesize or 'make' from light (photo). There are, of course some
plants which do not contain chlorophyll, and these generally get their
nutrition (food) by other means. Some examples are the fungi which
decompose dead, and sometimes living, tissue, for their food.
You will find that a green plant needs light to make food. If the
source of light is cut off, the plant dies. Mushrooms, which are
fungi, do not require light to make food (they decompose matter
as I mentioned above) and you can find mushrooms growing in almost
total darkness.
The process of photosynthesis is described in great detail in many
science books. It is really the process by which life as we know it
is able to continue and renew itself.
