Hi Lim Zhao,
Plants, like all other living organisms, need to make use of
stored chemical energy in order to perform their life functions -- to
grow, to transport nutrients, to reproduce, and to protect themselves.
They do this all the time, using free oxygen from the air and use the
sugars that they have stored inside to make carbon dioxide and water.
Sounds backwards from what a plant ought to be doing! Plants are
special in that they also perform an almost reverse reaction, that of
converting carbon dioxide and water and other nutrients found in the
soil into sugars plus oxygen, via photosynthesis, aided by the molecule
Here's a web page with lots of photosynthesis links
to learn more about this fascinating reaction.
Plants can only perform photosynthesis during the daytime, and
leafy trees drop their leaves in the autumn in temperate climates, so
they are unable to perform photosynthesis in the winter. They still
perform respiration in order to use stored energy and survive during
these times, though.
(published on 10/22/2007)