Why Do Plants
Have Leaves?


The picture at the right shows the
International Space Station. People will
live and work only in the relatively small,
slender cylinders in the middle of the
construction. The rest of the station -the flat, black things -- are solar panels.
These panels convert sunlight energy
into energy usable by people inside the
station.
Well, those solar panels are doing
exactly the main thing done by most
leaves on most kinds of green plants:
They are capturing sunlight energy,
which is something needed by all living
things, from bacteria to backyard trees
to people living in space. The problem
of acquiring energy is always one of
the most important considerations any
living thing has to deal with.
 Therefore,
a leaf's main job is usually this:
 To present its broad surface to the sun so
that inside the leaf's' green tissue the
almost-magical process of photosynthesis
can take place.
Why are leafs green
 http://www.youtube.com/watch?v=aAQ
Ypra4aUs Part 1
 http://www.youtube.com/watch?v=545rq
aOJQD8 Part 2
PHOTOSYNTHESIS

CO2 + 2H2O + sunlight ---> O 2 + (C H2O)n + H2 O
or...
carbon dioxide + water + sunlight --->
oxygen + carbohydrate + water

NOTE: the formula can be presented in other ways as well, for example by
representing the carbohydrate as C6 H12O6 instead of (C H2O)n
 Question : What is the reverse of photosynthesis?

Some carbohydrate remains in the leaf but mostly it's
transported elsewhere in the plant, perhaps into the
stem, or maybe into special underground storage
areas, such as the potato plant's potatoes.

Notice that when we burn wood, basically we're
doing the photosynthesis formula in reverse. We're
breaking down the carbohydrate and producing
carbon dioxide gas and water, plus energy, which,
like sunlight, feels hot and looks bright. In a real sense,
first sunlight was captured in the carbohydrate, then
the carbohydrate was kept for a while in the plant,
and now as the plant burns the sunlight's energy is
being released again.

So is it that simple?

http://www.youtube.com/watch?v=g78utcLQrJ4
http://www.youtube.com/watch?v=mYbMPwmwx8
8

http://www.youtube.com/watch?v=sQK3Yr4Sc_k
http://www.youtube.com/watch?v=3pD68uxRLkM
OTHER THINGS
LEAVES DO
 On



the tree:
they create shade that cools the forest in
the summer
they keep wind from drying out the forest
ecosystem
they provide food for a complex
community of herbivorous organisms,
including deer and many kinds of insects,
which in turn serve as food for insectivorous
birds
 Fallen



onto on the ground:
they are like a blanket that keeps the soil
from temperature extremes
they keep the soil from drying out
they decay and enrich the soil with organic
matter and nutrients that can be recycled
 http://www.youtube.com/watch?v=A4Ys
ook9Vj8
Down on the Forest Floor
 http://www.youtube.com/watch?v=n1i1c
kTF4zk
The Forest Floor
SOMETHING WORTH THINKING
ABOUT


It's worth reflecting about the fact that if we
humans were put into a room filled with
nothing but carbon dioxide, we'd die pretty
quickly. In the same way, if all
photosynthesizing plants were removed from
the Earth, before long we oxygen-needing
animals would die.
Now consider this: Right now humans are
destroying Earth's photosynthesizing plant
communities, especially rainforests and algae
in the oceans (agricultural herbicides and
many kinds of pollution drain into the oceans)
as if our lives did not depend on them...