Living organisms must concern themselves
with two things -- capturing energy and reproducing their kind.
On this page we will learn about how
organisms capture energy and
We tend to think that
everything green and
alive on the earth is
a plant. This is
true. The first
organisms were bacteria, and they
are still with us
today and still pumping out
tiny organisms are
prokaryotes, and they
made all higher life
on the earth possible
by altering the
atmosphere so that it
Great among the
bacteria are the
are still providing a
good part of the
appeared, making use
of the more abundant
These green organisms
grew in the oceans,
and some became
They also contributed
oxygen to the
True plants did not
appear until after
bacteria and algae
came out of the ocean
and began to grow on
land. It was on
land that the true
plants evolved, with
their stems, roots,
However, we will
The process of
provides both oxygen
and edible biomass
(leaves, grass, etc)
activity supports life
on the earth.
The earth is an almost closed system.
By this we mean that everything that is here is recycled: the
same molecules are used over and over again. Atoms do not wear
out, but chemical changes require energy. Energy eventually gets
transformed into heat and lost. Fortunately for us, the earth
does receive energy from the sun, which comes into our closed
system and makes life possible.
Photo synthesizers are the primary producers
on earth. They contain chloroplasts, which work as tiny
energy capturing factories.
There are reasons to
believe that chloroplasts
were once independent prokaryote cells that moved into larger
eukaryote cells long ago. Chloroplasts are tiny and green, and
they contain chlorophyll. They
still act like
prokaryotes, and reproduce themselves inside cells
by simply dividing into two identical parts.
So -- what exactly do the chloroplasts do?
Well, let's think for a minute. What are plants made out of?
Wood. Leaves. Tough fibers. Bark. Blossoms. Fruit. Plants
are made mostly out of carbohydrates. Carbon is a very
important component of plant tissues. Chloroplasts capture the
energy from the sun and also capture the carbon dioxide molecules
in the air or
dissolved in the
water.. They make food for the plant and for whatever animal
eats that plant.
have to work with?
Well, they have
water and air. There is carbon in the air in carbon
carbon dioxide is
also dissolved in
water. There is water
in lakes and seas as
well as in the ground.
The sun provides light
and heat energy. The plants use what they have: carbon dioxide, water,
and light. In a process called photosynthesis, plants capture
energy using only carbon dioxide, water, and light to make a
sugar called glucose. They also release oxygen and water molecules
into the air.
Here is a picture of what actually happens:
Let's see what is happening here. This plant will make one
molecule of glucose.
The plant has 6 carbon dioxide molecules in the air near it.
Each carbon dioxide molecule has one atom of carbon and two atoms
This is where all the carbon in plants comes from -- the air!
Amazing! Trees are made out of the carbon dioxide in the air!
Why do plants put roots into the soil? They need to get minerals
and water. Their roots cling to the soil so that the plant can
This plant has 12 water molecules in the soil near the roots.
Each water molecule has two atoms of hydrogen and one atom
of oxygen. Chemists would write down
The plant gathers up the carbon dioxide from the air. It sucks
up water with its roots.
6CO2 + 12
H2O -- and the sun is shining!
The plant breaks the water molecules apart. This releases
24 hydrogen atoms and 12 oxygen atoms.
The 12 oxygen atoms pair up to make 6 oxygen molecules. They
leave the plant and float out into the air. Later on animals
will breathe them in!
Now, what is left?
6 carbon dioxide molecules (one carbon atom and 2 oxygen atoms
24 hydrogen atoms (left over from splitting water molecules)
Here is the glucose
molecule, a kind of sugar. The plant makes itself out of glucose.
It makes cellulose and starches out of long strings of sugar.
Notice how five of the carbon atoms form a hexagon with just
one oxygen atom in it. Notice how each carbon atom has an oxygen
atom connected to it. Each carbon atom also has at least one
hydrogen atom attached to it as well.
Six oxygen atoms and 12 hydrogen atoms
are left over. They combine to make six water molecules and are
used by the plant or released into the air.
Glucose feeds animals as well as plants. There are glucose
molecules flowing in your blood right now!
This is the process that supports life
on earth. It is called photosynthesis. Plants use the sun's energy
to transform carbon dioxide
and water into a sugar called
glucose. Oxygen molecules and water molecules are released when
the glucose is made.
Now the next question is -- how do animals
use this sugar? Go on to the next page --