Maintaining Dynamic
Equilibrium
Photosynthesis
and Respiration
The Journey of a Carbon
Atom
Hi…I’m a Carbon Atom and I will be your
guide through this unit on photosynthesis
and respiration.
You will see that these two processes have
a lot to do with each other.
Chemical Equations
What do you notice about their two chemical equations?
Photosynthesis
CO2 + H2O + Sunlight
Enzymes
C6H12O6 + O2
Respiration
Enzymes
C6H12O6 + O2
CO2 + H2O + Energy
My Story…
As you know, carbon molecules like me are
found in many different places. We are
found in inorganic compounds like CO2
When I am with my friend the Hydrogen
atom in a compound, it is known as
organic. For example when we appear
together in glucose C6H12O6.
One day I was happily floating around in
the air as part of a carbon dioxide
molecule when I was sucked up into the
leaf of a blueberry bush!
This was a little bit of a disappointment
because I was enjoying floating around on
the breeze on a nice summer day!
The Leaf…
is where I entered the plant. The stoma on the
bottom side of the leaf are tiny holes. They
open and close with the help of guard cells to
exchange gases and water with the outside
environment.
 Conveniently, the leaf is the part of the plant
where photosynthesis takes place.
Into the Chloroplast!
 When I was sucked into the chloroplast I
knew I wouldn’t be part of carbon dioxide
for long!
Light Reactions
 You see, photosynthesis takes place in a specialized
organelle found in plant cells called the chloroplast.
Grana
The first phase takes place in the grana, where the
pigment chlorophyll is stored. The sunlight shines on
the chlorophyll and this splits molecules of water right
in half!
Dark Reactions
Stroma
 The hydrogen atoms from the water are carried
out of the grana into the stoma where I am
waiting with my oxygen friends.
Sugar!!
Hydrogen is attached to me and my friend
oxygen and you know what that means…
sugar!
Voila…I have gone from inorganic CO2 to an
organic carbohydrate!
Glucose – C6H12O6
That’s photosynthesis…let’s recap…
Photosynthesis Equation
__CO2 + __H2O + Sunlight
enzymes
C6H12O6 + __O2
The blueberry bush will use dehydration synthesis to attach me
to many other glucose molecules for storage. Do you know
what this polysaccharide is called??
I won’t stay for long
STARCH
So here I sit, now I am part of a starch
molecule that is stored in the blueberry
on this bush…
This sounds lovely…BUT there is a deer
sniffing at the bush and it looks like he
just might take a bite!
I’m in that berry…
Well here I go…
 Turns out that deer was hungry and I am
on the move again!
 He took a large bite and all of a sudden I
am in the deer’s mouth!
Digestion…
 That deer chewed me up nice and good and
now I am on the way down his esophagus and
into the stomach.
 You know since I am now part of a starch
molecule I am going to be broken down by
amylase into one molecule of glucose again.
Just like the good old days back in the leaf!
 When I am digested water is added to break
the starch molecule into it’s building blocks. Do
you remember the name of this process?
Hydrolysis
amylase
Starch + H2O
Glucose
Transport…
 Now that I am a single glucose molecule
I can be absorbed into the blood stream
of the deer.
 I will be carried to a cell that needs
energy…this is the life process we call
transport.
TROUBLE!
 This deer has come in contact with a
hunter!! He must run to get away!
Into a muscle cell
 The glucose molecule I am part of is
sucked up into a muscle cell! Glucose
will be used to help this deer run faster
and escape the hunter!
 The muscle cell will use the glucose
molecule to create energy to keep up its
hard work through the metabolic reaction
called cellular respiration.
Cellular Respiration
 These muscle cells need a lot
of energy to keep the deer
moving fast!
 They are loaded with
mitochondria, the organelle
where cellular respiration
takes place.
Respiration Equation
C6H12O6 + __O2
enzymes
ATP is like a mousetrap!
__ CO2 + __H2O + 36 ATP
Step one: Glycolysis
 Once my glucose molecule enters the cytoplasm
of the muscle cell, it is split apart during a process
called glycolysis. This only makes 2 ATP
molecules and makes me part of one of two
pyruvic acid molecules.
Step two: Krebs Cycle
 Now part of pyruvic acid I enter the
mighty mitochondria where I will really
supply some energy!
 Together with oxygen the deer has been
breathing in from the atmosphere we will
make 34 more ATP molecules to keep his
legs going!
CO2 Again!
 Once the ATP molecules
are made I become part of a
waste product carbon
dioxide!
 I am together with oxygen
once again as CO2!
Amazing how fast I have
come full circle!
Out into the atmosphere!
 The deer has no use for carbon dioxide
so the carbon dioxide molecule is carried
by the blood to the lungs and whoosh! I
am exhaled out into the summer breeze
once again…just in time to see the deer
escape the hunter!
 I am glad I could help!
Busy Day!
 So as you can see carbon atoms have a
very important job and we are constantly
changing form!
A Cycle…
 I started the day as a gas in the air (CO2)
 I was sucked up into a leaf and during
photosynthesis became part of glucose
(C6H12O6)
 A deer ate me and used me for energy to
escape a hunter! During this process of
cellular respiration I was converted back into
CO2
 This will all happen to me again before the day
is through!
A Cycle…
Oxygen and Glucose
Energy OUT
Energy IN
ATP
Carbon Dioxide and Water