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Here we have geranium leaves we have  A and leaf B today
what we're going to decide or figure out
is which leaf was kept in the dark for
two to three days and which one was
allowed to stay in the sunlight this
experiment is on photosynthesis and
remember for photosynthesis to occur
plants need sunlight water and CO2,  so
sunlight is key.   So one of these leaves
was deprived of sunlight, the way we're
going to test whether or not
photosynthesis occurred is we're gonna
test for starch which is a food storage
product that plants use,  so the first
step in our experiment, we're going to
boil the leaves for 30 to 45 seconds.  The
boiling will help break down the
cellulose cell wall of plants because
the next step after that is , is the  extraction
of our pigments,  so I'm gonna take leaf
A and make sure you keep it separate [from B].  I
have leaf A and Petri plate A I'm gonna
place it in the boiling water
make sure it's nice and submerged for
about 35 or  30 to 45 seconds , you're going to notice
a  change in consistency of the leaf its
going to get very limp and you can see
that the leaf really has changed.  I'm gonna
place it back into the A Petri plate. 
Now I'm going to do the  same thing with
our B leaf.  The  next step then is to extract
the pigments from the leaf so that we
can see our starch reaction.
So we've already boiled our leaves and
now we're gonna place them into the
boiling alcohol.  This is very dangerous
process.  A you can see, we're underneath the fume
hood and we're protected so now what
I'm going to do is I'm going to take the
leaf  A and put it into the alcohol.
Remember we're putting it in the alcohol so
that the chlorophyll and all the other
pigments will be extracted from the leaf.
That way we'll be able to see the starch
reaction when we add iodine to the leaf.
So there's the  A leaf here is the B
leaf.  You're gonna notice the water
turning very dark green.
So now we finished boiling I leaves and you can see the  color of the alcohol is
very very different.
We've extracted most of the pigments and
you're also going to notice that the
leaves are very very fragile now and
they're a very different color.   So here's
our leaf A that's been  boiled in our
alcohol and here is leaf B.
The next step is to rinse the excess
alcohol off,  then we're going to react
the leaf with iodine.   Now remember a
brown purple color will indicated starch
lack of such color will indicate no
starch. So no what I'm going to do is I'm going to
rinse off the excess alcohol from the
leaf. So this is our leaf B Make sure you
keep them straight.   There we have that
one,  and then our leaf A  here.  And so now that
we've rinsed the leaves,  I'm going to add
the iodine onto the leaf and the iodine
will turn a black brown color if there
is starch,  it'll stay this really  light
reddish color if  there's no starch.   Xo I'm
gonna start with leaf A adding iodine.
Now the reaction sometimes takes a
couple of minutes.
Now I'm going to add iodine to leaf B.
I'm just gonna cover the leaf with the
iodine.
And now we'll wait for the color change.
So here we the leaves and  I've
already added the iodine,  You'll notice that this
one's a really dark deep purple color.
Here,  this one on the other hand did not
really change color.  The color that you
see here is basically  because of the iodine, 
and so this is the leaf that produced
starch because starch reacts with iodine
to give you this color. This leaf does
not have starch therefore this leaf did
not carry out photosynthesis it was kept
in the dark.
This leaf carried out photosynthesis and
produced the starch that reacted with
the iodine to give you this color
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