Why hello again Biology learners.
Welcome back to lab day!
Today we are going to be looking at fermentation,
specifically alcoholic fermentation in yeast.
So I don't know about you but I love to show
up at the grocery store right when those big
loaves of french bread come right out of the
oven.
I could literally just stand there and eat
that entire thing, just crack it open and
pull out all that bread.
You know what, I'll be right back, hold on.
Oh no I gotta do this first before I can go
to the store.
So, anyways, the thing I love most about that
bread is it's light fluffiness and that great
bread smell that you get.
How do all those air holes end up in that
bread?
Well, it's the yeast.
When yeast are doing alcoholic fermentation
they are making not only ethyl alcohol, but
they are also making the gas CO2.
Now when we when bake the bread the ethyl
alcohol gets baked off, but the CO2 is what
leaves those nice fluffy bubbles in our bread,
makes our bread nice and light and fluffy.
So today we are going to be investigating
which sugar yeast likes best and we will know
which one yeast likes best because that will
be the one that produces the most carbon dioxide.
So the sugars we are testing today are glucose,
which is a monosaccharide, dextrose which
is also a monosaccharide, and we are also
testing two disaccharides, lactose and sucrose.
When you get back to your lab you are going
to see you have a baggie that has 5 balloons
in it and you have a piece of string.
You also have a little sauce cup that has
exactly 5 grams of yeast, this is enough for
your 5 balloons, you want to make sure you
make very good measurements.
I have an empty sauce cup which is going to
be my tare cup, remember back to the gummi
bear lab, we are going to use a tare cup.
Ihave a balance, I have a ruler, I haz sharpie,
and I also have a graduated cylinder.
First thing I am going to when I get back
to the back is that I am going to get my balloons
and I am going to label them.
So I have labeled this balloon here, this
is going to be my glucose balloon.
So I am going to label my balloons glucose,
sucrose, lactose, dextrose and then water,
because that is going to be our control.
Once I have done that I am going to get my
tare cup.
I'm going to put it on my balance and zero
it out so that my balance doesn't see the
cup.
And I am going to measure out 1 gram of yeast,
so I am going to measure one gram here.
Alright so I got one gram of yeast.
I'm going to take my balloon that says glucose
on it and I am going to pour that yeast into
the balloon, maybe.
Lets see here, my cup is a little fragile.
These cups should be bendable so you should
be able to do this without breaking them so
let me pour my yeast into my balloon here.
Now there is going to be some static issue
so you might need to use your finger to help
it along a little bit.
So I got my yeast in my ballon.
It's hanging out in there and now I am going
to go ahead and get my glucose solution.
Now all of your sugar solutions are hanging
out in a water bath because we are trying
to keep them to a certain temperature.
Yeast likes warm temperatures, so we are trying
to make sure your solutions stay there.
I am going to grab my glucose container, so
you can see it says glucose here, and I am
going to measure out 25 mL of glucose using
my graduated cylinder.
There we go.
I'm going to take these 25 mL of and I am
going to pour it into my balloon that has
the yeast in there already.
Alright.
Now I don't want any excess air in here, remember
we are trying to do anaerobic respiration
so we want to get rid of the air so I am going
to squeeze the air out and then I am going
to go ahead and tie this balloon off.
I am going to squish it so that I get that
yeast and glucose all mixed together and then
I need to make a couple of measurements.
First thing is I need to mass this balloon,
so I am going to put it on my balance, find
the mass, that is my initial mass of my balloon.
And then i need to measure the circumference
of my balloon so I am going to take my string,
and I am going to measure, here I need a helper
but I'm going to use my mouth.
No that's not going to work.
I'm going to measure around the circumference
of my balloon using my string and then I am
going to use my ruler to figure out what that
circumference is in centimeters.
So right now the circumference of my balloon
in centimeters is about 10.
So i am going to write that down for initial
circumference.
Now I am going to repeat this for all 4 of
my other balloons, including my control balloon,
and then I am going to let them sit for 20
minutes.
After 20 minutes we will come back and see
which balloon is the biggest which means that
yeast preferred that sugar and made the most
carbon dioxide.
I hope you enjoy the lab and don't eat the
balloons.
