Grade 7 Science- Mr Laura
Name:___________________ Date:_____________
Yeast- taken from http://scienceforkids.kidipede.com/biology/cells/yeast.htm
Yeast cells are a very common kind of eukaryote cell. They vary
in size, but are usually about 4 thousandths of a millimeter (4
microns) in diameter, too small to see without a microscope.
Yeast are one-celled creatures that eat starches and sugars.
Enzymes inside the mitochondria in the yeast cells use oxygen
to break up the food molecules into smaller molecules and let
out some energy for the cell to power itself. This process also
makes some carbon dioxide molecules, and the yeast cell
considers the carbon dioxide molecules to be garbage, puts them
in vacuoles, and gets rid of them through the cell membrane.
Yeast cells budding
When there's plenty of food, yeast cells
reproduce themselves to take advantage of it. To
reproduce, most yeast put out a small bud from
one side of themselves, and move a piece of
their nucleus into it, and then they gradually
pinch off the bud to make a new, smaller yeast
cell. Yeast can also reproduce in a more
complicated way through meiosis.
Some yeast cells are always floating around in
the air, where they are too small for you to see.
They like to get into berries and eat them. When
they get into a berry or other food, yeast cells eat
the starch or sugar and poop out carbon dioxide.
That's what makes champagne fizzy, and it's what makes bread rise: a lot of carbon dioxide gas
in it. (The word "yeast" comes from an old Indo-European word meaning "bubble" or "foam").
All forms of alcohol, like beer or wine, are made by certain yeast that eat sugar and poop out
alcohol. Yeasts often get into food when we don't want them to and make it go bad, like when
the cider gets fizzy, or the orange juice tastes funny. When yeasts get a chance to get inside you,
they can also cause diseases known as yeast infections. When babies get thrush in their mouths,
for example, that's a yeast infection.
- See more at: http://scienceforkids.kidipede.com/biology/cells/yeast.htm#sthash.3JA16l4M.dpuf
Grade 7 Science- Mr Laura
Name:___________________ Date:_____________
You can see what yeast does by making bread at home. It doesn't matter what recipe you use as
long as the recipe calls for yeast. You can buy little paper packets of yeast at any big grocery
store, and all you really need for bread is flour, water, and the yeast.
Your packet of yeast will say (or your recipe might say) to pour the yeast into warm water. That's
because when yeast are too cold they just sit still and don't bud into more yeast, and when yeast
are too hot they die. To make your bread rise you want lots and lots of happy warm yeast.
You'll need to leave your bread alone for a while to let it rise. That gives the yeast time to bud
over and over again and make a lot of baby yeast cells. The dough rises because it is full of
carbon dioxide gas pooped out by the yeast. The gas takes up more room than the flour
molecules did before the yeast broke them up.
After the bread is baked, look for the little holes in the
bread. Those were made by bubbles of the carbon dioxide
that popped during the baking. They make your bread all
fluffy and soft. (You could compare this yeast bread to pita
bread or matzoh, which are made without yeast, to see the
difference.)
When you bake the bread, the yeast all die, so there are no
live yeast in the bread you eat.
- See more at:
http://scienceforkids.kidipede.com/biology/cells/doing/yeast.htm#sthash.6OAmxEzG.dpuf