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Yeast comes in strange forms ...
This is a cake of yeast as used by breadmakers
Dried yeast as used in the kitchen and for home-brewing
Yeast is a living organism. It can be used to make bread and alcoholic drinks such as beer and wine.
Different species of yeast may cause infections such as thrush.
Yeast consists of single cells. They are smaller than animal and plant cells, but slightly larger than bacteria.
These cells also have several similarities with cells of (green) plants and animals, but lots of differences, which is why they are put into a kingdom of their own.
On the outside of the cell is a cell wall, but it is not made of cellulose.
Inside this is a membrane enclosing the cytoplasm.
A yeast cell contains a nucleus, like those in plant and animal cells
There are mitochondria in yeast cells.
There are no chloroplasts in yeast cells.
Yeast cells do contain ribosomes, the same size as ribosomes in animal and plant cells.
Some of these yeast cells have small outgrowths - buds - so they are about to reproduce.
Yeast cell (sectional view) -
click to label
in micrometres (µm) also known as microns
[1µm = 0.001mm = 0.000001m (10-6m)]
size / µm
much variation between strains and growing conditions
What you should know
Yeast is a single-celled organism.
Yeast cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall.
Notes on words:
The word yeast can be both singular and plural, but some people use the term yeasts for different but closely related species.
is the scientific name of (baker's or brewer's) yeast.
Saccharomyces means 'sugar fungus': yeast grows in fruit juice, especially grape juice, and sugar is usually added to bread dough.