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Textbook Reading
Lesson 1: nuclei. Cells without nuclei are
Prokaryotes called prokaryotes.
Introduction
You, me, a tree on your street, and
a bacterium in your body are all
alive. Being alive, all of these
things are made of one or more
cells, the smallest things that are
considered living. Cells have many
parts, and each part has an Figure 2 – Prokaryotic cells, like this one,
do not have a nucleus.
important role in helping the cell
carry out its functions. Some cells What are bacteria?
have a nucleus, which is kind of
like the brain of the cell. Nuclei When you hear the word “bacteria”
(that’s the plural of nucleus) what do you think of? If you’re like
control everything that happens in most people, you probably think of
the cell. things that can make you sick.
Although some bacteria do make
us sick, this is not true for all of
them. In fact, as we’ll see a little
later, some bacteria are very
helpful.
What is true about bacteria is that
they are made of only a single cell,
are prokaryotes, and are very
Figure 1 – The nucleus is sometimes common. They are the most
called the “brain” of the cell.
common living things on Earth. In
When you hear that nuclei control fact, there are more bacteria living
everything that happens in a cell, it in the mouth of a single person
might make you think that all cells than there are people on the
need to have a nucleus. In fact, planet!
however, many cells do not have
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