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Chapter 5 Lesson 2
What are Microorganisms?
Vocabulary Preview
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Microorganism: an
organism that is too small to
be seen with an unaided eye
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Bacteria: a certain type of
microorganism
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Mold: a kind of fungus
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Protist: a one-celled
organism that shares traits
with plants or animals
Kinds of Microorganisms
Microorganisms: are living things
that are too small to see without
a microscope.
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The environment contains
thousands of kinds of microorganisms.
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Most have only one cell.
You probably have some of this
kind of bacteria, called staph, on
your skin right now. Staph
bacteria can cause annoying
pimples or boils. They can also
cause serious infections of the
blood, bones, and lungs
Strep bacteria can
be a serious health
threat. They cause
illness in newborn
babies. They can
also harm
pregnant women,
children, older
adults, and adults
who have certain
other illnesses.
The blue coloring in this
cheese is actually mold.
This mold, which is
related to penicillin, is
safe to eat
Penicillin is a substance made by a mold. It
kills harmful bacteria. First used during
World War II, it prevented thousands of
deaths from infection.
Bacteria
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Bacteria: is a microorganism.
There are more bacteria on Earth than all
other living things together.
Bacteria may be shaped like rods, spirals,
or balls.
Mold
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Yeasts and molds are fungi that are
microorganisms.
Fungi look a little like plants, but they
can’t make their own food.
Fungi are decomposers.
They break down decaying plants and
animals in the environment.
Protists
Marine
Protists
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Single-celled
Protist
Protists are also microorganisms.
There are about 80,000 kinds of protists.
Some, like algae, make their own food.
Others, such as protozoans, hunt for food
like animals do.
Protists can be single-celled or multicelled.
Microorganisms
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Microorganisms are everywhere!
Certain bacteria in our digestive systems help
break down the foods we eat.
Without them, we could not use the nutrients in
the food.
Without other microorganisms, we would have
fewer foods to eat.
Bacteria turns milk into yogurt.
They also help produce certain kinds of cheese.
Yeast is a fungus that makes bread rise.
Helpful Microorganisms
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Many more microorganisms help people
that harm them!
Without phytoplankton in the ocean, we
wouldn’t have enough oxygen to breathe.
Other microorganisms make important
medicines such as penicillin.
These medicines kill bacteria that causes
diseases.
Plankton
Phytoplankton is made of bacteria and
protists that live near the surface of the
water. These organisms use
photosynthesis to make their own food.
They also release oxygen. Phytoplankton
produces at least half of the oxygen in the
air you breathe.
Helpful
Microorganisms
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Some microorganisms
remove harmful bacteria
from wastewater at water
treatment plants.
Others help clean up oil
spills.
Phytoplankton is the main
food for tiny fish, which
are eaten by bigger fish.
Without phytoplankton,
there would be few fish
that we could eat.
Helpful
Microorganisms
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Certain fungi help plants
take in nutrients from the
soil.
Without nutrients, the
plants wouldn’t grow
well, if at all.
There would be fewer
plants.
This would mean less
food for people and other
animals.
Helpful Microorganisms
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Microorganisms cause
dead things to decay.
Without them, Earth
would be covered in
dead plants and
animals.
We depend on
microorganisms in all
of these ways to
survive.
Harmful Microorganisms
Salmonella
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Some microorganism are
harmful.
The bacteria in Salmonella and
E.Coli can make you very sick.
They grow on raw chicken and
other meats, raw eggs, and
other raw foods.
Cooking kills them.
Harmful bacteria also grow on
cooked food that is left out of
the refrigerator for 2 hours or
longer.
This kind of algae can suddenly
“bloom,” or grow very quickly.
People call this reddish water a red
tide, though it has nothing to do
with tides. Some algae in a red tide
contain a poison that can kill fish.
The organism that
causes ringworm is a
fungus, not a worm.
Ringworm spreads
easily and grows best
on warm, moist skin.