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Chapter 5
Lesson 2
What are
microorganisms?
Microorganism
An organism
that is too
small to be
seen with the
unaided eye.
Bacteria
A certain type
of organism.
Mold
A kind of
fungus.
Protist
A single-celled
or multi-celled
organism that
shares traits
with plants and
animals.
Kinds of Microorganisms
• Thousand of kinds of microorganisms.
• Most single-celled.
• More bacteria on Earth than all living things
together.
• Bacteria may be shaped like rods, spirals, or
balls.
Kinds of Microorganisms
• 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.
Kinds of Microorganisms
• 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.
Kinds of Microorganisms
• 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.
Kinds of Microorganisms
• The blue coloring in this cheese is actually
mold. This mold, which is related to penicillin,
is safe to eat.
Kinds of Microorganisms
• Penicillin is made by a mold. It kills harmful
bacteria.
Kinds of Microorganisms
• Protists are also microorganisms.
• 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 multicellular.
Kinds of Microorganisms
Golden Alga
Amoeba catching its
prey.
Kinds of Microorganisms
• 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 turn milk
into yogurt. They also help produce certain
kinds of cheese. Yeast is a fungus that makes
bread rise.
Helpful and Harmful
Microorganisms
Ways microorganism are helpful.
• Phytoplankton in the ocean helps produce the
oxygen we breathe.
• Phytoplankton is made of bacteria and protists that
live near the surface of the water. They use
photosynthesis to make their own food. They also
release oxygen providing at least half of the oxygen
in the air you breathe.
Helpful and Harmful
Microorganisms
Ways microorganism are helpful.
• Used to make medicines like penicillin that kill
bacteria that cause disease.
• Remove harmful bacteria from wastewater at water
treatment plants and help clean up oil spills.
• Certain fungi help plants take in nutrients from the
soil helping them grow.
Helpful and Harmful
Microorganisms
Ways microorganism are helpful.
• Cause dead things to decay. Without them,
Earth would be covered with dead plants and
animals.
Helpful and Harmful
Microorganisms
Ways microorganism are harmful.
• The bacteria Salmonella and E. coli can make
you very sick. They grow on raw chicken and
other meats, raw eggs, and other raw foods.
• Harmful fungi can kill crops. They can
also rot wood, spoil food, and cause several
kinds of skin diseases, including athlete’s foot.
Helpful and Harmful
Microorganisms
Ways microorganism are harmful.
• Some kinds algae can suddenly grow very
quickly. This causes the water to turn red and
kills fish.
Helpful and Harmful
Microorganisms
Ways microorganism are harmful.
• The organism that causes ringworm is a
fungus, not a worm. Ringworm spreads easily
and grows best on warm, moist skin.