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Microbes
By: Ita P. Rodríguez
3rd Grade Homeschool Biology
What is a MICROBE?
 What makes a microbe? We suppose you need a microscope to see
them. That's about it.
 There is a huge variety of creatures in this section.
 They can work alone or in colonies.
 They can help you or hurt you.
 Most important fact is that they make up the largest number of living
organisms on the planet.
 If you spend your life studying them, you would be a
microbiologist.
 Some of them, like viruses, may not even be alive as we currently
define life.
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Prokaryotes
 Prokaryotes do not have an organized
nucleus. Their DNA is kind of floating around
the cell. It's clumped up, but not inside of a
nucleus.
Can You Exist Without a Nucleus?
 You can't, but they can.
 Most prokaryotes are bacteria and bacteria
can do amazing things.
 They are found everywhere on the planet.
Some scientists even think that they may be
found on other planets (maybe even Mars).
Some places you can find bacteria every day
are in your intestines, a cup of natural yogurt,
or a bakery.
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Prokaryotes
 Prokaryotes are the simplest of simple
organisms. Here's the checklist.
 Prokaryotes have no organized nucleus. The
DNA is clumped in an area but there is no
organized nucleus with a membrane.
 Prokaryotes do not usually have any
organelles. They will probably have
ribosomes inside of their cells, but ribosomes
are not technically considered organelles.
Bacterium
 No chloroplasts. No mitochondria. No nucleus.
Not much at all.
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Prokaryotes
 Prokaryotes are very small because they
don't have all of the normal cell machinery.
 Mind you, compared to a bacteria they are big,
but next to an amoeba, tiny.
In this picture, an ameoba
is going to eat a
prokaryote.
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Eukaryotes
 Eukaryotes are what you think of when you think
of a classic "cell" with a nucleus and organelles.
What makes a eukaryotic cell?
 Eukaryotic cells have an organized nucleus with
a nuclear envelope. They have a "brain" for the
cell.
 Eukaryotic cells usually have organelles. They
might have mitochondria, maybe a chloroplast, or
some endoplasmic reticulum.
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Eukaryotes
 Although limited in size by the physics of diffusion, eukaryotic cells
can get very large. There are even some extreme examples called
plasmodial slime molds that can be a meter wide.
 Generally, eukaryotic cells are a couple hundred times the size of a
prokaryotic cell.
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Eukaryotes
 Eukaryotic cells have extra stuff going on and extra parts attached.
 Since they have organelles and organized DNA they are able to create
parts.
 One example is the flagellum (a tail-like structure to help it move). They
could also create cilia (little hairs that help scoot the cell through the
water).
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Virus
Are Viruses Alive?
 We're starting with the smallest of the small here. Some
scientists argue that viruses are not even living things.
It's easier to give you a list of what they can't do as
opposed to what they can. What viruses can't do:
 They can't reproduce on their own. They need to infect
or invade a host cell. That host cell will do all the work to
duplicate the virus.
 They don't respond to anything. You can poke them or
set up barriers, it doesn't matter. They either function or
they are destroyed.
 They don't really have any working parts. While there
are some advanced viruses that seem fancy, viruses
don't have any of the parts you would normally think of
when you think of a cell. They have no nuclei,
mitochondria, or ribosomes. Some viruses do not even
have cytoplasm.
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Virus
 Every virus has a few basic parts.
 The most important part is a small
piece of DNA or RNA (never both).
That strand of nucleic acid is
considered the core of the virus.
 The second big part is a protein
coat to protect the nucleic acid.
That coat is called the capsid. The
capsid protects the core but also
helps the virus infect new cells.
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Virus
Types of Viruses:
 Helical virions: They are set up like a tube. The
protein coat winds up like a garden hose around
the core.
 Polyhedral virions: This shape group includes the
classic virus shape that looks like a dodecahedron
(has 12 sides).
 Complex virus: You may have seen this one in
books with the geometric head and long legs.
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Viruses Makes Us Sick
Symptoms may include:
 Fever
 Runny nose
 Coughing or sneezing
 Headache
 Nausea or vomiting
 Diarrhea
 Pain in the body
 Internal bleeding
 Blisters
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Viruses Makes Us Sick
Since viruses aren't alive, medicine won't
kill them. You can only treat the
symptoms. The best way is to prevent
an infection.
Preventing a viral infection:
 Wash hands
 Keeps hands away from mouth, nose,
and eyes
 Avoid sharing personal items like a
toothbrush
 Avoid sharing food and drinks with
other people
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Viruses Makes Us Sick
Viruses can affect any living organism.
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Bacteria
They Are Alive!
 Bacteria are the simplest of creatures
that are considered alive and they are
everywhere.
 They are in the bread you eat, the soil
that plants grow in, and even inside of
you.
 They are very simple cells that fall
under the heading prokaryotic.
 Bacteria are small single cells whose
whole purpose in life is to replicate.
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Bacteria
Types of Bacteria:
 Spherical shaped: They are in the
shape of little spheres or balls. They
usually form chains of cells like a row of
circles.
 Rod shaped: This shape group (like the
E. coli living in your intestine) are a
bunch of bacteria that look like hot
dogs. They can make chains like a set
of linked sausages.
 Spiral: These twist a little. Think about
balloon animals for these shapes. It's
like a balloon animal in the shape of a
corkscrew.
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Bacteria
What do good bacterias do?
 Some help plants absorb nitrogen from the soil.
 Some bacteria even live inside the stomachs of
cows to help them break down cellulose.
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Bacteria
What do bad bacteria do?
 Some cause diseases.
 Symptoms are the same as viral infections:
 Fever
 Runny nose
 Coughing or sneezing
 Headache
 Nausea or vomiting
 Diarrhea
 Pain in the body
 Internal bleeding
 Blisters.
Since bacteria are alive, you can kill them
with medicine called antibiotics.
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Protozoa
Protists
 Protozoa are also known as
protists. These are the bad boys of
the microbe world (bad meaning
"advanced").
 Protists are eukaryotes with special
structures that may be the base
organisms of multicellular
organisms.
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Protozoa
Slime Molds
 Slime molds are not molds like a fungus. They are actually
independent organisms. There are two big kinds of slime molds.
 Cellular slime molds are actually thousands of individual cells that team
up and work together. They specialize for a short time and some do the
eating, some work on reproduction, and some build special structures.
 Acellular slime molds might also be called plasmodial slime molds. They
can be huge, a couple of feet across, but they are still only one cell. They
are able to grow so large because the one cell is multinucleated. They
ooze across the ground of forests digesting everything they can. When it
comes time to reproduce, they release all sorts of spores (like a fungus).
Acellular
Cellular
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Protozoa
Amoebas
 Amoebas are small-single celled organisms that ooze from place to
place.
 They reach out with one part of the cell, a structure called a
pseudopod (it's like a foot).
 They don't really have a shape because they are constantly on the
move, hunting down food and eating by a process called
phagocytosis.
 They wrap themselves around the food and absorb it into their body for
digestion.
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Protozoa
Protists with Tails
 The next protists are called flagellates because they move with a
specialized tail called a flagellum.
 They live in water and the water inside of dirt.
 The flagella whip around like a not-so-coordinated fish tail. When it
whips, the protist scoots along though the water.
 They do not do well in dry areas. They need that liquid environment to
move.
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Protozoa
Protists with Hairs
 Cilia are short little hairs. The classic example of a ciliate protist is a
Paramecium.
 They are the very complex protists that have little hairs all over their body.
 The hairs flap and push the organism through the water.
 They can even hunt down food and attack them with a structure called a
trichocyst. Instead of surrounding their prey like an amoeba, they take in
the food through an oral groove (a protist version of a mouth).
 They even have a way of getting rid of the food through an anal pore.
 They might not seem like much to you, but the structures are very
advanced for a single-celled creature. They were the first creatures to
have them.
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Protozoa
Parasitic Protists
 Last, we'll talk about the parasites of the protist world. Not all protists
go about their life eating little bits of food in a pond.
 Some, called sporozoans, are nasty little parasites.
 These protists, like all parasites, cannot live on their own, and they harm
the host organism over time.
 A disease called malaria is caused by one example of a sporozoan
protist.
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Fungi
Fungus Among Us
 There are no such things as molds. All molds are actually fungi.

We always heard about mold in the shower or mold on the bread. Mold
is actually a type of fungus. It has a shape called a zygote to be exact.
 While yeasts are single celled fungi, molds are multicellular fungi.
 Bread takes one kind of fungus (yeast) to make it rise. If you leave the
bread out, another type of fungus comes in (bread mold) to break it
down. It's not amazing, but it's true!
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Fungi
Mushrooms
 So what is a mushroom or a puffball? Bunches of strands living
underground are called hyphae (pronounced hi-fah).
 Those strands are the basic fungus in action, decomposing leaves, or
rotting bark on the ground.
 When it's time to reproduce, they develop a stalk and cap. The
mushroom that you see popping out of the ground.
 On the bottom of that cap are a set of gills that have little clubs with fungus
spores.
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Fungi
Zygotes
 These have hyphae-like mushrooms but they reproduce in a different
way.
 When it's time to make more fungi, they create a stalk and release
something called zygospores (thus the name zygote).
 When your bread gets old and green or black, you are seeing a type of
zygote fungus in action. If you wait long enough, you will see the stalks
develop and the zygotes released.
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Fungi
Single Cells
 Sac Fungi are single celled fungi.
 Yeast is used to make several types of food for humans. We need
yeast to make breads.
 We also use them to make alcohol. It's a whole process called
fermentation. Sugars are broken down in an environment without
oxygen. It's called anaerobic fermentation. And voila, alcohol.
 Even though they are single celled, you may find them in colonies.
They reproduce very quickly and hang out together. It takes a lot of
them (because they are so small) to get a lot of work done.
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Lichen
 Lichens are special organisms.
They are actually two types of
organisms in one. It's all about a
fungus and some algae. Lichen is
two organisms working together.
 When you read about fungi we
talked about hyphae. Hyphae are
strands of the fungi that form a
mesh as they grow. In lichen are
actually cells of algae living between
those strands.
 The two organisms work together. The fungus acts as a protector from
the environment and loss of moisture. The algae go about their business
of photosynthesis and creating food. The fungus uses the energy and
the algae are protected and can survive.
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Lichen
 Lichens can live in places that many
organisms cannot.
 Lichens can even live on the side of a
rock.
 They don't need soil.
 Slowly the fungus can break down the
minerals in the rock. The algae provide
energy. They are a self-sufficient team.
 Scientists may call that team a
composite organism. They are both
able to be in places they could not go
alone. It's an advantage for their
survival.
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Lichen
Are we killing off the lichens of the world?
 In some places, yes. Indirectly we may be killing many species of
lichen in the same way that air and water pollution are killing off many
species of amphibians.
 Lichens are very delicate organisms. Changes in the levels of poisons
and toxins hurt the relationship that the fungi and algae have. Always
remember, even if the fungi can survive the poisons, if you hurt the
algae, the whole organism will die. They are dependent on each other.
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Good Microbes
Fixing nitrogen in soil: There are bacteria
that go through a process called fixing
nitrogen.
 These bacteria, living in the roots of plants,
actually help them absorb nitrogen from the
surrounding soil. The nitrogen is very important
for the growth of the plant, and these little
bacteria give them an advantage for survival.
Helping cows eat grass: In the bacteria
section we already told you about a species
that lives in the digestive system in cows.
 These bacteria help cows break down the
cellulose in plants. Similar bacteria live in all
sorts of grazing animals, helping them survive
off plant material.
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Good Microbes
Antibiotics: Scientists have even discovered fungi that will help you battle
bacterial diseases.
 So you get sick, the doctor looks at you and says you have a bacterial
infection, maybe bronchitis. He prescribes an antibiotic to help you get
better.
 Antibiotics are drugs designed to destroy bacteria by weakening their cell
walls. When the bacterial cell walls are weak, your immune cells can go in
and destroy the bacteria.
 Although there are many types now, one of the first antibiotics was called
penicillin. It was developed from a fungus (a fungus named Penicillium
found on an orange, to be exact).
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Bad Microbes
Diseases: Many species of bacteria cause disease in humans, animals, and
even plants.
 Humans worry about bacteria that cause botulism (bacteria living in spaces
without oxygen, such as cans), tetanus and E. coli. You should know that
there are also some good forms of E. Coli living in your intestines. They
help break down food and live a simple life (and yes, they make it smell
down there). There are also E. Coli that can be passed to you from
undercooked meat. These bad bacteria can make you very sick and even
kill you.
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Bad Microbes
A Role in Natural Selection: We don't know of any
viruses that are good for the world.
 They are an important piece of evolution and natural
selection. Weaker and older animals are more easily
infected. Those organisms are removed from the
population so that healthier animals can survive.
 But the virus life cycle only hurts the organisms. Some
even destroy cells in order to reproduce.
 And don't think you are the only one to get sick. Viruses
attack plants and even bacteria.
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Man and Microbes
 Scientists all over the world are experimenting with
viruses, bacteria, and fungi for hundreds of reasons.
Why mess around with these little creatures? They
are the simplest of all organisms. They can also be
the most deadly. That is reason enough to study
them.
Microbes to make medicine
 Scientists are working with microbes and the compounds they create to make
new medicines to save our lives.
 You might be vaccinated for pox or the flu.
 Scientists have studied those viruses to see how they act. Then they came up with
a way to teach your immune system to do battle. If you get sick at all, you will be
able to fight off the infection.
 Labs are also developing drugs that help you fight infections after you get the
disease. We already spoke about antibiotics. Labs are creating new and stronger
antibiotics every day.
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Man and Microbes
Microbes in War
 Although nobody likes to talk about it, humans have a
history of using disease and compounds created by
microbes in warfare.
 Labs were built to create chemical compounds that
would kill people.
 They also isolate diseases (viruses) that could be
released to infect entire populations of people.
 Most of the world has chosen not to develop diseases
for use in war. They realized how dangerous and
uncontrollable these diseases are. Once they are out,
they might not be able to be stopped.
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Man and Microbes
Cleaning the Environment
 Scientists are also working with microbes to help the environment.
 In reality, the environment did not need help; we're just trying to lower the
negative impact we have on the environment.
 Good examples are the bacteria that have developed to break down oil in
the water. If a tanker leaked and oil began to get into the water, these
bacteria could be released to break down the oil. The resulting compounds
would not hurt the environment.
 Scientists are also working with bacteria and fungi to help breakdown
garbage.
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THE END
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