Microbes
Microbes are microscopic organisms
that exist as single cells or cell
clusters. Microbiology is the study of
microbes, including their lives,
features, and impact on the natural
world. The characteristics of
microbes are numerous and diverse.
The large amount of variation within
this group helps explain how microbial
life has adapted to environmental conditions on Earth. In fact, it is thought
that microbes were the earliest life form present. Microbiologists use
classification systems to group microbes based on their similar
characteristics.
The five main groups for microorganisms are
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Viruses
Bacteria
Arcahea
Fungi
Protists
Microbiologists often group these organisms into
one of two general categories, based on cellular
structure. Prokaryotes are organisms that do not
have membrane-enclosed structures, called
organelles, in their cells. Specifically prokaryotes
lack a true nucleus that contains their genetic
material. This group includes bacteria and Archaea.
Prokaryote Cell
Fungi and protists are eukaryotic cells. Eukaryotes
contain membrane-enclosed organelles, like the nucleus,
and are generally larger and more complex than
prokaryotic cells. Viruses are not considered to be living
cells, so they are not classified as either prokaryotes or
eukaryotes.
Eukaryote Cell
Recent advances in technology have allowed scientists
to separate microbes into five main groups based on
genetic information. Scientists use laboratory methods
to compare the DNA sequences of microorganisms. Since
an organism’s genetic material determines its
characteristics, microbes with similar DNA have similar qualities.
Without the ability to compare DNA sequences, scientists might
not have realized that the bacteria and Archaea DNA
classified separately.
should be
Read the article and
answer the following
questions. The
questions are in order of
the article.
1. _____________________
are microscopic organisms
that exist as single cells or
cell clusters.
2. What is microbiology?
3. What were the earliest life
forms present on Earth? In
which Geologic Era did they
first exist? Precambrian,
Paleozoic, Mesozoic, or
Cenozoic
4. What do microbiologists use
classification systems to
group microbes?
5. List the 5 main groups of
microorganisms.
6. Microbiologists often group
these organisms into one of
two general categories –
one group has organelles
and one group does not.
What are the 2 groups?
7. What are membraneenclosed structures found in
eukaryotes?
8. In which category do Fungi
and protists belong?
9. Which type of organism is
most complex, a eukaryotes
or a prokaryote?
10. Are viruses prokaryotes or
eukaryotes? Why?
11. What do scientists use to
separate microbes into the 5
main groups?
12. Microbes with similar
__________________ have
similar qualities.
Viruses
Viruses are infectious agents that affect
cells of almost all types of organisms.
They are the smallest and simplest of
microbes. All viruses contain DNA or
RNA genetic material. A protein shell
called capsid encloses the genetic
material. Many viruses also have an
outer membrane surrounding them.
Most viruses are shaped like rods or
spheres.
Viruses have characteristics of both
living and nonliving things. Even
though they contain DNA or RNA, an
important characteristic of all loving
organisms, viruses cannot reproduce on their own. In order to
survive and reproduce, viruses must invade the cells of a living
organism, called a host. Viruses cannot take in or metabolize nutrients,
produce or get rid of wastes, or move around independently. For these
reasons viruses are not considered to be living organisms. In fact,
viruses are little more than traveling genetic material, floating harmlessly
through the environment until they reach a new host.
The typical virus goes through an infectious cycle with several stages:
 First, a virus must come into
contact with a cell.
 Then, the virus either enters
the cell or it attaches to the
cell membrane and releases
it genetic material into the
cell.
 Once inside the cell, the
virus takes over the cellular
machinery and forces it to
make viral proteins.
 The viral proteins are
assembled to make new
copies of the virus. This
process of entering a host and replicating is called infection.
 Eventually, the newly created viruses are released from the cell,
sometimes destroying the cell in the process. These new viruses
than float around until they come in contact with new potential
host cells. The length of time needed for this process to occur
ranges from a couple of hours to a few days.
Viruses infect all forms of life, from bacteria to people. Viral infections
are extremely common in cells throughout the human body. Although
viruses often damage or destroy the host cells they infect, this process
does not always cause disease. Many viruses enter the body,
reproduce, and leave the body without the host ever reacting to them.
Viral infection of a host cell is not necessarily bad. In rare cases, these
viruses may bring new genetic information that may be of use to the
host cell.
Read the article and answer the
following questions. The
questions are in order of the
article.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
What are viruses?
What are the smallest and
simplest microbes?
A virus contains ______ or
______ genetic material.
What is the name of the
protein shell that covers the
genetic material?
What are the 2 shapes of a
virus?
Viruses have
characteristics of both
__________ and
____________ things.
What can viruses not do on
their own?
What is a host?
Viruses cannot take in or
metabolize ________,
produce or get rid of
_______, or move around
_____.
Are viruses considered to
be living organisms?
What is the first step of an
infectious cycle?
The virus either enters the
cell or it attaches to the
___________
____________
What does the virus
“release into the cell?”
What does the virus “force”
the cell to do?
What is infection?
What happens to the newly
produced viruses once they
are released from the cell?
What is the length of time
for the infectious cycle?
Do viruses always cause
disease or cause harm?
Bacteria
Bacteria are simple, single
celled microorganisms. Since
their genetic material is not
enclosed by a nucleus, bacteria
are considered to be
prokaryotes. Bacteria can be
found alone, in pairs or in
groups of three or more. These
larger groups can look like
clumps or long chains. They can
form colonies of different
sizes, shapes, and colors,
including yellow, green, orange, brown, pink, or white.
Bacteria come in three main shapes:
rods, spirals, and sphere. The shape
of the bacterium comes from the tough
cell wall that surrounds the cell,
provides protection, and keeps the cell
from drying out. Microbiologists
sometimes classify these organisms
based on their shape. Bacteria are also
classified based upon whether they
absorb a dye called Gram’s stain. The
cell wall of some bacteria prevents
from taking in the dye. These are said
to be Gram-negative. Bacteria that
absorb the stain are called Grampositive.
In addition to the cell wall, many bacteria also have flagella
(singular: flagellum), or hair-like whips, that are attached to the
outside of the cell. By beating its flagellum, a bacterium can
propel itself forward. Other bacteria produce slime and glide
around their environment.
Bacteria are able to reproduce very quickly, sometimes making
copies of themselves in less than
15 minutes. The main way they reproduce is asexually by binary
fission. In this process, one bacterium duplicates its genetic
information, grows larger, and than splits in half to form two
daughter bacteria. In this way, bacterial populations can expand
to large numbers in a short amount of time when conditions are
good.
Read the article and answer the
following questions. The
questions are in order of the
article.
1. What are bacteria?
2. Are bacteria prokaryotes or
eukaryotes? How do
scientists know this?
3. Name 3 ways bacteria can
be found?
4. Name 5 colors bacteria are
found.
5. What are the 3 shapes of
the bacteria?
6. The shape of the bacterium
comes from the tough
___________ __________
that surrounds the cell,
provides
_______________, and
keeps the cell from
_____________
_________.
7. What is a Gram Stain?
8. What are the difference
between a Gram-positive and
a Gram-negative bacteria?
9. What is a flagella and what
do they help the bacteria
do?
10. Other bacteria produce
___________ and
_________ around their
environment.
11. How fast can some bacteria
reproduce?
12. What is the main way they
reproduce?
13. What happens in the binary
fission process?
14. Bacterial populations can
expand to large numbers in a
_____________ amount of
_________ when conditions
are _________________