Mr. Carl's E-Class

Topic:  Bacteria

The Bacteria Cell | Two Kingdoms of Bacteria | Reproduction in Bacteria
Survival Needs | Bacteria and the Living World | Links


The Bacteria Cell

Bacteria have been on the Earth for millions of years.  It wasn't until the late 1600s that scientists discovered bacteria.  In fact, bacteria were discovered by accident.

Anton van Leeuwenhoek accidentally noticed them while looking at scrapings from his teeth through a very simple microscope.  He did not know what they were, but he was essentially the first person to see bacteria.

Bacteria are prokaryotic cells.  What does prokaryotic mean?  (Answer)

Bacteria cells come in a variety of shapes and sizes.  For our purposes, however, we will focus on the three main shapes:  spherical, rodlike, and spiral.
Spherical
Rodlike
Spiral

All bacteria have the same basic structure.  Most bacteria cells have a cell wall.  The cell wall is rigid and provides protection for the bacteria cell.

Beneath the cell wall is the cell membrane.  What function does the cell membrane serve?  (Answer)

Since bacteria cells do not have a nucleus, the genetic material simply floats around in the cytoplasm.  Remember, the genetic material contains the instructions for all of the bacteria cell's fuctions.

Some bacteria cells have flagella or tiny whip-like structures.  A bacteria may have one flagellum or many flagella.  A bacteria will use its flagella to move in its environment.  Bacteria that do not have flagella cannot move on their own.  They rely on air or water currents, clothing, or other objects to carry them from place to place.

Why would a bacteria that has flagella be at an advantage over a bacteria that does not have flagella?  (Answer)

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Two Kingdoms of Bacteria
 
 
Archaebacteria
Eubacteria
Very old bacteria, i.e. evolved a long time ago.
More recently evolved bacteria.
Many live in extreme environments such as hot springs, salty water, and acidic environments.  Some live in or on organisms.
Live in or on organisms.
Autotrophic or heterotrophic.
Autotrophic or heterotrophic.
Can be harmful or helpful.
Can be harmful or helpful.
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Reproduction in Bacteria

Bacteria can reproduce at tremendous speeds.  Some bacteria can reproduce as often as once every 20 minutes!  However, bacteria have to have certain conditions in which to reporduce.  These conditions are not often met, and that is one thing that keeps bacteria from growing out of control.

Bacteria reproduce using two basic methods:  asexual reproduction and sexual reproduction.

Asexual reproduction involves only one individual or parent.  The offspring generated by asexual reproduction are exact duplicates of the parent.  Binary fission is the process by which a bacteria splits into two cells.  Each cell gets an exact copy of the parent cell's genetic material.


Binary Fission

Sexual reproduction involves the joining of two parent cells and the exchanging of genetic materials.  In sexual reproduction, the offspring will have a mixture of the parent cells' traits.  Conjugation is the proces by which bacteria join and exchange genetic materials.  Once genetic materials are exchanged, each bacteria cell will go through binary fission to produce an offspring with a new genetic makeup.

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Survival Needs

Bacteria have the same needs as many other organisms.  They must obtain food, break the food down, and protect themselves from their environment.

Some bacteria are autotrophs.  Some bacteria are able to harness the sun's light and convert it into energy much like plants do.  Other bacteria obtain food by breaking down chemicals within their environment.

Other bacteria must obtain food by consuming other substances.  These substances can include autotrophic or heterotrophic organisms, milk, meat, and decaying materials.

The process of breaking down food to obtain energy is called respiration.  Most bacteria need oxygen for this process.  Some bacteria do not need oxygen for this process.  Still other bacteria are killed if they are exposed to oxygen.

When bacteria encounter a hostile environment, they may form what is called an endospore.  An endospore is a small, round, thick-walled structure that houses the bacteria's genetic materials.  Endospores are very resistant and can protect a bacteria's genetic material from freezing, heating, and drying out for many years!

Once an endospore lands in a more suitable environment, it will open up and the bacteria will begin to grow and multiply again.

Why would it be advantageous for bacteria to be able to form an endospore?  (Answer)
 

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Bacteria and the Living World

When we read or hear the word "bacteria" we often think of getting sick.  However, not all bacteria are harmful.  Some bacteria are very helpful to humans.  In fact, without certain bacteria, human life would be a lot more difficult.

Bacteria are involved in the production of fuel, food, and medications.  Bacteria are also used in environmental recycling and clean-up.

Methane is a gas produced by bacteria that live in oxygen-free environments like the bottom of swamps and lakes.  Methane comprises approximately 20 percent of the Earth's natural gas deposits.

The next time you eat cheese or yogurt, thank bacteria.  Bacteria that grow in milk are responsible for the production of products like cheese, sour cream, and yogurt.

Some bacteria are decomposers.  That is, they feed on decaying matter and break it down.  If it wasn't for bacteria that act as decomposers, the world would be overrun by environmental wastes such as dead animal and plant materials.

Some bacteria are able to eat harmful substances like oil.  These bacteria are used to help clean up oil spills or gasoline leaks.

The human body is full of helpful bacteria.  In fact, if it wasn't for certain bacteria in your body, you would become ill.  The human digestive tract is full of these helpful bacteria.  Essentially, these bacteria serve two purposes - they help prevent other harmful bacteria from growing and they help humans digest their food.

Why do you think people tend to think bad things when they hear the word "bacteria"?  (Answer)
 

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Links

Check out a few of these links to learn even more.
 
  • Bacteria and Viruses
  • Introduction to Bacteria
  • FloraFood
  • Prokaryotes, Eukaryotes, and Viruses Tutorial
  • Molecular Structure
  • Cells Alive
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    Prokaryotic means that the cell does not contain a nucleus.
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    The cell membrane controls what substances pass into and out of the bacteria cell.
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    Bacteria with flagella could move wherever it needed to go.  They could move to find food or other things that they need.  Likewise, bacteria with flagella could avoid other cells that may try to harm them.  Bacteria without flagella must depend on fate to get the things they need and to avoid being destroyed.

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    Forming endospores would help bacteria stay alive when conditions are not favorble.  Likewise, the formation of endospores may make it difficult for humans to kill bacteria.
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    People tend to only hear about bacteria when they have done something harmful.  The media has not really played up the helpful roles that bacteria play in our society.  It is up to us to spread the word - not all bacteria are bad.
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