VirusChapter 4

Viruses

Traits of a Virus:

• Neither living or non-living

• Difficult for scientists to classify

• So small they can only be seen with an electron microscope

• Have many different shapes

• A virus is made of a chromosome-like part surrounded by a protein coat.

• The chromosome like part carries the hereditary material

• Viruses are not made of cells and have no cell parts.

• They do not grow or respond to changes in the environment.

• The Only trait that viruses share with living things is the ability to reproduce

• Viruses only reproduce inside living cells.

http://www.youtube.com/watch?v=A409yO-G1Mk

Grouping Viruses

• Scientists group viruses according to the kind of cell they infect.

• Each kind of virus infects a certain host.

• A host is an organism that provides food for a parasite.

• A parasite is an organism that lives in or on another living thing.

How Do They Spread?

• Human-viruses spread by insects, air, water, food and other people.

• Plants-virus spread by wind or by insects

The only way some viruses can enter a plant is by insects

How do they cause disease?

• Virus attaches itself to the cell• The chromosome like part enters the cell• The chromosome like part takes over the cell• The virus changes the hereditary material in the

host cell so that the host cell produces more viruses instead of performing its usual work.

• The cell breaks open and releases the new virus which invades other cells.

• Tissue damage and disease result.

Do Now:

Students may use books and/or notes:

• List two ways viruses differ from living things.

• Where must viruses be found if they are to reproduce?

• Viruses cause disease by reproducing rapidly. Examples are: polio, mumps, rabies, flu

• These are known as virulent viruses. They cause immediate disease.

• Other viruses may remain hidden in a cell for a long time without reproducing.

• This type of virus is called a dormant virus. Examples: cold sores (herpes)

Controlling Viruses• Diseases caused by viruses are hard to treat or cure.• There are no known drugs that destroy viruses• Certain white blood cells can surround and destroy a

virus.• If the virus is not captured and destroyed by these white

blood cells other white blood cells make chemicals called antibodies.

Antibodies• Help destroy viruses by attaching to them• Each antibody is specific to a certain virus• When human cells are first attacked by a virus the cells

produce interferon• Interferon is a chemical substance that interferes with

the way viruses reproduce.• Interferon will affect any type of virus that invades the

body

http://www.guardian.co.uk/science/2010/nov/01/viruses-immune-system-antibody

• Vaccines are substances made from weakened viruses

• The body reacts to a vaccine by producing antibodies against the disease.

Examples: polio, rubella, measles, influenza

Do Now:

• Are all vaccines necessary and safe? (write 3-4 sentences giving your opinion)

• How is the body’s reaction to a vaccine similar to its reaction when it is attacked by a virus?

• Articles: Pros/cons

http://video.foxnews.com/v/4214127/vaccines-and-autism/

Essay Assignment:

• Research a vaccine that the United States offers from either of the two websites and write a paragraph talking about the vaccine, what disease it prevents and how many deaths/severe illnesses this vaccine has prevented.

www.cdc.gov

www.chop.edu