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Since they need a host organism to reproduce– they are subject to evolutionary pressures which can cause change.
Viruses make more of themselves, but the only known way a virus can make more of itself is by taking over the host cell.
Over time a host cells immune system can learn from these encounters and develop strategies to prevent reinfection. So to survive, viruses must adapt or evolve, changing its surface proteins enough to trick the host cell into allowing it to attach.
Without a host cell to activate the change, the virus would not be able to change or evolve.
Cellular metabolism - the set of chemical reactions that occur in living organisms in order to build up and break down cellular components in a balanced fashion.
DNA and RNA is a product of cell metabolism, but in order for metabolic pathways to occur, enzymes are required, which are not present in viruses.
Virus molecules attack a host cell and insert their DNA into the cell two different ways.
One way:
Second Way:
Acellular- not composed of cells ( = "bodies of protoplasm made discrete by an enveloping plasma membrane
Viruses have a basic structure.
All viruses contain nucleic acid, either DNA or RNA (but not both), and a protein coat, which encases the nucleic acid.
1. Need energy/nutrients/water and a place to get them
2. Change over time
3. Have the capability to reproduce
4. Get rid of waste
5. React to stimuli
6. Are made of cells
Can you walk us through how a virus reproduces outside of a host cell?
You claimed the virus gets energy from the host, what does it use its energy for?
A virus does not not even need energy, nutrients, or water. Viruses have only one need: to find a host cell. Without attaching to a host cell (bacteria, plant or animal), viruses do not have any effect. Therefore, without a host, a virus ceases to exist and our immune system can catch it.
Merriam-Webster.com:
Matter characterized by the ability to metabolize nutrients, grow, reproduce, and respond and adapt to environmental stimuli. All known life-forms possess either DNA or RNA.
Oxford Dictionary.com:
The condition that distinguishes animals and plants from inorganic matter, including the capacity for growth, reproduction, functional activity, and continual change preceding death.
Biology-Online.org:
A distinctive characteristic of a living organism from dead organism or non-living thing, as specifically distinguished by the capacity to grow, metabolize, respond (to stimuli), adapt, and reproduce.
http://answers.webmd.com/answers/1198131/what-are-the-differences-between-bacteria
http://www.preservearticles.com/201101092882/characteristics-of-viruses.html
http://science.howstuffworks.com/life/cellular-microscopic/virus-human7.htm
http://www.uvm.edu/~biology/Classes/011/alive.pdf
http://people.eku.edu/ritchisong/301notes1.htm#metabolism
http://people.ysu.edu/~crcooper01/3702Ch16(S05).pdf
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http://www.miamisci.org/youth/unity/Unity1/Lubens/pages/characteristic.html
http://www.biology-online.org/dictionary/Acellular
http://www.ncbi.nlm.nih.gov/books/NBK8174/
http://www.oswego.org/webpages/rfavuzzi/files/VIRUS%20PKT.CH2%20BP.pdf