All cells share four common characteristics:
- a plasma membrane which separates a cell's internal organelles from the environment
- cytoplasm consisting of a jelly-like fluid that is home to other cellular structures
- DNA, the genetic material of the cell
- ribosomes, which produce proteins 

Commonalities of Eukaryotes & Prokaryotes

A eukaryotic cell has a membrane bound nucleus and membrane bound structures called organelles, which have specialized functions. Eukaryotic means "true nucleus" and the word organelle implies "little organ". Organelles have specific cellular functions similar to the way organs have specialized functions. 

Eukaryotic cell

A prokaryotic cell is a unicellular organism that lacks a defined nucleus and membrane bound organelles. As a result, many catabolic processes occur within the cytosol. 

Prokaryotic cell

Tulane University

In infectious disease epidemiology, an agent is an infectious organism or pathogen, such as a virus, bacterium, paraiste, etc. that can cause disease. 
Some factors that can influence an agent's ability to cause disease include: pathogenicity, virulence, addictive qualities, infectivity, ability to survive outside body, susceptibility to antibiotics, etc. 


Agent/Pathogen

https://courses.lumenlearning.com/suny-wmopen-biology1/chapter/prokaryotes-and-eukaryotes/

Lumen Learning

"a sign is any objective evidence of a disease that can be observed by others (for example a skin rash or lump)."

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