At the simplest level of construction, all cells possess a few fundamental components despite varying significantly in size, shape, structure, and function. These components include a cytoplasm (a gel-like substance composed of water and dissolved chemicals needed for growth), a plasma membrane (also called a cell membrane or cytoplasmic membrane) that contains the cytoplasm, one or more chromosomes containing the genetic blueprints of the cell, and ribosomes which are organelles used for the production of proteins.

Fundamental Components of Cells

A prokaryotic cell is a major category of cell that lacks a nucleus surrounded by a complex nuclear membrane. Instead, its genetic material is generally a single, circular chromosome located in a nucleoid region. While prokaryotic cells generally lack complex membrane-bound organelles, they often contain inclusions that compartmentalize their cytoplasm. Microorganisms composed of these cells are classified within the domains Archaea and Bacteria.

Prokaryotic Cell

Eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane and membrane-bound organelles in the cytoplasm, which are supported and held in place by an internal cytoskeleton. These cells, which can exist as independent, single-celled microorganisms or as part of multicellular organisms (comprising protozoans, algae, fungi, plants, and animals), feature plasma membranes structured as a bilayer consisting of ester-linked, straight-chain fatty acids and sterols, and they contain multiple, linear chromosomes associated with histones.

Eukaryotic 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/

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"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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