Bacteria and Viruses Prokaryotes: single cell organism that lacks a nucleus Divided into two groups, or domains, which are above kingdoms Eubacteria and Archaebacteria

Archaebacteria Live in extremely harsh environments Where there is no oxygen (in intestine) Where extremely hot (hot springs) Where it is extremely salty (Great Salt Lake) DNA in genes resembles eukaryotes

Eubacteria Eubacteria Larger of the two groups; most numerous organisms on earth Oldest forms of life on Earth Varied in shape and color Live almost everywhere Each bacterial cell performs the same basic functions that complex organisms perform

Structure of Bacteria Bacilli Cocci Spirilla Lacks a nucleus Has a cell wall that is tough rigid to support, shape, and protect the cell Shapes Bacilli – rod shaped Cocci – spherical Spirilla – spiral and corkscrew-shaped Movement: some use flagella but most do not move Bacilli Cocci Spirilla

How bacteria obtain energy Most are heterotrophs Feed on living organisms (parasitic) Eat other organisms Eat dead things Some are autotrophs Use sunlight to produce food Some are chemoautotrophs Can use energy in sulfur, ammonia, nitrites, or iron to make food

Growth and reproduction Under favorable conditions, undergoes binary fission Two new daughter cells are formed Asexual reproduction

Bacteria in nature Decomposers: recycle nutrients Nitrogen fixers: live on roots of plants and change nitrogen gas (N2) to ammonia (NH3) Pathogens: Cause disease such as food poisoning Human use: produce variety of food; helpful in cleaning environment How Control Bacteria Sterilization with heat or chemicals (bleach solution)

Size Comparison

Viruses Characteristic of a virus Not a cell so can’t perform all the functions of a living cell Requires a host to reproduce therefore is a parasite—an organism that survives by living on or in a host All kingdoms are affected by viruses Each type of virus can only infect a few specific kinds of cells

Structure of Viruses Structure of virus Core of hereditary material – either DNA or RNA Outer protein coat to protect virus from environment Can only be seen with an electron microscope Can have many shapes

Reproduction of Viruses Attaches to a cell Injects hereditary material into living cell Cell begins to produce new virus particles

Two types of infection In lytic infection, virus will cause cell to burst and virus particles will leave the original host cell In lysogenic infection, virus genetic material becomes part of the host DNA and is copied, or replicated, along with the host DNA