• Bacteria need to get energy, and may emit toxins or waste products.

• Viruses are the smallest and simplest life form known. They are 10 to 100 times smaller than bacteria.

• The biggest difference between viruses and bacteria is that viruses must have a living host - like a plant or animal - to multiply, while most bacteria can grow on non-living surfaces.

• Bacteria are intercellular organisms (i.e. they live in-between cells); whereas viruses are intracellular organisms (they infiltrate the host cell and live inside the cell). They change the host cell's genetic material from its normal function to producing the virus itself.

• There are some useful bacteria but all viruses are harmful.

• Antibiotics can kill bacteria but not viruses.

• An example of a disease caused by bacteria is strep throat and an example of an affliction caused by a virus is the flu.

Differences in reproduction

Bacteria carry all the "machinery" (cell organelles) needed for their growth and multiplication. Bacteria usually reproduce asexually. In the case of sexual reproduction, certain plasmids genetic material can be passed between bacteria. On the other hand, viruses carry mainly information - for example, DNA or RNA, packaged in a protein and/or membranous coat. Viruses harness the host cell's machinery to reproduce. Their legs attach onto the surface of the cell then the genetic material contained inside the head of the virus is injected into the cell. This genetic material can either use the cell's machinery to produce its own proteins and/or virus bits, or it can be integrated into the cell's DNA/RNA and then translated later. When enough "baby" viruses are produced the cell bursts, releasing the new viral particles. In a sense, viruses are not truly "living," but are essentially information (DNA or RNA) that float around until they encounter a suitable living host.