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Bacteria vs Viruses
Living Cells vs Infectious Particles
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Bacteria and viruses are both microscopic agents that can affect human health, but they are fundamentally different. Bacteria are living single-celled organisms with membranes, cytoplasm, DNA, ribosomes, and metabolism. Viruses are much smaller particles made of genetic material inside a protein coat, sometimes with a lipid envelope. Understanding the difference matters because diagnosis, prevention, and treatment depend on what kind of agent is causing the infection.
A typical bacterium is about 1 micrometer across, while many viruses are about 100 nanometers across, making the bacterium roughly 10 times wider and about 1000 times larger in volume. Bacteria can reproduce on their own by binary fission if they have nutrients and suitable conditions. Viruses cannot grow or divide by themselves, so they must enter a host cell and use its machinery to make new virus particles. Antibiotics can target bacterial structures such as cell walls or ribosomes, but they do not work on viruses, which is why antiviral drugs and vaccines are used for many viral diseases.
Key Facts
- Typical bacterium size: about 1 micrometer = 1000 nm.
- Typical virus size: about 100 nm, although sizes vary widely.
- A bacterium can reproduce by binary fission: 1 cell becomes 2 cells.
- A virus must infect a host cell to replicate because it has no independent metabolism.
- Antibiotics treat many bacterial infections, but antibiotics do not kill viruses.
- If diameter ratio is 1000 nm / 100 nm = 10, then approximate volume ratio is 10^3 = 1000.
Vocabulary
- Bacterium
- A bacterium is a living single-celled organism that has DNA, ribosomes, cytoplasm, and a cell membrane.
- Virus
- A virus is a non-living infectious particle made of genetic material surrounded by a protein coat, and sometimes a lipid envelope.
- Host cell
- A host cell is a living cell that a virus enters and uses to produce more virus particles.
- Antibiotic
- An antibiotic is a medicine that targets bacterial processes or structures, such as cell wall formation or bacterial ribosomes.
- Binary fission
- Binary fission is the process by which one bacterial cell copies its DNA and divides into two cells.
Common Mistakes to Avoid
- Calling viruses cells is wrong because viruses do not have cytoplasm, ribosomes, or independent metabolism.
- Using antibiotics for a viral infection is wrong because antibiotics target bacterial features that viruses do not have.
- Assuming bacteria and viruses are the same size is wrong because many bacteria are about 1 micrometer while many viruses are about 100 nanometers.
- Thinking all bacteria are harmful is wrong because many bacteria are harmless or beneficial, including bacteria in the gut and in food production.
Practice Questions
- 1 A bacterium is 1 micrometer wide and a virus is 100 nanometers wide. Convert 1 micrometer to nanometers and calculate how many times wider the bacterium is.
- 2 If one bacterium divides by binary fission every 30 minutes, how many bacteria will there be after 2 hours starting from one cell?
- 3 A patient has a sore throat caused by influenza virus. Explain why an antibiotic would not directly kill the virus, and name one type of treatment or prevention that could help with viral disease.