What are Bacteria and Viruses?
Bacteria and viruses are both microscopic, but they are fundamentally different kinds of biological entities. Bacteria are single-celled living organisms that can reproduce on their own, while viruses are not cells at all and can only reproduce by hijacking a host cell's machinery.
Bacteria are single-celled prokaryotic organisms with their own metabolism that reproduce by binary fission, doubling their population at a predictable rate. Viruses are non-living particles of genetic material in a protein coat that can only replicate by infecting and hijacking a living host cell.
- •Single-celled, living prokaryotic organism
- •Has a cell wall, ribosomes, and its own metabolism
- •Reproduces independently by binary fission
- •Many species are harmless or beneficial (e.g. gut flora)
- •Can be treated with antibiotics
- •Not a cell — just genetic material in a protein coat
- •No metabolism of its own; not considered fully alive
- •Can only reproduce by hijacking a living host cell
- •Always cause disease by damaging or killing host cells
- •Not affected by antibiotics; need antivirals or vaccines
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Step-by-step worked examples
A bacterial culture starts with 200 cells and has a generation time of 20 minutes. How many cells are present after 1 hour (60 minutes)?
Use N = N₀ × 2^(t/g). Number of generations = t/g = 60/20 = 3. N = 200 × 2³ = 200 × 8 = 1600 cells.
E. coli has a generation time of about 20 minutes. Starting from a single cell, roughly how many cells exist after 3 hours (180 minutes)?
Number of generations = 180/20 = 9. N = 1 × 2⁹ = 512 cells. This shows why bacterial infections can spread so fast without treatment.
A virus infects a single host cell. Describe, in order, the basic steps of its replication cycle inside that cell.
The virus attaches to and enters the host cell. It releases its genetic material and hijacks the host's ribosomes and machinery. The host cell is forced to make many copies of the viral genome and proteins. New virus particles assemble and burst out (lyse) the host cell, going on to infect more cells.
Flashcards
Quick quiz
Q1.How do bacteria typically reproduce?
Q2.Why are viruses generally not considered fully living organisms?
Q3.A bacterial culture starts with 50 cells and has a generation time of 30 minutes. How many cells are there after 90 minutes?
Q4.Why are antibiotics ineffective against viral infections?
The full card deck, worked steps and AI-tutor support for “What are Bacteria and Viruses?” are in Notek — study by hand before your exam.
Common mistakes
Thinking bacteria and viruses are basically the same thing. — Correct: Bacteria are living, single-celled organisms; viruses are not cells and cannot reproduce without a host.
Believing all bacteria are harmful. — Correct: Most bacteria are harmless or even beneficial, such as gut bacteria that aid digestion.
Assuming antibiotics can cure a viral infection like the flu. — Correct: Antibiotics only work on bacteria; viral infections need antivirals, vaccines, or the immune system's own response.
Forgetting that generation time varies between bacterial species. — Correct: Different bacteria double at very different rates — E. coli in ~20 minutes, others in hours or days.
FAQ
What is the difference between bacteria and viruses?
Bacteria are living, single-celled organisms that can reproduce independently, while viruses are non-living particles that can only replicate inside a host cell.
What is the formula for bacterial population growth?
N = N₀ × 2^(t/g), where N₀ is the starting population, t is elapsed time, and g is the generation (doubling) time.
How do you calculate bacterial population growth?
Divide elapsed time by the generation time to get the number of doublings, then multiply the starting population by 2 raised to that power.
Why can't antibiotics kill viruses?
Antibiotics target bacterial structures such as cell walls and ribosomes; viruses lack these structures entirely, so antivirals or vaccines are needed instead.