TEAS Ready🧬 Science · Biology · Lesson 7 of 7 · 6 min
Microorganisms and disease
🦠 An antibiotic will not cure the flu. Knowing why, and how each kind of microbe makes people sick, is basic nursing science.
💡 Key idea
Antibiotics target bacteria only; viruses need a host cell and are treated with antivirals or prevented with vaccines.
🧠 The idea
A PATHOGEN is any organism or agent that causes disease. BACTERIA are single-celled prokaryotes with ribosomes and, in most species, a cell wall; many are harmless or helpful, but some cause disease by invading tissue or releasing toxins (strep throat, tuberculosis). VIRUSES are not cells: they are genetic material (DNA or RNA) in a protein coat, and they can reproduce only inside a host cell, often damaging it (influenza, measles). FUNGI are eukaryotes with chitin cell walls, including yeasts and molds (ringworm, thrush). PROTOZOA are single-celled eukaryotes, some spread by water or insects (malaria is spread by mosquitoes). ANTIBIOTICS kill or slow bacteria by targeting bacterial structures such as the cell wall or ribosomes, so they do not work on viruses; antivirals and vaccines are used against viruses. Pathogens spread by direct contact, droplets, airborne particles, contaminated food or water, and vectors.
✏️ Worked example
A patient has a sore throat. A rapid test is negative for bacteria and the cause is a virus. Step 1: viruses lack cell walls and their own ribosomes. Step 2: antibiotics act on those bacterial targets, so they would not help. Step 3: overusing antibiotics also selects for resistant bacteria, which is why they are given only for bacterial infections.
📌 Takeaways
- Bacteria = prokaryotic cells; viruses = not cells, need a host; fungi and protozoa = eukaryotes.
- Antibiotics do not treat viral infections.
- Transmission routes: contact, droplet, airborne, food and water, vectors.
✅ Check yourself
Question 1 of 3
Why are antibiotics ineffective against the common cold?
- Antibiotics work only on protozoa
- The cold virus has a thicker cell wall
- Colds are caused by fungi with chitin walls
- Colds are caused by viruses, not bacteria
Show the answer and rationale
Answer: D
Colds are viral, and viruses have no cell wall or bacterial ribosomes for antibiotics to target. A cold virus has no cell wall at all, and antibiotics act on bacteria, not on protozoa or fungi.
Question 2 of 3
Which type of pathogen is a single-celled eukaryote, such as the organism that causes malaria?
- Virus
- Bacterium
- Prion
- Protozoan
Show the answer and rationale
Answer: D
Protozoa are single-celled eukaryotes; malaria is caused by a protozoan carried by mosquitoes. Bacteria are prokaryotes, and viruses and prions are not cells.
Question 3 of 3
Which feature is true of viruses?
- They have their own ribosomes
- They divide by binary fission
- They can only reproduce inside a host cell
- They have a nucleus surrounded by a membrane
Show the answer and rationale
Answer: C
Viruses must use a host cell's machinery to reproduce. They have no ribosomes and no nucleus, and binary fission is how bacteria divide.
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