LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- define a drug
- explain antibiotics
- distinguish bacteria and viruses
- explain resistance
THE BIG IDEA
How drugs alter body chemistry and why antibiotic use must be controlled.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
01
SECTION 01
Medicinal drugs and antibiotics
A drug modifies chemical reactions in the body. Antibiotics treat bacterial infections by killing bacteria or stopping growth.
DETAILED EXPLANATION
- They do not affect viruses, which lack bacterial targets and reproduce inside host cells.
- Some bacteria carry resistance alleles.
02
SECTION 02
Resistance
Antibiotics create selection pressure: susceptible bacteria die while resistant bacteria survive, reproduce and pass on resistance.
DETAILED EXPLANATION
- Unnecessary exposure increases opportunities for resistant strains such as MRSA to spread.
- Use antibiotics only when essential and as professionally directed.
- The bacterial population evolves; the patient's body does not become resistant.
1variation→
2antibiotic→
3susceptible die→
4resistant survive→
5resistant strain increases
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Drugs alter chemistry.
- Antibiotics act on bacteria only.
- Resistance spreads by natural selection.
- Essential-only use slows selection.