LEARNING OBJECTIVES
What you will be able to do
- define a drug
- explain antibiotics
- distinguish bacteria and viruses
- explain resistance
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How drugs alter body chemistry and why antibiotic use must be controlled.
Drugs alter chemical reactions in the body. In this syllabus, the main focus is the correct use of antibiotics and the biological consequences of bacterial resistance.
Resistance is an example of selection acting on a bacterial population; antibiotics select existing resistant variants rather than creating purposeful change.
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
- Some bacteria carry resistance alleles.
SECTION 02
Resistance
Antibiotics create selection pressure: susceptible bacteria die while resistant bacteria survive, reproduce and pass on resistance.
DETAILED EXPLANATION
- Use antibiotics only when essential and as professionally directed.
- The bacterial population evolves; the patient's body does not become resistant.
STEP-BY-STEP EXAM EXAMPLE
Explaining the rise of antibiotic resistance
- A bacterial population contains genetic variation; a few cells are resistant.
- The antibiotic kills susceptible bacteria.
- Resistant bacteria survive, reproduce and pass on resistance alleles.
- The resistant proportion increases over generations.
Answer: The antibiotic selects resistant bacteria; it does not cause a patient's body to become resistant.
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.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- define a drug
- explain antibiotics
- distinguish bacteria and viruses
- explain resistance