CIE iGCSE Biology- 15.1 Drugs- Study Notes- New Syllabus
CIE iGCSE Biology-15.1 Drugs- Study Notes – New syllabus
CIE iGCSE Biology-15.1 Drugs- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe a drug as any substance taken into the body that modifies or affects chemical reactions in the body
- Describe the use of antibiotics for the treatment of bacterial infections
- State that some bacteria are resistant to antibiotics which reduces the effectiveness of antibiotics
- State that antibiotics kill bacteria but do not affect viruses
Supplement
- Explain how using antibiotics only when essential can limit the development of resistant bacteria such as MRSA
What is a Drug?
Definition:
A drug is any substance taken into the body that modifies or affects chemical reactions in the body.
🔍 Key Characteristics of Drugs:
| Feature | Description |
|---|---|
| Substance | Can be natural (from plants) or synthetic (man-made). |
| Entry into the body | Taken through injection, swallowing, inhalation, or absorption. |
| Mode of action | Alters biochemical processes in cells — may speed up, slow down, or block reactions. |
| Target | Can affect the nervous system, metabolism, or specific organs. |
| Effect | May be medicinal (e.g., antibiotics) or harmful (e.g., narcotics). |
🧠 Examples of Drug Effects:
| Type of Drug | Effect on the Body |
|---|---|
| Painkillers | Block nerve signals to reduce pain |
| Antibiotics | Kill or stop the growth of bacteria |
| Stimulants | Increase brain activity and alertness |
| Depressants | Slow down brain function |
| Hallucinogens | Alter perceptions and cause hallucinations |
Drug = Any substance that changes body chemistry
Can treat illness or be abused
Affects brain, metabolism, or other systems
Antibiotics and Their Use in Treating Bacterial Infections
Definition:
Antibiotics are drugs used to kill bacteria or inhibit their growth, helping the body to fight bacterial infections.
🦠 How Antibiotics Work:
| Mechanism | Action |
|---|---|
| Bactericidal antibiotics | Kill bacteria directly (e.g. penicillin damages bacterial cell walls). |
| Bacteriostatic antibiotics | Stop bacteria from growing or reproducing, giving the immune system time to destroy them. |
❌ Important Note:
- Antibiotics do NOT work against viruses (e.g., colds, flu, COVID-19).
- This is because viruses reproduce inside cells, making it hard for antibiotics to target them without damaging body tissues.
💉 Examples of Bacterial Infections Treated:
- Pneumonia
- Tuberculosis (TB)
- Strep throat
- Urinary tract infections (UTIs)
⚠️ Risks of Misuse:
- Overuse or incorrect use of antibiotics can lead to antibiotic resistance (e.g. MRSA).
- Always complete the full course prescribed by a doctor, even if symptoms improve.
Antibiotics treat bacterial (not viral) infections
Kill or stop bacteria from multiplying
Misuse can lead to resistance – take only when necessary
Antibiotic Resistance in Bacteria
Key Statement:
Some bacteria are resistant to antibiotics, which reduces the effectiveness of antibiotic treatments.
🔍 What Is Antibiotic Resistance?
It occurs when bacteria mutate or develop mechanisms to survive exposure to antibiotics.
These resistant bacteria are not killed by the drug and continue to multiply. As a result, infections become harder to treat.
⚠️ Why It’s a Problem:
| Issue | Impact |
|---|---|
| Standard antibiotics fail | Infections last longer, can become severe |
| More difficult treatments | May require stronger or more toxic drugs |
| Spread of resistant strains | Increases public health risk |
🧫 Examples of Resistant Bacteria:
- MRSA (Methicillin-Resistant Staphylococcus aureus)
- Drug-resistant TB (Tuberculosis)
📘 Causes of Resistance:
- Overuse of antibiotics
- Incomplete courses of treatment
- Misuse (e.g. taking antibiotics for viral infections)
Some bacteria survive antibiotics = resistance
Infections become harder to treat
Always use antibiotics responsibly
Effect of Antibiotics on Bacteria and Viruses
Key Statement:
Antibiotics kill bacteria but do not affect viruses.
🦠 Why Antibiotics Work on Bacteria:
Bacteria are living cells with structures like cell walls and ribosomes.
Antibiotics target these structures to:
- Break down cell walls
- Stop protein synthesis
- Prevent bacterial reproduction
🧬 Why Antibiotics Do NOT Work on Viruses:
Viruses are not living cells – they are just DNA or RNA inside a protein coat.
Viruses reproduce inside host cells, making them hidden from antibiotics.
Antibiotics cannot enter host cells to destroy the virus without damaging your own cells.
❌ Common Misconception:
Colds, flu, and COVID-19 are caused by viruses, so antibiotics do not help.
Taking antibiotics unnecessarily increases the risk of antibiotic resistance.
Antibiotics = Only for bacterial infections
Viruses don’t have structures antibiotics can target
Never take antibiotics for viral illnesses
Limiting Antibiotic Resistance by Responsible Use
Key Idea:
Using antibiotics only when essential helps limit the development of resistant bacteria such as MRSA (Methicillin-Resistant Staphylococcus aureus).
🔍 Why Limiting Use Matters:
| Reason | Explanation |
|---|---|
| Reduces selection pressure | If antibiotics are overused, sensitive bacteria die, but resistant bacteria survive and multiply. |
| Prevents mutation spread | Less use = fewer chances for mutations that lead to resistance to develop and spread. |
| Protects antibiotic effectiveness | Responsible use keeps antibiotics effective for serious infections. |
🦠 What Happens If Overused:
- Non-resistant bacteria die.
- Resistant bacteria survive (e.g. MRSA).
- These resistant bacteria reproduce, spreading resistance.
- Infections become harder to treat, requiring stronger or more toxic drugs.
💡 MRSA Example:
MRSA is a type of Staphylococcus aureus bacteria that has become resistant to many antibiotics, including methicillin.
MRSA infections are difficult to treat and spread quickly in hospitals.
Prevented by using antibiotics only when truly necessary.
Only use antibiotics when essential
Reduces resistance development
Keeps antibiotics working for future infections