3.6.8Additional lessons
Antibiotics — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 77 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5How Antibiotics Work
Definition
- Definition Antibiotics are chemicals that kill bacteria or stop them from growing without seriously harming human cells.
Cell wall synthesis
- Cell wall synthesis Penicillin prevents bacteria from building their cell walls, so water enters by osmosis and the cell bursts.
Protein synthesis
- Protein synthesis Some antibiotics block bacterial ribosomes, which differ from the ribosomes of eukaryotic cells.
Selective toxicity
- Selective toxicity The drug targets processes that bacteria have and human cells lack, so it harms the bacterium but not the patient.
Part 2 of 5Why Antibiotics Do Not Work on Viruses
No metabolism
- No metabolism Viruses have no metabolism of their own, so they have nothing for antibiotics to block.
Inside host cells
- Inside host cells Viruses live inside human cells where antibiotics cannot attack them without harming the host.
No cell wall
- No cell wall Viruses lack cell walls and ribosomes, so antibiotics that target these structures are ineffective.
Antivirals
- Antivirals Different drugs, called antivirals, are needed to treat viral infections.
Part 3 of 5Discovery of Penicillin
1
In 1928 Alexander Fleming noticed that bacterial growth on an agar plate was prevented around a contaminating mould.
2
The mould, a Penicillium species, was releasing a substance that stopped bacteria from growing.
3
Howard Florey and Ernst Chain later purified penicillin and tested it on infected mice, with those treated surviving.
4
Trials in humans followed, and mass production made penicillin widely available.
5
The case shows how an unexpected observation can lead to an important discovery, which is an example of chance in science.
Part 4 of 5Using Antibiotics Well
Using Antibiotics Well
Complete the course
- Complete the course Stopping early may leave surviving bacteria that can multiply again and become resistant.
Match the pathogen
- Match the pathogen Antibiotics should be used only for bacterial infections.
Testing
- Testing Controlled trials show whether a new antibiotic is safe and effective.
Part 5 of 5Exam Checklist & Tips
3.6.8 – Key Points for the Exam
- Antibiotic A substance that kills or inhibits the growth of bacteria.
- Penicillin An antibiotic from the mould Penicillium that blocks cell wall synthesis.
- Selective toxicity Harming the pathogen but not the host.
- Antiviral A drug that treats viral infection.
Common Mistakes
- Saying antibiotics cure colds or influenza, which are caused by viruses.
- Stating that penicillin kills by dissolving the bacterial cell membrane, when it prevents cell wall formation.
- Thinking that antibiotics make the patient immune.
- Writing that Fleming made penicillin into a medicine by himself; Florey and Chain developed it.
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