The contents of the bacterial cell have a lower water potential than the surrounding fluid in the human body. Water enters the bacterial cell by osmosis, down the water potential gradient. This increases the internal pressure on the cell wall. Because the antibiotic has damaged the cell wall, it is weakened and cannot withstand the pressure, so the cell bursts (lysis).
This process is due to osmosis.
1. **Water Potential Gradient:** The cytoplasm inside a bacterial cell is a concentrated solution of salts, sugars, and other solutes. This means it has a lower water potential (or is more concentrated) than the surrounding body fluids.
2. **Osmosis:** Water always moves by osmosis from an area of higher water potential to an area of lower water potential across a partially permeable membrane. Therefore, water continuously enters the bacterial cell from the body fluids.
3. **Role of the Cell Wall:** A normal, healthy bacterial cell wall is strong and rigid. It prevents the cell from bursting by withstanding the high internal pressure (turgor pressure) created by the influx of water.
4. **Effect of Antibiotic:** The antibiotic damages this cell wall, making it weak. As water continues to enter by osmosis, the weakened wall can no longer withstand the increasing pressure, and the cell swells up and bursts (a process called lysis).
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