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When a bacterial cell is placed in a hypotonic solution, the concentration of solutes outside the cell is lower than inside. This means the surrounding solution is more dilute, and there is a higher concentration of water outside the bacterial cell. Due to osmosis, water moves from an area of high concentration to an area of low concentration.
In this scenario, water enters the bacterial cell as it strives to balance the solute concentrations on both sides of the cell membrane. This influx of water causes the cell to swell. Thankfully, most bacterial cells have rigid cell walls made of peptidoglycan, which offer some protection against the excessive intake of water. However, there is still a risk of the cell bursting if the water pressure (turgor pressure) becomes too high. This bursting is known as lysis.
In summary, the effects of a hypotonic solution on a bacterial cell are:

• Water enters the cell due to osmosis.
• The cell may swell and increase in size.
• Risk of cell bursting, though mitigated by the cell wall.

When a bacterial cell is placed in an isotonic solution, the concentration of solutes in the solution is the same as the concentration within the cell. This state of equilibrium means that the movement of water molecules across the cell membrane is balanced. Equal amounts of water enter and leave the cell through the process of osmosis, maintaining the same internal and external pressure.
Because there is no net movement of water into or out of the cell, the cell doesn’t change in size or shape. This condition is ideal for most cells, as it maintains their normal state without adding stress to the cellular membrane. This is analogous to the state of homeostasis, where the cell maintains a stable internal environment despite external changes.
Key characteristics of an isotonic solution effect include:

• Equal water movement into and out of the cell.
• No change in cell size or shape.
• Stable environment for cellular processes.

In a hypertonic solution, the concentration of solutes outside the bacterial cell is higher than inside the cell. This means there is a lower concentration of water outside compared to the inside. As a result, water molecules move out of the cell in order to achieve equilibrium.
As water exits the cell, the cell begins to shrink, a process known as plasmolysis. The cell membrane may pull away from the cell wall, creating gaps that can impair cell function. This loss of water and ensuing shrinkage can be detrimental to bacterial cells, leading to a halt in metabolic processes and potential cell death if the water loss is severe and prolonged.
The effects of a hypertonic solution can be summarized as:

• Water exits the cell due to higher external solute concentration.
• Cell shrinks or undergoes plasmolysis.
• Potential impairment of cell function due to water loss.