Correct Option: D. Loses water and shrivels Explanation of the Correct Answer: When a spirogyra cell is placed in a salt solution that is more concentrated than its internal cell sap, a process called osmosis occurs. Osmosis is the movement of water across a semi-permeable membrane from an area of lower solute concentration (inside the cell) to an area of higher solute concentration (outside the cell).

1. Understanding Osmosis:
2. Cells are surrounded by a semi-permeable membrane that allows water to pass through but restricts the movement of solutes (like salt).
3. In this scenario, the salt solution outside the spirogyra cell has a higher concentration of solutes compared to the cell sap inside the cell.
4. Water Movement:
5. Because the external environment (salt solution) has a higher concentration of solutes, water will move out of the spirogyra cell to the area of higher solute concentration (the salt solution).
6. This movement of water out of the cell causes the cell to lose water.
7. Resulting Effect:
8. As water leaves the cell, the internal pressure (turgor pressure) decreases, leading to the cell shrinking or shriveling. This is often referred to as plasmolysis, where the cell membrane pulls away from the cell wall due to the loss of water.

Why the Other Options are Incorrect:

• Option A: Remains unchanged:
• This option is incorrect because the spirogyra cell cannot remain unchanged in a hypertonic solution (more concentrated than its internal sap). The osmotic gradient will always drive water out of the cell, leading to changes.
• Option B: Takes up water and bursts:
• This option is incorrect because it describes a situation that occurs in a hypotonic solution (where the external environment has a lower concentration of solutes than the cell sap). In a hypertonic solution, the opposite occurs; the cell loses water, not gains it.
• Option C: Absorbs a little water:
• This option is also incorrect. In a hypertonic solution, the cell does not absorb water; instead, it loses water due to the osmotic pressure difference. The term "absorbs a little water" implies that the cell is in a more favorable environment, which is not the case here.

Summary of Key Points:

• Osmosis: Movement of water from low to high solute concentration.
• Hypertonic Solution: A solution with a higher concentration of solutes than the cell sap.
• Plasmolysis: The process where a cell shrinks due to loss of water in a hypertonic environment.
• Result: The spirogyra cell loses water and shrivels when placed in a concentrated salt solution.

This understanding of osmosis and the behavior of cells in different solutions is crucial for grasping concepts in cell biology and physiology.