When a Spirogyra filament is placed in a concentrated salt solution for 30 minutes, the cell would become

Step 1: Analyze the question Spirogyra is a green alga made of filaments of cylindrical cells, each with a cell wall, cell membrane, and a large central vacuole. The question asks what happens to these cells when they are placed in a concentrated salt solution for 30 minutes.

Step 2: The concept (osmosis) Osmosis is the movement of water from a region of high water potential (dilute solution) to a region of low water potential (concentrated solution) through a semi-permeable membrane.

• A concentrated salt solution has a lower water potential than the cell sap, so it is hypertonic to the cell.
• Water therefore leaves the cell by osmosis.
• The vacuole shrinks, and the cytoplasm and cell membrane pull away from the cell wall.

This pulling away of the cell membrane from the cell wall is called plasmolysis.

Step 3: Check each option

• A. Plasmolysed: Correct. Water is lost, and the protoplasm shrinks away from the cell wall.
• B. Turgid: This happens in a dilute (hypotonic) solution or in pure water, when water enters the cell. It is the opposite of what happens here.
• C. Shortened: The rigid cellulose cell wall keeps the filament's overall shape, so the cell does not noticeably shorten. Only the protoplasm shrinks inside.
• D. Elongated: This would need water to enter the cell, which does not happen in a hypertonic solution.

Step 4: Answer The cell becomes plasmolysed, which is option A.

Exam tip: Remember the pairs:

• Hypertonic (concentrated) outside → water leaves → plasmolysis
• Hypotonic (dilute) outside → water enters → turgid

Think "salt takes water out", just as salt draws water out of a slug or a pickled vegetable.