When a cell is placed in solution and the size of the cell increases, the concentration of solution is said to be

Step 1: Analyze the question The cell is placed in a solution and its size increases. This means water has moved into the cell by osmosis. We need the term describing the surrounding solution.

Step 2: The concept Osmosis is the movement of water from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) through a semi-permeable membrane.

Terms for the solution relative to the cell:

• Hypotonic: the solution has a lower solute concentration than the cell, so water enters the cell and the cell swells.
• Isotonic: the solute concentrations are equal, so there is no net movement and the size stays the same.
• Hypertonic: the solution has a higher solute concentration than the cell, so water leaves the cell and the cell shrinks (animal cells crenate, plant cells become plasmolysed).

Step 3: Apply to the question

• The cell swells, so water entered it.
• That means the surrounding solution is more dilute (has less solute) than the cell contents.
• So the solution is hypotonic.

Checking the options:

• A. Isotonic: no size change, so wrong.
• B. Dilute: this describes the solution loosely, but it is not the standard osmotic term. The question asks for the tonicity term, so it is not the best answer.
• C. Hypotonic: correct.
• D. Hypertonic: the cell would shrink, so wrong.

Answer: C. Hypotonic.

Exam tip: "Hypo" means "less" (like hypodermic, under the skin). A hypotonic solution has less solute, so water rushes into the cell and it swells. Remember: Hypo = Higher water entering = cell Highly swollen, and Hyper = cell shrinks.