Living cells placed in isotonic solution (0.9% saline) retain their size and shape. This is based on the concept of

Options

A. Osmosis
B. Diffusion
C. Facilitated diffusion
D. Transpiration

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Isotonic Solutions**: An isotonic solution is one where the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. In this case, a 0.9% saline solution is isotonic to human cells.

2. **Effect on Living Cells**: When living cells are placed in an isotonic solution, there is no net movement of water into or out of the cells. This is because the concentration of solutes is balanced on both sides of the cell membrane.

3. **Cell Shape and Size**: As a result of this balance, the cells retain their normal shape and size. They do not swell (as they would in a hypotonic solution) or shrink (as they would in a hypertonic solution).

4. **Concept of Osmosis**: The phenomenon of water movement across the cell membrane is governed by osmosis. Osmosis is defined as the movement of water through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

5. **Conclusion**: Therefore, the reason living cells placed in an isotonic solution retain their size and shape is based on the concept of osmosis.

**Final Answer**: The concept is based on osmosis.

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