What happens when a cell is placed in a hypotonic solution, a hypertonic solution, or an isotonic solution? What characteristic of the cell membrane allows substances to move in and out?

Question

Hypertonic -
Hypotonic -
Isotonic -

Answer 1

When a cell is placed in different types of solutions, the movement of water in and out of the cell is affected by the concentration of solutes in the solution relative to the concentration of solutes inside the cell. Here’s what happens in each case:

Hypertonic Solution:

• Definition: A hypertonic solution has a higher concentration of solutes compared to the inside of the cell.
• Effect on Cell: When a cell is placed in a hypertonic solution, water moves out of the cell to the outside solution in an attempt to equalize solute concentrations on both sides of the cell membrane. As a result, the cell shrinks or undergoes crenation (in animal cells); in plant cells, the cell membrane may pull away from the cell wall, a process called plasmolysis.

Hypotonic Solution:

• Definition: A hypotonic solution has a lower concentration of solutes compared to the inside of the cell.
• Effect on Cell: In a hypotonic solution, water moves into the cell, as the cell has a higher concentration of solutes. This can cause the cell to swell and potentially burst (lyse) if too much water enters. In plant cells, the influx of water helps maintain turgor pressure against the cell wall, which keeps the plant firm.

Isotonic Solution:

• Definition: An isotonic solution has the same concentration of solutes as the inside of the cell.
• Effect on Cell: In an isotonic solution, there is no net movement of water into or out of the cell, which means the cell maintains its shape and size. The concentration of solutes is balanced, ensuring that the cell remains stable.

Cell Membrane Characteristics:

The characteristic of the cell membrane that allows substances to move in and out is its selective permeability. The cell membrane is composed of a lipid bilayer with embedded proteins, which provides flexibility and regulates the movement of substances. Small nonpolar molecules can pass through easily, while larger or charged molecules may require specific transport proteins. This selective permeability helps maintain the internal environment of the cell (homeostasis) by controlling what enters and leaves the cell.