Tonicity in cells refers to the concentration of solute in a solution outside of a cell, relative to
A.
The solute concentration of the cytoplasm inside the cell.
B.
The permeability of the cell membrane.
C.
The swelling of the cell.
D.
The number of cell fragments inside the cell.
E.
The presence of a cell wall.
The Correct Answer and Explanation is:
The correct answer is A. The solute concentration of the cytoplasm inside the cell.
Explanation:
Tonicity refers to the relative concentration of solutes in a solution outside the cell compared to the concentration of solutes inside the cell. It affects the movement of water across the cell membrane through osmosis, which is driven by the concentration gradient of solutes. Understanding tonicity is crucial for predicting how cells will respond to changes in their extracellular environment.
1. Tonicity and Solute Concentration:
Tonicity is primarily determined by comparing the solute concentration outside the cell (in the extracellular fluid) to the solute concentration inside the cell (in the cytoplasm). There are three main types of tonic environments:
- Isotonic Solution: In an isotonic solution, the solute concentration outside the cell is equal to the solute concentration inside the cell. As a result, there is no net movement of water into or out of the cell, and the cell maintains its normal shape and volume.
- Hypertonic Solution: In a hypertonic solution, the solute concentration outside the cell is higher than that inside the cell. This causes water to move out of the cell into the extracellular fluid, leading to cell shrinkage or crenation.
- Hypotonic Solution: In a hypotonic solution, the solute concentration outside the cell is lower than that inside the cell. This results in water moving into the cell, causing it to swell and potentially burst, a process known as lysis.
2. Importance of Tonicity:
Tonicity is critical in medical and biological contexts because it affects cell volume and function. For instance, intravenous fluids used in medical treatments are carefully chosen to match the tonicity of body fluids to prevent adverse effects on cells. Understanding tonicity helps in maintaining proper hydration and cell integrity in various physiological and pathological conditions.
3. Exclusion of Other Options:
- B. Permeability of the Cell Membrane: While membrane permeability influences how easily water and solutes can cross the cell membrane, tonicity specifically relates to the concentration gradient of solutes.
- C. Swelling of the Cell: Swelling of the cell is a result of hypotonic conditions but is not the definition of tonicity itself.
- D. Number of Cell Fragments: This is not related to the concept of tonicity.
- E. Presence of a Cell Wall: The cell wall is a structural feature of plant cells, fungi, and some bacteria, and does not directly relate to the concept of tonicity, which primarily concerns the movement of water and solutes across the cell membrane.
In summary, tonicity is about comparing the concentration of solutes inside and outside the cell, making option A the correct choice.