Difference Between Endosmosis and Exosmosis

Main Difference – Endosmosis vs Exosmosis

Osmosis is the passive diffusion mechanism used by cells to pass water molecules across the cell membrane. Endosmosis and exosmosis are the two types of osmosis. The main difference between endosmosis and exosmosis is that endosmosis is the movement of water into the cell whereas exosmosis is the movement of water out of the cell. Endosmosis occurs when cells are placed in hypotonic solutions. Cells may swell as a result of endosmosis. Exosmosis occurs when cells are placed in hypertonic solutions. Cells shrink as a result of exosmosis. Isotonic solutions contain similar water potential to the cytoplasm and hence, neither endosmosis nor exosmosis occurs in these solutions.

Key Areas Covered

1. What is Endosmosis
– Definition, Mechanism, Result, Examples
2. What is Exosmosis
– Definition, Mechanism, Result, Examples
3. What are the Similarities Between Endosmosis and Exosmosis
– Outline of Common Features
4. What is the Difference Between Endosmosis and Exosmosis
– Comparison of Key Differences

Key Terms: Endosmosis, Exosmosis, Hypertonic Solutions, Hypotonic Solutions, Isotonic Solutions, Osmosis

What is Endosmosis

Endosmosis is the osmosis toward the inside of a cell or vessel. It occurs when the water potential of the cell surrounding is higher than inside the cells. Thus, the solute concentration of the surrounding solution is less than that inside the cytoplasm. This type of solutions is called hypotonic solutions. Water molecules move into the cell across the cell membrane in endosmosis. Cells swell as a result of the movement of water into them.

Difference Between Endosmosis and Exosmosis

Figure 1: Cells in Hypertonic, Isotonic, and Hypotonic Solutions

In plants, the absorption of capillary water from the soil by roots and the entrance of water into the xylem vessels occur by endosmosis.

What is Exosmosis

Exosmosis refers to the osmosis toward the outside of a cell or vessel. It occurs when the water potential of the cell surrounding is lesser than inside the cells. Consequently, the solute concentration of the surrounding solution is higher than that inside the cytoplasm. These types of solutions are called hypertonic solutions. Water molecules move out of the cell across the cell membrane in exosmosis. Cells shrink as a result of the movement of water out of them. Plant cells in the three types of solutions are shown in figure 2.

Main Difference - Endosmosis vs Exosmosis

Figure 2: Plant Cells in Hypertonic, Isotonic, and Hypotonic Solutions

If a cell is placed in a strong hypertonic solution, the cell can be dehydrated and die. This situation is referred to as plasmolysis. In isotonic solutions, cells become flaccid. In hypotonic solutions, cells become turgid. If a cell is placed in a strong hypotonic solution, it may burst. The movement of water from the root hair cells to the cortical cells of the root occurs by exosmosis.

Similarities Between Endosmosis and Exosmosis

Both endosmosis and exosmosis are two types of osmosis.
Water molecules move across the cell membrane in both endosmosis and exosmosis.

Definition

Endosmosis: Endosmosis refers to the osmosis toward the inside of a cell or vessel.

Exosmosis: Exosmosis refers to the osmosis toward the outside of a cell or vessel.

Water Movement

Endosmosis: Water moves into the cell during endosmosis.

Exosmosis: Water moves out of the cell during exosmosis.

Type of Solutions

Endosmosis: Endosmosis occurs when cells are placed in hypotonic solutions.

Exosmosis: Exosmosis occurs when cells are placed in hypertonic solutions.

Solute Concentration in the Surroundings

Endosmosis: Endosmosis occurs when the solute concentration of the surroundings is less than the solute concentration inside the cell.

Exosmosis: Exosmosis occurs when the solute concentration of the surroundings is higher than the solute concentration inside the cell.

Water Potential

Endosmosis: The water potential of the surroundings is higher than that of the cytosol in endosmosis.

Exosmosis: The water potential of the surroundings is less than that of the cytosol in exosmosis.

Result

Endosmosis: The cells may swell as a result of endosmosis.

Exosmosis: The cells shrink as a result of exosmosis.

Examples

Endosmosis: The absorption of capillary water from the soil by roots and the entrance of water into the xylem vessels are the examples of endosmosis in plants.

Exosmosis: The movement of water from the root hair cells to the cortical cells of the root is an example of exosmosis.

Conclusion

Endosmosis and exosmosis are the two types of osmosis in which the movement of water occurs across the cell membrane. Endosmosis is the movement of water into the cell when the cells are placed in a hypotonic solution. Exosmosis is the movement of water out of the cell when the cells are placed in a hypotonic solution. The main difference between endosmosis and exosmosis is the direction of the movement of water in each of the process.

Reference:

1. “Tonic Solutions, Exosmosis, Endosmosis, Plasmolysis.” India’s United Public Service Commission, 31 Aug. 2013, Available here.

Image Courtesy:

1. “Human Erythrocytes OsmoticPressure PhaseContrast Plain” By Zephyris – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Turgor pressure on plant cells diagram” By LadyofHats (Public Domain) via Commons Wikimedia