bio 2.8

Osmosis: The process of diffusion of free water across a selectively permeable membrane.
Aquaporins: Special channels that facilitate the fast movement of large quantities of water across the cell membrane.
Osmolarity: Total solute concentration in a solution.
- A solute is the substance being dissolved (e.g., salt, sugar).
- A solvent is the substance that dissolves a solute (e.g., water).
- A solution is a uniform mixture of one or more solutes dissolved in the solvent.

Tonicity: The measure of relative concentrations of solute between two solutions (inside vs. outside the cell).
Types of Tonicity:
- Hypertonic: Higher concentration of solute and lower concentration of solvent outside the cell, resulting in water moving out of the cell.
- Isotonic: Equal concentrations of solute and solvent inside and outside the cell; no net movement of water occurs.
- Hypotonic: Lower concentration of solute and higher concentration of solvent outside the cell, resulting in water moving into the cell.

In a hypertonic environment, water moves out of the cell to balance solute concentrations.
In a hypotonic environment, water moves into the cell, where there is more solute, which can lead to cell lysis in animal cells whereas plant cells become turgid.
In an isotonic environment, water moves in and out at equal rates, maintaining dynamic equilibrium.

Osmoregulation aids in maintaining water balance and internal solute composition.
In hypertonic conditions, plant cells undergo plasmolysis (water leaves, causing cell shrinkage).
Isotonic conditions result in a flaccid state.
Hypotonic conditions lead to turgidity, where water enters the cell, causing pressure against the cell wall (turgor pressure).

Osmoregulation is crucial for maintaining internal conditions:
- In hypertonic environments, animal cells may shrivel due to water exiting the cell.
- In isotonic conditions, cells remain stable (normal state).
- In hypotonic conditions, excessive water can enter, leading to lysis (bursting) of the cell.

Freshwater paramecium: an organism living in a hypotonic environment where it risks cell lysis from water influx.
- The paramecium uses a contractile vacuole to expel excess water.
If placed in saltwater (hypertonic environment), water would diffuse out, risking cell shriveling.

The external environment may be hypotonic, hypertonic, or isotonic relative to the cellular environment.
Water movement occurs from areas of low osmolarity to areas of high osmolarity.
Molecular movement across membranes maintains growth and homeostasis, crucial for survival.
Osmoregulation ensures organisms control their internal solute composition and maintain life.