What will happen if cells are placed in solutions with concentrations the same as or different from those of the cytoplasm?

This Demonstration illustrates the biological concept of tonicity, a measure of the osmotic pressure gradient between a cell and its surrounding solution. Water can travel across a cell membrane through a process called osmosis, and it always moves down its concentration gradient. Therefore, water will travel from a hypotonic solution, which has high water concentration (and low solute concentration) to a hypertonic solution, which has low water concentration (and high solute concentration). This Demonstration shows the movement of water for different tonicities.

Details

A solute is a substance dissolved in a liquid, the solvent: water in this Demonstration.

Osmosis is the movement of water across a cell membrane. Cells use osmosis to maintain concentration equilibrium (the concentrations of solute inside and outside the cell are equal). Changing the amount of water allows the cells to achieve equilibrium. When a cell is placed in a solution in which the concentrations are not the same as in the cell, the cell undergoes osmosis. The water travels down the concentration gradient from higher water concentration (and lower solute concentration) to lower water concentration (and higher solute concentration). In other words, water moves from a hypotonic region to a hypertonic region. Determining which fluid is hypotonic and hypertonic is relative.

When water leaves a cell, it shrinks, which is called plasmolysis. When water enters a cell, it expands, which creates turgor pressure on the walls of a plant cell and can cause the cell to explode.

In these snapshots, the solute concentration in the solution exceeds the solute concentration in the cell.

Snapshot 1: a hypotonic cell (smaller solute concentration, more water) is initially placed in a hypertonic solution (greater solute concentration, less water)

Snapshot 2: at

Snapshot 3: the cell continues to shrink (undergo plasmolysis) until it reaches equilibrium

The opposite would occur if the solute concentration in the cell exceeded the solute concentration in the solution.

Special thanks to the University of Illinois NetMath Program and the mathematics department at William Fremd High School.

References

[1] N. A. Campbell et al., AP Edition Biology, 8th ed., New York: Pearson/Benjamin Cummings, 2008.

[2] Hartnell College. "Hartnell College Biology Tutorials." (May 25, 2013) www.hartnell.edu/biology-tutorials.

Skill:

•  Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions

    
Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)

Solutions may be loosely categorised as hypertonic, hypotonic or isotonic according to their relative osmolarity

• Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water)
• Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water)
• Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow)

Osmotic Movement between Solutions:  Hypertonic (left) and Hypotonic (right)

Estimating Osmolarity

The osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities

• The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
• Water loss or gain may be determined by weighing the sample before and after bathing in solution
• Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)

Application:

•  Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity 

   as the cytoplasm to prevent osmosis

    
Tissues or organs to be used in medical procedures must be kept in solution to prevent cellular dessication

This solution must share the same osmolarity as the tissue / organ (i.e. isotonic) in order to prevent osmosis from occurring

Uncontrolled osmosis will have negative effects with regards to cell viability:

• In hypertonic solutions, water will leave the cell causing it to shrivel (crenation)
• In hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis)

In plant tissues, the effects of uncontrolled osmosis are moderated by the presence of an inflexible cell wall

• In hypertonic solutions, the cytoplasm will shrink (plasmolysis) but the cell wall will maintain a structured shape
• In hypotonic solutions, the cytoplasm will expand but be unable to rupture within the constraints of the cell wall (turgor)

Summary of the Effects of Solute Concentrations on Cells

What happens if cells are placed in solutions with the same or different concentrations than the cell?

What happens if a cell is in a solution that is exactly the same concentration outside as the concentration inside?

When the concentration of a solution is the same as that of the cell the solution is said to be?

What is the solution called when its concentration is the same as concentration inside the cell a hypertonic solution C hypotonic solution B isotonic solution d dilute solution?