D2.3 Water potential

Osmosis

The diffusion of water molecules from a region of lower solute concentration (higher water potential) to a region of higher solute concentration (lower water potential), through a partially permeable membrane.

True or False? Water moves out of a hypertonic solution.

False. A hypertonic solution has a higher solute concentration and lower water potential than the surrounding area so water moves into the solution.

Isotonic

An environment with the same water potential and solute concentration as the surrounding environment, meaning water moves in and out at the same rate, in dynamic equilibrium.

Partially permeable cell membrane

A membrane that allows some substances to pass through while preventing others from entering or leaving a cell.

Dynamic equilibrium

An environment where water particles move across a partially permeable membrane in both directions at the same rate, with no net movement of water.

True or False? Water acts as a solvent due to the formation of covalent bonds between water molecules and solute particles.

False. Water acts as a solvent due to the formation of hydrogen bonds (not covalent bonds) between water molecules and solute particles.

Polarity of water as a solvent

The polar nature of water allows it to form hydrogen bonds with ionic substances, where the partially positive hydrogen atoms are attracted to negatively charged ions, and the partially negative oxygen atom is attracted to positively charged ions.

Movement of water in a hypertonic environment

Water molecules move across the partially permeable membrane (into the cell) from the region of higher water potential to a region of lower water potential.

Osmosis effect on plant cell structure in a hypotonic environment

In a hypotonic environment, water moves into a plant cell by osmosis, the vacuole enlarges, pushing the cell membrane against the cell wall, making the cell rigid and firm (turgid).

Importance of osmosis-induced cell rigidity in plants

Provides support and strength, helping the plant stand upright with leaves held out to catch sunlight.

Water potential

A measure of the tendency of water to move from one area to another, with high water potential in solutions with a low solute concentration and low water potential in solutions with a high solute concentration.

Plasmolysis

When the cell membrane of a plant cell pulls away from the cell wall due to water loss in a hypertonic solution.

Animal cell response to concentrated sugar solution

Animal cells placed in a hypertonic solution will lose water by osmosis and become crenated (shrivelled up).

Animal cell response to distilled water

Animal cells placed in distilled water will gain water by osmosis and may burst due to the lack of a cell wall to create turgor pressure.

Plant cell response in a hypotonic solution

A plant cell becomes turgid as water enters the cell by osmosis, increasing turgor pressure.

Plasmolysis in a plant cell

The process where a plant cell's plasma membrane shrinks and pulls away from the cell wall due to water loss in a hypertonic solution.

True or False? A hypertonic solution causes animal cells to swell.

False. A hypertonic solution causes animal cells to lose water and become crenated (shrivelled).

Contractile vacuole in Amoeba

Removes excess water to prevent the cell from bursting in a hypotonic environment.

Turgor pressure

The pressure exerted by the increase in hydrostatic pressure, pushing the cell membrane against the cell wall in a plant cell as it takes in water.

Effect of hypotonic solution on animal cells

Animal cells will gain water, swell, and may burst as they lack a cell wall to prevent overexpansion.

True or False? An isotonic solution results in no net movement of water in or out of the cell.

True. Water particles move in and out of the cell at the same rate in both directions.

Medical importance of isotonic IV solutions

Prevent red blood cells from bursting or becoming crenated, ensuring proper oxygen transport and preventing blood clots.

Crenation

The process where animal cells shrivel up due to water loss when placed in a hypertonic solution.

Role of the cell wall in osmosis in plant cells

Prevents the plant cell from bursting when it takes in water by osmosis, creating turgor pressure to maintain structure and support.

Independent variable in osmosis practical with potato cylinders

The solute concentration of the solution in which the potato cylinders are placed.

Importance of drying plant tissue before weighing in osmosis investigation

To ensure excess water on the surface does not alter the results.

True or False? When a potato cylinder placed in a sucrose solution does not change in mass, this indicates no overall movement of water.

True. This occurs when the solution is isotonic and has the same concentration as the cell cytoplasm.

True or False? Potato cylinders placed in distilled water should gain mass due to osmosis.

True. Potato cylinders placed in distilled water will gain mass due to water entering the cells by osmosis.

Osmotic concentration

The measure of solute concentration in a solution, determining the direction of water movement during osmosis.

True or False? In an isotonic solution, a plant cell will change in mass.

False. In an isotonic solution, there is no net movement of water, so the plant cell will not change in mass.

Role of error bars in data analysis

Indicate the variability of data and help determine the significance of differences between mean values.

Positive percentage change in mass in osmosis experiment

Indicates that plant tissue has gained water by osmosis, due to being in a hypotonic environment.

Standard deviation

Measures the spread of data around the mean value, indicating the consistency of the data.

Standard error in an experiment

Represents how close the sample mean is to the true population mean, with smaller errors indicating more accurate results.

True or False? A hypertonic solution will cause plant tissue to increase in mass.

False. A hypertonic solution will cause plant tissue to decrease in mass as water moves out of the cells.

Significance of overlapping error bars

Suggest that the difference between mean values is not significant.

Potato cylinders in a solution with the same osmotic concentration as their cytoplasm

No net movement of water, and the potato cylinders' mass remains unchanged. The solution is isotonic.

Indication of plant tissue losing mass in solution of different concentration

Water has moved out of the plant tissue by osmosis, showing the surrounding solution has a higher solute concentration.

Sucrose concentrations indicating hypotonic environment

The region where the potato cylinders gained mass (approximately 0 to 0.4 mols/dm³ of sucrose solution).

Sucrose concentrations indicating hypertonic environment

The region where the potato cylinders lost mass (approximately 0.4 to 1.0 mols/dm³ of sucrose solution).

Sucrose concentrations indicating isotonic environment

The region where the potato cylinders neither gained nor lost mass (approximately 0.4 mols/dm³ of sucrose solution).