Water Potential (DP IB Biology)
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Define the term osmosis.
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Define the term osmosis.
Osmosis is 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.
Define the term isotonic.
An isotonic environment has the same water potential and solute concentration as the surrounding environment. This means that water moves in and out at the same rate, in dynamic equilibrium.
What is a partially permeable cell membrane?
A partially permeable cell membrane allows some substances to pass through while preventing others from entering or leaving a cell.
Define dynamic equilibrium in the context of osmosis.
Dynamic equilibrium refers to an environment where water particles move across a partially permeable membrane in both directions at the same rate.
As a result, there is no net movement of water, although particles do continue to cross the membrane.
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.
How does the polarity of water allow it to act as a solvent?
The polar nature of water allows it to form hydrogen bonds with ionic substances. The partially positive hydrogen atoms in water are attracted to negatively charged ions, while the partially negative oxygen atom is attracted to positively charged ions.
Describe the movement of water in a hypertonic environment.
A hypertonic environment has a lower water potential and higher solute concentration than the surrounding environment. As a result, 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.
How does osmosis affect 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 (called turgid).
What is the importance of osmosis-induced cell rigidity in plants?
The rigidity of plant cells due to osmosis provides support and strength for the plant, helping it stand upright with leaves held out to catch sunlight.
What is water potential?
Water potential is 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.
Define the term plasmolysis.
Plasmolysis is when the cell membrane of a plant cell pulls away from the cell wall due to water loss in a hypertonic solution.
How do animal cells respond to being placed in a concentrated sugar solution?
Animal cells placed in a concentrated sugar solution (hypertonic) will lose water by osmosis and become crenated (shrivelled up).
What happens to animal cells placed in distilled water?
Animal cells placed in distilled water (hypotonic) will gain water by osmosis and may burst due to the lack of a cell wall to create turgor pressure.
What happens to a plant cell in a hypotonic solution?
In a hypotonic solution, a plant cell becomes turgid as water enters the cell by osmosis, increasing turgor pressure.
Define the term plasmolysis.
Plasmolysis is 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).
What is the function of a contractile vacuole in Amoeba?
The contractile vacuole in Amoeba removes excess water to prevent the cell from bursting in a hypotonic environment.
Define the term turgor pressure.
Turgor pressure is the pressure exerted by the increase in hydrostatic pressure which pushes the cell membrane against the cell wall in a plant cell as it takes in water.
What is the effect of placing an animal cell in a hypotonic solution?
The animal cell will gain water, swell, and may burst as it lacks 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.
An isotonic solution results in no net movement of water in or out of the cell. Water particles move in and out of the cell at the same rate in both directions.
What is the medical importance of isotonic intraveous (IV) solutions?
Isotonic IV solutions prevent red blood cells from bursting or becoming crenated, ensuring proper oxygen transport and preventing blood clots.
Define the term crenation.
Crenation is the process where animal cells shrivel up due to water loss when placed in a hypertonic solution.
What is the role of the cell wall during osmosis in plant cells?
The cell wall prevents the plant cell from bursting when it takes in water by osmosis, creating turgor pressure to maintain structure and support.
What is the independent variable in a practical that involves immersing potato cylinders in solutions of different concentration?
The independent variable in the osmosis and potatoes practical is the solute concentration of the solution in which the potato cylinders are placed.
In an investigation into plant tissue and osmosis, why is it important to dry the plant tissue samples before weighing?
Plant tissue is patted dry before measuring the mass so that excess water on the surface of the plant tissue does not alter the results.
True or False?
When a potato cylinder placed in a sucrose solution does not change in mass, this indicates that no overall movement of water has occurred.
True.
When a potato cylinder is placed in a sucrose solution and does not change in mass, this indicates no overall movement of water. 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 the movement of water into the cells by osmosis. This will occur because distilled water provides a hypotonic environment (a lower osmotic concentration) compared to the cytoplasm of the potato cells.
Define osmotic concentration.
Osmotic concentration is 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, a plant cell will not change in mass because there is no net movement of water.
What is the role of error bars in data analysis?
Error bars indicate the variability of data and help determine the significance of differences between mean values in an experiment.
What does a positive percentage change in mass indicate in an osmosis experiment?
A positive percentage change in mass indicates that the plant tissue has gained water by osmosis. This is due to being in a hypotonic environment.
Define standard deviation.
Standard deviation measures the spread of data around the mean value, indicating the consistency of the data.
What does standard error represent in an experiment?
Standard error 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.
What is the significance of overlapping error bars?
Overlapping error bars suggest that the difference between mean values is not significant.
What happens to potato cylinders in a solution with the same osmotic concentration as their cytoplasm?
There is no net movement of water, and the potato cylinders' mass remains unchanged. The solution is isotonic.
What does it indicate if plant tissue loses mass when immersed in a solution of a different concentration?
If plant tissue loses mass when immersed in a solution, it indicates that water has moved out of the plant tissue by osmosis. This shows that the surrounding solution has a higher solute concentration than the contents of the plant tissue.
Which sucrose concentrations indicate a hypotonic environment?
A hypotonic environment is seen in the region of the graph where the potato cylinders gained mass. This is between approximately 0 and 0.4 mols/dm³ of sucrose solution.
Which sucrose concentrations indicate a hypertonic environment?
A hypertonic environment is seen in the region of the graph where the potato cylinders lost mass. This is between approximately 0.4 and 1.0 mols/dm³ of sucrose solution.
Which sucrose concentrations indicate an isotonic environment?
A isotonic environment is seen in the region of the graph where the potato cylinders neither gained or lost mass. This at approximately 0.4 mols/dm³ sucrose solution.
What is the definition of water potential?
Water potential is the potential energy of water, per unit volume, relative to pure water.
What unit is used to measure water potential?
The units of water potential are usually kilopascals (kPa).
True or False?
The water potential of pure water is 0 kPa.
True.
The water potential of pure water is given a value of 0 kPa at atmospheric pressure and 20°C.
How does the addition of solutes affect water potential?
As solutes are added to a solution, the water potential decreases into negative values, as solutions with a high solute concentration have a lower water potential.
Define the relationship between water potential and water movement.
Water potential describes the tendency of water molecules to move from a dilute solution to a solution with a high solute concentration, as solutions with a high water potential contain water molecules with greater potential energy for movement.
What is the direction of water movement in relation to water potential?
Water molecules move from an area of high water potential (higher potential energy) to an area of low water potential (lower potential energy).
What is the symbol used to represent water potential?
Water potential is represented by the symbol Ψ or Ψw.
Define the term solute potential (Ψs)?
Solute potential, also known as osmotic potential, is the effect that solutes in a solution have on water potential.
True or False?
Pure water with no dissolved solutes has a solute potential of zero.
True.
Pure water with no dissolved solutes has a solute potential of zero.
What is pressure potential (Ψp)?
Pressure potential, also referred to as turgor potential or turgor pressure, is the hydrostatic pressure to which water is subjected.
What is the formula for total water potential (Ψw)?
The total water potential of a solution is the sum of its solute potential and its pressure potential: Ψw = Ψs + Ψp.
True or False?
Negative pressure potentials occur in xylem vessels where sap is transported under tension.
True.
Negative pressure potentials occur in xylem vessels where sap is transported under tension.
Define the term hypotonic.
Hypotonic refers to a solution that has a lower solute concentration and higher water content compared to a cell's contents.
Explain what happens when plant tissue is placed in a hypotonic solution.
When plant tissue is placed in a hypotonic solution, the lower solute potential inside the plant cells compared to the surrounding solution causes water to move into the plant cells, increasing their turgor pressure.
Define the term hypertonic.
Hypertonic refers to a solution that has a higher solute concentration and lower water content compared to a cell's contents.
Explain what happens when plant tissue is placed in a hypertonic solution.
When plant tissue is placed in a hypertonic solution, the lower solute potential in the surrounding solution compared to the plant cells causes water to move out of the plant cells, reducing their turgor pressure and leading to wilting.