Water Potential

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Water as a Solvent

Water is a dipolar molecule: the hydrogen side is slightly positive and the oxygen side is slightly negative.
This uneven charge distribution allows water to form hydrogen bonds with other polar solute molecules and ions.
The interaction between a solvent (like water) and a solute is called solvation.
Water molecules orientate around polar solutes and ions, forming hydration shells around each solute particle.

Osmosis

Osmosis is the diffusion of water molecules from a less concentrated (dilute) solution to a more concentrated solution across a partially permeable membrane.
Water moves down its concentration gradient during osmosis.
The cell membrane is partially permeable: it allows small molecules like water through but not larger solute molecules.
Osmosis can also be described as the net movement of water from a region of lower solute concentration to a region of higher solute concentration through a partially permeable membrane.

Osmosis through a partially permeable membrane

Tonicity of Solutions

A hypotonic solution has a lower solute concentration (more dilute) than the cell cytoplasm, causing a net movement of water into the cell.
A hypertonic solution has a higher solute concentration (more concentrated) than the cell cytoplasm, causing a net movement of water out of the cell.
An isotonic solution has the same solute concentration as the cell cytoplasm, so there is no net movement of water into or out of the cell.
Water molecules are always moving into and out of cells due to kinetic energy; in an isotonic solution there is no net movement in a particular direction.

Effect of osmosis on animal cells

Osmosis in Animal Cells

Animal cells lack a supporting cellulose cell wall, so changes in volume are more severe than in plant cells.
In a hypertonic solution, an animal cell loses water by osmosis and becomes crenated (shrivelled).
Crenated red blood cells may become stuck in capillaries, leading to the formation of blood clots.
In a hypotonic solution, an animal cell gains water by osmosis and, without a cell wall to create turgor pressure, will continue to do so until the cell membrane bursts.
Multicellular organisms must maintain isotonic tissue fluid around their cells to prevent these harmful changes.
Some unicellular organisms like Amoeba live in freshwater (hypotonic to their cytoplasm) and use contractile vacuoles to pump out excess water and prevent bursting.

Osmosis in Plant Cells

In a hypotonic solution, water enters the plant cell by osmosis; the expanding protoplast pushes against the cell wall, building up turgor pressure.
The inelastic cell wall prevents the cell from bursting and also stops too much water entering.
A plant cell fully inflated with water is described as fully turgid; turgidity provides support and strength, keeping the plant upright and leaves held out to catch sunlight.
If plants do not receive enough water, cells cannot remain turgid and the plant wilts.
In a more concentrated (hypertonic) solution, water leaves the plant cell by osmosis; the protoplast shrinks and pulls away from the cell wall in a process called plasmolysis.
A plasmolysed plant cell is described as flaccid.

Effect of osmosis on plant cells

Medical Applications of Isotonic Solutions

Intravenous (IV) drips used to treat dehydration or deliver medicine must be isotonic to blood plasma.
The solution is usually a 0.9% sterile saline solution (saltwater).
A hypotonic IV solution would cause a net movement of water into red blood cells, causing them to burst and decreasing the oxygen-carrying capacity of blood.
A hypertonic IV solution would cause a net movement of water out of red blood cells, causing them to shrivel and become crenated, increasing the risk of blood clots.
Donated human organs for transplant must be kept in an isotonic saline solution to prevent damage to cells due to net water movement by osmosis.

Investigating Osmosis in Plant Tissue

The osmotic concentration of plant tissue can be estimated by bathing samples in solutions of different tonicity.
In a hypotonic solution, tissue increases in mass or length; in a hypertonic solution, tissue decreases in mass or length; in an isotonic solution, mass or length remains unchanged.
A common practical uses potato cylinders placed into a range of sucrose solutions (at least 5 different concentrations).
Potato cylinders are cut to the same length, blotted dry, initial mass measured, then left in solutions for a set time (e.g. 30 minutes) usually in a water bath at around 30°C.
After removal, cylinders are dried to remove excess liquid, then final length and mass are measured and recorded.
The percentage change in mass is calculated by dividing the change in mass by the initial mass and multiplying by 100.

Investigating osmosis in plant tissue

Interpreting Osmosis Data

A positive percentage change in mass indicates the potato gained water by osmosis, meaning the solution had a lower osmotic concentration than the potato.
Gained water makes potato cells turgid, exerting turgor pressure on cell walls, so the potatoes feel hard.
A negative percentage change in mass indicates the solution had a higher osmotic concentration than the potato, so water moved out of the cells.
The potato cylinder in the strongest sucrose concentration will decrease in mass the most due to the greatest concentration gradient; cells become flaccid and may be plasmolysed.
If a potato cylinder shows no change in mass, the solution had the same osmotic concentration as the potato cytoplasm, so there was no net movement of water.
The point where the line of best fit crosses the x-axis on a graph of percentage change in mass against sucrose concentration gives the concentration of sucrose inside the potato cylinders.

Statistical Analysis in Osmosis Experiments

Sufficient repeats are important to ensure reliable results; repeat values can be used to calculate a mean mass for each sucrose concentration.
Standard deviation measures the spread of data around the mean and is useful for comparing consistency between data sets.
Standard error indicates how close the sample mean is to the true population mean; a larger sample size gives a smaller standard error.
Standard error is calculated by dividing the standard deviation by the square root of the sample size (SE = S / √n).
On graphs of mean values, error bars show the standard error; overlapping error bars suggest the difference between means is not significant, while non-overlapping error bars indicate a significant difference.

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1.Which of the following best defines osmosis?
Easy
- AThe diffusion of water molecules from a less concentrated solution to a more concentrated solution across a partially permeable membrane
- BThe movement of any liquid from a high concentration to a low concentration across a freely permeable membrane
- CThe active transport of water molecules against a concentration gradient using ATP
- DThe diffusion of solute molecules from a high concentration to a low concentration across a partially permeable membrane
2.A plant cell is placed in a hypotonic solution. Which statement describes what happens?
Easy
- AIt will swell with water and become turgid
- BIt will burst
- CNothing will happen
- DIt will shrink and shrivel and become flaccid
3.The diagram shows red blood cells bathed in three solutions of different solute concentrations. Which row of the table correctly describes the three solutions?
Medium
- AI: Isotonic, II: Hypotonic, III: Hypertonic
- BI: Isotonic, II: Hypertonic, III: Hypotonic
- CI: Hypertonic, II: Hypotonic, III: Isotonic
- DI: Hypotonic, II: Isotonic, III: Hypertonic
4.When investigating osmosis in plant tissue, any changes to mass and length are recorded over a period of time. What are the most appropriate units of measurement for mass and length during this investigation?
Easy
- Ag and mm
- Bg and cm
- Ckg and cm
- Dkg and mm
5.Which of the following statements about water and osmosis are correct? (select all that apply)
Medium
- AWater is a dipolar molecule.
- BWater can form hydrogen bonds with polar solutes and ions.
- COsmosis is the diffusion of water molecules from a more concentrated solution to a less concentrated solution.
- DThe cell membrane is partially permeable, allowing small molecules like water through but not larger solute molecules.
- EWater movement across a partially permeable membrane requires ATP.
6.Which of the following are correct about the effects of osmosis on plant cells? (select all that apply)
Medium
- AIn a hypotonic solution, plant cells become turgid.
- BIn a hypertonic solution, plant cells undergo plasmolysis.
- CTurgor pressure is the pressure of the cell wall pushing against the protoplast.
- DPlasmolysis occurs when the cell wall pulls away from the cell membrane.
- ETurgidity provides support and strength to plants.
7.Water molecules are always moving into and out of cells due to kinetic energy, even when the cell is in an isotonic solution.
Easy
True or false?
8.If a plant cell is placed in a hypertonic solution, it will become turgid.
Easy
True or false?

Soal lainnya

9.Match each term with its correct description.
Medium
- Osmosis
- Turgor pressure
- Plasmolysis
- Crenation
- Shrinking of an animal cell in a hypertonic solution
- Diffusion of water across a partially permeable membrane
- Pressure of the protoplast against the cell wall
- Shrinking of the protoplast away from the cell wall in a plant cell
10.Arrange the steps of the potato osmosis experiment in the correct order.
Medium
- Cut potato cylinders to the same length.
- Blot the cylinders dry and measure their initial mass.
- Place cylinders into sucrose solutions of different concentrations.
- Leave for a set time, then remove and blot dry.
- Measure final mass and length.
11.Which of the following statements correctly describe osmosis? (select all that apply)
Medium
- AWater moves from a less concentrated (dilute) solution to a more concentrated solution across a partially permeable membrane
- BWater moves down its concentration gradient
- CSolute molecules move across the membrane from high to low concentration
- DWater moves from a region of lower solute concentration to a region of higher solute concentration
- EWater moves from a region of higher solute concentration to a region of lower solute concentration
12.A plant cell is placed in a hypertonic solution. Which of the following will occur? (select all that apply)
Medium
- AWater leaves the cell by osmosis
- BThe vacuole volume decreases
- CThe protoplast pulls away from the cell wall
- DThe cell becomes fully turgid
- ETurgor pressure increases
13.Which of the following are correct about the effects of placing animal cells in solutions of different tonicity? (select all that apply)
Medium
- AIn a hypotonic solution, an animal cell gains water and may burst
- BIn a hypertonic solution, an animal cell loses water and becomes crenated
- CIn an isotonic solution, there is no net movement of water into or out of the cell
- DIn an isotonic solution, water molecules stop moving across the membrane
- EIn a hypotonic solution, an animal cell shrivels and becomes flaccid
14.A student investigated osmosis in potato cylinders placed in sucrose solutions of different concentrations. Which of the following conclusions are valid based on the results? (select all that apply)
Hard
- AA positive percentage change in mass indicates the potato gained water by osmosis
- BA negative percentage change in mass indicates the solution had a higher osmotic concentration than the potato
- CThe point where the line of best fit crosses the x-axis gives the concentration of sucrose inside the potato cells
- DThe potato cylinder in the strongest sucrose concentration will have the greatest increase in mass
- EIf the potato cylinder neither gained nor lost mass, there was no net movement of water into or out of the cells
15.In an isotonic solution, there is no net movement of water into or out of a cell, but water molecules still move across the membrane in both directions.
Easy
True or false?
16.A plant cell placed in a hypotonic solution will burst because it has no cell wall to resist the incoming water.
Easy
True or false?
17.Arrange the following steps of the potato osmosis experiment in the correct order.
Medium
- Cut potato cylinders to the same length using a cork borer and scalpel
- Blot the potato cylinders dry and measure their initial mass
- Place the potato cylinders into sucrose solutions of different concentrations
- Leave the potato cylinders in the solutions for a set time, e.g., 30 minutes in a water bath at 30°C
- Remove the cylinders, blot them dry, and measure their final mass
18.Arrange the following steps to calculate the percentage change in mass of a potato cylinder.
Medium
- Measure the initial mass of the potato cylinder
- Measure the final mass of the potato cylinder after the experiment
- Calculate the change in mass by subtracting the initial mass from the final mass
- Divide the change in mass by the initial mass
- Multiply by 100 to get the percentage change
19.A potato cylinder has an initial mass of 2.00 g. After being placed in a sucrose solution for 30 minutes, its mass is 1.80 g. What is the percentage change in mass?
Medium
- A-10%
- B-20%
- C+10%
- D+20%
20.A plant cell is placed in a solution with a lower solute concentration than its cytoplasm. Which of the following describes the net movement of water and the resulting state of the cell?
Medium
- AWater moves into the cell and it becomes turgid
- BWater moves out of the cell and it becomes flaccid
- CWater moves into the cell and it bursts
- DWater moves out of the cell and it becomes plasmolysed
21.A red blood cell is placed in a hypertonic solution. Which of the following describes the net movement of water and the appearance of the cell?
Medium
- AWater moves out and the cell becomes crenated
- BWater moves in and the cell bursts
- CWater moves out and the cell becomes turgid
- DNo net movement of water occurs
22.A potato cylinder is placed in a 0.5 mol dm⁻³ sucrose solution. Its initial mass is 2.00 g and its final mass is 1.70 g. What is the percentage change in mass?
Medium
- A-15%
- B-30%
- C-0.15%
- D-0.30%
23.In an osmosis experiment, error bars on a graph show overlap for two mean values. What does this suggest?
Medium
- AThe difference between the means is not significant
- BThe difference between the means is significant
- CThe data is unreliable
- DThe sample size was too large
24.Which of the following statements about the potato osmosis experiment are correct? (select all that apply)
Medium
- AThe potato cylinders are blotted dry before weighing to remove excess liquid
- BThe percentage change in mass is calculated using the initial mass
- CA positive percentage change in mass indicates water moved out of the potato
- DThe experiment should be repeated to ensure reliable results
- EThe potato cylinders are left in the solutions for a set time, e.g., 30 minutes
25.Which of the following are valid conclusions from an osmosis experiment where potato cylinders are placed in sucrose solutions of different concentrations? (select all that apply)
Medium
- AThe point where the line of best fit crosses the x-axis gives the osmotic concentration of the potato cells
- BA negative percentage change in mass indicates the solution was hypertonic to the potato
- CThe potato cylinders in the highest sucrose concentration will have the greatest increase in mass
- DError bars can be used to show the variability of the data
- EThe experiment can be used to estimate the water potential of the potato cells
26.A plant cell placed in a hypertonic solution will become turgid.
Easy
True or false?
27.Which of the following best explains why the eight small cubes lost mass faster than the single large cube?
Medium
- AThe small cubes have a larger surface area to volume ratio
- BThe small cubes have a smaller surface area to volume ratio
- CThe small cubes have a higher water potential
- DThe small cubes contain more sucrose
28.Before weighing the cubes at each interval, the biologist blotted the outside of each cube with paper towel. Why?
Medium
- ATo remove excess liquid that would affect the mass reading
- BTo increase the rate of osmosis
- CTo keep the cubes at a constant temperature
- DTo prevent the cubes from drying out
29.A student cuts potato cylinders and places them into five sucrose solutions of increasing concentration. Before weighing each cylinder at the end of the experiment, the student blots it dry with a paper towel. What is the main reason for this step?
Medium
- ATo remove excess liquid from the surface so it does not add to the measured mass
- BTo stop osmosis by drying out the potato cells
- CTo make the potato cylinders feel firmer
- DTo remove solute that has entered the potato tissue
30.A student calculates the percentage change in mass of potato cylinders after 30 minutes in different sucrose solutions. Which of the following is the correct formula?
Hard
- A(change in mass ÷ initial mass) × 100
- B(change in mass ÷ final mass) × 100
- C(initial mass ÷ change in mass) × 100
- D(final mass ÷ initial mass) × 100
31.In a potato osmosis experiment, the line of best fit on a graph of percentage change in mass against sucrose concentration crosses the x-axis at 0.31 mol dm⁻³. What does this value represent?
Medium
- AThe sucrose concentration inside the potato cells
- BThe concentration of sucrose that causes plasmolysis
- CThe water potential of pure water
- DThe concentration of sucrose that gives the largest increase in mass
32.A student sets up five test tubes containing 10 cm³ of sucrose solutions of 0, 0.25, 0.5, 0.75 and 1.00 mol dm⁻³. One potato cylinder is placed in each tube. Which variable is the independent variable?
Medium
- AThe sucrose concentration of the solution
- BThe change in mass of the potato cylinders
- CThe temperature of the water bath
- DThe volume of sucrose solution used
33.A student plots mean percentage change in mass against sucrose concentration. At 0.2 mol dm⁻³ the mean is +12% with error bars of ±2%, and at 0.4 mol dm⁻³ the mean is +5% with error bars of ±2%. What can be concluded?
Hard
- AThere is a significant difference between the two means
- BThere is no significant difference between the two means
- CThe potato cells were plasmolysed at both concentrations
- DThe experiment was invalid because the error bars are too small
34.A student measures the initial length of a potato cylinder as 50 mm. After 30 minutes in a sucrose solution, its length is 45 mm. What is the percentage change in length?
Hard
- A−10%
- B−5%
- C−11.1%
- D+10%
35.Which of the following would improve the reliability of an osmosis experiment using potato cylinders? (select all that apply)
Hard
- AUsing at least five potato cylinders for each sucrose concentration
- BCalculating the mean mass for each concentration
- CUsing only one potato cylinder per concentration
- DKeeping the potato cylinders in the solutions for different lengths of time
- ECalculating the standard deviation for each set of repeats
36.A biologist investigates the solute concentration of turnip tissue from different parts of old and new tubers. Which of the following are valid sources of error in this investigation? (select all that apply)
Hard
- AThe tissue samples were not all the same size
- BThe sucrose solutions were not at the same temperature
- CThe percentage change in mass was calculated instead of the change in mass
- DThe tissue samples were blotted dry before weighing
- EThe balance was not calibrated to zero before use
37.In an osmosis experiment, if the error bars for two mean values overlap, this suggests that the difference between the means is not significant.
Medium
True or false?
38.A potato cylinder placed in a very concentrated sucrose solution will have the greatest decrease in mass because there is the greatest concentration gradient between the potato cells and the solution.
Medium
True or false?
39.Which of the following best describes why water is such a good solvent?
Easy
- AIt is dipolar, so it can form hydrogen bonds with polar solutes and ions
- BIt is non-polar, so it dissolves only non-polar substances
- CIt has a high density, so it can dissolve more solute per unit volume
- DIt is a small molecule, so it can squeeze between solute particles
40.The interaction between a solvent such as water and a solute is known as:
Easy
- ASolvation
- BOsmosis
- CDiffusion
- DPlasmolysis
41.What is the term for a plant cell that has lost water and whose cell membrane has pulled away from the cell wall?
Medium
42.What is the name of the structure in Amoeba that collects and pumps out excess water to prevent the organism from bursting?
Easy
43.A potato cylinder has an initial mass of 2.50 g. After being placed in a sucrose solution for 30 minutes, its mass is 2.20 g. Calculate the percentage change in mass. Give your answer to 1 decimal place.
Medium
44.Complete the sentence about osmosis.
Easy
Osmosis is the diffusion of water molecules from a ____ solution to a ____ solution across a partially permeable membrane.
45.Complete the table by naming the tonicity of each solution.
Medium
A solution with a lower solute concentration than the cytoplasm is ____. A solution with a higher solute concentration is ____. A solution with the same solute concentration is ____.
46.A potato cylinder has an initial mass of 2.50 g. After 30 minutes in a sucrose solution, its mass is 2.75 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
47.A potato cylinder has an initial mass of 3.00 g. After 30 minutes in a sucrose solution, its mass is 2.70 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
48.Complete the sentence about water potential.
Medium
Water potential is the tendency of water to move from one area to another, and pure water has the ____ water potential.
49.A potato cylinder has an initial mass of 2.50 g. After 30 minutes in a sucrose solution, its mass is 2.20 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
50.During the first 20 minutes, the single large cube lost 0.8 g. Calculate the rate of loss in mass per cm² per minute. Give your answer to 3 significant figures.
Hard
51.A potato cylinder has an initial mass of 2.00 g. After being placed in a sucrose solution for 30 minutes, its mass is 2.30 g. Calculate the percentage change in mass. Give your answer to 1 decimal place.
Easy
52.A potato cylinder has an initial mass of 4.00 g. After 30 minutes in a sucrose solution, its mass is 3.40 g. Calculate the percentage change in mass. Give your answer to 1 decimal place.
Medium
53.Describe the effect that a more dilute than normal blood plasma would have on red blood cells.
Medium
54.Explain why changes in cell volume affect animal cells more severely than plant cells.
Medium
55.Outline the effects on human heart tissue of being placed into a hypotonic solution.
Medium
56.A biologist investigated how surface area affects osmosis in potato cubes. Two cubes of potato, each with sides of 4 cm, were cut. One cube was placed into 40% sucrose solution. The other cube was cut into eight equal-sized smaller cubes and placed into 40% sucrose solution. The masses of the cubes were recorded at time intervals. Explain why the potato tissue changed in mass.
Hard
57.A biologist investigates the solute concentration of cells from different parts of turnip tubers of different ages. Suggest two possible sources of error that the biologist may have encountered when collecting the data in this investigation.
Hard
58.A potato cylinder has an initial mass of 2.50 g. After being placed in a sucrose solution for 30 minutes, its mass is 2.20 g. Calculate the percentage change in mass. Give your answer to 1 decimal place.
Medium
- A-13 %
- B-11 %
- C-12 %
- D-10 %
59.A potato cylinder has an initial mass of 2.50 g. After 30 minutes in a sucrose solution, its mass is 2.75 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
- A11 %
- B10 %
- C12 %
- D9 %
60.A potato cylinder has an initial mass of 3.00 g. After 30 minutes in a sucrose solution, its mass is 2.70 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
- A-11 %
- B-8 %
- C-9 %
- D-10 %
61.A potato cylinder has an initial mass of 2.50 g. After 30 minutes in a sucrose solution, its mass is 2.20 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
- A-11 %
- B-10 %
- C-13 %
- D-12 %
62.During the first 20 minutes, the single large cube lost 0.8 g. Calculate the rate of loss in mass per cm² per minute. Give your answer to 3 significant figures.
Hard
- A4.17 × 10⁻⁴ g cm⁻² min⁻¹
- B8.33 × 10⁻³ g cm⁻² min⁻¹
- C2.50 × 10⁻³ g cm⁻² min⁻¹
- D4.00 × 10⁻² g cm⁻² min⁻¹
63.A potato cylinder has an initial mass of 2.00 g. After being placed in a sucrose solution for 30 minutes, its mass is 2.30 g. Calculate the percentage change in mass. Give your answer to 1 decimal place.
Easy
- A17 %
- B15 %
- C16 %
- D14 %
64.A potato cylinder has an initial mass of 4.00 g. After 30 minutes in a sucrose solution, its mass is 3.40 g. Calculate the percentage change in mass. Give your answer to 1 decimal place.
Medium
- A-16 %
- B-13 %
- C-15 %
- D-14 %

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