IB Diploma · Biology D2.3
IB Biology D2.3: Water potential — Practice Questions & Answers
IB Biology D2.3 study notes: osmosis and water potential, hypertonic, hypotonic and isotonic solutions, turgor, plasmolysis and cell effects.
Here are 10 practice questions with full answers and explanations.
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Practice questions with answers
1
Multiple choice
Which interaction occurs between polar solutes and water molecules?
- Hydrogen bond formation
- Hydrophobic interaction
- Covalent bond formation
- Ionic bond formation between solute molecules
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WhyPolar solutes dissolve in water by forming hydrogen bonds with the polar water molecules.
2
Multiple choice
A cell placed in a solution with a higher solute concentration than its cytoplasm is in a:
- Hypertonic solution
- Hypotonic solution
- Isotonic solution
- Equilibrium state
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WhyA hypertonic solution has more solute than the cell, so water leaves the cell by osmosis.
3
Multiple choice
Osmosis is the net movement of water from:
- Low solute concentration to high solute concentration
- High solute concentration to low solute concentration
- Regions of equal solute concentration
- High pressure to low pressure
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WhyOsmosis is the net movement of water from a region of low solute concentration to high solute concentration.
4
Multiple choice
In a hypotonic solution, water moves into a plant cell, resulting in:
- Increased turgor pressure
- Plasmolysis
- Crenation
- Shrinkage
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WhyIn a hypotonic solution water enters the plant cell, raising turgor pressure as the cell pushes against its wall.
5
Multiple choice
Plant tissue placed in a hypertonic solution will experience:
- A decrease in length and mass
- An increase in length and mass
- No change in length or mass
- Increased turgor pressure
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WhyIn a hypertonic solution water leaves the plant tissue by osmosis, so its length and mass decrease.
6
Multiple choice
Animal cells in a hypotonic solution are likely to:
- Swell and burst
- Shrink
- Undergo plasmolysis
- Maintain their shape
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WhyIn a hypotonic solution, water enters the animal cell by osmosis, causing it to swell and burst (lyse).
7
Multiple choice
The shrinkage of animal cells in a hypertonic solution is known as:
- Crenation
- Turgor pressure
- Plasmolysis
- Lysis
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WhyCrenation is the shrinkage of animal cells as water leaves them by osmosis in a hypertonic solution.
8
Multiple choice
Freshwater unicellular organisms prevent bursting with:
- Contractile vacuoles
- Increased solute concentration
- A rigid cell wall
- Decreased membrane permeability
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WhyContractile vacuoles collect and expel excess water, preventing lysis in freshwater cells living in hypotonic surroundings.
9
Multiple choice
Turgor pressure in plant cells results from:
- Water moving into the cell
- Water moving out of the cell
- Equal water movement
- Solute movement out of the cell
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WhyTurgor pressure develops as water enters by osmosis and pushes the membrane against the rigid cell wall.
10
Multiple choice
Plasmolysis in plant cells occurs when:
- The cell membrane pulls away from the cell wall
- The cell wall bursts
- The cell becomes turgid
- The cell reaches equilibrium
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WhyIn a hypertonic solution water leaves the cell, so the shrinking protoplast pulls the membrane away from the wall.
Key terms in Water potential
Osmosis: The passive net movement of water across a partially permeable membrane from higher to lower water potential.
Water potential (Ψ): A measure of the tendency of water to move out of a system; pure water is zero and solutions are negative.
Solute: A dissolved substance; adding solute lowers (makes more negative) the water potential of a solution.
Hypertonic: A solution with a higher solute concentration (lower water potential) than the cell, causing water to leave the cell.
Hypotonic: A solution with a lower solute concentration (higher water potential) than the cell, causing water to enter the cell.
Isotonic: A solution with the same solute concentration and water potential as the cell, giving no net movement of water.
Turgor: The firm state of a plant cell when water entry presses the membrane against the cell wall, supporting the plant.
Plasmolysis: The pulling away of the plasma membrane from the cell wall when a plant cell loses water in a hypertonic solution.
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