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4. Movement of Water in Cells — Practice Questions
This chapter explores how water potential, osmolarity, and solute concentration drive the essential movement of water into and out of cells to maintain homeostasis.
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(Multiple Choice — Click to Reveal Answer)
1. What is the primary factor that determines the direction of water movement across a membrane?
(A) Solute size
(B) Solute concentration
(C) Membrane thickness
(D) Temperature
Answer
(B) — Water moves from regions of lower solute concentration (higher water potential) to higher solute concentration (lower water potential).
2. In which type of environment would a plant cell become flaccid?
(A) Hypotonic
(B) Isotonic
(C) Hypertonic
(D) Acidic
Answer
(B) — In an isotonic solution, there is no net movement of water, and plant cells become limp or flaccid.
3. Which organelle in freshwater protists helps remove excess water to prevent bursting?
(A) Chloroplast
(B) Contractile vacuole
(C) Central vacuole
(D) Lysosome
Answer
(B) — The contractile vacuole pumps out excess water that enters due to osmosis.
4. If a plant cell has a total water potential lower than the surrounding solution, what will happen?
(A) Water will enter the plant cell
(B) Water will leave the plant cell
(C) No net water movement
(D) Solutes will move into the plant cell
Answer
(A) — Water flows from areas of higher to lower water potential, so if the solution has higher water potential, water will enter the cell.
5. What term describes the solution with a greater solute concentration compared to another solution?
(A) Isotonic
(B) Hypotonic
(C) Hypertonic
(D) Hydrophilic
Answer
(C) — A hypertonic solution has a higher solute concentration and thus a lower water potential than a hypotonic solution.
6. In osmosis, water moves toward the side with:
(A) Lower solute concentration
(B) Higher solute concentration
(C) Higher temperature
(D) Larger molecules
Answer
(B) — Water moves toward the side with a higher solute concentration (lower water potential).
7. Which term describes the bursting of an animal cell due to excess water intake?
(A) Plasmolysis
(B) Crenation
(C) Cytolysis
(D) Turgor pressure
Answer
(C) — Cytolysis is the bursting of an animal cell in a hypotonic environment.
8. In a hypotonic environment, a plant cell will become:
(A) Flaccid
(B) Plasmolyzed
(C) Turgid
(D) Shrunken
Answer
(C) — Water enters the plant cell, filling the central vacuole and making the cell turgid (firm).
9. Which component directly affects the solute potential (Ψs) of a solution?
(A) Temperature
(B) Solute concentration
(C) Pressure potential
(D) Membrane composition
Answer
(B) — Solute concentration influences solute potential: more solutes lower Ψs.
10. If a red blood cell is placed in a hypertonic solution, it will:
(A) Swell
(B) Burst
(C) Shrink
(D) Remain the same
Answer
(C) — In a hypertonic solution, water exits the cell, causing it to shrink (crenation).
11. What factor increases the rate of osmosis across a membrane?
(A) Lower temperature
(B) Greater solute concentration difference
(C) Decrease in membrane surface area
(D) Higher molecular weight of solutes
Answer
(B) — A larger solute concentration difference creates a steeper water potential gradient, increasing osmosis rate.
12. What effect does increasing pressure potential (Ψp) inside a plant cell have on its overall water potential (Ψ)?
(A) Increases water potential
(B) Decreases water potential
(C) No change
(D) Only affects solute potential
Answer
(A) — Increasing pressure potential raises overall water potential, opposing water influx.
13. Which term describes the total potential energy of water in a system compared to pure water?
(A) Solute potential
(B) Osmolarity
(C) Water potential
(D) Diffusion gradient
Answer
(C) — Water potential (Ψ) predicts the direction of water movement.
14. What type of solution causes plasmolysis in plant cells?
(A) Isotonic
(B) Hypotonic
(C) Hypertonic
(D) Neutral
Answer
(C) — In hypertonic solutions, water exits plant cells, causing plasmolysis (membrane pulling away from the wall).
15. Which of the following correctly describes an isotonic solution for animal cells?
(A) Water enters faster than it leaves
(B) Water leaves faster than it enters
(C) No net water movement occurs
(D) Solutes diffuse into the cell
Answer
(C) — In an isotonic environment, water enters and exits the cell at equal rates, maintaining cell size.
16. Which factor would lower the water potential of a solution?
(A) Adding more solute
(B) Increasing pressure
(C) Decreasing solute concentration
(D) Heating the solution
Answer
(A) — Adding solutes makes water potential more negative, decreasing it.
17. If a plant cell is placed in pure water, what is the net movement of water?
(A) Into the cell
(B) Out of the cell
(C) No movement
(D) Depends on temperature
Answer
(A) — Water moves into the cell because pure water has the highest water potential.
18. What does a solute potential of zero indicate?
(A) No solutes are present
(B) Solution is hypertonic
(C) Solution is hypotonic
(D) High solute concentration
Answer
(A) — Pure water has a solute potential of zero because no solutes are present.
19. Which solution type would cause a freshwater protist to constantly expel water using a contractile vacuole?
(A) Hypotonic
(B) Hypertonic
(C) Isotonic
(D) Saline
Answer
(A) — In hypotonic environments, water continuously enters cells, requiring expulsion by contractile vacuoles to prevent lysis.
20. What is the correct formula for calculating water potential (Ψ)?
(A) Ψ = Ψs + Ψp
(B) Ψ = Ψs × Ψp
(C) Ψ = Ψs ÷ Ψp
(D) Ψ = Ψs - Ψp
Answer
(A) — Water potential is the sum of solute potential and pressure potential: Ψ = Ψs + Ψp.
21. When comparing two solutions, the one with more solutes is said to be:
(A) Hypotonic
(B) Hypertonic
(C) Isotonic
(D) Anhydrous
Answer
(B) — A hypertonic solution has a higher solute concentration compared to another solution.
22. A plant wilts because its cells lose water. This is an example of exposure to a:
(A) Hypotonic environment
(B) Hypertonic environment
(C) Isotonic environment
(D) Aquaporin malfunction
Answer
(B) — In hypertonic environments, plant cells lose water and become plasmolyzed, leading to wilting.
23. Which statement about osmosis is true?
(A) It requires energy input
(B) Water moves from high to low water potential
(C) Water moves toward higher water potential
(D) It moves solutes directly across the membrane
Answer
(B) — Water naturally moves from areas of high to low water potential without requiring energy.
24. What is the main function of aquaporins in a cell membrane?
(A) Transport ions
(B) Allow rapid water transport
(C) Synthesize solutes
(D) Maintain turgor pressure
Answer
(B) — Aquaporins are channel proteins that facilitate the movement of water across membranes.
25. If a cell's environment becomes hypotonic, what immediate cellular response is expected?
(A) Cell shrinks
(B) Cell becomes flaccid
(C) Cell swells
(D) Cell undergoes plasmolysis
Answer
(C) — In a hypotonic environment, water enters the cell, causing it to swell.
26. If a plant cell’s solute potential becomes more negative and pressure potential remains constant, what happens to its water potential?
(A) Increases
(B) Decreases
(C) Stays the same
(D) Becomes positive
Answer
(B) — A more negative solute potential lowers the overall water potential.
27. Which condition would cause the greatest water uptake by a plant cell?
(A) High solute potential and low pressure potential
(B) Low solute potential and high pressure potential
(C) Low solute potential and low pressure potential
(D) High solute potential and high pressure potential
Answer
(C) — A very negative water potential (low solute and pressure potentials) favors water inflow.
28. When a red blood cell is placed in pure water, it bursts. Which best explains this event?
(A) Water moves out due to active transport
(B) Water moves into the cell by osmosis
(C) The plasma membrane actively pumps in water
(D) Solutes diffuse out causing shrinkage
Answer
(B) — Water moves into the cell down its water potential gradient, causing the cell to swell and lyse.
29. Which situation would result in no net movement of water across a membrane?
(A) Cell in hypotonic environment
(B) Cell in hypertonic environment
(C) Cell in isotonic environment
(D) Cell with higher solute concentration than surroundings
Answer
(C) — In isotonic conditions, water enters and leaves the cell at equal rates, with no net movement.
30. What happens to water potential if pressure potential inside a plant cell increases significantly?
(A) Water potential becomes more negative
(B) Water potential remains unchanged
(C) Water potential becomes more positive
(D) Water stops moving
Answer
(C) — Increased pressure potential makes the overall water potential less negative (more positive), reducing water entry.
31. Which type of environment would cause a plant to lose turgor pressure most rapidly?
(A) Hypotonic solution
(B) Isotonic solution
(C) Hypertonic solution
(D) Pure water
Answer
(C) — In a hypertonic solution, water exits plant cells, leading to loss of turgor pressure and wilting.
32. A freshwater fish placed in a saltwater tank would experience which of the following effects at the cellular level?
(A) Water enters cells causing swelling
(B) Water leaves cells causing shrinkage
(C) Cells remain unchanged
(D) Solutes move into cells causing swelling
Answer
(B) — Saltwater is hypertonic to the fish’s cells, so water leaves the cells, causing shrinkage and dehydration.
33. Which best describes the role of solutes in affecting water movement across membranes?
(A) Solutes increase water potential
(B) Solutes lower water potential
(C) Solutes increase osmotic pressure but not water potential
(D) Solutes prevent any water movement
Answer
(B) — Adding solutes makes the water potential more negative, encouraging water to move toward the solute-rich side.
34. What is the immediate result of placing a plant cell into a solution with a higher water potential than the cell’s interior?
(A) Water leaves the cell
(B) No net water movement
(C) Water enters the cell
(D) The cell wall collapses
Answer
(C) — Water enters the cell, increasing turgor pressure.
35. Which of the following statements about osmosis and water potential is correct?
(A) Water moves toward higher water potential
(B) Water moves from low to high solute concentration
(C) Water moves from high to low solute concentration
(D) Solutes move with water during osmosis
Answer
(B) — Water moves toward higher solute concentration (lower water potential) in osmosis.
36. Define osmosis in one sentence.
Answer
Osmosis is the passive movement of water molecules across a selectively permeable membrane from areas of higher water potential to lower water potential.
37. What happens to the pressure potential of a plant cell when its central vacuole fills with water?
Answer
The pressure potential increases as the vacuole expands and presses the plasma membrane against the cell wall, generating turgor pressure.
38. Why can’t animal cells withstand excess water intake as plant cells can?
Answer
Animal cells lack a rigid cell wall to counteract osmotic pressure, making them prone to bursting in hypotonic solutions.
39. What is plasmolysis?
Answer
Plasmolysis is the process where a plant cell’s plasma membrane pulls away from the cell wall due to water loss in a hypertonic solution.
40. How does a contractile vacuole help freshwater protists survive in hypotonic environments?
Answer
It actively expels excess water that enters the cell to prevent bursting.
41. If solute concentration inside a cell increases while the external environment remains unchanged, what happens to the cell’s water potential?
Answer
The cell’s water potential becomes more negative, promoting water influx.
42. Why is water potential always lower (more negative) in solutions with high solute concentrations?
Answer
Solutes bind free water molecules, reducing the number of molecules available to move freely and lowering water potential.
43. In terms of water potential, what direction does water always move?
Answer
Water always moves from areas of higher (less negative) to lower (more negative) water potential.
44. Describe one difference between an isotonic environment for plant cells versus animal cells.
Answer
In an isotonic environment, animal cells maintain normal shape, but plant cells become flaccid because they require turgor pressure for firmness.
45. What does a negative pressure potential inside a plant cell indicate?
Answer
Negative pressure potential (tension) suggests that the cell is losing water and becoming plasmolyzed.
46. What is the primary factor causing turgor pressure in plant cells?
Answer
The influx of water into the central vacuole, pressing the plasma membrane against the cell wall.
47. Why are aquaporins critical for cells in highly variable environments?
Answer
Aquaporins enable rapid water movement across membranes, allowing cells to quickly adjust to osmotic changes.
48. If a plant cell has a solute potential of –0.6 MPa and a pressure potential of 0.3 MPa, what is its overall water potential?
Answer
Water potential = –0.6 + 0.3 = –0.3 MPa.
49. How does a plant maintain turgor pressure even during minor water loss?
Answer
The cell wall provides structural support, resisting collapse even when minor water loss occurs.
50. What cellular structure prevents plant cells from bursting in hypotonic solutions?
Answer
The rigid cell wall counteracts osmotic pressure and prevents plant cells from bursting.