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4. Movement of Water in Cells — Practice Questions 2
This chapter explains how water potential, osmolarity, and solute concentrations regulate the movement of water in biological systems, maintaining homeostasis and cell integrity.
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(Multiple Choice — Click to Reveal Answer)
1. In which direction does water move when two solutions of different water potentials are separated by a membrane?
(A) Toward the solution with higher water potential
(B) Toward the solution with lower water potential
(C) Toward the solution with less solute
(D) Randomly without preference
Answer
(B) — Water always moves toward the solution with the lower water potential (more negative Ψ).
2. Which of the following best defines solute potential (Ψs)?
(A) The pressure exerted by water against the membrane
(B) The contribution of solute concentration to the total water potential
(C) The absolute amount of solute present
(D) The permeability of the membrane to water
Answer
(B) — Solute potential reflects how solute concentration lowers a solution's water potential.
3. Which situation best describes a hypertonic environment for a plant cell?
(A) The solution has fewer solutes than the cell interior
(B) The solution has more solutes than the cell interior
(C) The solution has an equal number of solutes as the cell interior
(D) The solution has no solutes at all
Answer
(B) — A hypertonic environment has a higher solute concentration and lower water potential than the cell.
4. What happens to the water potential of a solution when more solute is added?
(A) It becomes more positive
(B) It becomes less negative
(C) It becomes more negative
(D) It remains unchanged
Answer
(C) — Adding solutes makes the water potential more negative by lowering the free energy of water.
5. What will occur if an animal cell is placed in a hypotonic solution?
(A) It will shrink
(B) It will remain the same
(C) It will swell and may burst
(D) Solutes will leave the cell
Answer
(C) — Water enters the cell, increasing volume and possibly causing lysis if the cell lacks structural support.
6. Which structure in plant cells prevents bursting when excess water enters?
(A) Plasma membrane
(B) Cell wall
(C) Cytoskeleton
(D) Ribosomes
Answer
(B) — The rigid cell wall provides resistance against excessive internal pressure from water influx.
7. A red blood cell placed in a hypertonic solution will:
(A) Gain water and swell
(B) Lose water and shrink
(C) Stay the same
(D) Undergo plasmolysis
Answer
(B) — Water moves out of the cell, causing it to shrink (crenation).
8. Which organelle most directly regulates water balance in freshwater unicellular organisms?
(A) Nucleus
(B) Contractile vacuole
(C) Mitochondrion
(D) Endoplasmic reticulum
Answer
(B) — The contractile vacuole actively expels excess water to prevent lysis.
9. If a plant cell is placed in distilled water, what immediate effect is expected?
(A) The cell shrinks
(B) The cell becomes turgid
(C) The plasma membrane detaches from the wall
(D) The cell lyses
Answer
(B) — Water enters the cell, and turgor pressure builds up, making the cell firm (turgid).
10. Which of the following terms describes a solution with the same solute concentration as a cell's cytoplasm?
(A) Hypertonic
(B) Hypotonic
(C) Isotonic
(D) Anhydrous
Answer
(C) — In an isotonic solution, there is no net water movement and the cell maintains its shape.
11. What happens to water movement if two solutions are isotonic relative to each other?
(A) Water moves rapidly into one side
(B) Water moves rapidly out of one side
(C) Water moves equally in both directions
(D) No movement of water occurs at all
Answer
(C) — Water moves equally across the membrane without a net gain or loss.
12. What will happen to a plant cell’s turgor pressure if placed in a hypertonic environment?
(A) It will increase
(B) It will decrease
(C) It will stay the same
(D) It will fluctuate
Answer
(B) — Water exits the cell, reducing turgor pressure and causing the plant to wilt.
13. What term describes the cellular condition when a plant cell membrane pulls away from the cell wall?
(A) Crenation
(B) Cytolysis
(C) Plasmolysis
(D) Turgidity
Answer
(C) — Plasmolysis occurs when water loss causes the plasma membrane to shrink away from the cell wall.
14. Which of the following would have the highest (least negative) water potential?
(A) Distilled water
(B) Seawater
(C) Sugar solution
(D) Saltwater
Answer
(A) — Pure distilled water has the highest possible water potential (Ψ = 0).
15. What determines the direction of water movement across a selectively permeable membrane?
(A) Solute molecular size
(B) Solute molecular weight
(C) Water potential gradient
(D) Temperature only
Answer
(C) — Water moves from high water potential to low water potential areas.
16. If solute concentration increases inside a cell, what happens to the cell’s solute potential (Ψs)?
(A) Becomes more positive
(B) Becomes less negative
(C) Becomes more negative
(D) Stays the same
Answer
(C) — Adding solutes makes solute potential more negative, lowering the overall water potential.
17. In which environment does a plant cell lose the least amount of water?
(A) Strong hypertonic solution
(B) Strong hypotonic solution
(C) Pure water
(D) Isotonic solution
Answer
(C) — In pure water, water enters the cell, and no water is lost.
18. Which component helps water move more quickly through plasma membranes?
(A) Protein pumps
(B) Aquaporins
(C) Ribosomes
(D) Ion channels
Answer
(B) — Aquaporins are specialized channel proteins for rapid water transport.
19. Which solution would most likely cause a plant cell to undergo plasmolysis?
(A) Distilled water
(B) Isotonic solution
(C) Hypertonic solution
(D) Hypotonic solution
Answer
(C) — In a hypertonic environment, water leaves the plant cell, causing plasmolysis.
20. Which process moves water across the plasma membrane in osmosis?
(A) Active transport
(B) Simple diffusion
(C) Exocytosis
(D) Facilitated diffusion through aquaporins
Answer
(D) — Water moves by facilitated diffusion through aquaporins.
21. If a plant cell's water potential is –0.7 MPa and the surrounding solution is –0.3 MPa, what happens to water movement?
(A) Water moves into the cell
(B) Water moves out of the cell
(C) No water movement occurs
(D) Depends on solute size
Answer
(B) — Water moves toward the solution with the less negative (higher) water potential, so water leaves the cell.
22. In an isotonic solution, what change occurs to the volume of an animal cell?
(A) Increase
(B) Decrease
(C) No significant change
(D) Burst
Answer
(C) — In an isotonic environment, animal cells maintain a stable volume.
23. What does a very negative solute potential indicate about a solution?
(A) It has few solutes
(B) It has a high water potential
(C) It has many solutes
(D) It is pure water
Answer
(C) — A very negative solute potential indicates a high solute concentration.
24. When does water flow out of a plant cell into the external environment?
(A) When external Ψ is lower than internal Ψ
(B) When internal Ψ is lower than external Ψ
(C) When solutes inside the cell are higher
(D) When pure water surrounds the cell
Answer
(B) — Water moves from higher to lower water potential, so if external Ψ is higher, water flows out.
25. What term describes the total potential energy of water in a system compared to pure water under identical conditions?
(A) Osmolarity
(B) Turgor pressure
(C) Water potential
(D) Plasmolysis
Answer
(C) — Water potential (Ψ) quantifies the free energy of water relative to pure water.
26. Which of the following would cause an increase in water potential inside a plant cell?
(A) Adding solutes
(B) Increasing pressure potential
(C) Decreasing cytoplasmic volume
(D) Removing aquaporins
Answer
(B) — Increasing pressure potential raises overall water potential inside the cell.
27. If the external solution has a water potential of –0.5 MPa and the cell’s water potential is –0.7 MPa, which direction will water move?
(A) Into the cell
(B) Out of the cell
(C) No net movement
(D) Depends on temperature
Answer
(A) — Water moves from higher water potential (–0.5) to lower water potential (–0.7).
28. Which describes an environment where water moves into an animal cell, potentially causing lysis?
(A) Hypertonic environment
(B) Isotonic environment
(C) Hypotonic environment
(D) Saline environment
Answer
(C) — A hypotonic environment causes water influx into cells, leading to swelling and potential lysis.
29. Which factor has the greatest influence on solute potential (Ψs) in biological systems?
(A) Pressure
(B) Solute concentration
(C) Temperature
(D) Membrane thickness
Answer
(B) — Solute concentration is the primary factor affecting solute potential.
30. What occurs when a plant cell's plasma membrane detaches from the cell wall due to water loss?
(A) Crenation
(B) Turgor
(C) Plasmolysis
(D) Cytolysis
Answer
(C) — Plasmolysis results from water loss in a hypertonic environment.
31. A plant cell has a solute potential of –0.8 MPa and a pressure potential of 0.5 MPa. What is the water potential (Ψ)?
(A) –1.3 MPa
(B) –0.3 MPa
(C) 0.3 MPa
(D) –0.8 MPa
Answer
(B) — Ψ = Ψs + Ψp = (–0.8) + 0.5 = –0.3 MPa.
32. Which scenario would most likely cause a loss of turgor pressure in a plant cell?
(A) Cell placed in hypotonic solution
(B) Cell placed in hypertonic solution
(C) Cell placed in isotonic solution
(D) Cell placed in distilled water
Answer
(B) — In a hypertonic environment, water leaves the cell, reducing turgor pressure.
33. What is the immediate effect on water movement if external solute concentration suddenly decreases?
(A) Water moves into the cell
(B) Water moves out of the cell
(C) Water stops moving
(D) Solutes move into the cell
Answer
(A) — Lower external solute concentration means higher water potential outside, driving water into the cell.
34. If a cell's pressure potential becomes negative, what does this imply about the internal conditions?
(A) Water is entering the cell
(B) The cell is under tension and losing water
(C) Water potential is increasing
(D) Solute concentration is decreasing
Answer
(B) — Negative pressure potential indicates tension, often due to water loss.
35. Which best explains why plant cells can survive better in hypotonic environments compared to animal cells?
(A) Plant cells use active transport
(B) Plant cells have strong plasma membranes
(C) Plant cells have rigid cell walls
(D) Plant cells lack aquaporins
Answer
(C) — The rigid cell wall prevents excessive swelling, protecting plant cells from lysis.
36. What happens to an animal cell placed in a hypotonic solution?
Answer
Water enters the cell, causing it to swell and potentially burst due to lack of a rigid cell wall.
37. Why does adding solutes to water decrease its water potential?
Answer
Solutes bind free water molecules, lowering their ability to move freely and decreasing the water potential.
38. What is the main role of the plant cell wall in osmoregulation?
Answer
The cell wall provides structural support and resists excessive expansion due to water influx.
39. Describe the effect of placing a plant cell in a strongly hypertonic solution.
Answer
Water leaves the cell, causing plasmolysis where the plasma membrane pulls away from the cell wall.
40. How does pressure potential influence water movement in plant cells?
Answer
Higher pressure potential pushes water out or prevents further water influx, balancing internal water pressure.
41. Why do freshwater organisms require adaptations like contractile vacuoles?
Answer
To expel excess water continuously entering the cell due to a hypotonic environment and prevent lysis.
42. What would happen to water movement if two adjacent solutions had identical water potentials?
Answer
There would be no net movement of water between the two solutions.
43. Which two factors are combined to determine the overall water potential of a plant cell?
Answer
Solute potential (Ψs) and pressure potential (Ψp).
44. How does a decrease in external solute concentration affect osmosis into a cell?
Answer
It increases water potential outside the cell, causing water to flow into the cell.
45. Why is pure water assigned a water potential value of zero?
Answer
Because pure water has the maximum possible free energy, with no solutes to lower its potential.
46. How does a plant benefit from maintaining high turgor pressure?
Answer
High turgor pressure supports structural rigidity, keeps leaves expanded, and aids in plant growth.
47. What happens to a red blood cell in an isotonic solution?
Answer
The cell maintains its normal shape with no net water movement.
48. How does the opening of aquaporins impact the rate of osmosis?
Answer
Opening aquaporins greatly increases the rate of water movement across the membrane.
49. What does a very negative water potential inside a plant cell suggest about its internal environment?
Answer
It suggests high solute concentration and strong tendency to absorb water if available.
50. How does saltwater affect freshwater organisms if they are suddenly transferred into it?
Answer
They lose water rapidly to the hypertonic environment, leading to cell shrinkage and dehydration.