Plant Cell Osmosis and Transport Practice Quiz (8 questions)

1. What happens to a plant cell placed in a hypertonic solution?

A. Water enters, shrinking the protoplast away from the cell wall in plasmolysis.

B. Water leaves, shrinking the protoplast away from the cell wall in plasmolysis.

C. Water enters, expanding the protoplast and producing turgidity.

D. Water leaves, expanding the vacuole while the protoplast remains against the wall.

Answer: (B)

Explanation

In a hypertonic solution, water leaves the plant cell and the protoplast shrinks away from the cell wall, a process called plasmolysis. Turgidity is the contrasting response associated with water entering the cell in a hypotonic solution.

2. As water enters a plant cell in a hypotonic solution, what does turgor pressure describe?

A. The outward pressure the expanding protoplast exerts on the cell wall.

B. The inward pressure the vacuole exerts as the protoplast shrinks.

C. The inward pressure the cell wall exerts on the expanding protoplast.

D. The outward pressure the cell wall exerts as water leaves the protoplast.

Answer: (A)

Explanation

Turgor pressure is the outward pressure on the cell wall as water enters and expands the protoplast. Wall pressure is the related but opposite-direction force, acting inward on the cell contents.

3. What role do aquaporins play in water movement across cell membranes?

A. They form ion channels that prevent water from crossing membranes.

B. They bind water inside the cell and prevent its diffusion.

C. They form water channels that enable massive diffusion of water.

D. They pump water across membranes by using cellular energy.

Answer: (C)

Explanation

Aquaporins are water-channel proteins that allow massive diffusion of water. They are channels for water rather than energy-driven pumps.

4. What can diffuse very quickly through hydrophilic passages?

A. Some ions and large proteins.

B. Water molecules and some ions.

C. Water molecules and all dissolved sugars.

D. Dissolved sugars and membrane lipids.

Answer: (B)

Explanation

Hydrophilic passages allow water molecules and some ions to diffuse very quickly. The stated passage function does not include large proteins or dissolved sugars.

5. What does cotransport mean in membrane transport?

A. Two substances diffuse downhill through a membrane channel without using a transport protein.

B. The downhill movement of one solute drives the uphill transport of another substance through a transport protein.

C. A carrier protein moves a substance downhill along its concentration gradient without coupling it to another solute.

D. A proton pump uses ATP to move hydrogen ions uphill and directly transports nutrients alongside them.

Answer: (B)

Explanation

Cotransport couples one solute’s downhill diffusion to the uphill transport of another substance through a transport protein. A carrier that moves a substance downhill without coupling it to another solute describes facilitated diffusion instead.

6. After photosynthesis, into which cells do plants load sucrose before vascular bundles distribute it throughout the plant?

A. Guard cells

B. Leaf-vein cells

C. Root-hair cells

D. Xylem vessel cells

Answer: (B)

Explanation

Sucrose produced by photosynthesis is loaded into leaf-vein cells, then vascular bundles distribute it to other parts of the plant. Root-hair cells are associated with absorbing water and minerals, not the stated initial sucrose-loading step.

7. What role does the rigid cell wall play when water enters a plant cell and the protoplast expands?

A. It prevents inward pressure from developing against the cell contents.

B. It draws water into the vacuole by lowering the cell’s solute concentration.

C. It restricts protoplast expansion, helping the cell become firm.

D. It allows the protoplast to detach from the wall as the cell swells.

Answer: (C)

Explanation

The cell wall limits expansion of the water-filled protoplast, resulting in a firm, turgid cell. The protoplast moves away from the wall during water loss in a hypertonic solution, not as water enters.

8. When water diffuses across a membrane through aquaporins, what do these proteins provide?

A. Gates that prevent ions from crossing the membrane

B. Carriers that couple water movement to sucrose uptake

C. Pumps that use ATP to move water uphill

D. Channels that enable rapid diffusion of water

Answer: (D)

Explanation

Aquaporins are water-channel proteins that allow water to diffuse rapidly. ATP-powered pumps move substances using energy, rather than serving as water channels.