Biology Practice Test: Cell Transport
- Cell Transport
- 10 questions
- 13 minutes
This test covers how substances cross the cell membrane, with and without energy. Tip: first decide which way the concentration gradient runs; movement down the gradient is passive, movement against it needs energy.
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Question 1
In the lungs, oxygen moves from the air in the alveoli into the blood by passing directly through the lipid bilayer of the cell membranes. No energy from the cell is used. Which process is this?
Correct answer: D
Oxygen is a small, nonpolar molecule, so it slips through the lipid bilayer down its concentration gradient. Facilitated diffusion is also passive, but it needs a channel or carrier protein.
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Question 2
A student fills a dialysis tubing bag with a 20% sugar solution, ties it shut and places it in a beaker of distilled water. The tubing lets water pass but not sugar. What will most likely happen to the bag after one hour?
Correct answer: A
Water moves by osmosis toward the side with more dissolved solute, which is inside the bag. Sugar cannot cross the tubing, so only water moves, and it moves inward.
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Question 3
A paramecium lives in fresh pond water and constantly pumps water out of its cell with a contractile vacuole. Why does it need to do this?
Correct answer: B
The inside of the cell has more dissolved solutes than fresh water, so water enters by osmosis. Without the contractile vacuole the cell would swell and could burst.
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Question 4
A white blood cell surrounds a bacterium with its membrane and takes it into the cell inside a large vesicle. What is this process called?
Correct answer: D
Phagocytosis, or cell eating, is the type of endocytosis that takes in large particles such as whole bacteria. Pinocytosis takes in small droplets of fluid, not whole cells.
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Question 5
Kidney cells that reabsorb a lot of water have many aquaporins in their membranes. What do aquaporins do?
Correct answer: B
Aquaporins are channel proteins for water. Water still moves passively down its gradient through them, so no ATP is used.
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Question 6
Hospitals give many patients an IV solution of 0.9% saline, which is isotonic to red blood cells. What happens to red blood cells in an isotonic solution?
Correct answer: C
In an isotonic solution the solute concentration is the same inside and outside, so there is no net movement of water. That is why isotonic fluids are safe to put into the blood.
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Question 7
A plant cell is placed in distilled water. Water enters the cell, but the cell does not burst. What prevents it from bursting?
Correct answer: C
As the cell swells, the rigid cell wall presses back. This turgor pressure stops further net water entry, which is also what keeps plant stems firm.
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Question 8
A student drops food coloring into three beakers of still water at 5 °C, 25 °C and 60 °C. In which beaker will the color spread evenly the fastest, and why?
Correct answer: A
Diffusion is caused by the random motion of molecules, and that motion speeds up as temperature rises. So the dye spreads fastest in the warmest water.
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Question 9
Cells lining the small intestine take in glucose together with sodium ions. Sodium flows into the cell down its gradient through a carrier protein, and this flow drags glucose in against the glucose gradient. The sodium gradient is kept up by a sodium-potassium pump that uses ATP. Which term best describes how glucose enters these cells?
Correct answer: A
Glucose moves against its own gradient, so this is active transport, but the energy comes indirectly from the sodium gradient built by ATP. Facilitated diffusion only moves molecules down their gradient.
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Question 10
At a synapse, a nerve cell releases neurotransmitter molecules that are stored in vesicles. The vesicles fuse with the cell membrane and empty their contents outside the cell. Which process is this?
Correct answer: B
In exocytosis, vesicles fuse with the cell membrane and release their contents outside the cell. Endocytosis is the opposite direction, bringing material into the cell.
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