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📝 Vacuoles function in plant cells (8 MCQs)

📖 From Principles of Biochemistry • 1. The Foundations of Biochemistry • 8 questions available

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What is Vacuoles function in plant cells?

Definition:
Vacuoles are large, membrane-bound organelles in plant cells that occupy a significant portion of the cell volume, serving multiple functions including storage of water, nutrients, pigments, and waste products, maintenance of turgor pressure for structural support, and roles in detoxification, autophagy, and intracellular signaling, with their membrane being called the tonoplast.

Working:
Vacuoles work by accumulating solutes and water to generate osmotic pressure, which drives water uptake and maintains turgor, where the water potential can be expressed as $\Psi = \Psi_s + \Psi_p$ , with $\Psi_s$ being solute potential and $\Psi_p$ pressure potential, and the vacuole also stores secondary metabolites and sequesters toxins, protecting the cytoplasm from harmful substances.

Example:
A simple example is a wilted plant, where loss of water from vacuoles reduces turgor pressure, causing the plant to droop, but upon watering, vacuoles regain water, restoring turgor and making the plant stand upright, demonstrating the vacuole's role in maintaining cell rigidity and plant structure.

Reason:
Vacuoles are essential for plant survival as they provide mechanical support, store essential nutrients, and facilitate responses to environmental stress, and understanding their function is important in agriculture for improving crop resilience, drought tolerance, and nutritional quality of fruits and vegetables.

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📝 All Vacuoles function in plant cells MCQs

Q1. A plant cell is transferred from a nutrient-rich solution into a dilute external solution. After several minutes, its vacuole becomes larger while the surrounding cytoplasm remains closely associated with the cell boundary. Which interpretation best explains the observation?

A.Water entered the vacuole because the external solution had greater water availability, increasing internal volume and turgor ✅

B.Solutes were actively pumped out of the vacuole, forcing water to leave the cell

C.The vacuole synthesized cellulose, directly increasing the cell's volume

D.Water entered because the vacuole contains no dissolved substances

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The vacuole contains dissolved solutes and therefore contributes strongly to the cell's internal osmotic environment. In a dilute external solution, water tends to enter the cell, and the vacuole expands. This increases turgor pressure and helps maintain cellular structure.

Q2. Two otherwise similar plant cells have equal total cell volumes. Cell A stores most of its soluble ions and organic compounds in its vacuole, whereas Cell B keeps much of the same material in the cytosol. Which prediction is most reasonable?

A.Cell A can compartmentalize potentially disruptive substances while maintaining a controlled cytosolic environment ✅

B.Cell A must always have a lower osmotic pressure than Cell B

C.Cell B cannot perform metabolic reactions because its cytosol contains stored solutes

D.Both cells must have identical intracellular organization because their total volumes are equal

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: A major advantage of vacuolar storage is compartmentalization. By isolating ions, metabolites, pigments, and other substances, the vacuole can support storage and osmotic regulation while preventing excessive changes in the chemical conditions of the cytosol.

Q3. A researcher blocks a membrane transport process required for accumulating solutes inside a plant vacuole. The external solution remains unchanged. Which sequence is most likely after the treatment?

A.Reduced solute accumulation → reduced osmotic attraction for water → vacuolar shrinkage → reduced turgor ✅

B.Increased solute accumulation → increased water entry → permanent increase in turgor

C.No change in vacuolar volume because water movement is unrelated to solute concentration

D.Reduced solute accumulation → increased water entry → increased turgor pressure

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Vacuolar solute concentration influences water movement. If solutes can no longer accumulate effectively, the osmotic driving force for water entry decreases. Consequently, the vacuole may lose water, reducing its volume and the cell's turgor.

Q4. A student claims, 'Because vacuoles mainly store materials, removing a large vacuole from a plant cell should have little effect on cell physiology as long as the nucleus remains.' Which criticism is strongest?

A.The vacuole also contributes to ion and metabolite storage, osmotic balance, water relations, and cellular volume regulation ✅

B.The vacuole is the site where all nuclear DNA is stored

C.The vacuole directly produces all cellular ATP, so its removal stops respiration immediately

D.The vacuole is required to assemble ribosomes in the nucleus

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The reasoning incorrectly treats storage as the only vacuolar function. Vacuoles participate in osmotic regulation, storage of ions and metabolites, degradation of selected materials, and maintenance of cellular volume and turgor.

Q5. A graph records relative vacuolar volume as external solute concentration increases. The measured values are: external concentration 0.1 M0.1\,M → 120%120\%, 0.2 M0.2\,M → 105%105\%, 0.3 M0.3\,M → 88%88\%, 0.4 M0.4\,M → 70%70\%. Which conclusion is best supported by the data?

A.Increasing external solute concentration is associated with decreasing vacuolar volume ✅

B.Increasing external solute concentration causes the vacuole to accumulate unlimited water

C.Vacuolar volume is independent of external solute concentration

D.The vacuole increases in volume whenever the surrounding solution becomes more concentrated

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The data show a consistent inverse relationship between external solute concentration and relative vacuolar volume. As the surrounding solution becomes more concentrated, the tendency for water to leave the cell increases, producing progressive vacuolar shrinkage.

Q6. A plant cell exposed to a concentrated external solution loses water and its vacuole shrinks. After returning the cell to a favorable dilute solution, the vacuole gradually expands again. Which combination best explains both observations?

A.Water movement responds to differences in effective solute concentration, while the vacuole acts as a major intracellular water reservoir ✅

B.The vacuole converts external solutes directly into water during recovery

C.The nucleus pumps water into the vacuole using DNA as an energy source

D.Cell-wall cellulose dissolves during shrinking and reforms during expansion

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: The vacuole is central to plant-cell water balance because it contains substantial dissolved solutes and occupies much of the cell volume. Concentrated external conditions promote water loss, whereas favorable conditions can restore water and vacuolar volume.

Q7. A researcher measures vacuolar volume before and after exposing cells to two solutions. In solution X, volume changes from 100100 to 125125 arbitrary units; in solution Y, it changes from 100100 to 7878. Assuming other variables are controlled, what can be inferred most directly?

A.Solution X favors net water entry into the cells, whereas solution Y favors net water loss ✅

B.Solution X necessarily contains more total nutrients than solution Y

C.Solution Y must contain no dissolved solutes

D.The vacuole actively converts water into solutes in solution X

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: An increase in vacuolar volume indicates net water gain, while a decrease indicates net water loss. Therefore, solution X favors water entry and solution Y favors water loss, although the exact solute identities cannot be determined from volume alone.

Q8. A mutant plant has defective vacuolar ion storage and also shows poor tolerance to sudden changes in external osmolarity. Which explanation best integrates the two observations?

A.Impaired ion compartmentalization can disrupt osmotic control, limiting the cell's ability to regulate water movement and maintain stable internal conditions ✅

B.Ion storage affects only pigmentation, so the osmotic phenotype must be unrelated

C.Defective vacuoles should increase tolerance because fewer ions are present inside the cell

D.The phenotype proves that vacuoles directly control DNA replication during osmotic stress

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Vacuolar ion storage and osmotic regulation are closely connected. Properly controlled ion accumulation helps establish intracellular osmotic conditions and water balance. Defects can therefore make cells less capable of responding to rapid external osmotic changes.

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