Question

Outermost layer surrounding the vacuole is called
(a)Tonoplast
(b)Vacuolar membrane
(c)Both A and B
(d)Vacuolar cell wall

Answer 1

Hint: The vacuole is separated from the other components of the cell by a membrane. The membrane also plays an important role in maintaining the cell’s turgor pressure.

Complete answer:
The membrane surrounding the vacuole is called the tonoplast/vacuolar membrane and is a single membrane. Tonoplast separates the cytoplasmic contents from the vacuoles. Tonoplasts help in the uphill transport of several ions and other materials in the plant, thereby allowing their vacuole concentration to be higher than that of the cytoplasm.

Additional Information: Almost all the mature plant cells have one large vacuole that occupies nearly 30% of the cell's total volume, and in some specific cell types and at certain conditions, the vacuole occupies nearly 80% of the cell’s total volume. The vacuole is surrounded by the tonoplast and is filled with the cell sap. The vacuole acts as a storage organelle in the plant cell.
Apart from storage, the vacuole’s main function is to maintain turgor pressure. Turgor pressure is the internal pressure by which the cells push the plasma membrane against the cell wall. Proteins found in the tonoplast are called aquaporins which control the flow of water into and out of the vacuole via active transport, pumping of the potassium ions into and out of the vacuolar interior. The water diffuses into the vacuole and causes pressure on the cell wall because of osmosis. If the loss of water leads to a significant decline in turgor pressure, the cells will undergo plasmolysis (protoplast contraction because of lack of water).
So, the correct answer is, ‘Both A and B’.

Note: Tonoplast is a semi-permeable membrane. The semi-permeable membrane permits the entry of particles or substances based on its size whereas selectively permeable membrane permits substances based on its properties. For selectively permeable membranes the size is not a factor.