The correct option is (a).
Explanation
The vacuole is a membrane-bound space found in the cytoplasm of plant cells. It is bounded by a single membrane called the tonoplast. Vacuoles play a crucial role in maintaining the turgidity of the cell and facilitating the storage of various substances.
Statement-wise Analysis
- Statement 1 is Correct: In mature plant cells, the central vacuole is very large and can occupy 50 to 90 per cent of the total cell volume. This large volume helps push the cytoplasm against the cell wall, maintaining turgor pressure.
- Statement 2 is Incorrect: The vacuole contains water, sap, excretory products, and other materials not immediately useful for the cell. However, it also acts as a storage site for essential nutrients, including ions, sugars, and amino acids. Therefore, the claim that it never stores nutrients is factually wrong.
- Statement 3 is Incorrect: While vacuoles are most prominent in mature cells, they are not "always absent" in young plant cells. Young cells (such as those in the meristematic region) typically contain multiple small vacuoles (pro-vacuoles) that eventually fuse to form the large central vacuole as the cell matures.
Key Takeaway
Vacuoles in plant cells are large, central organelles bounded by the tonoplast that store cell sap (water, ions, excretory products, and nutrients) and provide structural support through turgidity.