Which one of the following tissues in plants is usually without protoplast and regarded as dead cells?

Sclerenchyma is a simple permanent tissue in plants characterized by cells with highly thickened, lignified walls. At maturity, these cells lose their protoplast (the living content of the cell) and are considered dead cells. Their primary function is to provide mechanical strength and structural support to the plant.

• Parenchyma: These are living cells with thin cellulose walls and a functional protoplast, primarily involved in storage and photosynthesis.
• Collenchyma: These are living cells with unevenly thickened walls (at corners), providing flexibility and mechanical support to growing parts.
• Xylem parenchyma: This is the only living component of the xylem tissue; other elements like tracheids, vessels, and xylem fibres are dead at maturity.

Therefore, among the given options, only sclerenchyma cells are typically dead and lack a protoplast.