Which of the following is an example of a living plant cell, devoid of nucleus ?

Question

Accepted Answer

The correct option is 3: Sieve cell

Sieve cells, which are part of the sieve tube elements in the phloem tissue of flowering plants (angiosperms), represent one of the most remarkable adaptations in plant biology. The question asks for a cell that is both *living* and *devoid of a nucleus*, and the sieve tube element fits this description precisely. At maturity, these cells undergo a highly specialized differentiation process where they deliberately lose their nucleus, ribosomes, and large central vacuole. This process of autolysis is essential to create an open channel, or lumen, which maximizes the efficiency of mass flow for the translocation of sugars and other organic nutrients throughout the plant. Although they lack their own nucleus, they are fundamentally alive because they retain an active plasma membrane, a thin layer of cytoplasm, and essential mitochondria. Their entire metabolic function and survival are regulated by the adjacent, nucleated companion cells, which are interconnected through plasmodesmata. Therefore, the sieve cell is metabolically alive but anucleate, making it the correct answer.

The incorrect option is 1: Companion cell

The companion cell, which lies immediately alongside the sieve tube element (sieve cell), is an integral part of the phloem tissue. Far from being devoid of a nucleus, the companion cell is characterized by having a very prominent, large nucleus, dense cytoplasm, and numerous mitochondria. It is the powerhouse and "life support" for the sieve cell, as its nucleus directs the synthesis of all proteins and controls the metabolic activity for both itself and its anucleate partner. The primary role of the companion cell is to load and unload sugars into and out of the sieve tube element, which it accomplishes using its own fully functional, nucleated cellular machinery.

The incorrect option is 2: Endosperm cell

Endosperm cells are typically found in the seeds of flowering plants and serve as the main storage tissue for nutrients that will support the developing embryo or seedling upon germination. These cells are metabolically highly active, responsible for synthesizing and storing starches, proteins, and lipids. Crucially, the endosperm cells are fully nucleated and living; in most angiosperms, they are actually triploid (containing three sets of chromosomes, or 3n), a result of double fertilization. Since they possess a complete, functional nucleus that directs all cellular processes, they do not meet the criterion of being "devoid of nucleus."

The incorrect option is 4: Sclereids

Sclereids are a type of sclerenchyma cell, a tissue that provides mechanical support and protection to plant parts, such as the hard shells of nuts or the gritty texture in pear fruits. The defining characteristic of sclereids, like all mature sclerenchyma cells, is the presence of an extremely thick, lignified secondary cell wall. Unfortunately, the formation of this thick wall is achieved only through the programmed death of the cell's protoplast. This means that mature sclereids are fundamentally **dead** cells, lacking a nucleus, cytoplasm, and all other living components. Since the question specifically asks for a *living* plant cell, sclereids cannot be the correct answer.