Question

A common structural feature of vessel elements and sieve tube elements is (a) enudeate condition (b) thick secondary walls (c) pores on lateral walls (d) presence of P-protein.

Short answer

(a) enucleate condition.

Step-by-step solution

Understand What Vessel Elements and Sieve Tube Elements Are

Before solving the exercise, it's important to understand what vessel elements and sieve tube elements represent. These are both types of cells found in the vascular tissue of plants. Vessel elements are part of the xylem, responsible for water transport, and sieve tube elements are part of the phloem, responsible for transporting sugars and other organic molecules.

Assess Each Option Against Known Characteristics

Evaluate each of the given options by comparing them against the known characteristics of vessel elements and sieve tube elements. The goal is to find a common structural feature shared by both cell types.

Identify the Correct Option

Vessel elements and sieve tube elements do share a common feature, which is an enucleate condition- they both lack a nucleus at maturity. Thick secondary walls are characteristic of vessel elements but not sieve tube elements, pores on lateral walls are also more characteristic of vessel elements, and although P-protein is found in sieve tube elements, it's not a feature of vessel elements.

Key concepts

Vessel Elements

Vessel elements are a fundamental component of the xylem, which is one of the two types of transport tissues in plants, the other being phloem. The primary function of xylem vessel elements is to conduct water and minerals from the roots throughout the plant. These cells are elongated and tubular, aligning end to end to form continuous vessels.

One of the unique characteristics of vessel elements is that they become 'enucleate' at maturity. This means they lack a nucleus, which provides more room for the transport of water and minerals. Moreover, these cells are known for having thick secondary walls that are strengthened by lignin – a complex organic polymer that strengthens the cell walls and helps maintain the rigidity of the plant.

Thick Secondary Walls and Pores

Part of what enables vessel elements to be so effective is the presence of pores on their lateral walls, known as pits, which allow for the horizontal transfer of water between different vessel elements. These pits also play a crucial role in preventing air embolisms within the xylem vessels.

Sieve Tube Elements

Sieve tube elements are the principal components of the phloem, the vascular tissue responsible for transporting sugars, amino acids, and other organic nutrients. Unlike xylem, phloem transport is bidirectional, moving substances to wherever they are needed in the plant.

Like vessel elements, sieve tube elements are also enucleate. This shared trait aids in the efficient flow of nutrients within these cells. However, one distinguishing feature of sieve tube elements is the presence of sieve plates – porous end walls that allow the flow of nutrients between connected cells.

Sieve Plates and Companion Cells

These sieve plates are critical to the functionality of phloem, but unlike vessel elements, sieve tube elements lack the thick secondary walls. Instead, they rely on companion cells – adjacent cells that retain their nucleus and support the metabolic needs of sieve tube elements. The presence of P-protein in sieve tube elements is another distinctive feature that helps in sealing damage to the phloem and thus maintaining the pressure flow mechanism of nutrient transport.

Plant Vascular Tissue

Plant vascular tissue is an essential system that includes both xylem and phloem. It's akin to the circulatory system in animals and serves as the main conduit for the transport of water, nutrients, and organic compounds within a plant.

The vascular tissue is strategically located within plants to maximize efficiency in transport and support. Besides vessel elements and sieve tube elements, the vascular tissue includes other cell types like tracheids, fibers, and parenchyma cells, each with specialized functions contributing to the overall vitality of plants.

Integration and Support

The synergy between vessel elements and sieve tube elements is crucial for plant survival, ensuring that water and nutrients are appropriately distributed, even in varying environmental conditions. The plant vascular tissue not only facilitates transport but also provides structural support, allowing plants to grow tall and thrive in diverse ecosystems.