Question

Unidirectional flow of water, minerals, some organicnitrogen and hormones occurs through (a) xylem (b) phloem (c) \(\mathrm{root}\) (d) vascular tissue.

Short answer

The unidirectional flow of water, minerals, some organic nitrogen, and hormones occurs through (a) xylem.

Step-by-step solution

Identify the Function of Plant Tissues

To solve this exercise, it's important to recognize the functions of various plant tissues. Xylem is responsible for the transport of water and minerals from the roots to the rest of the plant. Phloem transports organic compounds like sugars and some hormones from the leaves to other parts of the plant. Roots are involved in the absorption of water and minerals. Vascular tissue includes both xylem and phloem.

Match the Function with the Correct Tissue

The exercise specifies the unidirectional flow of water, minerals, some organic nitrogen, and hormones. This description matches the function of xylem, which transports these substances in one direction - upwards from the roots.

Eliminate Incorrect Options

Since phloem actually carries substances in both directions, and its main transport material is organic compounds generated in photosynthesis, it doesn't match the description of unidirectional flow of water and minerals. Roots are the absorbent part and not the transport tissue. Vascular tissue is too general a term for this specific function.

Select the Correct Answer

Based on the functions of plant tissues, the correct answer is the tissue responsible for unidirectional transport which is (a) xylem.

Key concepts

Xylem

The xylem is like the plant's plumbing system, conducting water and dissolved minerals from the roots to various parts of the plant. It consists of a series of interconnected cells that form tubes extending from the root tips to the leaves. Water, being crucial for processes like photosynthesis and nutrient transport, travels through the xylem in a unidirectional stream, typically upward.

This unidirectional flow is possible thanks to the cohesion-tension theory, where the evaporation of water from the leaves (transpiration) creates tension that pulls water upwards through the xylem vessels. These vessels are made up of dead cells arranged in tubes, providing a low-resistance path for water transport. Not only does the xylem move water and minerals, but it also supports the plant structurally, much like steel bars in concrete, helping maintain its upright position.

Phloem

On the other side of the coin, we have phloem, a component of the vascular tissue in plants that serves a different yet equally vital function. Unlike the xylem, the phloem moves nutrients – specifically, the sugars produced by photosynthesis in the leaves – to various parts of the plant where they are needed, such as growing tissues and storage organs.

The phloem's movement of sugars, also known as translocation, occurs in all directions, making it a bidirectional system. This process relies on pressure created by osmotic differences, known as the pressure-flow hypothesis. The living cells, known as sieve-tube elements, are closely connected end-to-end, forming channels through which the nutrient-rich sap flows. These cells are assisted by companion cells, which help in maintaining pressure and loading and unloading materials into and out of the phloem.

Vascular Tissue

Vascular tissue serves as the transportation network of a plant, made up of the xylem and phloem, each having integral responsibilities in sustaining plant life. This complex system distributes water and nutrients throughout the plant and is key in the evolutionary success of vascular plants, allowing them to grow larger and inhabit a variety of terrestrial environments.

As the backbone of plant transport, vascular tissue not only facilitates the movement of essential substances but also provides structural support. In larger plants and trees, this system becomes even more important, as distances increase between the roots, leaves, and other parts where resources are absorbed or used up. With the xylem and phloem working together, vascular tissue ensures that energy produced in the leaves can reach every cell, and that water and minerals drawn from the soil can reach the leaves.