Question

When the cut end of a shoot is placed in a solution of safranin, the presence of dye could be located in (a) Cortex (b) Tracheid elements (c) Phloem (d) Pith

Short answer

The correct answer is (b) Tracheid elements.

Step-by-step solution

Identify the function of each part of the plant

To solve this problem, first distinguish functions of the given tissues. Cortex is the outermost layer in plant stems. Tracheid elements are part of xylem and are responsible for transporting water and minerals from roots to other parts of the plant. Phloem translocates photosynthetic and other products from leaves to all other parts of the plant. Pith, located at the center of the stem, mainly serves for storage.

Determine where capillary action happens in a plant

Capillary action in plants mainly occurs in xylem tissue as it is responsible for the upward movement of water from the roots to the top parts of the plants. Since tracheid elements are part of the xylem, capillary action would expectedly occur here.

Choose the correct location for Safranin

Considering the aforementioned points, Safranin, when absorbed by the plant, would be located within the tracheid elements, as this is where the majority of water transport happens by capillary action.

Key concepts

Tracheid Elements

Tracheid elements are specialized, elongated cells found in the xylem of vascular plants. They play a vital role in transporting water and dissolved minerals from the roots to different parts of the plant. These elements are tubular in shape and possess thick secondary walls that provide structural support.
The tracheid elements rely on ungrowing cavity connections between nearby cells to move water effectively. This way, water can travel upwards through the plant by passing from one tracheid to the next. Interestingly, tracheids are also important for plant support due to their lignified walls that help the plant maintain its structure.

Xylem

Xylem is a type of vascular tissue in plants, integral to the plant’s internal transport system. It is composed of various cell types, including tracheids and vessel elements, that collectively enable the movement of water and nutrients.
As the main pipeline in a plant's vascular system, xylem conducts water from the roots to leaves and other parts. This process happens through a combination of factors, including transpiration pull and capillary action. Xylem tissues are typically located in the innermost part of the plant stem, providing a robust pathway for transport.

Capillary Action

Capillary action is a phenomenon where liquid moves against gravity through narrow spaces. This action is fundamental in plants, allowing the movement of water from roots to leaves. It relies on intermolecular forces like cohesion and adhesion to pull water along small tubes.
In plants, capillary action occurs predominantly in the xylem vessels. Water molecules adhere to the walls of xylem cells and cohere with other water molecules, enabling the upward movement. This effective water transport is crucial for maintaining plant hydration and physiological functions.

Cortex

The cortex is a layer of tissue in plant stems and roots found just beneath the epidermis. It is composed of parenchyma cells and functions to provide storage and support.
In the stem, the cortex surrounds the vascular bundles and provides a protective barrier. It stores nutrients and water that the plant can use during times of scarcity. Additionally, its porous nature facilitates the exchange of gases needed for metabolic processes.

Phloem

Phloem is another type of vascular tissue in plants, but unlike xylem, it transports organic nutrients, primarily products of photosynthesis, such as sugar.
This transport happens from the leaves where photosynthesis occurs, to non-photosynthetic parts of the plant. Phloem consists of living cells like sieve tube elements and companion cells, which work together to move the sugar through a process known as translocation. The movement in phloem can occur in multiple directions based on the plant's needs, unlike the unidirectional flow in xylem.

Pith

The pith is located at the center of many plant stems and primarily serves a storage function. It consists of loosely packed parenchyma cells with large vacuoles storing nutrients and other organic compounds.
In young plants, the pith is often soft and acts as a reserve for food materials. As plants mature, the pith can become lignified, contributing to the structural support of the stem. However, for many plants, it remains a vital storage center throughout the life of the plant.