Question

A girdled plant (upto bast) may survive for some time b it will eventually die, because (a) water will not move downwards (b) water will not move upwards (c) sugars and other organic materials will not m downwards (d) sugars and other organic materials will not m. upwards.

Short answer

The girdled plant will eventually die because (d) sugars and other organic materials will not move upwards.

Step-by-step solution

Understand the concept of girdling

Girdling involves the removal of a ring of bark (including the cambium layer) from around the entire circumference of a tree or plant stem. This disrupts the flow of nutrients and water between the roots and the leaves because the phloem (which transports sugars and other metabolic products downwards) is located on the outer layers of the stem.

Determine the direction of disrupted flow

Since girdling removes the phloem but leaves the xylem (which transports water upwards) intact, water can still move upwards to the leaves, but the transport of sugars and other organic materials, which move downwards from the leaves to the rest of the plant, is interrupted.

Identify the consequence of disrupted flow

Without the transport of sugars and other organic materials from the leaves (where they are produced during photosynthesis) to the roots and other parts of the plant, the resources of the plant below the girdle are depleted, leading to its eventual death.

Key concepts

Plant Vascular System

The plant vascular system is akin to a network of highways within a plant, conducting essential substances to different parts, similar to how roads transport vehicles to various destinations. This system is primarily composed of two main types of tissues: the xylem and the phloem.

The xylem is responsible for the upward transportation of water and minerals from the roots to the leaves. Picture the xylem as pipes that draw water from the soil through the roots, delivering it to the leaves for essential processes like photosynthesis and transpiration. On the other hand, phloem transports the sugars and other organic compounds produced by the plant. It’s like a delivery service that distributes the food created in the leaves to the rest of the plant body, ensuring every part gets the nutrients needed for growth and development.

These two systems work in tandem to keep the plant healthy and functioning properly. Any disruption to either system, such as through girdling, can impair the plant's ability to sustain itself, eventually leading to its demise if not rectified.

Phloem Function

Imagine the phloem as the plant’s food delivery route. It is a key component in the life of a plant, as it functions primarily to distribute the sugars and amino acids, which are fundamental building blocks and energy sources for plant cells.

This distribution process in the phloem is known as translocation. During translocation, the phloem moves the sugars from the 'kitchen', the leaves, where they are made through photosynthesis, to various 'dining areas', such as growing roots, shoots, and fruits. Without this movement, the plant’s growth would be stalled as the necessary energy and building materials would fail to reach the areas in need.

The phloem's unique structure, containing cells with perforated ends called sieve tube elements, allows for the efficient flow of this 'nutritional sap'. Companion cells closely associated with the sieve tubes provide metabolic support and regulate the flow of sap. If the phloem is damaged, the plant can no longer distribute these crucial nutrients, spelling trouble for its survival.

Sugars Transportation in Plants

Transportation of sugars in plants is a vital process for their growth and energy supply. To envision how this works, think of the plant as a busy factory. The leaves work as solar panels, capturing sunlight to convert carbon dioxide and water into sugars during photosynthesis - this is the plant's 'product'.

Once these sugars are produced, they don’t just stay in the leaves; they are transported through the phloem to other parts of the plant. This movement is directed downwards to the roots and outwards to other growth areas. The sugars serve as the main energy source that fuels cellular activities and as building blocks for growth.

The process is controlled and efficient, with loading into the phloem occurring actively where sugars are concentrated and unloading where they are consumed or stored. This ensures that every part of the plant gets its share of the energy pie. Interfering with this process, such as by girdling, can be likened to cutting off the supply chain in an industry; the 'factory' can no longer operate normally, and thus production - in the plant’s case, growth and maintenance - grinds to a halt.