Question

Assertion: Phloem is the principal food conducting tissue. Reason: It has been recognized by girdling or ringing experiment.

Short answer

Yes, the assertion is correct, and the reason given verifies this because girdling or ringing experiment demonstrates the vital role of Phloem in transporting food in plants.

Step-by-step solution

Understanding key concepts

Firstly, understand that Phloem is a type of plant tissue that serves for transporting food made during photosynthesis from the leaves to other parts of the plant. These include the stems and roots.

Understanding girdling or ringing experiment

In botany, a girdling or ringing experiment consists in removing a ring of bark around a tree trunk. As the Phloem lies just under the bark, it gets removed. This interrupts the downward transport of food, leading to an accumulation of sugars above the girdle and a deficiency below it.

Linking the assertion and reason

Given that girdling or ringing experiment clearly shows the role of Phloem in conducting food in plants, it validates the assertion that Phloem is the principal food conducting tissue in plants.

Key concepts

Plant Transport System

The plant transport system is a complex network responsible for the distribution of essential substances throughout the organism. In plants, there are two main types of vascular tissue: xylem and phloem. The xylem conducts water and dissolved minerals from the roots to the rest of the plant, operating primarily through capillary action and the transpiration pull.

On the other hand, the phloem is the principal food-conducting tissue. It transports the organic compounds produced during photosynthesis, namely sugars, from the leaves to other parts of the plant where needed. This process is known as translocation and is critical for the growth and development of plant tissue. Unlike xylem, which can only transport substances in an upward direction, phloem can move nutrients both up and down the plant structures, allowing for the flexibility necessary to meet the nutritional demands of various tissues.

How Do Phloem Cells Work?

Phloem cells, such as sieve tube elements and companion cells, are alive and utilize energy in the form of ATP to actively transport food substances. This energy-driven process allows for the targeted distribution to actively growing regions like buds, fruits, and storage organs like roots.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy in the form of glucose. This biochemical process takes place in specialized organelles called chloroplasts found predominantly in plant leaves.

The general equation for photosynthesis is: \[ 6CO_2 + 6H_2O + light energy \rightarrow C_6H_{12}O_6 + 6O_2 \.\] During this process, carbon dioxide and water are transformed into glucose and oxygen, the latter being released as a byproduct. The glucose produced not only serves as an energy source for the plant but also as a starting material for other organic compounds necessary for plant growth and development.

The Role of Phloem in Photosynthesis

After glucose is synthesized, it must be distributed throughout the plant — a role that falls to the phloem. This emphasizes the phloem’s integral role in ensuring that energy produced in the leaves reaches all parts of the plant.

Girdling Experiment

The girdling experiment, also known as ringing, is a method used historically to understand the function of phloem. This experiment involves removing a strip of bark from around the entire circumference of a woody plant's stem or branch. Since the phloem layer lies directly under the bark, this process effectively removes the phloem in the girdled area and disrupts its transport function.

As a result, food substances such as sugars, which are produced in the leaves via photosynthesis, accumulate above the girdled section because they can no longer be transported downwards. This accumulation can sometimes lead to a swelling of the stem just above the girdle. Below the girdle, however, the roots and other tissues begin to starve due to the lack of food being transported to them, which can result in root dieback and, potentially, the death of the plant.

Significance of the Experiment

This direct evidence confirms that the phloem is vital for transporting nutrients and that disabling it leads to observable consequences. It also solidifies the understanding that phloem is the main tissue responsible for the distribution of the products of photosynthesis from the leaves to the rest of the plant.

Plant Tissue Function

In the study of plant biology, understanding the specific functions of different plant tissues is essential. Plant tissues are classified into several types, each with a unique role in the plant's survival and development. The main types include dermal, vascular, and ground tissue. Dermal tissue covers the exterior of the plant, protecting it from damage and water loss. Ground tissue fills the interior of the plant, providing support, storage, and photosynthetic functions.

The vascular tissue is further divided into xylem and phloem, as previously discussed. While xylem is responsible for the uptake and transport of water and minerals, phloem plays a key role in distributing the products of photosynthesis. The function of these tissues is essential for plant growth, and any disruption can have severe implications for plant health.

Interaction Between Tissues

These tissue systems do not operate in isolation; instead, they work together synergistically. For example, the products of photosynthesis transported by the phloem are required by all cells for energy, and this includes the cells of both xylem and phloem tissues. Understanding these interactions helps in grasping how plants manage to thrive across diverse environments.