Question

Ringing/girdling experiments demonstrate (a) phloem is responsible for translocation of food (b) xylem is responsible for ascent of sap (c) transpiration pull (d) both (a) and (b).

Short answer

(a) Phloem is responsible for translocation of food. The ringing/girdling experiments demonstrate interruption in the downward movement of food in the plant which signifies the role of phloem in food translocation.

Step-by-step solution

Understanding Ringing/Girdling Experiments

Firstly, understand that ringing, or girdling, is an experiment where a ring of bark from a tree, which includes the phloem layer, is removed. This disrupts the flow of substances in the phloem but leaves the xylem intact.

Observing the Effects of the Experiment

After a while, one can observe that the part of the tree above the ring swells, indicating accumulation of food substances, while the part below the ring does not show such swelling. This is evidence that the transport of synthesized food is affected.

Identifying the Impacted Transport System

Since the phloem is removed during girdling and it leads to the accumulation of foods above the girdle, it can be concluded that phloem is responsible for the downward translocation of food from leaves to other parts of the plant.

Excluding Other Processes

The experiment does not directly provide information regarding the xylem or the process of the ascent of sap. Nor does it indicate the mechanism behind transpiration pull, which involves the xylem.

Key concepts

Phloem Translocation of Food

The phloem forms a crucial component of the plant transport system, specifically involved in the process of translocating nutrients. This is especially important for the distribution of carbohydrates, like the sugar sucrose, which are produced during photosynthesis in the leaves. Imagine the phloem as a network of highways, with sugar molecule 'vehicles' traveling to 'cities' (other parts of the plant) that need them.

During the girdling experiment, by removing a ring of bark containing the phloem, you essentially create a roadblock on the highway. The immediate swelling observed above the girdle highlights a traffic jam of nutrients, proving that the 'vehicles' transporting food via the phloem can no longer reach their destinations below the girdle. Since the swelling indicates an accumulation of food, it confirms that the phloem is indeed responsible for the translocation of food from leaves to the rest of the plant.

Key Takeaway:

• Phloem is essential for distributing food within the plant.
• Girdling interrupts this process, resulting in the accumulation of sugars above the girdle.

Ascent of Sap

In stark contrast to the phloem, the xylem’s role is largely centered around the transport of water and dissolved minerals from the roots to the upper parts of the plant. The fascinating process known as the 'ascent of sap' involves a mechanism where water is continuously pulled upward, similar to how a straw works when you sip a drink.

Water molecules stick to each other through cohesion and to the xylem walls through adhesion, creating a continuous water column. The xylem transports this water column upwards, in part due to the negative pressure created by the evaporation of water from the leaves – a process known as transpiration.

Girdling experiments primarily demonstrate the function of the phloem and do not specifically address the ascent of sap since it is managed by the xylem, which remains undamaged during the process. However, understanding the ascent of sap offers insight into how plants can move water against gravity without requiring energy-consuming pumps.

Key Takeaway:

• Xylem facilitates the upward movement of water and nutrients.
• The process is driven by cohesion, adhesion, and transpiration pull.

Plant Transport System

The plant transport system is an intricate design, likened to the circulatory system in animals. It consists of two main components: the xylem, which distributes water and minerals, and the phloem, which conveys food and other organic substances.

Both operate simultaneously, ensuring the survival and growth of the plant. The xylem can be likened to 'water pipes', while the phloem compares to 'food delivery routes'. While girdling experiments shed light on the role of the phloem in food distribution, it is important to recognize the interdependence of both systems in maintaining plant health.

Girdling experiments indirectly underscore the efficiency and vulnerability of the plant transport system. When one pathway is obstructed, as in the phloem during these experiments, it leads to immediate and visible consequences, showing how critical each pathway's integrity is to the overall system's function.

Key Takeaway:

• The plant transport system is made up of the xylem and phloem, each with distinct functions.
• The integrity of both systems is vital for nutrient distribution and plant health.