Problem 48 - Objective Biology for NEET

Question

Phloem transports (a) Water (b) Mineral (c) Food materials (d) All of these

Step-by-Step Solution

Answer

The correct answer is (c) Food materials.

Step 1: Understanding phloem

Phloem is a complex tissue of a plant which mainly functions to transport food materials (mainly sucrose) from leaves (where they are synthesized) to the parts where they are needed.

Step 2: Evaluating the given options

Let's match the function of the phloem with the given options: (a) As xylem is mainly responsible for the transportation of water, this option can be eliminated. (b) Phloem does not primarily transport minerals – this is also a major function of xylem. (c) As discussed in Step 1, the food material is transported by the phloem, so this is a correct option. (d) Since phloem does not transport all of these materials, this option is incorrect.

Key Concepts

Plant Transport System

Plants possess an intricate transport system that is tasked with the movement of substances from one part of the plant to another. This system consists of two primary types of tissues: xylem and phloem. The xylem is responsible for transporting water and dissolved minerals absorbed from the soil up to the leaves. This transport is critical for photosynthesis and maintaining the structural integrity of the plant.

The phloem, on the other hand, is specialized in transporting food materials – primarily sucrose – that are synthesized during photosynthesis in the leaves. These nutrients are then distributed to various parts of the plant, including growing regions like the stem and roots, as well as to storage organs such as fruits, seeds, and tubers. This bidirectional flow of nutrients is essential for growth, development, and reproduction of the plant.

Phloem vs Xylem

While the phloem and xylem are both integral components of the plant transport system, they have distinct functions and structures. Xylem vessels are typically hollow tubes made up of dead cells that create a continuous channel for water and mineral movement from the roots to the rest of the plant. The functioning of xylem relies on physical processes such as transpiration pull and root pressure.

In contrast, phloem consists of living cells, such as sieve tube members and companion cells, which actively facilitate the transport of food materials. Unlike xylem, phloem transport uses energy in the form of ATP to move food substances from source tissues, like leaves, to sink tissues, where the sugars are used or stored. This active transport process within the phloem is termed 'translocation'. Understanding the difference between these two systems is crucial for comprehending how plants sustain themselves and distribute vital nutrients internally.

Transport of Food Materials in Plants

The transport of food materials in plants is predominantly handled by the phloem tissue. This process is essential because the food, synthesized as sugars during photosynthesis in leaf cells, needs to reach other non-photosynthetic parts of the plant. This distribution ensures that all cells receive the energy necessary for their metabolic processes.

Food translocation in phloem occurs from the 'source' to the 'sink'. The source is typically the green leaves or storage organs that release the sugars, while the sink can be any part of the plant that requires or stores these sugars. This transport process is facilitated by a pressure-flow mechanism involving the loading and unloading of sugars into the phloem system, ultimately driving the flow throughout the plant. This explanation broadens our understanding of the phloem's precise role in food distribution within plants and its vital importance to plant health and growth.