In higher plants, which tissue is primarily responsible for the transport of food (organic nutrients) and other substances produced during photosynthesis?

Introduction / Context:
Plants need to transport water, minerals, and food throughout their bodies. Different tissues perform these transport functions. This question focuses on which tissue carries food material produced in leaves to various parts of the plant. Understanding the roles of xylem and phloem is fundamental in plant anatomy and physiology and is frequently tested in exams.

Given Data / Assumptions:

• The question is about transport of food and other organic substances in plants.
• The options are xylem, phloem, chloroplast, and none of these.
• We assume knowledge of the difference between food transport and water transport.

Concept / Approach:
Phloem is the vascular tissue responsible for translocation of organic nutrients, mainly sucrose, from leaves where photosynthesis occurs to roots, stems, fruits, and storage organs. This process is called translocation. Xylem, on the other hand, conducts water and dissolved minerals from roots to aerial parts. Chloroplasts are organelles within cells where photosynthesis takes place; they are not entire transport tissues. Therefore, the correct approach is to associate phloem with food transport.

Step-by-Step Solution:
Step 1: Recall that leaves synthesize food through photosynthesis, producing sugars and other organic molecules. Step 2: Know that this food must be transported from leaves to other parts that do not photosynthesize, such as roots and developing fruits. Step 3: Recognize that phloem tissue, composed of sieve tubes, companion cells, phloem fibres, and phloem parenchyma, conducts these organic solutes in various directions as needed. Step 4: Remember that xylem is specialized to transport water and dissolved minerals from roots to shoots and leaves, not primarily food. Step 5: Note that chloroplasts are sites of food production within leaf cells but are not the pathway for long distance transport of nutrients. Step 6: Therefore, the tissue responsible for transporting food and other substances is phloem.
Verification / Alternative check:
Textbook diagrams of vascular bundles in stems and leaves label xylem and phloem side by side. Arrows in these diagrams often point upwards in xylem for water and minerals and bidirectionally in phloem for transport of sucrose and other nutrients. The process of loading and unloading sugar into phloem near source (leaves) and sink (roots and fruits) regions is described under phloem translocation. This clear distinction between the roles of xylem and phloem confirms that phloem is the correct answer.

Why Other Options Are Wrong:
Xylem: Although xylem is a transport tissue, it mainly transports water and minerals, not the food made in leaves.
Chloroplast: These are organelles that carry out photosynthesis inside cells, but they do not form a conducting tissue that transports food through the plant.
None of these: This is incorrect because phloem clearly matches the description of the tissue responsible for food transport.

Common Pitfalls:
Students may sometimes confuse xylem and phloem simply because they are both part of the vascular system. A helpful memory tip is to remember the phrase xylem up and phloem down, indicating that xylem mainly moves water upward, while phloem can move food both upward and downward to where it is needed. Associating phloem with phood (food) is another simple way to reinforce the correct function.

Final Answer:
The tissue responsible for transport of food and other organic substances in plants is Phloem.