Phloem Structure: Sieve Tubes for Food Transport

The food-conducting complex tissue in plants is called phloem. It comprises several cell types, including sieve tube elements, companion cells, phloem parenchyma, and phloem fibres.

The question asks for the tubular part with perforated walls involved in food conduction.

Identifying the Sieve Tube

• Sieve tube elements are the principal conducting cells of the phloem. They are elongated, tubular cells joined end to end.
• The end walls of adjacent sieve tube elements have perforations, forming structures called sieve plates. These allow the passage of phloem sap (sugars).
• Collectively, these elements form a continuous sieve tube.

Therefore, the sieve tube fits the description of being tubular and having perforated walls (via the sieve plates) for food conduction.

Why Other Options Are Incorrect

• Companion cells: These cells are closely associated with sieve tube elements but are primarily involved in metabolic support, not direct conduction through perforations.
• Phloem parenchyma: These cells are involved in storage and radial transport, not the primary longitudinal conduction pathway.
• Sieve plate: While perforated, the sieve plate is only the end wall structure between sieve tube elements, not the entire tubular conducting channel. The sieve tube itself is the functional unit described.

Correct Answer: Sieve tube