In vascular plants, the sieve tubes and companion cells are present in the

Step 1: Analyze the question The question asks which tissue in vascular plants contains sieve tubes and companion cells.

Step 2: Explain the concept Vascular plants have two main transport tissues:

• Xylem transports water and mineral salts from the roots upward. It contains vessels, tracheids, xylem fibres and xylem parenchyma.
• Phloem transports manufactured food (sucrose and amino acids) from the leaves to other parts of the plant. This is called translocation. It contains sieve tubes, companion cells, phloem fibres and phloem parenchyma.

Step 3: Work through the options

• A. Cambium: This is a meristematic tissue that produces new xylem and phloem cells, so it is responsible for secondary growth. It does not contain sieve tubes or companion cells itself.
• B. Cortex: This is the ground tissue between the epidermis and the vascular bundles. It is mostly parenchyma and is used for storage and support.
• C. Xylem: It has vessels and tracheids, which are dead, lignified cells. It has no sieve tubes.
• D. Phloem: Sieve tubes are living, elongated cells with perforated end walls called sieve plates. Each one is supported by a companion cell, which has a nucleus and many mitochondria and controls the sieve tube's activities. This matches the question.

Step 4: Answer The correct answer is D. phloem.

Exam tip: Remember "P" for Phloem, "P" for Provides food, and that sieve tubes and companion cells work as a pair. Xylem handles water and is dead and lignified, while phloem handles food and is living.