Which of the following tissues does not provide support in flowering plants?

Analyze the question: We need the tissue that does NOT provide support in a flowering plant. Three options support the plant in some way, and one does not.

Explain the concept: Supporting tissues in flowering plants include:

• Collenchyma: its cell walls are thickened with cellulose and pectin, so it supports young stems, petioles and leaves.
• Sclerenchyma: its cell walls are thickened with lignin, so it gives strong, rigid support.
• Xylem: its vessels and fibres are lignified, so it conducts water and also gives strength to the plant (wood is mostly xylem).
• Parenchyma: its thin-walled cells are packed with water, so they become turgid and give support to herbaceous plants. When they lose water the plant wilts.

Phloem: Its main job is to transport manufactured food (sucrose and amino acids) from the leaves to other parts of the plant. It contains sieve tubes and companion cells. It does have some fibres, but its basic function is translocation, not support.

Step-by-step elimination:

• A. Collenchyma gives support. Eliminate.
• B. Parenchyma gives support through turgidity. Eliminate.
• C. Xylem gives support through lignified walls. Eliminate.
• D. Phloem is mainly for transport of food. It is the one that does not provide support.

Answer: D. Phloem

Exam tip: Remember it this way: "Xylem supports and carries water, phloem only carries food." In questions like this, ask what each tissue's main job is. Collenchyma and sclerenchyma are the "support" tissues, xylem is the "water and support" tissue, and phloem is the "food transport" tissue.