Out of different types of tissues found in plants, which one of the following is a complex tissue?

Correct — C, Xylem. A simple tissue is made of one kind of cell; a complex tissue is made of more than one kind of cell working together as a unit. Xylem qualifies because it is built from four different cell types — tracheids, vessels, xylem parenchyma and xylem fibres — of which the conducting elements are dead at maturity while the parenchyma stays alive. Phloem is the other complex tissue of plants, made of sieve tubes, companion cells, phloem parenchyma and phloem fibres. The three rejected options are each a single-cell-type simple tissue.

• (a)Parenchyma — A simple permanent tissue of one cell type — thin-walled living cells with large intercellular spaces. It stores food and, when it contains chloroplasts, photosynthesises; it does not combine cell types.
• (b)Sclerenchyma — Also simple: uniformly thick, lignified, dead cells that give the plant its hardness. Coconut husk fibre is sclerenchyma, and it too is a single kind of cell.
• (d)Collenchyma — A simple living tissue with cellulose thickening at the corners, giving young stems flexibility. Like the other two it is defined by one cell type, which is exactly what a complex tissue is not.

Plant tissues divide first into meristematic and permanent. Permanent tissue then divides into simple and complex. Simple permanent tissues — parenchyma, collenchyma and sclerenchyma — are each made of a single kind of cell. Complex permanent tissues are made of more than one kind and act as a functional unit; there are two of them, xylem and phloem, and together they form the vascular tissue that carries water, minerals and food through the plant.

The wording 'complex tissue' has a precise textbook meaning, so this item is decided by definition rather than by function. Three options end in -enchyma and are the three simple tissues that always appear together in a list; the odd one out is the vascular tissue, and that is the answer. If phloem had been offered as well, both would have been correct, which is why the examiner has offered only one of the pair.

• A simple tissue has one cell type; a complex tissue has several acting as one unit.
• Xylem and phloem are the only two complex permanent tissues of plants.
• Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres, and carries water and minerals upward.
• Phloem consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres, and carries food in both directions.
• Parenchyma, collenchyma and sclerenchyma are the three simple permanent tissues.

• Reading 'complex' as 'complicated' rather than as 'made of more than one cell type'.
• Forgetting that phloem is equally a complex tissue — it simply was not offered here.
• Assuming xylem is entirely dead; xylem parenchyma is alive at maturity.

A definition item — the exam wants the simple-versus-complex classification, not what xylem does.

• practice — not a real PYQ

  Which one of the following components of xylem consists of living cells?

  • (a)Tracheid
  • (b)Vessel
  • (c)Xylem parenchyma
  • (d)Xylem fibre

  Answer(c) Xylem parenchyma — the conducting elements and fibres are dead and lignified at maturity, while the parenchyma remains alive and stores food.

• practice — not a real PYQ

  Which one of the following is a simple permanent tissue in plants?

  • (a)Xylem
  • (b)Phloem
  • (c)Collenchyma
  • (d)Vascular bundle

  Answer(c) Collenchyma — it is made of a single kind of living cell thickened at the corners; xylem and phloem are complex tissues.