Biology · Anatomy of Flowering Plants · NEET
Xylem has four elements: (1) tracheids, (2) vessels, (3) xylem fibres, and (4) xylem parenchyma. Tracheids and vessels are the water-conducting elements. Fibres give support. Parenchyma stores food. Remember all four for NEET — a common question asks which cells build the xylem.
Only xylem parenchyma is living. Tracheids, vessels and xylem fibres are all dead at maturity (they lose their protoplasm and become hollow tubes). This is a favourite NEET point: if a question asks the only living xylem element, the answer is xylem parenchyma.
Tracheids are long, single cells with tapering ends and no perforations — water passes slowly through pits in their walls. Vessels are made of many short cells (vessel elements) joined end to end, with perforated (open) end walls that form one long continuous tube. So water flows faster and more freely through vessels than through tracheids.
Tracheids are dead. They are elongated, tube-like cells with thick, lignified walls and an empty lumen (no living contents). Being dead and hollow lets them act as pipes for water flow. Both tracheids and vessels are dead conducting elements.
No. Gymnosperm xylem has tracheids only and lacks vessels. Vessels are a characteristic feature of angiosperm xylem. NEET has directly tested this — see the 2024 PYQ below where Statement II uses exactly this fact.
Xylem fibres are dead sclerenchyma cells with thick walls that give mechanical support to the plant. Xylem parenchyma is the only living element; it stores food materials like starch and fats and helps in the sideways (radial) conduction of water. Together they support and store while tracheids and vessels conduct.
Given below are two statements. Statement I: Parenchyma is living but collenchyma is dead tissue. Statement II: Gymnosperms lack xylem vessels but presence of xylem vessels is the characteristic of angiosperms. In the light of the above statements, choose the correct answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Xylem is a complex permanent tissue because it is made of more than one type of cell (tracheids, vessels, fibres and parenchyma) that work together as one unit. Phloem is the other complex tissue.
Xylem mainly conducts water and dissolved minerals upward (unidirectionally) from the roots to the stem and leaves. Xylem parenchyma can also help move water sideways (radially).
Pits are thin, unthickened spots in the lignified walls where water can move from one conducting cell to the next. Tracheids rely fully on pits, since their end walls are not perforated like those of vessels.
Tracheids are the more primitive conducting element and are found in all vascular plants, including gymnosperms. Vessels are more advanced and appear mainly in angiosperms.
