Biology · Anatomy of Flowering Plants · NEET
| Number of xylem strips | Diarch to tetrarch (2 to 4) | Polyarch (more than 6) |
| Found in | Dicot root | Monocot root |
| Pith | Small or absent | Large and well developed |
| Secondary growth | Present (dicot root) | Absent (monocot root) |
These words just count the number of xylem strips (also called xylem patches or bundles) seen in a root's cross-section. Diarch = 2 strips, triarch = 3, tetrarch = 4, pentarch = 5, hexarch = 6, and polyarch = more than 6 (many). The prefix tells the number and 'arch' means the xylem points. This is a favourite NEET matching point.
A dicot root has FEW xylem strips. It is usually diarch to tetrarch, meaning 2 to 4 xylem patches. NCERT says dicot roots have fewer xylem bundles. So if a root shows only 2, 3 or 4 xylem strips, it is a dicot root, not a monocot root.
A monocot root is POLYARCH. NCERT states there are usually MORE THAN SIX xylem bundles in the monocot root. So counting more than six xylem strips is a direct sign of a monocot root. This is one of the safest identification lines for NEET.
Polyarch does not mean one fixed number. It simply means 'many', that is more than six xylem bundles. NCERT uses the words 'usually more than six (polyarch)'. You do not count an exact number in NEET; you just know polyarch = many = monocot root.
No. Diarch/tetrarch/polyarch COUNT the xylem strips. Exarch/endarch tell the POSITION of protoxylem (the first-formed xylem). A monocot root is polyarch AND exarch at the same time: many strips, with protoxylem pointing outward. Both words describe the same root but answer different questions, so do not mix them up.
For NEET you do not need a deep reason; you need the fact. Monocot roots naturally form many xylem groups arranged in a wheel (polyarch), and they also have a large, well-developed pith. Dicot roots form fewer xylem groups and have little or no pith. This pairing (polyarch + large pith = monocot root) is what examiners test.
The transverse section of a plant part showed polyarch, radial and exarch xylem, with endodermis and pericycle. The plant part is identified as :
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A dicot root can be diarch (2 xylem strips) and is usually diarch to tetrarch. A monocot root is polyarch (more than six). So diarch always points to a dicot root.
No. By NCERT, dicot roots have FEW xylem bundles, usually 2 to 4 (diarch to tetrarch). Polyarch (more than six) belongs to the monocot root.
Monarch means one single xylem strip. It is rare in NEET plants; the common examples are diarch (2), tetrarch (4) and polyarch (many, in monocot roots).
No, mainly to roots. In roots the xylem and phloem lie on separate radii (radial bundles), so we count xylem strips as arches. Stems have conjoint bundles, so we do not use diarch/polyarch for stems.
No. Radial means xylem and phloem lie on different radii (true for all roots). Polyarch counts HOW MANY xylem strips there are. A monocot root is both radial and polyarch.
