NCERT Class 11-Biology: Chapter –6 Anatomy of Flowering Plants Part 9

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Question 6:

Distinguish between the following:

a. Exarch and endarch condition of protoxylem

b. Stele and vascular bundle

c. Protoxylem and metaxylem

d. Interfasicular cambium and intrafasicular cambium

e. Open and closed vascular bundles

f. Stem hair and root hair

Answer:

(a) Exarch and endarch condition of protoxylem: In stems, the protoxylem lies towards the centre (pith) and the metaxylem lies towards the periphery of the organ. This type of primary xylem is called endarch. In roots, the protoxylem lies towards periphery and metaxylem lies towards the centre. Such arrangement of primary xylem is called exarch.

(b) Stele and vascular bundle: All tissues on the inner side of the endodermis such as pericycle, vascular bundles and pith constitute the stele. The vascular system consists of complex tissues, the phloem and the xylem. The xylem and phloem together constitute vascular bundles.

(c) Protoxylem and metaxylem: Primary xylem is of two types- protoxylem and metaxylem. The first formed primary xylem elements are called protoxylem and the later formed primary xylem is calledmetaxylem.

(d) Interfasicular cambium and intrafasicular cambium; In dicot stems, the cells of cambium present between primary xylem and primary phloem is the intrafascicular cambium. The cells of medullary rays, adjoining these intrafascicular cambium become meristematic and form the Interfasicular cambium.

(e) Open and closed vascular bundles: In dicotyledonous stems, cambium is present between phloem and xylem. Such vascular bundles because of the presence of cambium possess the ability to form secondary xylem and phloem tissues, and hence are called open vascular bundles. In the monocotyledons, the vascular bundles have no cambium present in them. Hence, since they do not form secondary tissues they are referred to as closed.

(f) Stem hair and root hair: The root hairs are unicellular elongations of the epidermal cells and help absorb water and minerals from the soil. On the stem the epidermal hairs are called trichomes or stem hairs. The trichomes in the shoot system are usually multicellular. They may be branched or unbranched and soft or stiff. They may even be secretory. The trichomes help in preventing water loss due to transpiration.

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