Biology handbook for neet. (Dr Anand Mani)

84 ^|

A Handbook of Biology

THË GRØÜÑD TÏSSÜË SÝSTËM

All tissues except epidermis and vascular bundles constitute the ground tissue.

It consists of simple tissues

(parenchyma, collenchyma

and sclerenchyma).

Ground tissue is divided

into three zones- cortex,

pericycle, & pith.

Parenchymatous cells are

present in cortex, pericycle,

pith and medullary rays,

in the primary stems and

roots.

In leaves, the ground tissue

consists of thin-walled

chloroplast containing cells

and is called mesophyll.

THË VÅSÇÜLÅR TÏSSÜË SÝSTËM

It consists of complex tissues (xylem and phloem).

Xylem and Phloem together constitute

vascular bundles. Based on the presence

or absence of cambium, vascular bundles

are of 2 types:

Open type: In this, cambium is present

between phloem and xylem. So vascular

bundles can form secondary xylem and

phloem tissues. E.g. dicotyledonous stems.

(AIPMT Mains 2011)

Closed type: In this, cambium is absent.

Hence, they do not form secondary tissues.

E.g. monocotyledons. (NEET 2018)

Based on the arrangement of xylem and

phloem, vascular bundles are of 2 types:

Radial type: Xylem and phloem are arranged in an

alternate manner on different radii. Seen in roots.

Conjoint type: Xylem and phloem are situated

at the same radius of vascular bundles. Seen in

stems and leaves. Conjoint vascular bundles

usually have phloem located only on the outer

side of xylem.

Phloem

Xylem

(a) Conjoint close

(b) Radial

Phloem

Xylem

Phloem

Xylem

Cambium