Anatomy of Flowering PlantsMind Map

A flowering plant body is made of tissues grouped into tissue systems. Meristematic tissues are actively dividing and are found at specific regions such as root tips, shoot tips, internodes and lateral sides. They give rise to permanent tissues, whose cells lose the ability to divide and become specialised. Permanent tissues are simple when made of one type of cell, such as parenchyma, collenchyma and sclerenchyma, and complex when made of multiple cell types, such as xylem and phloem. The epidermal tissue system forms the protective outer covering with epidermis, stomata, root hairs and trichomes. The ground tissue system includes cortex, endodermis, pericycle, pith and mesophyll. The vascular tissue system consists of xylem and phloem, arranged differently in roots, stems and leaves.

Xylem and phloem are complex permanent tissues because each contains more than one cell type. Xylem conducts water and minerals from roots to aerial parts and provides mechanical support. It consists of tracheids, vessels, xylem fibres and xylem parenchyma; except xylem parenchyma, most xylem elements are dead at maturity. Phloem transports organic food, mainly from leaves to other plant parts. It consists of sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Gymnosperms and pteridophytes lack sieve tubes and companion cells but have sieve cells. Vascular bundles may be radial in roots or conjoint in stems and leaves. They may be open if cambium is present or closed if cambium is absent. Exarch xylem is typical of roots, while endarch xylem is typical of stems.

Root anatomy is identified by epiblema, cortex, endodermis, pericycle and radial vascular bundles. The outermost layer is epiblema or piliferous layer, often bearing root hairs for absorption. Cortex is made of thin-walled parenchyma with intercellular spaces and stores food. The innermost layer of cortex is endodermis, which has Casparian strips made of suberin and regulates water entry into the stele. Pericycle lies just inside endodermis and gives rise to lateral roots and, in dicots, part of vascular cambium and cork cambium during secondary growth. Xylem and phloem are arranged radially and alternately. Xylem is exarch. Dicot roots usually have fewer xylem bundles and small or absent pith, while monocot roots have many xylem bundles and large pith.

Stem anatomy is recognised by epidermis with cuticle, cortex or ground tissue, vascular bundles and pith. In dicot stems, the epidermis is followed by collenchymatous hypodermis, cortical parenchyma, endodermis, pericycle and vascular bundles arranged in a ring. Each vascular bundle is conjoint, collateral and open because cambium is present between phloem and xylem. Xylem is endarch, meaning protoxylem lies toward the centre. Medullary rays occur between vascular bundles, and pith is well developed. In monocot stems, hypodermis is sclerenchymatous, ground tissue is undifferentiated and vascular bundles are numerous, scattered and closed. Each monocot vascular bundle is surrounded by a sclerenchymatous bundle sheath and contains a protoxylem lacuna. NEET frequently tests ring versus scattered arrangement and open versus closed bundles.

Secondary growth is the increase in thickness or girth of plant organs due to activity of lateral meristems. It is common in dicot stems and roots and usually absent in monocots. In dicot stem, vascular cambium forms a continuous cambial ring by joining intrafascicular cambium within vascular bundles and interfascicular cambium between bundles. This cambium cuts secondary xylem toward the inside and secondary phloem toward the outside. More secondary xylem is produced than secondary phloem, leading to wood formation. Cork cambium or phellogen develops in the outer cortical region and produces cork or phellem outward and secondary cortex or phelloderm inward. Together phellem, phellogen and phelloderm form periderm. Annual rings, heartwood, sapwood and bark are key NEET terms from secondary growth.

Leaf anatomy is adapted for photosynthesis, gaseous exchange and transpiration control. A dicot leaf is usually dorsiventral, meaning the upper and lower surfaces are structurally different. It has upper epidermis with cuticle, lower epidermis with more stomata, and mesophyll differentiated into palisade parenchyma and spongy parenchyma. Palisade cells are chloroplast-rich and perform maximum photosynthesis, while spongy parenchyma has intercellular spaces for gas exchange. Vascular bundles occur in veins and are surrounded by bundle sheath cells; xylem is toward the upper epidermis and phloem toward the lower epidermis. A monocot leaf is isobilateral, with similar upper and lower surfaces, stomata on both sides, undifferentiated mesophyll and bulliform cells on the upper epidermis. Bulliform cells help leaf rolling during water stress.

The epidermal tissue system forms the outermost covering of the plant body and includes epidermal cells, stomata, root hairs, trichomes and specialised cells such as bulliform cells. Epidermal cells are compactly arranged and usually covered by a waxy cuticle in aerial parts to reduce water loss. Root epidermis, called epiblema, generally lacks cuticle and forms root hairs that increase absorptive surface area. Stomata are pores surrounded by guard cells and sometimes subsidiary cells; they regulate gaseous exchange and transpiration. In dicots, guard cells are kidney-shaped, while in grasses they are dumb-bell shaped. Trichomes on stems may reduce transpiration, provide protection or secrete substances. Bulliform cells in monocot leaves are large, thin-walled cells that help leaves roll during water stress.

Dicot and monocot anatomy can be mastered by comparing root, stem and leaf together. Dicot roots usually have fewer xylem bundles, small or absent pith and secondary growth, while monocot roots have polyarch xylem, large pith and no secondary growth. Dicot stems have vascular bundles in a ring, open bundles with cambium, collenchymatous hypodermis and distinct pith. Monocot stems have scattered closed bundles, sclerenchymatous hypodermis, undifferentiated ground tissue and protoxylem lacuna. Dicot leaves are dorsiventral with palisade and spongy mesophyll, while monocot leaves are isobilateral with undifferentiated mesophyll and bulliform cells. NEET identification becomes easy when you first decide the organ, then check vascular bundle pattern, cambium, pith and mesophyll.

NEET questions from Anatomy of Flowering Plants are usually based on recognition, comparison and labelled structure-function relationships. The fastest strategy is to identify the organ first: root, stem or leaf. Roots have radial vascular bundles and exarch xylem. Stems have conjoint bundles and endarch xylem. Leaves have upper and lower epidermis, mesophyll and vascular bundles with xylem facing upward. Next decide dicot or monocot using bundle number, arrangement, cambium, pith, palisade mesophyll or bulliform cells. For tissue questions, remember cell nature and function: parenchyma is living and storage-based, collenchyma is flexible support, sclerenchyma is dead mechanical support, xylem conducts water and phloem conducts food. For secondary growth, track cambium products and cork cambium derivatives.