Thursday, April 10, 2014

CHAPTER: 12 HISTOLOGY AND ANATOMY OF FLOWERING PLANTS REVISION NOTES

CHAPTER: 12 HISTOLOGY AND ANATOMY OF 
FLOWERING PLANTS

Tissues - a group of similar cells performing same function. 

Types of plant tissues - meristematic tissues and permanent tissues. 

Meristematic tissues 

·         Have power of cell division

Characteristics features 

·         Cells are thin walled

·         No intercellular places 

·         Abundant cytoplasm

·         Retains power of cell division

Classification based on position. Three types

1.       Apical meristem

2.       Lateral meristem

3.       Intercalary meristem

Based on the origin – three types 

1.       Promeristem- embryo/ seedlings

2.       Primary meristem

3.       Secondary meristem

Permanent tissues:

 

I.Simple permanent tissues

1.       Parenchyma( storage)-living

2.       Collenchymas (support ) below epidermis, living

3.       Sclerenchyma – sclereids and fibres- dead

II.Compound permanent tissues

·         Xylem- xylem vessels, xylem tracheids, xylem parenchyma, xylem fibres

·         Phloem – sieve tubes, sieve cells, companion cells, phloem parenchyma

Tissue system in plants :

1.       Epidermal tissues

2.       Vascular tissues

3.       Ground /fundamental tissues

Meristematic tissues

·         Growth in plants is largely restricted to specialized regions of active cell division called meristem.

·         Apical meristems are the meristems which occur at the tips of roots and shoots and produce primary tissues

·         Intercalary meristem are the ones which occur between mature tissues 

·         Lateral meristem occurs in mature regions of roots and shoots and appear later than primary meristem

Permanent tissues/ mature:

 

·         The newly formed cells from primary and secondary meristems which become structurally and functionally specalised and lose the ability to divide are permanent tissues

I.Simple tissues. (made up of only one type of cells ) 

1.       Parenchyma 

o   major component within organs

o   Isodiametric,spherical, oval,round, polygonal,elongated in shape. 

o   Thin cell walls made of cellulose. 

o   Closely packed or have intercellular spaces

o   Function. Photosynthesis, storage, secretion. 

2.       Collenchymas – 

·         occurs in layers below epidermis, either in homogeneous layer or in patches

·         Thickened at the corners due to pectin, cellulose, oval, spherical, polygonal

·         Assimilate food when chloroplasts is present

·         Intercellular spaces absent- function. Mechanical support 

3.        Sclerenchyma -  

·         long narrow cells, lignified walls, with pits

·         Dead- fibers-thick walled, elongated, pointed

·         Sclereids- spherical, dead, narrow cavity-lumen

·         Found in – guava, pear, sapota

·         Function. Mechanical support

II. Complex tissues (more than one type of cells) 

1.       Xylem. Conducting tissue for  water and minerals

·         Tracheids. Elongated or tube like cells, dead, main water transporting element

·         Vessels. Long cylindrical, lignin in cell walls, large central cavity, devoid of protoplasm.

·         Xylem fibres- lumens present, septate/aseptate

·         Xylem parenchyma- living thin- walled, cell walls, cellulose, store food as starch or fat, tannins

2.       Phloem - (transports food material)

·         Sieve tubes- long, tube like, perforated, forms sieve plates

·         Companion cells – pit is present , helps in maintenance of pressure gradient in the sieve tubes

·         Phloem parenchyma – elongated, tapering, dense cytoplasm, cell wall, cellulose, pits

·         Phloem fibres - unbranched, pointed, quite thick. 

Tissue system :

1.       Epidermal tissue system

·         Cuticle present- contains stomata ( guard cells, subsidiary cells, stomatal apparatus )

·         Trichomes – (on stem) multicellular, secrete oils. Root hairs- single celled.

2.       Ground tissues 

·         Tissues except epidermal and vascular tissues. 

·         Mesophyll. ( collenchymas, sclerenchyma, parenchyma )

3.       Vascular tissue system

·         Cambium. ( lateral meristem )

·         Radial vascular bundle – in roots

·         Conjoint open vascular bundle  - in dicot stem and leaves 

·         Conjoint closed vascular bundle – in monocot stem and leaves

Anatomy of dicotyledonous and monocotyledonous plants:

1.       Dicotyledonous root

Epidermis – root hair – cortex ( Parenchyma ) endodermis – suberin layer as casparian strips

Pericycle (lateral roots) pith is small – conjuctive tissues ( between xylem and phloem )

Cambium ring  ( 2-4 xylem and phloem )

Stele ( endodermis, pericycle, vascular bundle and pith )

2.       Monocotyledonous root 

No cambium in the vascular bundles.  (6 vascular bundles and are scattered) called polyarch - pith is large – since no cambium, and no secondary growth 

3.       Dicotyledonous stem 

·         Epidermis, cuticle, trichomes, hypodermis (collenchymas)

·         Cortical layer ( parenchyma ) endodermis(starch sheath)

·         Pericycle - vacular bundles – medullary rays 

·         Vascular bundles are in a ring

·         Conjoint, open, and endarch protoxylem

·         Pith is larger  (parenchyma)

4.       Monocotyledonous stem

·         Epidermis – hypodermis ( sclerenchyma ) scattered vascular bundles, sclerenchyma. 

·         Bundle sheath – vascular bundles are conjoint, closed, no cambium 

·         Peripheral  vascular bundle are smaller than central 

·         No secondary growth- no trichomes

·         Water containing cavities are present- no distinct pith 

Stem :

1.       Trichomes present / absent

2.       Vascular bundle scattered/ rings

3.       Vascular bundles closed/ open – cambium

4.       Pith present /absent

Leaves :

1.       Dorsiventral leaf /dicot leaf:

·         Epidermis are adaxial epidermis (upper) and abaxial epidermis (lower)

·         Cuticle – stomata is more on lower epidermis

·         Mesophyll – it has two types of cells , palisade parenchyma and spongy parenchyma

·         Vascular system  vascular bundle are present in vein and midrib

·         Reticulate venation –vascular bundle are surrounded by bundle sheath

2.       Isobilateral / monocot leaf:

·         Same anatomy –  but no spongy parenchyma and stomata on both side

·         Bulliform cells – parallel venation

Secondary growth:

·         Primary growth- apical meristem ( grows length wise )

·         Secondary growth –increase  in girth

·         It involves lateral meristem vascular cambium and cork cambium 

·         Vascular cambium

Formation of cambial ring

·         Intrafacicular cambium

·         Interfascicular cambium

·         Activity of cambial ring

·         Formation of secondary xylem secondary phloem

·         More active on the inner side so more xylem

·         Spring early wood –more active and light coloured

·         Autumn late wood – less active and dark coloured

·         The two kinds of wood that appear as alternate concentric rings, constitute an annual ring

·         Heart wood – dead, elements, highly lignified provides mechanical support

·         Sap wood – peripheral region , secondary xylem, light in colour, conduction of water and minerals

Cork cambium:

 

·         Cortical and epidermis layer get broken 

·         Replaced to provide new protective cell layers

·         Cork cambium/ phellogen –develop in cortex region and produce new cells towards both sides

·         Outer cells form cork / phellum

·         Inner cells form secondary cortex / phelloderm 

·         Bark  - soft early bark – formed early in the season

·         Late / hard bark – formed late in the season

·         Lenticels. Lens shaped openings  helps in exchange of gases. 

Secondary growth in roots:

·         Wavy ring – later becomes circular

·         Secondary growth occurs in gymnosperms too (except in monocots) as monocot do not have cambium.

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