Class 11 Biology Chapter 6 Anatomy Of Flowering Plants Notes

             Anatomy Of Flowering Plants

Anatomy : Anatomy is the study of internal structure of organisms. Plant anatomy includes organisation and structure of tissues.

Tissue : A group of similar cells alongwith intercellular substance which perform a specific function.

Meristematic tissues : The meristematic tissue is made up of the cells which have the capability to divide. Meristems in plants are restricted to a specialised regions and responsible to the growth of plants.

Meristems

Apical meristem	Intercalary meristem	Lateral meristem
Occurs at the tips of roots and	Occurs between mature tissue	Occurs in the mature
shoots Primary meristem	Primary meristem	regions of roots and shoots Secondary meristem
Increase the length of plant	Capable of forming branch	Appears later than pri-
	and flower	mary meristem and res- ponsible for secondary
		growth

Axillary bud : The buds which are present in the axils of leaves and are responsible for forming branches or flowers.

Permanent tissues : The permanent tissues are derived from meristematic tissue and are composed of cells, which have lost the ability to divide.

Types of Permanent Tissue

Simple Complex

Parenchyma Collenchyma Sclerenchyma Xylem Phloem

Parenchyma : Thin walled cells, with intercellular spaces, cell wall is made up of cellulose. It performs the function like photosynthesis, storage, secretion.

Collenchyma : It is formed of living, closely packed isodimetric cells. It’s cells are thickened at the corners due to deposition of cellulose and pectin. It provides mechanic support to the growing parts of the plant.

Sclerenchyma : It is formed of dead cells with thick and lignified walls.

They have two types of cells : fibres and sclereids.

Xylem : Xylem consists of tracheids, vessels, xylem fibres and xylem pa- renchyma. It conducts water and minerals from roots to other parts of plant.

Protoxylem : The first formed primary xylem elements.

Metaxylem : The later formed primary xylem.

Endarch : Protoxylem lies towards the centre and metaxylem towards the periphery of the organ.

Phloem : Phloem consists of sieve tube elements, companion cells, phloem fibres and phloem parenchyma. Phloem transports the food material from leaves to various parts of the plant.

Protophloem : First formed phloem with narrow sieve tubes.

Metaxylem : Later formed phloem with bigger sieve tubes.

The Tissue System :

1. Epidermal tissue system : It includes cuticle, epidermis, epidermal hairs, root hairs, trichomes and stomata.
2. The ground tissue system : It is made up of parenchyma, collenchyma, sclerenchyma. In dicot stems and roots the ground tissue is divided into hypodermis cortex, endodermis, pericycle, medullary rays and pith.
3. The vascular tissue system : It includes vascular bundles which are made up of xylem and phloem.

Vascular Bundles

Radial bundles Conjoint bundles (Xylem and phloem occur (Xylem and phloem are situated at on different radii) the same radius of vascular bundle)

Collateral bundles Bicolateral bundles Concentric bundles Open Closed

(with cambium) (without cambium)

Anatomy of Root

Dicot Root	Monocot Root
Cortex is comparatively narrow. Endodermis is less thickened casparian stripes are more prominent. The xylem and phloem bundles varies from 2 to 5. Pith is absent or very small. Secondary growth takes place with the help of vascular cambium and cork cambium	Cortex is very wide. Endodermal cells are highly thickened Casparian strips are visible only in young roots. Xylem and phloem are more than 6 (polyarch). Well developed pith is present. Secondary growth is absent.

Anatomy of Stem

Dicot Stem	Monocot Stem
The ground tissue is differentiated into cortex, endodermis, pericy and pith. The vascular bundles are arranged in a ring. Vascular bundles are open, without bundle sheath and wedge-shaped outline. The stem shows secondary growth due to presence of cambium between xylem and phloem. Stomata have kidney-shaped guard cells.	The ground tissue is made up of similar cells. The vascular bundles are scat tered throughout the ground tissue. Vascular bundles are closed, surrounded by sclerenchymatous bundle sheath, oval or rounded in shape. Secondary growth is absent. Stomata have dumb bell-shaped guard cells.

Secondary growth in dicot stem : An increase in the girth (diameter) in plants. Vascular cambium and cork cambium (lateral meristems) are involved in secondary growth.

1. Formation of cambial ring : Intrafascicular cambium + interfascicular cambium.
2. Formation of secondary xylem and secondary phloem from cambial ring.
3. Formation of spring wood and autumn wood.

 

1. Development of cork cambium (phellogen)

Cork Cambium Cork (phellem) - From outer cells

Sec. cortex (phelloderm) - From inner cells

(Phellogen + Phellem + Phelloderm) = Periderm

Secondary growth in dicot roots : Secondary growth in dicot root occurs with the activity of secondary meristems (vascular cambium). This cambium is produced in the stele and cortex, and results in increasing the girth of dicot roots.

Anatomy of Leaf

Dorsiventral (Dicot) Leaf	Isobilateral (monocot) Leaf
Stomata are absent or less abundant on the upper side. Mesophyll is differentiated into two partsupper palisade parenchyma and lower spongy parenchyma. Bundle sheath is single layered and formed of colourless cells. Hypodermis of the mid-rib region is collen- chymatous.	The stomata are equally distributed on both sides. Mesophyll is undifferentitated. Bundle sheath may be single or double layered. Hypodermis of the mid-rib region is sclerenchymatous.