CLASS 11TH BIOLOGY CHAPTER- 6 ANATOMY OF FLOWERING PLANTS NCERT QUICK REVISION NOTES FOR NEET AND CBSE EXAM
ANATOMY OF FLOWERING PLANTS
There are two types of tissues
(i) Meristematic
(ii) Permanent
(i) 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:
1. Apical meristem
• Occurs at the tips of roots arid shoots.
• Primary meristem.
• Increase the length of plant.
2. Intercalary meristem
• Occurs between mature tissue.
• Primary meristem.
•Occur in grasses and regenerate parts removed by grazers.
3. Lateral Meristem
• Occurs in the mature region of roots and shoots.
• Secondary meristem.
• Appears later than primary meristem and responsible for secondary growth.
Axillary bud: The buds which are present in the axils of leaves (Consist of cells left behind from shoot apical meristem) and are responsible for forming branches of flowers.
(ii) PERMANENT TISSUES: The permanent tissues are derived from meristematic tissue, are composed of cells, which have lost the ability to divide and have become
structurally and functionally specialised.
TYPES OF PERMANENT TISSUE
(i) Simple
• Parenchyma
• Collenchyma
• Scierenchyma
• Parenchyma: Living, thin walled isodiametric cells, with interceullar spaces, cell wall is made up of cellulose. It performs the functions like photosynthesis, storage, secretion.
• Collenchyma: It is formed of living, closely packed cells. Its cells are thicknened at the corners due to depositon of celluose and pectin. It provide mechanical support to the grow ing parts of the plant. It is either found in homogenous layer or patches.
• Sclerenchyma: It is formed of dead cells with thick and lignified walls. Provide mechanical support to organs. They have two types of cells: fibres and sclereids.
(a) Fibers-are thick walled, elongated and pointed cells.
(b) Sclereids-are spherical, oval or cylindrical, highly thickened dead cells with narrow lumen. Found in walls of nut, pulp of fruits like guava, seed coat of legumes and leaves of tea.
(ii) complex
• Xylem
• Phloem
• Xylem : Xylem consists of tracheids vessels, xylem fibres parenchyma. It conducts water and minerals from roots to other parts of plant.
(a) Tracheids-Tube like cells with thick and lignified walls and tapering ends; dead, without protoplasm.
(b) Vessel-long cylindrical structure made up of many cells with large central cavity, devoid of protoplasm. Present in angiosperms.
(c) Xylem fibres-highly thickened walls; with obliterated lumens; septate aseptate.
(d) Xylem parenchyma-living and thin walled; cell walls made up cellulose, store food material in form of starch or fat.
Radial conduction of water takes place by ray parenchymatous cells
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; in stem.
Exarch: Protoxylem toward periphery and metaxylem towards centre, in roots.
• Phloem :Phloem consists of sieve tube elements, companion cells, phloem and phloem parenchyma; Phloem transports the food material from leaves fibres to various parts of the plant.
(a) Sieve tube elements :
• long tube like structures arranged longitudinally.
• associated with companion cells.
• end walls are perforated to form sieve plates.
• functions of sieve tubes are controlled by the nucleus of companion cells.
(b) Companion cells
• Specialised parenchymatous cells associated with sieve tube elements.
• Connected with sieve tube elements by pit fields present between their common longitudinal walls.
• hep maintain pressure gradient in sieve tubes.
(c) Phloem Parenchyma
• made up of elongated, tapering cylindrical cells with dense cytoplasm and nucleus.
• cell wall made of cellulose with pits through which plasmodesmatal connections exist between cells.
• store food material.
(d) Phloem fibers (bast fibers)
• are sclerenchymatous; absent in primary phloem but present in secondary phloem.
• elongated, unbranched pointed, needle like apices with thick cell walls.
Protophloem: First formed phloem with narrow sieve tubes.
Metaphloem: 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.
(a) Cuticle-Waxy thick layer outside epidermis, prevents the loss of water.
(b) Epidermis: Outer most layer of primary plant body.
(c) Epidermal hair: help in absorbing water and mineral from soil.
(d) Trichomes: help in preventing water loss due to transpiration.
(e) Stomata: Regulate process of transpiration and gaseous exchange.
Stomatal apparatus: The stomatal aperture, guard cells and surrounding subsidiary cells are together called stomatal apparatus.
Casparian Strips: The Tangential as well as radial walls of endodermal cells of dicot roots have deposition of water impermeable, waxy material Suberin in the form of casparian strips.
2. The ground tissue system: It is made up of parenchyma, collenchyma, sclerenchyma. In dicot stems and roots (both monocots and dicots) 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.
• Dicot Root
1. Cotext is comparatively narrow.
2. Endodermis is less thicknened casparian strips are more prominent.
3. The xylem and phloem bundles varies from 2 to 5.
4. Pith is absent or very small.
5. Secondary growth takes place with the help of vascular cambium and cork cambium.
• Monocot Root
1. Cortex is very wide.
2. Endodermal cells are highly thickened Casparian strips are visible only in young roots.
3. Xylem and phloem are more than 6 (polyarch).
4. Well developed pith is present.
5. Secondary growth is absent.
Casparian Strips-The tangential as well as radial walls of endodermal cells of dicot roots have deposition of water impermeable, waxy material, suberin in the form of casparian strips.
ANTOMY OF STEM:
• Dicot Root
1. The ground tissue is differentiated into cortex, endodermis,pericycle and pitch.
2. The vascular bundles are arranged in a ring.
3. Vascular bundles are open, without surrounded bundle sheath and wedge-shaped outline.
4. The stem shows secondary growth due to presence of cambium between xylem and phloem.
• Monocot Root
1. The ground tissue is made up of similar cells.
2. The vascular bundles are scattered throughout the ground tissue.
3. Vascular bundles are closed, by sclerenchymatous bundle sheath, oval or rounded in shape.
4. Secondary growth is absent.
Secondary growth dicot stem-An increase in the girth (diameter) in plants. Vascular cambium and cork cambium (laternal 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.
4. Development of cork cambium(phellogen)
Cork Cambium (Phellogen)
• 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:
• Dorsiverntral (Dicot) Leaf
1. Stormata are absent or less abundant on the upper side.
2. Mesophyll is differntiated into two parts upper palisade parenchyma and lower spongy parenchyma.
3. Bunldle sheath is single layered and formed of colourless cells.
4. Hypodermis of the mid-rib region, is collenchymatous.
5. Stomata have kidney shaped guard cells.
• Isobilateral (monocot) Leaf
1. The somtata are equally distributed on both sides.
2. Mesophyll is undifferentiated.
3. Bundle sheath may be single or double layered.
4. Hypodermis of the mid-rib region is sclerenchymatous.
5. Stomata have dumb bell shaped guard cells.
SPRING WOOD AND AUTUMN WOOD:
• Spring Wood
1. Also called early wood.
2. Cambium is active.
3. Xylary elements more.
4. Vessels with wide cavities.
5. Light in colour, low density.
• Autumn Wood
1. Also called late wood.
2. Cambium less active.
3. Xylary elements less.
4. Vessels narrow.
5. Dark, high denisty.
HEARTWOOD AND SAPWOOD:
• Heartwood
1. Central or innermost region of stem which is hard, durable and resistant to attack of Microorganisms and insects.
2. Not involved in conduction of water, gives mechanical support to stem.
• Sapwood
1. Peripheral region stem, light in colour
2. Involved in conduction of water and mineral
Lenticels- Produced when phellogen cuts off parchymatous cells on outer side. These cells rupture the epidermis forming lens shaped opening called lenticels. Function- Permit exchange of gases.
Bulliform cells- Large, empty, colourless adaxial cells with vein in leaves which maintain turgidity of leaves.
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