Anatomy of flowering plants chapter 6 cbse, class 11 Biology notes. This cbse Biology class 11 notes has a brief explanation of every topic that NCERT Biology syllabus has.
You will also get ncert solutions, cbse class 11 Biology sample paper, cbse Biology class 11 previous year paper.
Anatomy of Flowering Plants
Anatomy is the study of the structure of an organism. Plant anatomy helps in knowing the structural peculiarities of different group of plants and indicates the structural adaptation to diverse environments.
Tissue is a group of cells having a common origin and usually performing common functions
Meristematic tissue is composed of a group of similar and immature cells which can divide and form new cells. These tissues divide to form new cells which give rise to permanent tissues.
Characteristics of Meristematic Tissue
- They are living and contain undifferentiated mass
- The shape is spherical, polygonal or rectangular.
- The cells are compactly arranged without intercellular spaces
- Nucleus is large
- Cell wall is thin with only a primary wall. There is no secondary wall.
Classification of Meristematic Tissue
Meristem is classified in three ways, i.e., position in the plant body, functions and origin.
Classification Based on Position
Meristems can be divided into three types, based on their position in the plant body.
The meristems that occur at the tips of root and shoot and produce primary tissues are called apical meristems.
The Root Apical Meristem (RAM) present at the tip of a root while the Shoot Apical Meristem (SAM) present at the distinct most region of the stem axis.
During the formation of leaves, some cells constitute the axillary bud. These buds are present in the axil of leaves that form a branch or a flower.
The meristems which occur between mature tissues are intercalary meristems. They generally occur in grasses.
Both apical and intercalary meristems appear at initial stage of the plant which contribute to the formation of the primary plant body. They are present mostly at the base of node, internode and leaf
Lateral meristems occur in the mature regions of roots and shoots of many plants. It produces a woody axis and appears later than primary meristem. They are cylindrical meristems. They are responsible for producing the secondary tissues.
Classification Based on Functions
The meristems are classified on the basis of their functions as
Protoderm: It is the outermost portion of the primary meristem which is found at the apex of the stem and root.
Procambium: It develops into primary vascular tissues which forms the isolated strands of elongated cells
Ground Meristem: It develops into the ground tissue. Their cells are thin-walled, living and isodiametric.
Classification Based on Origin
Primary Meristems: Primary meristems are found in the growing apical regions of the root and shoot and derived during the early embyonic stages.
Secondary Meristems: They appear in later stages of development in the plant body. These meristems lie lateral in position in both the stem and root.
The meristematic cells gradually become mature or permanent. They are composed of cells in which the growth has stopped.
Permanent tissues can be divided into two types
- Simple Permanent Tissues
- Complex Permanent Tissues
Simple Permanent Tissues
The tissues in which all cells are similar in structure and function are called simple tissues. They are groups of homogenous cells which perform the same function.
Parenchyma is a living tissue which is composed of thin-walled isodiametric cells. It is also known as primary tissue. Each parenchyma cell encloses a large central vacuole and peripheral cytoplasm containing the nucleus.
Parenchyma is present in cortex, mesophyll and some other parts of the flower. They store the food and provide turgidity to softer parts of the plant.
Functions of parenchyma
- It helps in storage of food, water and air,
- Perform vital activities like photosynthesis, respiration and conduction
- Helps in wound healing, grafting, etc Provides buoyancy in aquatic plants.
- Parenchyma cells associated with xylem and phloem help in conduction of water, and food materials.
Collenchyma is a simple, living mechanical tissue. These cells are thickened at corners due to cellulose, hemicellulose and pectin.
They are spherical or polygonal and often contain chlorophyll.
These cells are composed of more or less elongated cells with thick, primary non-lignified walls and no intercellular spaces.
Functions of collenchyma
- Provides mechanical support to the growing parts of the plant, such as the young stem and petiole of a leaf.
- They are capable of photosynthesis, as they contain chloroplasts.
The sclerenchyma are supportive tissue having highly thick walled narrow cells with little or no protoplasm due to deposition of cellulose or lignin.
They are of two types: fibres and sclereids. It provides mechanical support to mature plant organs to tolerate bending, shearing, compression etc.
Functions of sclerenchyma
- Provides mechanical strength and support.
- Surface fibres help in dispersal of seeds.
Complex Permanent Tissues
Complex permanent tissues are a group of cells having common origin and working together as a unit. These complex tissues in vascular plants are xylem and phloem. These two constitute the complex tissues in plants and work together as a unit.
Xylem is a complex permanent tissue which carries water and mineral nutrients upwards from the root to the leaves.
The xylem tissues are composed of four components
Tracheids: Tracheid are elongated, tubular and primitive cells with tapering end walls. They are dead cells and do not contain protoplasts.
They provide mechanical support and carry water and dissolved mineral elements from roots to leaves.
Vessels: Vessels are long, cylindrical, tube-like structures made up of many cells. Each cell is with lignified walls and a large central cavity.
These cells are devoid of protoplasm and their members are interconnected through perforations in their common walls. The presence of these vessels is a characteristic feature of angiosperms.
Xylem Fibres: The sclerenchymatous fibres which are associated with the xylem are called xylem fibres.
These fibres have lignified cell walls which are usually thicker than the walls of the tracheids in the same wood. They are found in both primary and secondary xylem. The xylem fibres provide mechanical strength.
Xylem Parenchyma: These cells are the only living component of the xylem. Xylem parenchyma stores food in the form of starch.
They assist directly or indirectly in the conduction of water upward through the vessels and tracheids.
The xylem parenchyma are subdivided into two types Primary Xylem and Secondary xylem. The primary xylem is furthur divided into two types, i.e., protoxylem and metaxylem.
In stems, the protoxylem (first formed primary xylem) lies towards the centre (pith) and the metaxylem (latter formed primary xylem)
lies towards the periphery of the organ. This type of primary xylem is called endarch.
In roots, the protoxylem lies towards the periphery and the metaxylem lies towards the centre. Such an arrangement is called exarch.
Secondary Xylem is composed of tracheary elements, rays, fibres and interspersed axial parenchyma cells. The cells which are formed toward the inside of the cambia are called secondary xylem.
It is a food conducting complex permanent tissue. Phloem helps with the transportation of food from leaves to various plant parts
The first formed primary phloem which has narrow sieve tubes called protophloem and the latter formed phloem has bigger sieve tubes called metaphloem.
Phloem consists of four types of cellular components:
Sieve Elements: These tube elements are long, tube-like structures arranged longitudinally and are associated with the companion cells.
Companion Cells: These cells are specialised parenchymatous cells, which are associated with the sieve tube elements. Usually, a single companion cell is found associated with a sieve tube member.
Phloem Parenchyma: This phloem is made up of elongated, tapering cylindrical cells. They generally store food materials and other substances like resins, latex and mucilage. This is absent in most of the monocotyledons.
Phloem Fibres: The phloem fibres are made up of sclerenchymatous cells. The cell wall of these fibres is quite thick. They lose their protoplasm and become dead at maturity. The phloem fibres of jute, flax and hemp have important economic uses.
Epidermal Tissue System
These tissues are the outermost covering of the whole plant body, which consists of epidermal cells, stomata, epidermal appendages such as epidermis, cuticle, stomata, epidermal extensions.
- Epidermis is single layered, parenchymatous with waxy thick layers of cuticle to prevent water loss.
- Stomata is present in epidermis of leaves which regulates the transpiration and gaseous exchange.
- In dicots, stomata is bean-shaped having two guard cells closing the stomatal pore. In monocots, the stoma is dumbbell-shaped.
- Epidermis contains a number of hairs. Root hairs are unicellular and Trichomes are present on stems, which are multicellular.
The Vascular Tissue System
- This tissue system consists of complex tissues of xylem and phloem
- Xylem and phloem together form vascular bundles.
- Dicots have cambium present between xylem and phloem
- Cambium forms secondary vascular tissues
- Dicots have an open vascular bundle
- Monocots have a closed vascular bundle Roots have a radial arrangement of vascular bundles
- Stem and leaves have a conjoint arrangement of vascular bundles
- The outermost layer (Epiblema) of dicot root is epidermis containing unicellular root hairs.
- The cortex consists of several layers of thin-walled parenchyma cells that ends with innermost layer endodermis
- Endodermis is having waxy material suberin and casparian strips, which is impermeable to water.
- Monocot root is similar to the dicot root in many respects but polyarch xylem bundles are present
- These root has epidermis, cortex, endodermis, pericycle, vascular bundles and pith as compared to the dicot root which have fewer xylem bundles
- The outermost layer is the epidermis with cuticle and Trichomes and stomata
- The cortex consists of three layers; outermost hypodermis, middle layer of parenchyma cells and innermost layer called endodermis.
- Endodermis cells are rich in starch grains. Pericycle and radially located medullary rays are present on the inner side of the endodermis.
- A number of vascular bundles are arranged in a ring. Each vascular bundle is conjoint, open and with endarch protoxylem
- The hypodermis is made up of sclerenchymatous.
- All vascular bundles are conjoint, closed and scattered.
- Every vascular bundle is surrounded by a sclerenchymatous bundle sheath.
- Phloem parenchyma is absent. Water-containing cavities are present within the vascular bundles.
Dorsiventral (Dicotyledonous) Leaf
- It is known as dorsiventral leaf due to distinct dorsal and ventral side
- This leaf has three parts viz. epidermis, mesophyll and vascular system.
- The epidermis covers both the upper and lower surface
- The upper epidermis is called adaxial and lower one is called abaxial epidermis.
- More numbers of stomata are present on the abaxial epidermis.
- Mesophyll cells are palisade parenchyma and spongy parenchyma and perform photosynthesis
- The palisade parenchyma is placed coaxially.
- The spongy parenchyma is situated below the palisade parenchyma and extends to the lower epidermis.
- Large spaces and air cavities are there between the cells of spongy parenchyma.
- Vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.
Isobilateral (Monocotyledonous) Leaf
- Known as isobilateral as both sides are similar
- Stomata are equally distributed on both the surface
- The mesophyll is not differentiated into palisade and spongy parenchyma.
- Some epidermal cells in grasses are modified into large empty cells called bulliform cells, they help in minimising water loss
- Vascular bundles are of the same size