Great assignment for biology chapter "anatomy of flowering plants" for neet

Class 11 Biology Chapter 6 – Anatomy of Flowering Plants Notes

Anatomy of Flowering Plants

The following section discusses the anatomical bifurcation of plants.

The Tissues

A tissue is a cluster of cells that belong to a common origin and share similar functionalities. Various tissues make a plant body. A plant carries two types of tissues: meristem and permanent. This classification is based on the cells’ ability to divide. Meristem tissue cells can divide, but permanent tissue cells cannot.

Given below is a detailed discussion on both the meristematic and permanent tissues.

Meristematic Tissue

Meristems of different shapes and sizes contribute to plant growth. These are specific regions of fast cell division. These tissues have been classified into two categories based on their origins: primary meristem and secondary meristem.

Primary Meristem

Primary meristems make primary plant bodies and remain present in the life of the plants on an earlier note. Primary meristems are of two types: Apical and Intercalary Meristems.

Apical Meristem: An apical meristem is a kind of meristem seen at the tips of roots and shoots. These meristems are the significant reasons behind the production of primary tissues. When leaves find their forms and stems get elongated, some cells in the shoot meristem at the top of the branch create axillary buds. The branches can be noticed in the leaf axils. They can develop further branches and flowers. 

Apical meristem has two forms: root apical meristem and shoots apical meristem. Root apical meristem is found at the root tips, and shoot meristem can be seen at the shoot tips. 

Intercalary Meristem: Intercalary meristems are the meristems that are located between mature tissues. These can be found in grasslands. One of the core functions of the intercalary meristem is to replenish the portions eaten or damaged by the herbivorous animals. 

Secondary Meristem

Secondary or lateral meristems are found in the plants’ evolved sections of roots and shoots. In most cases, the meristems widen the stem’s circumference and produce a woody axis. The branches appear only after the primary meristem has come out. Secondary meristems are made of fascicular vascular cambium, cork cambium, and inter fascicular cambium. The secondary tissues are made of secondary meristems. 

Permanent Tissue

Permanent tissues are cells separated from meristems and have particular structures and functionalities. These tissues cannot divide further. Simple tissues that are created out of similarly formed and functioned cells are known as permanent tissues. A permanent tissue formed of various kinds of cells is called complex tissue.

Simple Permanent Tissue: Simple permanent tissues are of three types: parenchyma, collenchyma, and sclerenchyma. 

Parenchyma: The most typical type of simple tissue is parenchyma tissue. The tissue is made up of isodiametric cells. The cells can be seen with various shapes depending on their functions. 

The tissues comprise cellulose-formed thin walls with limited intercellular spaces. The cells play a vital role in photosynthesis, storage, and secretion. 

Collenchyma: The collenchyma is found in the hypodermis layer under the Epidermis in the dicotyledonous plants. The tissue comprises substantially thicker cells at the corners because of pectin, cellulose, and hemicellulose. The cells come in various shapes and sizes. Most of them contain chloroplast. There are no intercellular spaces in collenchyma as food is stored in the cells with chloroplasts. 

The collenchyma tissue provides mechanical support for plant growth. They attribute the feature of bending without breaking. These tissues can be found in the younger sections of a tree, like a stem and the petiole of a leaf. Collenchyma has been divided into three categories. 

Lamellar Collenchyma: The lamellar collenchyma cells follow the lamellar patterns. The cell walls are thicker. Due to this kind of disposition, the cell resembles the shape of a lamellar or plate. 

Angular Collenchyma: This collenchyma produces immense quantities. The tissue cells resemble the shapes of angles with pectin disposition at the cell corners.

Lacunar Collenchyma: The cells contain larger intercellular spaces, with pectin dispositions on the intracellular space walls. The margins get thickened with time.

Sclerenchyma: Sclerenchyma is the most functional mechanical tissue. The lifeless cells are thin and long with thicker walls. The disposition of lignin on the harder wall creates some visible pits. There are two types of sclerenchyma tissues – Sclereids and Sclerenchymatous fibres. 

Sclereids: The cells carry a small, thick-walled interior and pointed ends. Sclereids are uneven, and their cells have a narrow lumen and many pits. The pit cavity is branching. Torch categorised the cells based on their shapes.

Stone or Grit Cells or Brachysclereids: The cell formation is spherical or oval. The cells are present in the endocarp of drupe fruits which causes the endocarp to harden. These can also be found in the endocarp of coconuts, mangoes, almonds, walnuts, and other fruits and nuts. These cells are seen in the fleshy section of the pear. It gives the pear a gritty texture. 

Macro-Sclereids or Malpighi Cells or Rod Cells: These are tiny, rod-shaped cells. The cells can be seen in seed coats of legume plants. The presence of this cell hardens the seed. The cells enable the leguminous seeds to stay dormant.

Astero Sclereids: The cells are star-shaped. These are found in floating leaves like those of lotus and victoria. 

Osteria-Sclereids: These cells are also known as prop cells. The cells resemble the structure of pillars. The endpoint of these cells extends to create a bony structure. The cells are found in the leaves of Hakea and Osmanthus. 

Trichoselereids: These cells have been commonly termed internal hairs. The spine-like, divided cells can also be seen in floating leaves. 

Sclerenchymatous Fibres: The fibres are classified into two categories depending on their structure. 

Libriform Fibres: The fibres are thick and long with simple pores. These are found in the phloem, xylem, hypodermis layer, and pericycle. 

Fibre Tracheids: In comparison to the other fibres, these are thicker. The fibres have edge holes which are found in the xylem.

Sclerenchymatous Fibres have been classified into a few types depending on the positions: surface fibres, wood fibres, and bast fibres. 

Surface fibres: The surface fibres are also known as filling fibres. These can be found on the plant body surfaces. The cotton fibres are not lignified. Therefore, these are not considered to be genuine fibres. Cotton comprises two types of fibres – long strands and small strands. Fuzz is the term used to denote tiny threads. It is a filling fibre. 

Wood fibres: Wood fibres are stiff fibres. The hardness comes due to the lack of flexibility. The fibres cannot be crocheted in a way to make them useful. They are primarily found in the xylem.

Bast fibres: Bast fibres are also known as commercial fibres. These fibres are flexible and can be knitted easily. Phylum produces the best fibres from jute and sun hemp. It has high economic value.

Complex Permanent Tissue: A complex tissue is created out of various cell types. This is why tough tissue is a collection of diverse cells. There is no complex tissue in gametophytes. Two kinds of complex tissues are common: xylem and phloem. 

Xylem: Nageli coined the term xylem. Xylem not only supplies water and nutrients to the plants but also acts as mechanical support for the plant. Xylem can be segregated into two types based on the development – primary and secondary. Primary xylem originates from procambium. There is no medullary ray in the primary xylem, and the secondary xylem grows as a consequence of secondary growth. Vessels, xylem, and tracheids are the core constituents of the xylem. 

Vessels: The features of vessels are:

The vessel is an advanced conductive element of the xylem.

Vessels share a similar structure to that of tracheids.

Vessels are xylem’s dead components.

Vessels are found in the xylem of angiosperms mostly. Along with that, some gymnosperms like Ephedra and Welwitschia also have vessels. 

Vessels carry larger lumens than the tracheids lumens.

Vessels can function as a pipeline to supply water.

Vessels have simple pits.

Tracheids: The features of tracheids are:

These are the elongated cells with narrow ends, and the lumens are more prominent than those of the fibres.

It produces long rows while uniting at the ends. The rows run from the roots to the leaves via stems.

Tracheids are lignified and dead cells. The cell walls are thicker due to the deposition of lignin. The pits on the walls of the tracheids are mostly bordered. The tracheids of Gymnosperm plants contain the most bordered pits.

The lignin depositions carry a significant role in pitted thickening.

In tracheids, different forms of lignin can be seen.

Xylem: The features of xylem fibre include:

The xylem fibres are dead.

The vessels and tracheids become stronger with xylem fibres.

Xylem fibres are more plentiful in the secondary xylem and offer vessel strength. 

The xylem parenchyma is the reason behind water radial conduction. 

Water Conduction Elements of Xylem

Tracheids and vessels together are called water-conducting elements or Hadrome. Xylem comprises three types of water-conducting elements.

Centrifugal: Protoxylem creates along the centre axis, but metaxylem forms away from the centre in this kind of growth. This condition is known as Endarch, for example, angiosperm and gymnosperm stem.

Centripetal: Protoxylem is created away from the centre and near the pericycle, whereas; the metaxylem develops towards the centre, resembling a centripetal structure. Exarch is the word used to denote this element. Example: roots.

Centrifugal and centripetal: In such conditions, elements originate from both sides of protoxylem components. As a consequence, the metaxylem encircles the protoxylem. Mesarch is the scientific term used to describe this condition. Example: fern stem.

Phloem: Nageli coined the term phloem. One of the core jobs of phloem is to supply organic material from one location to another. Phloem is divided into two kinds based on the development process: primary and secondary phloem. Primary phloem originates from procambium, while secondary phloem comes from vascular cambium. The phloem is more active during a shorter period than the xylem. It is made of four various types of cells. The cells are sieve cells, companion cells, phloem fibres, and phloem parenchyma. 

Sieve Cells: The sieve cells are alive and made up of thin-walled cells. A full-grown sieve cell does not have a nucleus. Therefore, these cells are active without nuclei. Every sieve cell comprises a central vacuole. The cytoplasm of the sieve cells flows around it in a thin layer. The cells are angiosperms which are organised end-to-end to create a tube form. A sieve plate exists between two sieve cells, and the scale is permeable. Only the pores on the cells allow passage. Callose creates a thicker layer on the pores during the fall season. For this reason, it is referred to as a callus pad. It disappears during spring. Sieve cells in gymnosperms and pteridophytes do not create sieve plates; they are arranged in an uneven pattern. The walls contain sieve plates. The cells have a unique protein base which is called P-protein. It contributes to the food function and cures the damaged sieve cells.

Companion Cells: The companion cells can be seen in Angiosperms. A live cell with a large nucleus is known as a companion cell. The core controls the sieve cell functions. The sieve cells and the companion cells are formed during the same time. These ar