CBSE Class 11 Biology Revision Notes Chapter 6

CBSE Class 11 Biology Revision Notes Chapter 6 – Anatomy of Flowering Plants

The revision notes on Class 11 Biology Chapter 6 – Anatomy of Flowering Plants summarise all the important topics that students will come across in this chapter. Students can use these notes to effectively prepare for their exams and for last-minute revisions. These notes are easily accessible from the Extramarks’ website for students to refer to.

Access 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.

1. 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. 

1. 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. 

2. 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.

1. 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.

1. 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. 
2. 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.
3. Astero Sclereids: The cells are star-shaped. These are found in floating leaves like those of lotus and victoria. 
4. 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. 
5. 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. 

1. Libriform Fibres: The fibres are thick and long with simple pores. These are found in the phloem, xylem, hypodermis layer, and pericycle. 
2. 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. 

1. 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. 
2. 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.
3. 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:

1. The vessel is an advanced conductive element of the xylem.
2. Vessels share a similar structure to that of tracheids.
3. Vessels are xylem’s dead components.
4. Vessels are found in the xylem of angiosperms mostly. Along with that, some gymnosperms like Ephedra and Welwitschia also have vessels. 
5. Vessels carry larger lumens than the tracheids lumens.
6. Vessels can function as a pipeline to supply water.
7. Vessels have simple pits.

• Tracheids: The features of tracheids are:

1. These are the elongated cells with narrow ends, and the lumens are more prominent than those of the fibres.
2. It produces long rows while uniting at the ends. The rows run from the roots to the leaves via stems.
3. 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.
4. The lignin depositions carry a significant role in pitted thickening.
5. In tracheids, different forms of lignin can be seen.

• Xylem: The features of xylem fibre include:

1. The xylem fibres are dead.
2. The vessels and tracheids become stronger with xylem fibres.
3. Xylem fibres are more plentiful in the secondary xylem and offer vessel strength. 
4. 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.

3. 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. 
4. 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.
5. 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 are also known as sister cells. Plasmodesma joins the cytoplasm of companion cells with sieve cells. Conifers contain a unique cell type connected to the sieve cells. They are also known as albuminous cells.
6. Phloem Fibres: Libriform fibres are the phloem fibres found in the phloem. These fibres support the sieve cells. The central role of the fibre is to offer mechanical support. The fibres are used to create ropes, garments, mats, and other essential household items.
7. Phloem Parenchyma: Phloem parenchyma is also known as bast parenchyma. The cells are alive and surrounded by thin walls. The cells are capable of storing food materials. The core function of phloem parenchyma is food conduction in a radial direction and food storage. 

Special Tissue or Secretary Tissue

1. Lactiferous Tissue

The lactiferous tissues are created from long and branching cells with thin walls. Latex means the milky potion which fills the cells. It is also known as plant milk. Plants of petrocrops kind produce latex. 

Latex comprises saccharides, starch granules, alkaloid minerals, and waste components. 

You can notice Dumbbell-shaped granules in latex. Latex helps plants by protecting them from grazing animals. The latex also protects the plants from fungal and bacterial infections. Two forms of lactiferous tissues include latex cells and latex vessels.

1. Latex Cells: The latex cells are the latex tubes and ducts that are not functional. These are multinucleated cells with long branches. These cells are also called coenocytic cells—examples: euphorbia, calotropis, etc.
2. Latex Vessels: Latex vessels ate the articulated vessels. The cell walls of meristem cells dissolve and create latex vessels. Examples include the banyan tree. The fruit wall of opium is made of highly grown latex channels. 
3. Glandular TissueGlandular tissues resemble gland shapes, as the name implies. The glands store the secretory or excretory glands. These two types of glands present in the epithelial tissues produce latex tubes. As a natural consequence, these have been termed unicellular glands found on the leaf surfaces. These are spiny glands containing formic acid. There are two kinds of multicellular glands – external and internal glands.

• External Glands: External Glands are born on the plant surface or emerge from the Epidermis. The Glands are seen in various shapes and sizes. 

1. Digestive Glands: Insectivorous plants consist of digestive glands. The plants compensate for their nitrogen lacking with these glands. 
2. Oil Glands: The oil glands supply volatile oil. The glands are primarily found in Eucalyptus leaves and the exterior wall of citrus fruits.
3.  Nectar Glands: Nectar glands are tissue-embedded glands. These can be found in flower plants. The plants release the nectar to attract insects.
4. Internal Glands: Internal glands can be found within the tissues. These Glands include the following types:

• Mucous Secreting Glands

• Oil Glands

• Water Glands

• Gum and Resin Glands

Tissue System

The tissue system can be divided into three sections based on labour division. Each method comprises a combination of tissue organisations performing unique functions.

• Epidermal Tissue System: The system includes the Epidermis and the cells, hair, and pores associated with the Epidermis.

• Ground Tissue System: It is the most extensive tissue system, including the hypodermis, cortex, endodermis, and medullary rays.

• Vascular Tissue System: The system is made up of xylem and phloem.

Types of Vascular Bundles

Vascular bundles are of four types, depending on the arrangement of the various parts. 

• Conjoint Collateral Vascular Bundles: Conjoint collateral vascular bundles have the xylem and phloem positioned on the same radium. These are primarily seen in gymnosperms and angiosperms. The bundle contains a series of states. Open vascular bundles can be found in dicots and gymnosperms. The closed ones are seen in monocots. 
• Conjoint Bi-collateral Vascular Bundles: On each side of the xylem, two phloem regions are present. The vascular bundles contain two cambium belts on each side. It can only be seen when the vascular bundle is open. 
• Radial Vascular Bundles: The radial vascular bundles contain xylem and phloem with different radii. All tree roots have radial vascular bundles. The growth pattern of the xylem in these vascular bundles is centripetal. So, the vascular bundles are known as Exarch. 
• Concentric Vascular Bundles: In such a vascular bundle, either xylem surrounds the phloem or vice-versa. The concentric vascular bundles are closed and can be categorised into two classes:
• Amphicribral or Androcentric: In an androcentric vascular bundle, the xylem is surrounded by phloem. The xylem development in these vascular bundles is centrifugal. These are also known as mesangial vascular bundles. These types of vascular bundles can mostly be found in lower ferns and lower gymnosperms.
• Amphivasal or Lepto Centric: In this vascular bundle, the xylem entirely encircles the phloem, and the phloem is located at the centre. These vascular bundles are created out of angiosperms. The column is the core mass of vascular tissue, with or without the medulla, and the endoderm covers it. Based on the hypothesis, the stele is the core part of the plant, including the vascular system and the associated factors.

 Tissues which are present inside the stele are known as interstellar tissues, and the tissues present outside the stele are known as extra stellar organisation. The endoderm encircles it. The endodermis is an integral part of the cortex.

Types of Steles

• Monostele or Protostele: The stele is the most primitive type, containing solid xylem covered by phloem. The kind of stele does not consist of the pith. It can be classified into the following categories.
• Actinoatele: It is a star-shaped structure with divergent ribs. Examples include isoetes and Psilotum. 
• Haplostele: A thick layer of phloem encircles the xylem in this stele. The core xylem is cylindrical.
• Plectostele: The section where the xylem is divided into separated plates parallel to each other. Example: Lycopodium species. 
• Siphonostele: It is a stele with a pith at the centre of an empty vessel. There are two kinds of siphonostele.
• Ectophloic Siphonostele: The phloem stele is present outside the xylem in the ectophloic siphonostele.
• Amphiphloic Siphonostele: In such a type of vascular bundle, the xylem is encircled by phloem on both sides.
• Solenostele: Solenostele is a stele which creates the leaf spaces in the vascular tissues. The areas are formed due to the damage in the lead’s central vascular tissue, and these stele fragments are known as solenosteles. 
• Eustele: In such a type of stele, the vascular bundles can be noticed arranged in a circle with medullary rays in the spaces between the circles. These are found in dicots and gymnosperms. 
• Dictyostele: It is called dictyostele when the central vascular column of the solenostele is fragmented into many segments. It is mainly found in ferns. 
• Atactostele: It is the most grown stele. This is the main feature of monocots. 

Anatomy of a Dicot Stem

The fundamental structure of the stem of a dicot plant possesses the following characteristics.

• Epidermis: It is the outermost layer of the stem. It contains multicellular stem hair and stomata. It protects the stem. 
• Hypodermis: It is the layer placed under the Epidermis. The thick coating is made up of various cells and collenchyma, which contain chloroplasts. It is photosynthetic.
• Cortex: Cortex has parenchyma. The main functions include food storage. It is also known as endodermis.
• Endodermis: The cell shapes resemble a barrel. The cells store starch in the stem of dicotyledonous plants, which is why it has also been termed “starch sheath”.
• Pericycle: The layer between the endoderm and the vascular bundle can be seen. It is also known as hard bast. The cells are made up of sclerenchyma tissue and parenchyma. 
• Vascular Bundles: The bundles create a ring pattern. It is a well-grown pitch that is open conjoint collateral endarch. 

Anatomy of a Monocot Stem

A monocot strain comprises the following features:

• Epidermis: It is the outermost layer with stomata, but it does not have multicellular hair. 
• Hypodermis: It contains two to three layers of sclerenchyma tissue.
• Ground Tissue: Ground tissue refers to the entire parenchymal cells that reach the centre. The cortex, endoderm, and perimeter are the same in ground tissue.
• Vascular Bundles: These are presented in scattered forms in ground tissues. The bundles connecting the centre are more extensive and less in number. 

• Pith and Stele: Monocots contain Atactostele, which is a well-grown stele.

Anatomy of Dicot Root

• Epidermis: The latter has unicellular root hair. It is also known as Rhizodermis or the Piliferous layer.
• Cortex: The section is created of parenchymal cells. The cells outside the cortex are suberized.
• Endodermis: It is a layer located between vascular tissue and cortex. In the innermost layers of the endoderm, Casparian strips are located. 
• Pericycle: It is a single, thick layer composed of parenchyma. Lateral roots are born out of the pericycle. The stems are endogenous as the branches come from the outside, unlike the roots.
• Vascular Bundles: The bundles are radial and Exarch, created with xylem and phloem. The number of bundles ranges from two to six. The cambium is made of conjugative tissue during the secondary growth process. Consequently, the cambium layers are created on the roots after the secondary growth is over.
• Pith: It is located in the centre. It is flexible due to underdeveloped and non-existent features. 

Root and Leaf Anatomy of Monocots

The inner structure of the monocot is similar to that of dicots. Only the numbers of vascular bundles in monocots are more than in dicots. Pith is well-developed in the monocot roots. The exception includes onion, where the vascular bundle number is less.

Types and Internal Structure of the Leaf

The leaves can be divided into Dorsal Ventral Leaves and Isobilateral leaves. 

Let us have a look at the differences between the two:

1. The dorsal leaves are connected at the right angles of the stem, and the isobilateral leaves are located parallel to the branch.
2. The dorsal leaves can be seen in dicots. Exceptionally, Eucalyptus has isobilateral leaves.
3. The dorsal-ventral leaves possess different structures on both sides, but the isobilateral leaf structures are similar on both sides.
4. Monocotyledonous plants contain isobilateral leaves.

Secondary Growth 

The growth in the diameter of plant organs is known as secondary growth. The permanent internal organ structure is created by apical meristem. The structure starts forming in the initial weeks of the year. The structure is known as the primary structure. It is only found in monocots and ferns.

Average secondary growth is noticeable on the stems and roots of dicots and gymnosperms. There is no secondary growth because the vascular cambium in monocots is absent. But some monocots might have secondary growth like palm, agave, coconut, yucca, etc.

Secondary Growth in Dicot Stem

• Secondary Growth in Vascular Region: The secondary growth in the vascular area begins earlier than in the cortical region. The process proceeds through the following steps:
• Formation of the vascular ring cambium
• The activities of vascular cambium
• Formation of annual rings
• Secondary Growth in the Cortical Region: As the secondary vascular tissue is added, the circular diameter of the xylem widens, and the cortical region feels the pressure and is stretched to the point that it breaks. The protective tissues of the Epidermis try to rejuvenate to compensate for the loss. The cambium plug can only fill the loss. Cork cambium originated from the hypodermis or the outer layer of the cortex that becomes the meristem. 

Bark

Bark refers to the tissues outside the vascular cambium. Barks are divided into two sections:

• Outer Bark: The tissues present outside the cork cambium are known as outer bark. These barks are dead. 

• Inner Bark: The space between the vascular cambium and cork cambium is known as the inner bark. It is a living zone. 

Therefore, the bark contains both living and non-living tissue. It is essential for a plant’s survival. The absence of living tissues leads the tree to a maximum loss of water and food shortage. 

Types of Bark

• Ring Bark: Ring bark resembles the shape of a complete ring around the stem. After an entire cambium ring gets formed, it is called ring bark. In previous days, people used ring barks as writing materials. Ring barks can be seen in trees like eucalyptus.
• Scaly Bark: Scale bark forms around a tree in fragments. Scaly barks can only be noticed when there is no ring of cork cambium.

Secondary Growth in Dicot Root

Secondary growth is essential for plant roots as it ensures strength in aerial parts and fulfils the water and mineral requirements. Secondary growth cannot be seen in the roots of the monocot plants. At this phase, the conjunctive tissue becomes the meristem in the roots of dicotyledonous plants, creating a vascular cambium filament which offers a carved shape. The ring shape of the vascular cambium is wavy at the initial level, and then the pressure of the secondary xylem makes it round. The action of the root’s vascular cambium and the stem’s vascular cambium is the same. The vascular cambium externally creates the secondary xylem and phloem. The section has been intricately explained in the Notes of Class 11 Biology Chapter 6.

Functions of the Secondary Meristem (Cambium)

The functions of the secondary meristem include:

• Wound healing: When a stem is damaged, the living cells of the wound create a cambium layer. The newly formed cambium produces an outward cork which covers the damaged section. Thus, the wound heals quickly. 
• Abscission: The plant leaves fall off after vegetative destruction. The woody dicot leaves and gymnosperms fall off before death due to abscission. The occurrence of leaves separating from the plant is known as abscission. 

Anomalous Secondary Growth in Stem

The ways the anomalous secondary growth happens in a plant:

1. Anomalous/Abnormal Position of Vascular Cambium.
2. Abnormal Activity of Vascular Cambium.
3. Sequence of Successive Ring of Vascular Cambium.
4. External Stelar Vascular Cambium.
5. Interxylary Cork.
6. Cork cambium from Epidermis.

Secondary Growth in Monocotyledons 

The vascular is created from the outer spaces of the ground tissue in the plants like yucca, dracaena, agave, aloe, etc. Parenchyma is formed on the outer side of the vascular cambium. Still, the vascular bundles originate inside the vascular cambium—the stem circumference increases without cambium in some plants like palms, Musa, and tulips. The apical meristem in these plants is of a particular kind, and they are called primary thickening meristem. They are the reasons behind the plants’ growth in both length and girth. 

CBSE Class 11 Biology Revision Notes Chapter 6 – Anatomy of Flowering Plants 

Class 11 Biology Chapter 6 notes cover many vital concepts. This revision notes of this chapter discuss meristem tissues, primary meristem, secondary meristems, apical meristem, intercalary meristem, and permanent tissues. In addition, the ideas of parenchyma, collenchyma, sclerenchyma, and fibres, sclereids, sclerenchymatous fibre, xylem, tracheids, vessels or tracheids xylem fibres and vessels are presented in detail in the revision notes.

What to Expect in Notes of Chapter 6 Biology Class 11?

Chapter 6 Biology Class 11 notes cover the crucial concepts of the Anatomy of Flowering Plants. The CBSE revision notes help students in their learning process by explaining the most critical topics in an easy-to-understand language. Elaborate explanations and well-explained diagrams of each topic have been provided in the revision notes.