1.7.1 What is inside a plant. (2).pdf

CHAPTER 7- WHAT IS INSIDE A PLANT? 1.7.1. Scope: In plants, cells are arranged to form tissues that are integrated to form different organs. The apical part of the plant contains meristematic tissue that divides indefinitely forming new tissues. The meristematic tissues give rise to permanent tissue...

CHAPTER 7- WHAT IS INSIDE A PLANT? 1.7.1. Scope: In plants, cells are arranged to form tissues that are integrated to form different organs. The apical part of the plant contains meristematic tissue that divides indefinitely forming new tissues. The meristematic tissues give rise to permanent tissues that form different parts of the plant and are specialised to take up different functions. 1.7.2. Scope: Plant tissues are organised to form epidermal, ground, and vascular tissue systems. These tissue systems are adapted to take up different functions in the roots, stems, and leaves. Plants exhibit both physiological and morphological adaptations to survive in various types of environments. PLANT TISSUES Plant tissues are of two types on the basis of their dividing capacity: - 1. Meristematic tissue (growing tissue) 2. Permanent tissue MERISTEMATIC TISSUE  These are living tissues which are composed of immature cells that are capable of division throughout life.  These tissues are found in growing regions of plants.  Cells have thin cell wall, dense cytoplasm and do not have vacuoles.  Cells contain prominent and large nucleus.  Cells are metabolically highly active, so store food is absent.  Cells are compactly arranged because they do not have intercellular spaces. Function: - Meristematic tissue is responsible for the growth in length and width(girth) of plant body. Classification of meristematic tissue A) Based on Origin and development (A) Promeristem: 1.7 What is inside a plant?/12/sc/2024 1   The meristem where foundation of new organs or of their part is laid down is called promeristem. [during embryonic development]  They occupy very small area at the tips of stem and root.  It differentiates into primary meristem. (b) Primary meristematic tissue  It originates from promeristem.  Remains meristematic from the embryonic condition throughout entire plant life at the growing apices of roots, stems, primordial of leaves.  Both apical meristems and intercalary meristems are primary meristems because they appear early in life of a plant and contribute to the formation of the primary plant body. (c) Secondary meristematic tissue  It develops from primary permanent tissue.  Fascicular vascular cambium, interfascicular cambium and cork-cambium.  Responsible for producing the secondary tissues. B) Based on location in plant body 1. Apical meristem  Position: At the root tip and shoot tip.  Function: To increase in length of the axis. 2. Lateral meristem  Position: On the lateral side of stem and root.  Function: To increase in diameter of plant. 3. Intercalary meristem  Position: At the base of the leaf/internodes/ leaf.  Function: To increase the length of the plant or its organs. 2. Permanent tissue -They are formed by division and differentiation of meristematic tissue. They are composed of those cells which have lost the power of division (temporarily or permanent) and attain a permanent shape, size and function. Cells may be living or dead. Cells may be oval, rounded, polygonal or elongated. Permanent tissues are of two types: - (a) Simple permanent tissue (b) Compound or complex permanent tissue 1.7 What is inside a plant?/12/sc/2024 2 (a) Simple permanent tissue: - These tissues are made up of similar types of cells, that perform a common function. They are protective and supportive in nature. Simple tissues are of three types: (i) Parenchyma (ii) Collenchyma (iii) Sclerenchyma (i) Parenchyma: - *It is a living and basic packing tissue which consists of relatively unspecialized cells. *Cells of these tissues have thin cell wall which is made up of cellulose. *Cells of these tissues have dense cytoplasm with small nucleus and large vacuole. *They are usually loosely packed because intercellular spaces are present between cells. Functions: -Storage of food and provide support to the plant. Parenchyma is the first evolved permanent tissue which is present in all soft parts of plant (therefore called as universal tissue). Parenchyma provides turgidity to cells. Modifications of parenchyma : 1. Epidermal parenchyma-some parenchymal cells are compactly arranged to form the epidermis. In some plants, the epidermis is covered by cuticle or bears unicellular hairs/multicellular hairs[trichomes] and minute pores called stomata. 2. Chlorenchyma :- Such type of parenchyma in which abundant quantity of chloroplasts are found. They are present in mesophyll of leaves. In dorsiventral leaf of dicot plant, two types of parenchyma tissues are present. (i) spongy tissue (ii) palisade tissue 3. Aerenchyma :- Parenchyma is made up of rounded cells which surrounds the large air cavities. It is found in aquatic plants or hydrophytes.e.g. petiole of water hyacinth. It provides buoyancy to the aquatic plants to help them float. 4. Prosenchyma :- Parenchymatous cells become long and taper at both the ends.e.g. It is found in pericycle of root. It provides mechanical support. 5. Storage parenchyma- for storing water and food, eg storage of water in xerophytes or storage of starch grains [xylem and phloem parenchyma] 6. Parenchyma cells which store resins, tannins, gum and oils are also so called idioblast. 7. Succulent parenchyma-found in some xerophytes, responsible for storing water. 1.7 What is inside a plant?/12/sc/2024 3 ii. Collenchyma (Flexible tissue) Cells of this tissue are living, elongated or vary in structure. Cells of this tissue are irregularly thickened at the corners due to the deposition of pectin. It is present below the epidermis of leaf and herbaceous stem in the form of hypodermis. Intercellular spaces are very little or absent between cells of this tissue. Collenchyma are usually absent in monocots and in roots. Cells of collenchyma contain few chloroplasts. Functions: - 1. It provides mechanical support (tensile strength) and elasticity. 2. It protects the cracking of lamina margin due to action of wind. 3. It provides flexibility to plant. 4. It allows easy bending in various parts of plant (leaf and stem) without breaking. (iii) Sclerenchyma: - 1. Sclerencyma cells are dead cells and they are devoid of protoplasm. 2. The walls of cells of sclerenchyma are greatly thickened with deposition of lignin. Such cell walls are called lignified. [Lignin is a complex polymer which acts as a cement and hardens cell wall. Lignin makes the cell wall impermeable so important substances are unable to pass through it. As a result, cells that are heavily lignified do not have living content (protoplasm)] 3. Due to excessive thickening of the wall of a sclerenchymatous cell, its cavity or lumen becomes nearly absent. The cells of sclerenchyma are closely packed without intercellular spaces. 4. They are found in stems (around the vascular bundle), roots, veins of leaves, hard coverings of seed and nuts. Function: - It is the main mechanical tissue which provides mechanical support. Sclerenchymatous cells are of two types in structure: 1. Fibres 2. Sclereids 1.7 What is inside a plant?/12/sc/2024 4 1. Sclerenchyma fibres:- They are highly elongated, narrow and spindle shaped with pointed or oblique end walls. The fibres are closely packed without intercellular spaces. The walls of fibres are often so thick that the cell cavity or lumen is nearly absent. Often oblique thin areas are found in their walls. These are called pits. Sclerenchyma fibres constitute the major mechanical tissue of the plants and are abundantly found in plants. Commercial fibres obtained from plants (e.g. Jute, Flax, Hemp, Husk of coconut etc.) usually are sclerenchymatous fibers. 2. Sclereids (grit or stone cells): - They are highly thickened and irregularly shaped dead cells. They are found in various parts of the plant such as cortex, pith, phloem, hard seeds etc. The grit of pulp of some fruits (such as guava, apple, pear etc.) is due to the presence of sclereids in it. The main function of sclerenchyma is to provide mechanical support to the plants. Sclereids provide strength to seed covering and grittiness to the pulp of many fruits. (B) Compound or complex permanent tissue: The complex tissues consist of more than one type of cells. All these cell co-ordinate to perform a common function. Complex tissues transport water, mineral salts (nutrients) and food material to various parts of plant body. Complex tissues are of the following two types: (i) Xylem or wood (ii) Phloem or bast (i) Xylem: - Wood/Xylem is made up of four types of cells - 1. Tracheids 2. Tracheae or vessels 3. Xylem fibres 4. Xylem parenchyma 1.7 What is inside a plant?/12/sc/2024 5 1. Tracheids: Tracheids are dead elongated cells with tapering ends. Their walls are thick, lignified provided with pits. They also conduct water. Since tracheids do not have open ends like the vessels, so the water has to pass from cell to cell via the pits. Tracheids have secondary thickenings in their walls and are of the following types-  annular-thickenings deposited in the form of rings at regular interval.  spiral- thickenings deposited in the form of spiral in the inner side.  reticulate- thickenings deposited in the form of spirals which remains crisscross or in the form of reticulum.  scalariform- thickenings deposited in the form of transverse bands.  pitted-has uniform thickenings in the inner surface along with some unthickened areas.  Such unthickened areas are pits, which are of two types-i. Simple pits: has uniform width. ii. bordered pit: has broader base and narrow lumen or cell cavity. The cell wall between two bordered pit forms a swelling known as torus. It regulates the movement of substances. 2. Vessels or tracheae: Very long tube-like structures formed by a row of cells placed end to end.  The transverse walls between the vessels are completely dissolved to form continuous channels or water-pipes.  They also have thickenings like that of the tracheids.  vessels are absent in pteridophytes and gymnosperms.  Tracheids and vessels help in long distance conduction of water and minerals upward from the root system to various parts of plant.  Tracheids and vessels provides mechanical support. 3. Xylem fibre /wood fibre: These are dead and lignified sclerenchymatous cells which are mainly supportive in function. 4. Xylem parenchyma/wood parenchyma: It is formed of living parenchymatous cells which helps in storage of food and lateral conduction of water and minerals. Based on the type of growth-xylem is of two types-  Primary xylem-is associated with the primary growth and develops from the procambium.  Primary xylem is of two types-protoxylem [early formed xylem with narrow vessels] and metaxylem [late formed xylem with large vessels]  Secondary xylem-related with secondary growth and develops from the vascular cambium. Depending on the arrangement of protoxylem and metaxylem, xylem is of the following types  Endarch is the arrangement in which the proto xylem is directed towards the centre and meta xylem elements towards the periphery....  Exarch : Whereas exarch is the arrangement in which the proto xylem is directed towards the periphery and meta xylem towards the centre.  Mesarch : in this condition, metaxylem remains in the centre surrounded by the protoxylem. 1.7 What is inside a plant?/12/sc/2024 6  (ii) Phloem: It is also made up of four types of cells 1. Sieve tubes: Sieve tubes are slender, tube-like structures composed of elongated thin-walled cells, placed end to end. Their end walls are perforated by numerous pores and are called sieve plates. Walls of sieve tubes are perforated. The nucleus of each sieve cell degenerates at maturity, however, cytoplasm persists in the mature cell. Thus, nuclei are absent in mature sieve tube elements. The cytoplasm of one sieve tube element is continuous with those of the sieve elements above and below by cytoplasmic connections passing through the pores of the sieve plate. Although sieve tube elements do not have nuclei, but they still remain living. It is so because they are dependent on adjacent companion cells which develop from the same original meristematic cell. The two cells together for a functional unit. Leptome: Main part of phloem involved in conduction of food, which is sieve tube. Companion cells are present only in phloem of angiospermic plants. 2. Companion cells: These are associated with sieve tubes. These are smaller cells having dense cytoplasm and prominent nucleus. The companion cells help the sieve tubes in the conduction of food material. Sieve cells & companion cells are so called sister cell because they originate from single mother cell. 3. Phloem parenchyma: These are living and thin walled cells. It is also known as bast parenchyma. It helps in conduction of food in radial direction. It stores various materials e.g. Resin, Latex, Mucilage. 4. Phloem fibers: These are dead and sclerenchymatous cells. Phloem or bast fibers of some plants are source of commercial fibers e.g. Jute, Hemp, Flex. They provide mechanical support to the conducting elements. Function of phloem: Phloem transport photosynthetically prepared food materials from the leaves to the storage organs and latter from storage organs to the growing regions of the plant body. Primary and secondary phloem.  The primary phloem is comprised of the protophloem and the metaphloem.  Both the protophloem and the metaphloem arise from the procambium. However, the protophloem is the first to develop.  The metaphloem may be differentiated from the protophloem in terms of cellular components and morphology.  For instance, the sieve elements of the metaxylem are relatively longer, conspicuous, and with a wider lumen. 1.7 What is inside a plant?/12/sc/2024 7  The companion cells are always present in metaphloem as opposed to those in protophloem that are often absent. Phases of Plant Growth 1. Meristematic Phase The cells in the root and shoot apex of a plant are constantly dividing. They represent the meristematic phase of growth. The cells in these regions have large nuclei and are rich in protoplasm and their cell walls are thin and contain cellulose. 2. Elongation Phase The cells in the zone just after the meristematic region represent the phase of elongation. The characteristics of cells in this zone are cell enlargement, increased vacuole formation and new cell wall deposition. 3. Maturation Phase Just close to the phase of elongation, but away from the apex lies the phase of maturation. The cells in this region reach their maximum size with respect to their protoplasm and cell wall thickening. 1.7.2- Tissue systems in plants. 1.7.2. Scope: Plant tissues are organized to form epidermal, ground, and vascular tissue systems. These tissue systems are adapted to take up different functions in the roots, stems, and leaves. Plants exhibit both physiological and morphological adaptations to survive in various types of environments. All the tissues of a plant which perform the same general function, regardless of position or continuity in the body, constitute the tissue system. Some of the most important types of plant tissue system and their function are as follows: 1. Epidermal Tissue System 2. Ground Tissues System 3. Vascular Tissue System. 1.7 What is inside a plant?/12/sc/2024 8 1. Epidermal Tissue System:  This tissue system consists of the outermost skin or epidermis of the plant organs.  Epidermis is generally uniseriate or single- layered and protective in function. Many-layered epidermis, called multiple epidermis, is present in the leaves of banyan and roots of orchids.  Epidermal cells are of modified parenchymatous type. In surface view, they look irregular in shape.  They are compactly arranged without leaving intercellular spaces. The cells are living with peripheral cytoplasm, round central vacuole, nucleus and minute leucoplasts.  Chloroplasts are present only in the epidermal cells of aquatic and shade plants and guard cells of the stomata. Epidermal modifications i. Stomatal Guard Cells Stomatal guard cells are part of the epidermal tissue that serves several functions in plants. Guard cells also contain chloroplasts that allow for photosynthesis. ii. Trichomes Are (epidermal hairs) are tiny hairs located on the epidermal tissue. Like stomatal guard cells, trichomes are also more specialized and thus have well-defined shapes that contribute to their functions. iii. Cuticle- In plants leaves, epidermal cells are located on the upper and lower part of the leaf where they form the upper and lower epidermis. The cuticle, however, is located on the upper epidermis for the most part. In plants, this is the outermost part that is secreted by the epidermis. iv. Bulliform cells or motor cells are large, bubble-shaped epidermal cells that occur in groups on the upper surface of the leaves of many monocots that make the leaves curl during water stress. When water is abundant, it bulges and shrink when less water is present, curling the leaf which helps to reduce water loss due to evaporation. v. Aerial roots -Some aerial roots have multiple-layered epidermis called velamen, which consists of nonliving compact cells with lignified strips of secondary walls. These cells provide support, prevent water loss, and assist the plant in absorbing water. Example orchids. 1.7 What is inside a plant?/12/sc/2024 9  Bulliform cells 2. Ground Tissue System:  The system is formed from ground meristem that forms the interior of plant organs with the exclusion of epidermal and vascular systems. It is divided into following parts: i. Hypodermis: It is situated below the epidermis. It is multilayered and made up of parenchymatous and sclerenchymatous cells. ii. General Cortex: This consists of parenchymatous cells with or without chloroplasts. iii. Endodermis: Endodermis is single layered made up of parenchymatous cells. The radial and internal walls of endodermal cell are thickened; a band of lignin or suberin knows as casparian strip is sometimes found on the radial and transverse wall of every cell. iv. Pericycle: It is single or multilayered and is situated in between endodermis and vascular bundles. It is made up of sclerenchymatous and parenchymatous cells. v. Pith: The central portion in stems and roots is called pith or medulla. It is made up of parenchymatous cells with intercellular spaces. In dicot stem the pith is large and well developed; in dicot roots the pith is either absent or small; in monocot roots large pith is present; in monocot stem the vascular bundles are scattered and the ground tissue is not marked into different parts. 3. Vascular Tissue System:  It consists of the vascular bundles or conducting strands present in the different plant organs. 1.7 What is inside a plant?/12/sc/2024 10  This tissue system is continuous in roots, stems and leaves. A vascular bundle is composed of two complex tissues—xylem and phloem, also called hadrome and leptome respectively.  In stems of dicotyledons and gymnosperms a strip of lateral meristem, called cambium, is present between xylem and phloem, and this is responsible for growth in thickness of the stems. According to the position of xylem and phloem, the vascular bundles are of the following types: i. Radial:  Here xylem and phloem occur as separate patches and remain arranged on alternate radii. Radial vascular bundles found only in roots. ii. Conjoint- In this type xylem and phloem together form a bundle and thus lie on the same radius. Conjoint bundles are of the following three types:  Collateral: Xylem and phloem lie on the same radius, xylem towards the centre and phloem towards the periphery. When cambium is present in collateral bundles, such bundle is called open, e.g. in dicot stems and collateral bundle without cambium is called closed, e.g. in monocot stems.  Bi-collateral: It is a collateral bundle where xylem is in the centre, two strips of cambium, outer and inner, and two patches of phloem, outer and inner, occur on the two sides of xylem. Thus, the sequence is outer phloem, outer cambium, xylem, inner cambium and inner phloem. This type of bundle is present in Cucurbita family.  Concentric: Here, one type of tissue surrounds the other. If xylem is in the centre surrounded by phloem, the bundle is called hadrocentric or amphicribral, as in fern; and when phloem is surrounded by xylem, the bundle is leptocentric or amphivasal. 1.7.3- PLANT ANATOMY-SYSTEM IN PLANTS Investigate to illustrate the variation amongst monocot and dicot plants in terms of their anatomies giving scientific evidence. 1.7 What is inside a plant?/12/sc/2024 11  SHOOT SYSTEM- The aerial part of the plant which develops from the plumule is called stem. ANATOMY OF DICOT STEM Part of Dicot Structure/Function Stem Epidermis Outermost single layer of parenchymatous cells, presence of stomata and trichomes, thickened and cutinized. Provides protection against physical damage and pathogens; helps minimize water loss through cuticle. Cuticle Waxy layer on the epidermis that reduces water loss and protects against pathogens. Hypodermis: Lies below the epidermis and is composed of 4 or 5 layers of collenchymatous cells, thickened at the corners against the intercellular spaces due to deposition of cellulose and pectin. It provides mechanical strength and elasticity to the peripheral portion of the stem particularly the young and growing organs. Cortex It lies below the hypodermis. It consists of a few layers of thin-walled, large, rounded, or oval, living parenchymatous cells, having intercellular spaces Provides mechanical support and storage of carbohydrates and other nutrients. Endodermis It is the single innermost layer of the cortex which separates the cortex from vascular bundles. Cells are somewhat barrel shaped and compactly arranged, having no intercellular spaces and are parenchymatous. Usually, the cells contain starch grains and thus the endodermis maybe termed as starch sheath. They serve as food reserve. The radial and the transverse walls are thickened due to the deposition of lignin forming casparian strips. Regulates the movement of water and nutrients into the vascular tissue; contains the Casparian strip to control ion uptake. Pericycle It lies in between the endodermis and vascular bundles. It is generally composed of sclerenchymatous and parenchymatous cells Gives rise to lateral roots and provides structural support to the vascular tissue. Vascular These are arranged in a ring around the central pith and inner to the pericycle. Bundles These are conjoint, collateral, open and wedge-shaped. The size of the bundles varies in different species. Contains xylem (for water and mineral transport) and phloem (for nutrient transport); provides structural support to the stem. Xylem It lies towards the pith of vascular bundles. It consists of tracheids, vessels, xylem parenchyma, xylem fibers. Tracheids and vessels consists of smaller protoxylem and larger metaxylem. Endarch xylem Transports water and minerals absorbed by roots from soil to the rest of the plant; provides structural support. Phloem It lies just below the sclerenchymatous patch of pericycle and is composed of following elements such as sieve tubes, companion cells, and phloem parenchyma. Transports organic nutrients (like sugars) produced during photosynthesis to other parts of the plant; also provides structural support. Cambium: It lies in between xylem and phloem. It consists of a narrow strip of meristematic cells having large nuclei and dense cytoplasm, called fascicular cambium. 1.7 What is inside a plant?/12/sc/2024 12  It is responsible for secondary growth in thickness of the plant body. Pith: It occupies the central portion of the stem. It is composed of thin walled parenchymatous cells which are rounded or polygonal, with or without intercellular spaces. Food is stored in this region. Medullary rays: These are the thin-walled, radially elongated parenchymatous cells present in between vascular bundles. These store food materials and help in internal translocation of water. T.S of Dicot Stem ANATOMY OF MONOCOT STEM Part of Monocot Stem Structure/Function It is the single outermost layer composed of small, thin-walled, somewhat barrel-shaped parenchymatous cells which are tightly packed without intercellular species. It is externally covered with thick cuticle. A few stomata are present on epidermis. Usually trichomes or hairs are lacking. Provides protection against physical damage and pathogens; helps minimize water loss Epidermis through cuticle. Cuticle Waxy layer on the epidermis that reduces water loss and protects against pathogens. It comprises of 2-3 layers of thick-walled lignified sclerenchymatous cells, without intercellular spaces. Cortex Provides mechanical support and stores carbohydrates and other nutrients. It contains a continuous mass of thin-walled, round parenchymatous tissue which lies below the hypodermis. The intercellular spaces are present. Cells are rounded or polygonal in shape. Ground tissue: There is no differentiation of general cortex, endodermis, pericycle, pith, and rays. 1.7 What is inside a plant?/12/sc/2024 13  Part of Monocot Stem Structure/Function Vascular bundles are irregularly lodged in this region Stores nutrients and provides flexibility to the stem Vascular bundles are irregularly scattered in the ground tissues. These are conjoint, collateral, and closed type. Vascular bundles occurring in the peripheral region are smaller in size and compactly arranged. In contrast, those occurring towards the central region are larger in size and widely placed. All the vascular bundles have similar structure. Each vascular bundle consists of xylem towards the center and phloem towards the Vascular periphery without cambium (exarch). It is oval in shape and surrounded by a sheath of Bundles sclerenchymatous tissue. It is V or Y shaped, bearing two large metaxylem vessels with wider cavities and pitted thickening at the lateral arms. Few tracheids are present in between the metaxylem vessels. Protoxylem vessels are only one or two, smaller, narrow cavities having annular or formed lysigenously by disintegrating by disintegration or breaking of some cells or parenchyma tissue and rarely protoxylem vessels. Xylem Thin-walled xylem parenchyma is present around the protoxylem vessels. It lies outside the xylem and is partly present near the metaxylem vessels. It is composed of sieve elements and companion cells. In a mature bundle, the protophloem gets crushed just below the sheath. So, the inner portion is meta-phloem. Transports organic nutrients (like sugars) produced during photosynthesis to other parts of Phloem the plant; also provides structural support. Regulates the movement of water and nutrients into the vascular tissue; may contain a Endodermis Casparian strip. Pith Storage of nutrients and provides some support in certain species. 1.7 What is inside a plant?/12/sc/2024 14 Root system: Entire root axis of an organism together constitutes the root system. Primarily, the first root axis is formed as soon as a radicle emerges onto of the seed during seed germination. This root is termed primary root. A number of lateral roots may emerge from this root. Laterals arise endogenously and are placed away from the roots tip. ANATOMY OF DICOT ROOT The transverse section of the dicot root shows the following plan of arrangement of tissues from the periphery to the center. Part of Dicot Root Function It is also termed as rhizoderm or piliferous layer. It is outermost single layer of root which is composed of thin-walled, closely packed parenchymatous cells without intercellular spaces. The cuticle and stomata are absent. Epidermis/ Most of epidermal cells extend out in form of tubular unicellular root hairs. Epiblema Protects the root and helps in absorption of water and minerals from the soil. Root Hairs Increase surface area of the root for efficient absorption of water and minerals. It is located below the epiblema. It consists of many layers of thin-walled rounded or polygonal parenchymatous cells with sufficiently developed intercellular spaces between them. Cells of cortex consists of leucoplasts and store starch grains. Sometimes, outer layer of cortex becomes cutinized and forms exodermis of root. Cortex Cortex cells store food and conduct water from epiblema to the inner tissues. It is the innermost layer, made up of single layer of barrel shaped compact parenchymatous cells without intercellular spaces. The radial walls of this layer are often thickened and sometimes this thickening extends to the inner walls also. Deposition of suberin and lignin causes the thickening. Due to deposition, strip or bands like structures are formed which Endodermis are known as casparian strips or casparian bands. Cells of the endodermis that are located 1.7 What is inside a plant?/12/sc/2024 15  Part of Dicot Root Function opposite the proto-xylem elements are thin-walled and termed as passage cells as they facilitate the passage of water from roots to the xylem. Endodermis acts as a watertight jacket around the stele. It is located internal to the endodermis and made up of single layer of thin walled parenchymatous cells containing abundant protoplasm. It is very important layer as part of vascular cambium is formed from it. Pericycle Gives rise to lateral roots and provides structural support to the vascular tissue. These are arranged in a ring but xylem and phloem form an equal number of separate bundles placed on different radii. As xylem and phloem are alternately arranged, the vascular bundles are termed as radial bundles. Vascular Contains xylem and phloem for transport of water, minerals, and nutrients between the root Cylinder and the rest of the plant. It appears in conical in shape. The cells in T.S. appear polygon, and are thick walled. The protoxylem lies towards the periphery, so the xylem is called exarch. The protoxylem vessels bear annular and spiral thickenings while metaxylem vessels have Xylem reticulate and pitted thickenings. It lies alternate to xylem patches. The patches are smaller and consist of sieve tubes, companion cells and phloem parenchyma. The phloem fibers are absent. Transports organic nutrients (like sugars) from the leaves to the root and other parts of the Phloem plant. This occupies only a small area in the center and consists of few compactly arranged, thin- walled parenchymatous cells without any intracellular space. Pith Sometimes the pith is nearly obliterated owing to the wood vessels meeting in the center. 1.7 What is inside a plant?/12/sc/2024 16 ANATOMY OF MONOCOT ROOT Parts of Structure/functions monocot root Epidermis/ It is the outermost layer composed of compact parenchymatous cells having no Epiblema/ intercellular spaces and stomata. Rhizodermis The tubular unicellular root hairs are also present on this layer Both epiblema and root hairs are without cuticle. In older parts, epiblema either becomes impervious or is shed. Epiblema and root hairs absorb water and mineral salts. Cortex: It lies just below the epidermis. Cortex consists of thin walled multilayered parenchyma cells having sufficiently developed intercellular spaces among them. Usually in an old root of Zea mays, a few layers of cortex undergo suberization and give rise to a single or multi-layered zone- the exodermis. This is a protective layer which protects internal tissues from outer injurious agencies. The starch grains are abundantly present in the cortical cells. Cortex functions as: a) conduction of water and mineral salts from root hairs to inner tissues b) storage of food c) Protection when exodermis is formed in older parts. Endodermis: The innermost layer of the cortex is termed as endodermis. It is composed of barrel-shaped compact cells that lacks intercellular spaces among them. Young endodermal cells have an internal strip of suberin and lignin which is called casparian strip. The strip is located close to the inner tangential wall. There are some unthickened cells opposite to the protoxylem vessels known as passage cells which serve for conducting of fluids. The function of endodermis is to regulate the flow of both inward as well as outward. 1.7 What is inside a plant?/12/sc/2024 17  Pericycle: It lies just below the endodermis and is composed of single layered sclerenchymatous cells intermixed with parenchyma. Vascular The vascular tissue contains alternating strands of xylem and phloem. tissue: The phloem is visualized in the form of strands near the periphery of the vascular cylinder, beneath the pericycle. The xylem forms discrete strands, alternating with phloem strands. The center is occupied by large pith which maybe parenchymatous or sclerenchymatous. The number of vascular bundles is more than six, hence called as polyarch. Xylem is exarch i.e. the protoxylem is located towards the periphery and the metaxylem towards the center. Vessels of protoxylem are narrow and the walls possess annular and spiral thickenings in contrast, metaxylem are broad and the walls have reticulate and pitted thickenings. Phloem consist of sieve tubes, companion cells and phloem parenchyma. The phloem strands are also exarch having protophloem towards the periphery and metaphloem towards the center. Conjunctive In between the xylem and phloem bundles, there is the presence of many layered tissues: parenchymatous or sclerenchymatous tissue. These help in storage of food and help in mechanical support. Pith: It is the central portion usually composed of thin-walled parenchymatous cells which appear polygonal or rounded in T.S. Intercellular spaces may or may not be present amongst pith cells. In some cases, pith becomes thick walled and lignified. Pith cells serve to store food. LEAF ANATOMY Venation Venation is the pattern of veins in the blade of a leaf. The veins consist of vascular tissues which are important for the transport of food and water. Leaf veins connect the blade to the petiole, and lead from the petiole to the stem. 1.7 What is inside a plant?/12/sc/2024 18 The venation pattern of a leaf is classified as reticulated, parallel, or dichotomous. In reticulated venation, the veins are arranged in a net-like pattern, in that they are all interconnected like the strands of a net. Reticulated venation is the most common venation pattern, and occurs in the leaves of nearly all dicotyledonous Angiosperms, whose embryos have two cotyledons (seed leaves) as in flowering plants such as Maple, Oak, and Rose. In parallel venation, the veins are all smaller in size and parallel or nearly parallel to one another, although a series of smaller veins connects the large veins. Parallel venation occurs in the leaves of nearly all monocotyledonous Angiosperms, whose embryos have one cotyledon, as in flowering plants such as lilies and grasses. In dichotomous venation, the veins branch off from one another like the branches of a tree. This is the rarest venation pattern, and occurs in the leaves of some ferns and in the gymnosperm tree, Ginkgo biloba.[NOT REQUIRED] ANATOMY OF DICOT LEAF (Dorsiventral leaf) A transverse section through the mid rib region of a typical dorsiventral leaf reveals the following structure. 1. Epidermis- Both upper and lower epidermis are usually made up of a single layer of cells that are closely packed.  The cuticle on the upper epidermis is thicker than that of lower epidermis.  Stomata are more in number on the lower epidermis than on the upper epidermis [hypostomatic]. The main function of the epidermis is to give protection to mesophyll. The cuticle helps to check transpiration. Stomata are used for transpiration and gas exchange. 2. Mesophyll : The entire tissue between the upper and lower epidermis is called the mesophyll, differentiated into palisade and spongy parenchyma. 1.7 What is inside a plant?/12/sc/2024 19   Palisade parenchyma  Below the epidermis, vertically elongated cylindrical cells in one or more layers without intercellular spaces form palisade parenchyma. Palisade parenchyma cells contain more chloroplasts than the spongy parenchyma cells. The function of palisade parenchyma is photosynthesis.  Spongy parenchyma  Below palisade parenchyma towards lower epidermis, irregularly shaped, loosely arranged cells with numerous air spaces form spongy parenchyma.  Spongy cells facilitate the exchange of gases with the help of air spaces.  The air space that is found next to the stoma is called sub-stomatal cavity 3. Vascular tissues (in the veins)-  Vascular bundles are conjoint, collateral and closed. Xylem is present towards the upper epidermis, while the phloem towards the lower epidermis.  Vascular bundles are surrounded by a compact layer of parenchymatous cells called bundle sheath or border parenchyma.  Protoxylem vessels are present towards the upper epidermis. Phloem consists of sieve tubes, companion cells and phloem parenchyma. Phloem fibres are absent.  Xylem consists of vessels and xylem parenchyma. Tracheids and xylem fibres are absent. ANATOMY OF MONOCOT LEAF (Isobilateral leaf) A transverse section passing through the midrib region of an iso-bilateral leaf (Maize) reveals the following structure. 1. Epidermis –  Both upper and lower epidermis are usually made up of a single layer of cells that are closely packed. Cuticle and trichomes are present in both the layers.  Stomata are equal in number on both layers. This condition is described as amphistomatic.  A few cells in the upper epidermis are enlarged to form motor cells called bulliform cells. Helps in rolling and unrolling of leaves to prevent transpiration. 2. Mesophyll  It is ground tissue that occurs between the two epidermal layers not differentiated into palisade and spongy parenchyma.  It is composed of many layers of loosely arranged, spherical or oval chlorenchyma cells. Has few intercellular spaces. 3. Vascular bundles-  Each vascular bundle is surrounded by a bundle sheath composed of a single layer of compactly arranged cells. Xylem is found towards upper epidermis and phloem is towards lower epidermis.  The vascular bundle is described as conjoint and collateral with endarch xylem.  The oldest and the largest vascular bundle is found in the centre. It is known as midrib vein. The bundle sheath of the midrib vein is connected to the upper and lower epidermal layers by sclerenchyma cells representing bundle sheath extensions or hypodermal sclerenchyma. 1.7 What is inside a plant?/12/sc/2024 20  Characteristic Monocot Leaf Dicot Leaf Branched network of veins (reticulate Veins Parallel veins venation) Often broad with a distinct petiole (leaf Leaf Shape Typically linear or elongated stalk) Leaf orientation isobilateral dorsiventral Stomata Found on both the epidermis/ Mostly found on the lower surface in an Distribution amphistomatic organized pattern/ hypostomatic Vascular Bundles in Scattered vascular bundles throughout the Arranged in a net-like pattern with a Midrib leaf, with no distinct midrib prominent midrib Differentiated into spongy and palisade Mesophyll Usually single-layered [undifferentiated] parenchyma Xylem and Xylem and phloem bundles are typically Xylem and phloem bundles are large and Phloem small and scattered arranged in a ring around the central region Chloroplast Chloroplasts often randomly distributed in Chloroplasts mainly concentrated in palisade Arrangement mesophyll cells mesophyll Motor cells Present in the upper epidermis Absent 1.7.4-Plants Adaptations in Different Habitats Construct arguments to support or refute the idea that adaptive features of plants are directly related to the environment where they grow. Adaptations build up in due course and production as a comeback to the ever-changing environment. They allow an organism to reduce competition for space and nutrients, reduce predation and increase reproduction. There are however, several factors that can limit these adaptations: availability of water, light, predation and temperature. Desert plants look very different from plants that live near the ocean or in the mountains. Each type of plant thrives in a different type of environment. 1.7 What is inside a plant?/12/sc/2024 21 There are five main types of nutrients that plants use is: Nitrogen, Phosphorous, Potassium, Calcium, and Magnesium. Nutrients are substances that provide energy and materials for plants to grow. There are five main types of nutrients that plants use, but not all plants use them equally. For example:  A pine tree might use a lot of nitrogen but not very much phosphorous, but  A cactus might use a lot of phosphorous and not much nitrogen. Plants have adaptations to help them survive (live and grow) in different areas. These adaptations might make it very difficult for the plant to survive in a different place. This explains why certain plants are found in one area, but not in another. For example: Desert plants grow far apart so that they can get water and nutrients from a larger area. The sharp spines of a cactus keep animals from eating it. Plants in the high mountains grow close to the ground as protection from the wind. The leaves, stems, roots, and reproductive parts of plants can be very different depending on where the plant lives. In the same way Mosses are soft cushiony plants that live in damp places. Mosses have few or no stems. They are non-vascular plants. They grow close to the ground. They hold soil in a forest and prevent it from being washed away by heavy rains. These plants have no roots so most of them grow close to the ground to keep from drying up. Some mosses, known as sphagnum peat mosses, absorb water like sponges and hold the water in their stems. The mosses often form wet, spongy quilts between the trees in damp forests. Examples of Plant Adaptations in Different Environments An adaptation is just a mutation that worked out well for a plant or animal. Plants adapt in many ways to be able to survive or thrive in their surroundings. Discover several plant adaptation examples specific to different environments.  Desert Plant Adaptations Living in a desert environment poses unique challenges for plant life. Desert plants have to adapt to harsh conditions characterized by extreme temperatures and very little rainfall.  Root Structure 1.7 What is inside a plant?/12/sc/2024 22 Plants that grow in the desert have adapted the structure of their roots to be able to thrive with very little rainfall. Some plants have adapted to take advantage of any rainfall that occurs while others have adapted to look for water very deep in the ground. shallow root structure - Some desert plants have shallow roots that spread out over a wide area. This allows them to get as much rainwater as possible during the rare occasions that it rains. deep tap roots - Not all desert plants have shallow roots. Some develop extremely long tap roots that go down very deep into the ground. These deep tap roots are an adaptation that allows the plants to reach water deep below the surface.  Leaf Waxing Nearly all desert plants produce a waxy coating on their leaves or have prickly spines. These features help keep water from evaporating out of the leaves. This is an adaptation to help prevent dehydration in a desert climate.  Night Blooming Some desert plants bloom only at night, which is an adaptation to the extreme heat of the desert sun and certain animal adaptations.  Preventing dehydration - Blooming during the daytime in the desert could cause plants to dehydrate very quickly. The adaptation to nighttime blooming helps keep desert plants from losing a lot of water (dehydrating) through their blooms.  Helping with pollination - Because many desert insects are nocturnal (an example of an animal adaptation), blooming at night helps ensure that desert plants get properly pollinated.  Reproducing Without Seeds While desert plants can reproduce by seeds, some don’t have to reproduce that way. For example, some cacti will break off pieces of themselves. These pieces can root and form new cacti rather than having to start from seeds. Since seeds require water to sprout, there would not be as many cacti in the desert without this adaptation.  Drought Resistance Desert plants have roots that can handle drying out without dying. This adaptation is also referred to as desiccation resistance. PLANT ADAPTATIONS [REFERENCE ONLY] Biome Plant Adaptations Large leaf size to capture more light Presence of poisonous parts for defense against herbivores Brightly colored flowers for effective pollination Various water adaptations (aquatic, boggy, muddy)Resistance to root rot due to wet conditions Some plants grow tall to reach sunlight (e.g., cattails) Tropical Rainforest Some plants float on water (e.g., water lilies) Rapid growth during wet season; turn brown to conserve water in dry season Baobab trees store water in trunks Acacia trees have deep tap roots and are fire-resistant Kangaroo Paw tolerates drought and high temperatures Hydrophilic root systems for water extraction Tropical Savanna Trees drop leaves to conserve energy and water 1.7 What is inside a plant?/12/sc/2024 23  Biome Plant Adaptations Conical shape of evergreen trees to shed snow Dark green needles for efficient photosynthesis Taiga (Boreal Small surface area of needles to reduce water loss Forest) Waxy coating on needles for protection against cold and wind Pneumatophores (vertical roots) for oxygenation in waterlogged soil Aerial roots (prop roots, stilt roots) for stability and oxygenation Viviparous propagule production for salt tolerance Salt-excreting glands on leaves Mangroves Ability to turn leaves to reduce sun exposure and water loss Low-growing plants close to ground to avoid strong winds Dormancy through winter; reproducing through division Dark coloration for heat absorption Hairy coverings for insulation Clumping for mutual protection against wind Dish-like flowers to concentrate solar heat Small leaves to retain moisture Perennial growth to survive short growing season Tundra Ability to grow on bare rock (e.g., lichens, mosses) Plants have several basic needs for better survival. They need solar light, water, air and minerals or nutrients for good growth. They also need to be able to reproduce in order to ensure that their species survives. Some of the main threats to the survival of plants include a lack of sunlight, a lack of water, a lack of good soil and a proper space. In the same way an abundance of water, air, solar radiation (UV rays) and the activities of animals are also harmful for plants. There are many challenges that plants face in order to survive. How well plants adapt to their changing environments will determine their future. Assignment questions 1. How does the ability of meristematic tissue to differentiate contribute to the growth and development of plants? 2. How is the distribution of meristematic tissues related to varying growth patterns during different phases of plant growth 3. How is the modification of the external structure of plants related to their distribution in different environmental conditions? 4. Why do the structures vary amongst the epidermal, vascular and ground tissue systems? 5. How does the organization of tissues to form tissue systems benefit a plant? 6. Relate the difference in the anatomies between the monocot and dicot plants to their survivability in a variety of environments. 7. How do the differences in the anatomy of leaves amongst monocot and dicot plants relate to their differences in physiological processes? 8. How do environmental conditions affect the development of adaptive features in plants? 9. Do plants exhibit temporary adaptations like in animals? How? 10. How are adaptations in plants regulated? 11. Draw a comparison between the cells of the meristematic tissue in plants and the stem cells of animals. 1.7 What is inside a plant?/12/sc/2024 24 12. Tissue culture is a growing field of plant propagation that has widespread applications across education and agriculture. How is it possible to multiply plants using tissues? 13. Monocot plants are usually used as roofing materials and making brooms. How does the anatomical features of monocot plants support the mentioned utilities? 14. Southern foothills in Bhutan are warmer, receive heavy rainfall and experience more windstorms. It is also observed that broad-leaved plants and monocot plants grow more in such places. Relate the pattern of distribution to the anatomy of the plants. 15. Complete the following worksheet Sl. No. Tissue Description Function 1 Epidermis 2 Hypodermis (Collenchyma/Sclerenchyma) 3 General cortex (Parenchyma) 4 Endodermis 5 Pericycle 6 Medullary rays 7 Phloem 8 Xylem 9 Pith 16. "Cacti are a diverse group of desert plants that can be grown in climate variability." Explain. 17. Pheophyta like algae exists without vascular bundle. Comment 1.7 What is inside a plant?/12/sc/2024 25