Chapter 3 Plant Morphology & Anatomy PDF

CHAPTER 3 PLANT MORPHOLOGY & ANATOMY At the end of this session, you should be able to: Label, explain the distribution and functions of plant tissues in root, stem and leaf of monocots and dicots. Explain the primary & secondary growth.  Plant mor...

CHAPTER 3 PLANT MORPHOLOGY & ANATOMY At the end of this session, you should be able to: Label, explain the distribution and functions of plant tissues in root, stem and leaf of monocots and dicots. Explain the primary & secondary growth.  Plant morphology  Plant morphology is the study of the physical form and external structure of plants.  which is the description of the physical form and external structure of plants,  Plant morphology is useful in the visual identification of plants.  Plant anatomy  Plant anatomy is the study of plant tissues and cells in order to learn more about the way they are constructed and how they work.  OR the study of the internal structure of plants.  Plant anatomy is now frequently investigated at the cellular level, and often involves the sectioning of tissues and microscopy. MORPHOLOGY OF FLOWERING PLANTS  Angiosperms are characterized by the presence of roots, stems, leaves, flowers and fruits.  The underground part of the flowering plant is the root system while the portion above the ground forms the shoot system.  THE LEAF  The leaf is a lateral, generally flattened structure borne on the stem.  It develops exogenously at the node and bears a bud in its axil – the axillary bud, which later develops into a branch.  Leaves originate from shoot apical meristems and are arranged in an acropetal order.  They are the most important vegetative organs for photosynthesis. A typical leaf consists of three Parts of leaf main parts: Lamina The lamina or the leaf blade is the green expanded part of the leaf with v eins and v einlets. a middle prominent v ein, = the midrib. Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials. Leaf base The leaf is attached to the stem by the leaf base and may bear two lateral small leaf like structures called stipules. In monocotyledons, the leaf base expands into a sheath cov ering the stem partially or wholly – Sheathing leaf base. In some leguminous plants the leaf base may become swollen – Pulvinus leaf base. Petiole helps hold the blade to light. Long thin flexible petioles allow leaf blades to flutter in wind, thereby cooling the leaf and bringing fresh air to leaf surface.  Leaf Venation  Venation is the arrangement of veins and the veinlets in the lamina of leaf.  There are two types of leaf venation 1. Reticulate/netlike venation – When the veinlets form a network. e.g., Dicotyledons. 2. Parallel venation – When the veins run parallel to each other within a lamina. e.g., Monocot.  Morphological variation  Plants exhibit natural variation in their form and structure.  all organisms vary from individual to individual,  plants exhibit an additional type of variation.  Within a single individual, parts are repeated which may differ in form and structure from other similar parts.  This variation is most easily seen in the leaves of a plant, though other organs such as stems, root and flowers may show similar variation.  There are three primary causes of this variation: positional effects, environmental effects, and juvenility.  Morphological variation Types of leaves Simple Compound - Single leaf blade - Leaf has number of leaflets Pinnate Palmate  Leaves arrangement  Phyllotaxy = the pattern of Whorled = If more than two arrangement of leaves on stem leaves arise at a node and form a or branch whorl Alternate = a single leaf Opposite = a pair of leaves arise at arises at each node in each node and lie opposite to each alternate manner other Leaf shapes  Modification of leaves For support – conv erted into tendrils for climbing. e.g., peas. For defense – converted into spines. e.g., cactus. For food storage – The fleshy leav es of onion and garlic. For photosynthesis (phyllode) – The petioles expand, become green and synthesis food. e.g., Australian acacia. For insectivory – pitcher plant, v enus-fly trap. Morphological variation in flowers  Flowering plants reproduce by pollination.  Flower is a structure for sexual reproduction in flowering plants (angiosperms). ❖ Varies in their construction (morphology). ❖ A "complete" flower has:  a calyx of outer sepals  a corolla of inner petals.  The sepals and petals together form the perianth.  stamens (male part), - produce pollen grains,  carpels (female part), contain one or more ovules  Types of flower  Flower can vary in the type of structure present:  A flower containing all four modified leaves is said to be complete  If a flower that lacks any of these modified leaves is said to be incomplete  Types of flower  A "perfect" flower has both stamens and carpels, ("bisexual" or "hermaphroditic").  A "unisexual" flower is one in which either the stamens or the carpels are missing,  "staminate" = having only functional stamens (male flower)  "carpellate" (or "pistillate") = having only functional carpels (female flower).  If separate staminate and carpellate flowers are found on the same plant = is called monoecious.  If separate staminate and carpellate flowers are always found on different plants = is called dioecious Ovary position Ovary position Placentation is the arrangement of Placentation ovules within the ovary.  Marginal  The placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows. e.g., pea.  Axile  When the placenta is axial and the ovules are attached to it in a multi- locular ovary. e.g., tomato and lemon.  Parietal  the ovules develop on the inner o Basal wall of the ovary or on peripheral o the placenta develops at the base part. of ovary and a single ovule is  Ovary is one-chambered but it attached to it. e.g., sunflower, becomes two chambered due to marigold. the formation of the false septum o Free Central (Replum) e.g., mustard and o When the ovules are borne on Argemone. central axis and septa are absent. e.g., Dianthus, Primrose. The calyx : Totality of sepals in the flower. Calyx with free sepals Calyx with connate (united) sepals: The corolla : Totality of petals in the flower Corolla with free petals Corolla with connate (united) petals FLOWER TO FRUIT - FERTILIZATION  FRUIT  The fruit is a characteristic feature of the flowering (Angiosperm) plants.  It is a mature or ripened ovary, developed after fertilization.  If a fruit is formed without fertilization of the ovary, it is called a parthenocarpic fruit.  Generally, the fruit consists of pericarp(a wall) and seeds.  The pericarp may be dry or fleshy.  When pericarp is thick and fleshy, it is differentiated into the outer epicarp, the middle mesocarp and the inner endocarp.  The function of a fruit is to hold and protect the seeds.  THE SEED  The ovules after fertilization, develop into seeds.  A seed is made up of a seed coat and an embryo.  The embryo is made up of a radicle, an embryonal axis and one (monocot) or two cotyledons (dicot). Structure of a Dicotyledonous Seed  Seed coat – The outermost covering of a seed. The seed coat has two layers, the outer testa and the inner tegmen.  Hilum – The hilum is a scar on the seed coat through which the developing seeds were attached to the fruit.  Micropyle – it is a small pore present above the hilum.  Embryo – it consists of an embryonal axis and two cotyledons.  Cotyledons – These are often fleshy and full of reserve food materials.  Radicle and plumule – they are present at the two ends of the embryonal axis.  Endosperm – the endosperm formed as a result of double fertilization, is a food storing tissue. Structure of Monocotyledonous Seed  Seed Coat – the seed coat is membranous and generally fused with the fruit wall, called Hull.  Endosperm – The endosperm is bulky and stores food.  Aleuron layer – The outer covering of endosperm separates the embryo by a proteinous layer.  Embryo – The embryo is small and situated in a groove at one end of the endosperm.  Scutellum – one large and shield shaped cotyledon  Embryonal axis – ends are known as plumule and radicle.  Coleoptile and coleorhiza – are the sheaths which are enclosed the plumule and radicle respectively.  MORPHOLOGY OF THE STEM  Stem is the ascending part of the axis bearing branches, leaves, flowers and fruits.  It develops from the plumule of the embryo of a germinating seed.  bears nodes and internodes.  Nodes are the region of the stem where leaves are born  internodes are the portions between two nodes.  The stem bears buds, which may be terminal or axillary.  The main functions of the stem are: spreading out branches bearing leaves, flowers and fruits. conducts water, minerals and photosynthates. storage of food, support, protection and of vegetative propagation.  Modifications of Stem  MODIFICATION FOR FOOD STORAGE Underground stems of Yam, ginger, turmeric, are modified to store food in them. act as organs of perennation to tide ov er conditions unfavourable for growth.  MODIFICATION FOR SUPPORT Stem tendrils dev elop from axillary buds, are slender and spirally coiled help plants to climb Eg: gourds (cucumber, pumpkins, watermelon) and grapevines.  Modification for defense modified into woody, straight and pointed thorns. found in Citrus, Bougainvillea. protect plants from browsing animals.  Modification for photosynthesis (phylloclade) Some plants of arid regions modify their stems into flattened, or fleshy cylindrical structures. They contain chlorophyll and carry out photosynthesis.  Modifications of Stem  Modification for vegetative propagation Runner – Underground stems spread to new niches and when older parts die new plants are formed. e.g., grass and strawberry Stolon – a slender lateral branch arises from the base of the main axis and after growing aerially for some time arch downwards to touch the ground. e.g., mint and pegaga Offset – A lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots. eg., kiambang (water lettuce). Sucker – the lateral branches originate from the basal and underground portion of the main stem, grow horizontally beneath the soil and then come out obliquely upward giving rise to leafy shoots. e.g., banana, pineapple and Chrysanthemum.  Morphology of the root  Root are developed from Radicle of the embryo of a germinating seed.  the direct elongation of the radicle (dicot plant) leads to the formation of primary root.  It bears lateral roots of several orders that are referred to as secondary, tertiary, etc. roots.  The primary roots and its branches constitute the tap root system.  In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots.  These roots originate from the base of the stem and constitute the fibrous root system.  roots arise from parts of the plant other than the radicle and are called adventitious roots.  Functions of the root  The main functions of the root system are:  Absorption of water and minerals from the soil,  providing a proper anchorage to the plant parts,  storing reserve food material and  synthesis of plant growth regulators.  Regions of the Root  Root cap Cov er the root apex thimble-like structure protects the tender apex of the root as it makes its way through the soil.  Region of meristematic tissue present at a few millimeters above the root cap. The cells are v ery small, thin-walled and with dense protoplasm. They div ide repeatedly.  Region of root elongation cells undergo rapid elongation and enlargement are responsible for the growth of the root in length.  Region of maturation The cells gradually differentiate and mature. the epidermal cells form v ery fine and delicate, thread-like structures called root hairs. root hairs absorb water and minerals from the soil.  Modifications of Root  change their shape and structure  modified to perform functions other than absorption and conduction of water and minerals.  MODIFICATION FOR FOOD STORAGE get swollen and store food.  MODIFICATION FOR SUPPORT Prop roots – vertically downward roots originates from heavy branches to support them. Stilt roots – oblique downward roots coming out of the lower nodes of the stem to support weak stem.  MODIFICATION FOR RESPIRATION plants growing in swampy areas, roots come out of the ground and grow vertically upwards. called pneumatophores help to get oxygen for respiration.  Plant Tissue  Tissue System is a group of tissues organized into a structural and functional unit  It is a larger units of the plant body.  The organs that they form will be organized into patterns within a plant which will aid in further classifying the plant.  Plant tissues are categorized broadly into three tissue systems: a) the epidermis, ✓ Cells forming the outer surface of the leaves and of the young plant body b) the ground tissue, less differentiated than other tissues.  manufactures nutrients by photosynthesis and stores reserve nutrients. c) the vascular tissue.  Consist of the xylem and phloem.  transport fluid and nutrients internally.  Plant tissues can also be divided differently into two types: Meristematic tissues Permanent tissues. Plant Tissue  Plant Tissue Apical meristems Meristematic Lateral tissue meristems TYPES OF PLANT TISSUES Intercalary meristems Parenchyma Simple/ ground Collenchyma tissue: Sclerenchyma Permanent Xylem tissue Complex /Vascular tissue Phloem Epidermis Dermal tissue Periderm  MERISTEMATIC TISSUE  Meristems are places in plants where cell div ision is occurring  consists of activ ely div iding cells,  leads to increase in length and thickness of the plant.  occurs in the tips of stems or roots.  Cells in these tissues are roughly spherical or polyhedral, to rectangular in shape,  have thin cell walls and dense protoplast  Tiny v acuoles and a large nucleus  Meristems contribute to both primary (taller/longer) and secondary (wider) growth.  Primary growth is controlled by root apical meristems or shoot apical meristems,  secondary growth is controlled by the two lateral meristems, called the vascular cambium and the cork cambium.  Not all plants exhibit secondary growth.  There are three types of meristems: 1. Apical Meristems 2. Lateral Meristems 3. Intercalary Meristems  1. APICAL MERISTEMS  are located at or near the growing tips of roots and shoots.  form growing parts at the apices of roots and stems  As cells in apical meristems divide and elongate, shoot tips and root tips grow longer.  are responsible for increase in length of the stem and root.  This vertical growth is known as primary growth (growth of a tree in height).  Each apical meristem will produce embryo leaves and buds as well as three types of primary meristems: 1. protoderm, 2. ground meristems, 3. procambium. 1. APICAL MERISTEMS Shoot apical meristem (SAM)  1. APICAL MERISTEMS Root apical meristem (RAM) (a) Root cap. (b) Root apical meristem. (c) Ground meristem. (d) Protoderm. (e) Epidermal tissue of the root. (f) Vascular tissue (central stele).  2. LATERAL MERISTEMS  cause to increase in diameter and girth of tree.  results in the formation of secondary growth (horizontal growth) – tree trunk girth.  occurs beneath the bark of the tree (Cork Cambium) and in vascular bundles of dicots (vascular cambium). 1.The vascular cambium, produce secondary xylem & new phloem the first type of lateral meristem, is a thin, branching cylinder is responsible for the increase the thickness, or girth, of the plant. 2. The cork cambium, produce bark, covering old stem & roots (periderm) the second type of lateral meristem, a thin cylinder only found in woody plants, produce the outer bark. 2. LATERAL MERISTEMS  3. INTERCALARY MERISTEM  located in between permanent tissues.  present at the base of node, inter node and on leaf base.  responsible for growth in length of the plant and increasing the size of the internode,  are found in monocot (do not have a vascular cambium or a cork cambium)  Help in growth of branches and leaves  The intercalary meristem is responsible for the regrowth of cut grass.  PERMANENT TISSUE Permanent tissues are made of cells that are produced by the meristems are formed to various shapes and sizes depending on their intended function in the plant (cell differentiation). Sometimes the tissues are composed of the same type of cells throughout (simple tissue), or sometimes they are mixed (complex tissue). There are 3 types of permanent tissues: 1. simple permanent tissues 2. complex permanent tissues 3. special or secretory tissues (glandular).  1. Simple tissues  A tissue that made up of single type of cells which are: similar in origin; similar in structure similar in function  They are: a) Parenchyma b) Collenchyma c) Sclerenchyma  cells are basically sphere shaped. PARENCHYMA  cells have thin walls,  flatten at the points of contact.  have large central vacuoles  Have intercellular spaces (allow diffusion of gases)  may contain various secretions including starch, oils, tannins, and crystals.  Some parenchyma cells have many chloroplasts (found in leaves)  This type of tissue is called chlorenchyma (photosynthesis)  Some have large central vacuole and contain air = Aerenchyma  DISTRIBUTION OF Form the majority of stem, roots, PARENCHYMA TISSUE and edible portions of higher plant. In the cortex and pith of stems Cortex of roots The mesophyll of leaves Occur within the xylem and phloem of vascular bundles  Functions of Parenchyma  Storage of starch, protein, fats, oils and water in roots, tubers (potatoes), seed endosperm (cereals) and cotyledons(peanuts)  Gives support and shape to plants.  secretion – secreted resins, tannins, hormones, enzymes and sugary nectar.  perform photosynthesis (chlorenchyma)= mesophyll cells  Wound repair and the potential for renewed meristematic activity  aeration (aerenchyma) provides buoyancy and helps aquatic plants in floating.  Cells are elongated COLLENCHYMA  Contain chloroplast,  alive at maturity  protoplast died in lignified cells.  The primary cell walls are thickened (in the corners) by cellulose and pectin  Common in young stems and leaf petioles  Functions: provide structural support, particularly in growing shoots and leaves. makes up the resilient strands in stalks of celery.  SCLERENCHYMA  Occur throughout the plant body.  Long or stellate in shape.  cell walls consist of cellulose, hemicellulose and lignin.  Have both primary & secondary cell walls  Characterized by thickening secondary walls  Cells often dead when matured  important strengthening and supporting elements in plant parts that have ceased elongation.  makes the plant hard and stiff.  SCLERENCHYMA Two types of sclerenchyma cells exist: Sclereids Cell of variable shape: small cluster/solitary cells/star shaped cell/simple stone Common in the walnut shells and in the pits of stone fruits (pear fruits) Fibers Aggregates form a continuous cylindrical, long, narrow cells, pitted cell and tapered ends. Abundant in the wood, inner bark and leaf veins of great economic importance, since they constitute the source material for many fabrics (e.g. flax, hemp, jute, and ramie).  2. Complex permanent tissues  are made up of more than one type of cells and they work together as a unit.  They transport water, salt and food material to various parts of the plant body.  Complex tissues are of two types. a) Xylem b) Phloem  They are both conducting tissues and constitute a vascular bundle.  The cells have thick walls Xylem  Most are dead cells  consists of: tubular structures tracheids, allows them to transport water and vessels, minerals vertically xylem parenchyma ✓ stores food ✓ helps in the sideways conduction of water. xylem fibres.  supportive in function.  xylem are involved in the movement of water through a plant from its roots to its leaves.  Water: Is absorbed from the soil through root hair cells Is transported through the xylem vessels up the stem to the leaves Evaporates from the leaves (transpiration)  Components of xylem 1. Tracheids:  Tracheids are elongated or tube-like 2. Vessels: dead cell  long cylindrical,  hard, thick and lignified cell walls.  tube like structure with lignified walls  Components Their ends are tapering,of xylem blunt or  wide central lumen. chisel-like.  cells are dead as these do not have  Their function protoplast. conduction of water  cells are arranged in longitudinal providing mechanical support to series in which the partitioned walls the plant. (transverse walls) are perforated (looks-like a water pipe)  main function transport of water and minerals. It also provides mechanical strength.  Components of xylem 3. Xylem fibers:  are elongated,  lignified and pointed at both the ends.  Functions: helps in conduction of water and nutrients from root to the leaf provides mechanical support to the plant. 4. Xylem Parenchyma:  The cells are living and thin walled.  main function is to store starch and fatty substances.  made up of four types of Phloem elements: sieve tubes, companion cells, phloem fibers phloem parenchyma. Sieve tubes are tubular cells with perforated walls.  Phloem is unlike xylem in that materials can move in both directions in it.  Except for phloem fibres, phloem cells are living cells.  are involved in translocation.  Components of phloem 1. Sieve tube:  are elongated, tube-like slender cells placed end to end.  The transverse walls at the ends are perforated (sieve plates).  main function:  translocation of food, from leaves to the storage organs of the plants. 2. Companion Cells:  are elongated cells attached to the lateral wall of the sieve tubes.  mostly found in angiosperms. 3. Phloem Parenchyma:  are living cells which have cytoplasm and nucleus.  Their function is to store food materials. 4. Phloem fibers  are elongated, lignified  provide mechanical strength to the plant body.  Roles of Phloem Main function is to conducts food & metabolites materials from leaves throughout the plant Also provides structural support done by the fibers. Food materials are conducted in solution through the sieve tube members. Sieve tube members are long slender cells with porous ends called sieve plates. Sieve tube members are joined end-on-end to form long sieve tubes  3. DERMAL TISSUE SYSTEM  The dermal tissue system is the outer covering of the plant.  Consist of an epidermis  Made of a single layer or multiple layers of cells.  cells of epidermal tissue form a continuous layer (without intercellular spaces).  Cells are lack of chloroplast  The dermal tissue system protects the soft tissues of plants and controls interactions with the plants' surroundings.  Dermal tissue consists of: 1. Epidermis 2. Periderm  3. DERMAL TISSUE SYSTEM 1. EPIDERMIS  are the outermost layer of the primary plant body,  covers roots, stems, leaves, floral parts, fruits and seeds.  They are one layer thick with cuticle.  cells are relativ ely flat  The small pores in the epidermis of the leaf are called stomata (gas exchange & transpiration).  Stomata are control by two kidney-shaped cells called guard cells.  The Epidermis of plant in dry habitat is thicker coating by cutin (protection against water loss).  Epidermal cells often secrete a waxy, water-resistant layer on their outer surface  For protection against loss of water, mechanical injury and invasion by parasitic fungi.  Some of the many types of cells in the epidermis are:  Trichomes = Epidermal hairs lower water loss by decreasing the flow of air over the plant surface, which in turn, slows the loss of water from the plant.  buIIiform ceIIs = Glandular hairs prevent herbivory by storing substances that are harmful to insects.  Epidermal cells of the roots commonly bear root hairs that greatly increase the total absorptive surface area (absorb water). 2. PERIDERM  They are the outermost layer of stems and roots of woody plants.  They are also called as barks (dead cells).  They replace epidermis in plants that undergo secondary growth.  They are multilayered structures.  They include cork cells, which are nonliving cells that cover the outside of stems and roots.  The periderm protects the plant from injuries, pathogens and also from excessive water loss.  Plant Organs  organs composed of one or more tissues.  Three major types of plant organs: ❖ Roots ❖ Stems ❖ leaves  Flowers and fruits evolved from stems and leaves Plant Organs The plant body consists of two basic parts: the shoot system and the root system. Shoot System Root System  includes organs such as  includes roots and modified leaves, buds, stems, flowers, stem structures (tubers and and fruits rhizomes)  usually it develops  it develops above ground. underground.  The functions of the shoot  The functions of the root system system includes: includes: ❖ Photosynthesis ❖ Anchorage ❖ Reproduction ❖ Absorption ❖ Storage ❖ Storage ❖ Transport ❖ Transport ❖ Production of certain ❖ Hormone production hormones  Leaf  The leaves are the organs of photosynthesis  Leaves contain chlorophyll,  uses light energy to change carbon dioxide and water into glucose  They have stomata, which allow gas exchange and transpiration Monocot vs Dicot leaf  The stem is the organ which holds the Stem leav es upright in the air and facing the light  It carries water and minerals to the leaves, and food around the plant  The stem is normally div ided into nodes and internodes  the nodes hold buds which grow into one or more leav es, inflorescence (flowers), conifer cones, roots, other stems etc.  Part of stem: Leaf scar - is the mark left on a stem after a leaf falls. Terminal bud - is the main area of growth in most plants. Lenticel - it function as a pore, providing a medium for the direct exchange of gases between the internal tissues and atmosphere. Flower bud – have not yet bloomed into a full-size flower. Growth rings - also referred to as tree rings or annual rings, can be seen in a horizontal cross section cut through the trunk of a tree.  Monocot VS Dicot Stem Dicot stems have their vascular bundles in a ring arrangement. Monocot stems have scattered vascular Dicot stems have bundles in a ring bundles. surrounding parenchyma cells in a pith Monocot stems have most of their region. vascular bundles near the outside edge of Between the bundles and the epidermis the stem. are smaller (as compared to the pith) The bundles are surrounded by large parenchyma cells making up the cortex parenchyma in the cortex region. region. There is no pith region in monocots.  The root is the organ which Root provides anchorage for the plant  root hairs provides a big surface area in water and minerals taking from the soil  a root can also be aerial (growing above the ground) or aerating (growing up above the ground or especially above water).  Root tip Part of root Meristem = a region of rapid mitosis, which produces the new cells for root growth. root cap = a sheath of cells that protects the meristem from abrasion and damage as the root tip grows through the soil.  The Region of Elongation cells produced by mitosis undergo a period of elongation in the direction of the axis of the root (respond with gravitropism).  The Region of Differentiation dev elop the differentiated tissues of the root. Epidermis = A single layer of flattened cells at the surface. the root hairs - increase the surface area for the uptake of water from the soil. Cortex = A band of parenchyma cells that develops beneath the epidermis. It stores food. Endodermis Stele Pericycle = the outer boundary of the stele. Secondary roots branch from it. Xylem = arranged in bundles in a spoke like fashion. Phloem = alternates with xylem.