Plant Form and Function PDF

PLANT FORM AND FUNCTION Clark Cyryll C. Iñigo September 28, 2024 OBJECTIVES 1. Explain the different plant structure and its role in plant’s growth and development 2. Discuss the nature of transport system in plants 3. Discuss the mechanism of plant reproduction 4. Elucidate the r...

PLANT FORM AND FUNCTION Clark Cyryll C. Iñigo September 28, 2024 OBJECTIVES 1. Explain the different plant structure and its role in plant’s growth and development 2. Discuss the nature of transport system in plants 3. Discuss the mechanism of plant reproduction 4. Elucidate the role of hormones in plant responses in its environment 2 Plant Structure Roots rely on sugar produced by photosynthesis in the shoot system Shoots rely on water and minerals absorbed by the root system. Three basic organs evolved: roots, stems, and leaves 3 Roots Roots are multicellular organs with important functions: ✓ Anchoring the plant ✓ Absorbing minerals and water ✓ Storing organic nutrients 4 Taproot system A taproot system consists of one main vertical root that gives rise to some large lateral roots, or branch roots. Adventitious roots arise from stems or leaves 5 Fibrous root system Characterized by many thin lateral roots with no main root. In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area. 6 Modified roots Prop Roots support tall top heavy plants Pneumatophores air roots” enable root systems to capture oxygen 7 Modified roots Buttress roots support tall trunks of some tropical trees “like buttresse Storage roots a specialized underground organ that undergoes modifications during its development to store nutrients 8 Stems Nodes, the points at which leaves are attached. Internodes, the stem segments between nodes An axillary bud is a structure that has the potential to form a lateral shoot, or branch Apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot. 9 Modified Stems Bulbs swollen underground stems that are really large buds with adventitious roots at the base. Corms consists of stem, with a few papery, brown nonfunctional leaves on the outside, and adventitious roots below. 10 Modified Stems Rhizomes Horizontal stems that grow underground, often close to the surface Runners and stolons A stem with long internodes that grows underground (stolons) Stems with long internodes, which, unlike rhizomes, usually grow along the surface of the ground (runners) 11 Modified Stems Tubers Swelling stems that may accumulate at the tips of stolons Tendrils Stems present in climbing plants which twine around supports and aid in climbing 12 Modified Stems Cladophyll Flattened photosynthetic stems that resemble leaves 13 Leaves Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves: Most monocots have parallel veins. Most eudicots have branching veins 14 Leaves Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves: Most monocots have parallel veins. Most eudicots have branching veins 15 Modified Leaves Modified leaves (bracts) Large, modified leaves which surround the true flower and performs as petals Spines Thorny structures that reduces leaf surface to prevent water loss 16 Modified Leaves Reproductive leaves Tiny but complete plantlets that is capable of growing independently into a full-sized plant Window leaves Succulent, cone-shaped leaves with transparent tips found in arid regions 17 Modified Leaves Shade leaves Leaves that receive less sunlight and are significantly larger than sun leaves Insectivorous leaves leaves that trap insects, with some digesting their soft parts. 18 Tissue System ✓ Dermal tissue system ✓ Vascular tissue system ✓ Ground tissue system 19 Dermal Tissue System In nonwoody plants, the dermal tissue system consists of the epidermis. A waxy coating called the cuticle helps prevent water loss from the epidermis. In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots. Trichomes are outgrowths of the shoot epidermis and can help with insect defense 20 Vascular Tissue System The vascular tissue system carries out long-distance transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots Phloem transports organic nutrients from where they are made to where they are needed. 21 Ground Tissue System Tissues that are neither dermal nor vascular are the ground tissue system. Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex. Both have plastids for storage. Ground tissue includes cells specialized for storage, photosynthesis, and support. 22 Types of Plant Cells Parenchyma - ground: thin flexible cell walls: photosynthesis, storage. Collenchyma - ground: thicker cell walls for flexible support. Sclerenchyma - ground: thick secondary cell walls reinforced with lignin for rigid, sturdy support. 23 Sclerenchyma cells Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin. They are dead at functional maturity. There are two types: Sclereids are short and irregular in shape and have thick lignified secondary walls. Fibers are long and slender and arranged in threads. 24 Xylem Tracheids are found in the xylem of all vascular plants. Vessel elements are common to most angiosperms and a few gymnosperms. Vessel elements align end to end to form long micropipes called vessels. These are water conducting cells that are dead at maturity 25 Phloem Sieve-tube elements are alive at functional maturity, though they lack organelles. Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube. Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells. 26  Meristems A plant can grow throughout its life; this is called indeterminate growth. Some plant organs cease to grow at a certain size; this is called determinate growth Types of plants based on growth: a. Annuals – complete life cycle in a year b. Biennials- requires two growing seasons c. Perennials- live for many years Meristems are growth regions - have perpetual embryonic tissue that allows for indeterminate growth. 27 Apical Meristems Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots. Apical meristems elongate shoots and roots, a process called primary growth 28 Lateral Meristems Lateral meristems add thickness to woody plants, a process called secondary growth Types of lateral meristems: a. Vascular cambium - adds layers of vascular tissue called secondary xylem = wood and secondary phloem. b. Cork cambium - replaces the epidermis with periderm, which is thicker and tougher 29 Root Apical Meristems The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil. Growth occurs just behind the root tip, in three zones of cells a. Zone of cell division b. Zone of elongation c. Zone of differentiation 30 Root Apical Meristems The primary growth of roots produces the epidermis, ground tissue, and vascular tissue. In most roots, the stele is a vascular cylinder. The ground tissue fills the cortex, the region between the vascular cylinder and epidermis. The innermost layer of the cortex is called the endodermis. 31 Shoot Apical Meristems A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip. Axillary buds develop from meristematic cells left at the bases of leaf primordia. Lateral shoots develop from axillary buds on the stem’s surface. In most eudicots, the vascular tissue consists of vascular bundles that are arranged in a ring. In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring. 32 Shoot Apical Meristems 33 Tissue organization of leaves The epidermis in leaves is interrupted by stomata, which allow CO2 exchange between the air and the photosynthetic cells in a leaf. Each stomatal pore is flanked by two guard cells, which regulate its opening and closing. The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis. 34 Vascular Cambium The vascular cambium is a cylinder of meristematic cells one cell layer thick. It develops from undifferentiated parenchyma cells. In cross section, the vascular cambium appears as a ring of initials. The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside. 35 Cork cambium The cork cambium gives rise to the secondary plant body’s protective covering, or periderm. Periderm consists of the cork cambium plus the layers of cork cells it produces. Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm. Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air. 36 Resource Acquisition and Transport The success of plants depends on their ability to gather and conserve resources from their environment. The transport of materials is central to the integrated functioning of the whole plant. Diffusion, active transport, and bulk flow work together to transfer water, minerals, and sugars. 37 Shoot architecture Stems serve as conduits for water and nutrients, and as supporting structures for leaves. Phyllotaxy, the arrangement of leaves on a stem, is specific to each species. Light absorption is affected by the leaf area index, the ratio of total upper leaf surface of a plant divided by the surface area of land on which it grows. Leaf orientation affects light absorption 38 Plant Transport Transport begins with the absorption of resources by plant cells. The movement of substances into and out of cells is regulated by selectively permeable membrane. Diffusion across a membrane is passive transport. The pumping of solutes across a membrane is active transport and requires energy. Most solutes pass through transport proteins embedded in the cell membrane. 39 Plant Transport The most important transport protein for active transport is the proton pump. Proton pumps in plant cells create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work. They contribute to a voltage known as a membrane potential. Cotransport - a transport protein couples the diffusion of one solute to the active transport of another. 40 Diffusion of water Physical pressure increases water potential. Negative pressure decreases water potential. 41 Diffusion of water If a flaccid cell from an isotonic solution is placed in an environment with a higher solute concentration, the cell will lose water and undergo plasmolysis. If the same flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid. 42 Diffusion of water Turgor loss in plants causes wilting, which can be reversed when the plant is watered. Aquaporins are transport proteins in the cell membrane that allow the passage of water. The rate of water movement is likely regulated by phosphorylation of the aquaporin proteins. 43 Major pathways of transport Transport is also regulated by the compartmental structure of plant cells. The plasma membrane directly controls the traffic of molecules into and out of the protoplast. The plasma membrane is a barrier between two major compartments, the cell wall and the cytosol. 44 Major pathways of transport Transmembrane route: out of one cell, across a cell wall, and into another cell Symplastic route: via the continuum of cytosol Apoplastic route: via the cell walls and extracellular spaces 45 Bulk Flow Efficient long distance transport of fluid requires bulk flow, the movement of a fluid driven by pressure. Water and solutes move together through tracheids and vessel elements of xylem, and sieve-tube elements of phloem. Efficient movement is possible because mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm. 46 Bulk Flow Most water and mineral absorption occurs near root tips, where the epidermis is permeable to water and root hairs are located. Root hairs account for much of the surface area of roots. After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals. 47 Transpiration Plants lose a large volume of water from transpiration, the evaporation of water from a plant’s surface. This creates a negative pressure at the stomate opening (where water was lost). Water is replaced by the bulk flow of water and minerals, called xylem sap, from the steles of roots to the stems and leaves. 48 Transpiration At night, when stomates are closed, transpiration is very low. Root cells continue pumping mineral ions into the xylem of the vascular cylinder, lowering the water potential. Water flows in from the root cortex, generating root pressure. Root pressure sometimes results in guttation, the exudation of water droplets on tips or edges of leaves … usually in small plants. 49 Transpiration Pull Water is pulled upward by negative pressure in the xylem Water vapor in the airspaces of a leaf diffuses down its water potential gradient and exits the leaf via stomata. (This creates a low - a negative pressure). Transpiration produces negative pressure (tension) in the leaf, which exerts a pulling force on water in the xylem, pulling water into the leaf. 50 Cohesion and Adhesion The transpirational pull on xylem sap is transmitted all the way from the leaves to the root tips and even into the soil solution. Transpirational pull is facilitated by cohesion of water molecules to each other (so water column rises unbroken) and adhesion of water molecules to the xylem vascular tissue. 51 Xylem Sap The movement of xylem sap against gravity is maintained by the transpiration- cohesion-tension mechanism. Transpiration lowers water potential in leaves, and this generates negative pressure (tension) that pulls water up through the xylem. There is no energy cost to bulk flow of xylem sap. 52 Stomata Leaves generally have broad surface areas and high surface-to-volume ratios. These characteristics increase photosynthesis and increase water loss through stomata. About 95% of the water a plant loses escapes through stomata. Each stoma is flanked by a pair of guard cells, which control the diameter of the stoma by changing shape. 53 Stomatal Opening and Closing Changes in turgor pressure open and close stomata. These result primarily from the reversible uptake and loss of potassium ions by the guard cells. Generally, stomata open during the day and close at night to minimize water loss. 54 Xerophytes Xerophytes are plants adapted to arid climates. They have leaf modifications that reduce the rate of transpiration. Some plants use a specialized form of photosynthesis called crassulacean acid metabolism CAM where stomatal gas exchange occurs at night. 55 Translocation The products of photosynthesis are transported through phloem by the process of translocation. Phloem sap is an aqueous solution that is high in sucrose = disaccharide. It travels from a sugar source to a sugar sink 56 Translocation A sugar source is an organ that is a net producer of sugar, such as mature leaves. A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb. Sugar must be loaded into sieve-tube elements before being exposed to sinks. Transfer cells are modified companion cells that enhance solute movement between the apoplast and symplast. 57 Translocation In many plants, phloem loading requires active transport. Proton pumping and cotransport of sucrose and H+ enable the cells to accumulate sucrose. At the sink, sugar molecules are transported from the phloem to sink tissues and are followed by water. 58 Angiosperm Angiosperm flowers can attract pollinators using visual cues and volatile chemicals. Many angiosperms reproduce sexually and asexually. Symbiotic relationships are common between plants and other species. 59 Alternation of Generation Diploid (2n) sporophytes produce spores by meiosis 2n ---> n these spores (n) grow into haploid (n) gametophytes. Gametophytes produce haploid (n) gametes by mitosis fertilization of gametes produces a zygote = sporophyte cell (2n). 60 Flower Structure Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle. Flowers consist of four floral organs: sepals, petals, stamens, and carpels. 61 Flower Structure A stamen consists of a filament topped by an anther with pollen sacs that produce pollen. A carpel / pistil has a long style with a stigma on which pollen may land. At the base of the style is an ovary containing one or more ovules. 62 Flower Structure Complete flowers contain all four floral organs. Incomplete flowers lack one or more floral organs, for example stamens or carpels. Clusters of flowers are called inflorescences. 63 Development of Male Gametophytes Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers. If pollination succeeds, a pollen grain: generative nucleus ---> 2 SPERM, and tube nucleus ---> produces a pollen tube that grows down into the ovary and discharges 2 sperm near the embryo sac. The pollen grain consists of the two- celled male gametophyte and the spore wall. 64 Development of Female Gametophytes Within an ovule, megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes. 65 66 Pollination In angiosperms, pollination is the transfer of pollen from: anther to stigma Pollination can be aided by environmental agents such as: wind, water, bee, moth and butterfly, fly, bird, bat, or water. 67 Double Fertilization After landing on a receptive stigma, a pollen grain produces a pollen tube that extends between the cells of the style toward the ovary. Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac in the ovule. Sperm + egg = zygote 2n Sperm + two polar nuclei = endosperm 3n One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm. 68 Seed Development After double fertilization, each ovule develops into a seed. The ovary develops into a fruit enclosing the seed(s). 69 Endosperm Development Endosperm development usually precedes embryo development. In most monocots and some eudicots, endosperm stores nutrients that can be used by the seedling. In other eudicots, the food reserves of the endosperm are exported to the cotyledons. 70 Structure of Mature Seed The embryo and its food supply are enclosed by a hard, protective seed coat. The seed enters a state of dormancy. In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two thick cotyledons (seed leaves). Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl. 71 Structure of Mature Seed A monocot embryo has one cotyledon. Grasses, such as maize and wheat, have a special cotyledon called a scutellum. Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root. 72 Seed Dormancy Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling. The breaking of seed dormancy often requires environmental cues, such as temperature or lighting changes. 73 Seed Germination Germination depends on imbibition, the uptake of water due to low water potential of the dry seed. The radicle (embryonic root) emerges first. Next, the shoot tip breaks through the soil surface. 74 Fruit Form and Function A fruit develops from the ovary. It protects the enclosed seeds and aids in seed dispersal by wind or animals. A fruit may be classified as dry, if the ovary dries out at maturity, or fleshy, if the ovary becomes thick, soft, and sweet at maturity. 75 Fruit Form and Function Fruits are also classified by their development: Simple, a single or several fused carpels. Aggregate, a single flower with multiple separate carpels. Multiple, a group of flowers called an inflorescence. 76 Fruit Dispersal Fruit dispersal mechanisms include: Water Wind Animals 77 Asexual Reproduction Many angiosperm species reproduce both asexually and sexually. Sexual reproduction results in offspring that are genetically different from their parents. Asexual reproduction results in a clone of genetically identical organisms. 78 Asexual Reproduction Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction. In some species, a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems. Apomixis is the asexual production of seeds from a diploid cell. 79 Asexual Reproduction Asexual reproduction is also called vegetative reproduction. Asexual reproduction can be beneficial to a successful plant in a stable environment. However, a clone of plants is vulnerable to local extinction if there is an environmental change. Sexual reproduction generates genetic variation that makes evolutionary adaptation possible. 80 Self-Fertilization Many angiosperms have mechanisms that make it difficult or impossible for a flower to self-fertilize. Dioecious species have staminate and carpellate flowers on separate plants. The most common is self- incompatibility, a plant’s ability to reject its own pollen. 81 Hormones Hormones are chemical signals that coordinate different parts of an organism. Any response resulting in curvature of organs toward or away from a stimulus is called a tropism = a growth response. Tropisms are often caused by hormones. 82 Auxin Stimulates elongation in coleoptiles Can be synthetic or naturally occurring. Most important auxin: Indole Acetic Acid (IAA) which stimulates cell elongation Major site of synthesis is the shoot apical meristem IAA diffuses down the stem and different plant parts 83 Cytokinins Triggers cell division in plants Zeatin is the naturally occurring cytokinin in plants Produced in actively growing tissues like the root tips, the embryos and the developing fruits Distributed through the xylem 84 Gibberellins Stimulates stem elongation through cell elongation and cell division. Synthesized in meristematic regions, young leaves, and developing seeds Gibberellic acid 3 is the natural gibberellin in plants Dwarf varieties cannot produce sufficient gibberellins Applying gibberellin causes the internodes to elongate 85 Ethylene The only gaseous plant growth regulator Produced by wounded tissues, ripening fruits, and aging plant parts It slows down rather than promotes plant growth Best known as fruit-ripening agent 86 Abscisic Acid Growth inhibitory hormone Causes buds and seeds to become dormant Also known as stress hormone because it brings about the closing of stomata during conditions of drought or water stress 87  Gravitropism of growing stems and other plant parts of growing toward sources stems and other plant parts of light. of growing stems and other plant toward parts of light. sources toward sources of light. In general, stems are positively In general, phototropic, growingstems are positively toward a light In general, stemssource, are positively phototropic, while growing most roots toward do not a light respond phototropic, growing toward to light or, in aexceptional source, light while most rootsexhibit cases, do not respond source, while most onlyrootstodolight a weak not respond or, negativein exceptional phototropiccases, exhibit to light or, in exceptional response. cases, only exhibit a weak negative phototropic only a weak negative phototropic response. response. 88 Brassinosteroids Known to be present throughout the plant kingdom Needed for plant growth and development 89 Tropism Positive or negative growth responses of plants to external stimuli that usually come from one direction. Some responses occur independently of the direction of the stimuli and are referred to as nastic movements. 90 Phototropism Involve the bending of growing stems and other plant parts toward sources of light. In general, stems are positively phototropic, growing toward a light source, while most roots do not respond to light or, in exceptional cases, exhibit only a weak negative phototropic response. 91 Gravitropism The response of a plant to the gravitational field of the earth. Gravitropic responses are present at germination when the root grows down and the shoot grows up. 92 Thigmotropism Response of a plant or plant part to contact with the touch of an object, animal, plant, or even the wind. 93 Other tropisms Electrotropism (respone to electricity) Chemotropism (response to chemicals) Traumotropism (response to wounding) Thermotropism (response to temperature) Aerotropism (response to oxygen) Geomagnetotropism (response to magnetic fields) Skototropism (response to dark) 94 References Lisa A. Urry, Michael L, Cain, Peter V. Minorsky, Steven A, Wasserman, Jane B. Reece (2017), Campbell Biology Eleventh Edition, Pearson, New York. ISBN 10:0-134-09341-0 Formacion, M. J., Gacutan, M. V. C., & Katalbas, M. S. S. (2011). Fundamentals of Biology (1st ed.). Rex Book Store. 95