Lecture 4. Structure and Physiology of Plants PDF

Lecture 4. Structure and Physiology of Plants Learning Objectives 1. Discuss the different organ systems of plants. 2. Enumerate the different plant tissues and their functions. 3. Explain reproduction in angiosperms.  Dicot- angiosperms, having an embryo with two cotyledons, leaves...

Lecture 4. Structure and Physiology of Plants Learning Objectives 1. Discuss the different organ systems of plants. 2. Enumerate the different plant tissues and their functions. 3. Explain reproduction in angiosperms.  Dicot- angiosperms, having an embryo with two cotyledons, leaves are reticulate venation, flowers arranged in multiple of four or five Monocot- herbaceous angiosperms, having an embryo with a single cotyledon, parallel venation, flowers arranged in multiples of threes 2 Dicot and Monocot Stem 3  Part Function 1. Cuticle protective film covering the outermost skin layers of leaves 2. Epidermis protective tissue that covers the entire surface of the plant, regulates gas exchange, regulates secretion of metabolic substances 3. Hypodermis outermost cell layer of the cortex, immediately under the epidermis, in shoots hypodermis maybe composed of parenchyma, collenchyma, or sclerenchyma 4. Chlorenchyma chlorophyll-containing parenchyma of plants 5. Cortex lying below the epidermis but outside of the vascular bundles. The cortex is composed mostly of large thin-walled parenchyma cells of the ground tissue system 4 6. Ground forms the bulk of the plant body. It is used for tissues storing food and providing physical support to the plant. There are mainly three types of ground tissues, they are parenchyma, collenchyma and sclerenchyma. 7. Parenchyma living cells that have ability to divide throughout lifetime, thin cell walls, stores food and provide turgidity, found in leaf, fruits, and young stems 8. Sclerenchyma plant tissue providing mechanical stiffness and strength, includes fibers and sclereids, composed of dead cells with heavily thickened walls containing lignin and cellulose 9. Vascular a collection of tissues in a plant that transport bundles water, nutrients, and minerals up from the roots to the leaves and flowers. The xylem tissue carries water and minerals up from the roots, 5  while the phloem tissue carries sugars and other nutrients down from the leaves 10. Protoxylem primary xylem that develops first during primary growth, grows before maturation 11. Metaxylem formed after protoxylem during primary growth, grows after maturation, extensive lignification 12. Phloem carries sugars and other nutrients down from the leaves 13. Endodermis the innermost layer of cortex in land plants. It is a cylinder of compact living cells, the radial walls of which are impregnated with hydrophobic substances (Casparian strip) to restrict apoplastic flow of water to the inside 14. Pericycle a unique layer of cells in plants, named after its position, encircling the vascular tissue in stems and roots 6 15. Cambium layer of actively dividing cells between xylem and phloem tissues that is responsible for the secondary growth of stems and roots (secondary growth occurs after the first season and results in increase in thickness) 16. Bundle sheath a layer of cells in plant leaves and stems that surrounds a vascular bundle 17. Pith soft region comprised of parenchyma cells found not just in the central portion of the stem but also in the roots of certain plants 7 Monocot Stem 8 Dicot Stem 9 Dicot and Monocot Root 10  Part Function 1. Root hair cylindrical extensions of root epidermal cells that are important for acquisition of nutrients, microbe interactions, and plant anchorage 2. Piliferous the root-hair zone is also known as layer rhizodermis or epiblema. It is the region where the epidermis of a root is present at a short distance from the root tip which produces ample root hairs and also functions in the process of uptake of water and nutrients 3. Epidermis epidermal cells of plants produce root hairs, the tubular outgrowths that increase the surface of the roots. The epidermal cells of roots that produce root hairs are called trichoblasts, whereas epidermal cells without 11  the capability of root hair formation are called as atrichoblasts 4. Cortex serve as a storage area for reserve foods. The innermost layer of the cortex in the roots of vascular plants is the endodermis. The endodermis is responsible for storing starch as well as regulating the transport of water, ions and plant hormones 5. Endodermis the cylindrical boundary that separates the inner vascular tissue from the outer cortex and functions as an apoplasmic barrier for selective nutrient uptake 6. Protoxylem first formed xylem in which the lignification starts before the completion of the elongation. It is usually made up of tracheids, vessels, and xylem parenchyma. The late 12  formed xylem is called metaxylem and it bears larger tracheids and vessels 7. Stele central part of the root or stem containing the tissues derived from the procambium, these include vascular tissue, in some cases ground tissue (pith) and a pericycle, which, if present, defines the outermost boundary of the stele. Outside the stele lies the endodermis, which is the innermost cell layer of the cortex 8. Pericycle a primary root tissue that forms the cell layer surrounding xylem, phloem, and procambium cells 9. Metaxylem formed after protoxylem during primary growth, grows after maturation, extensive lignification 13 10. Phloem carries food downward from the leaves to the roots 11. Xylem plant vascular tissue that conveys water and dissolved minerals from the roots to the rest of the plant and also provides physical support. Xylem tissue consists of a variety of specialized, water-conducting cells known as tracheary elements 12. Pith the soft region comprised of parenchyma cells found not just in the central portion of the stem but also in the roots of certain plants. The primary function of the pith is to transport nutrients throughout the plant and then store the nutrients within its cells 14 Monocot Root 15 Dicot Root 16 Reproductive Structures of Plants Flowers are the reproductive structures of plants Male and female reproductive structures can be found in the same individual plant. Structure Function Petals May be brightly coloured and scented to attract insects Anthers Produce male gametes (in pollen grains) Stamens The male parts of the flower consisting of the anther held up on the filament Filament thin tubular part of stamen, which extends and supports the pollen sac at the top, it carries nutrients to the anther, where the pollen develops Stigma The top of the female part of the flower which collects pollen grains Ovary The bottom of the female part of the flower, produces the female gametes (in ovules) Nectary May be present to produce sugary nectar to attract insects Sepals Protect the unopened flower bud 17  Microsporogenesis o Microspores (haploid: n) are produced from microsporocytes (diploid: 2n) by meiosis o occurs in the microsporangium (pollen sac) o meiosis results in four haploid microspores o Microgametophyte (pollen) develops from microspore Megasporogenesis o Megaspores (haploid: n) also called macrospores are produced from megasporocytes (diploid: 2n) by meiosis o occurs in the megasporangium (ovule) o meiosis results in four haploid megaspore nuclei o Megagametophyte (embryo sac) develops from megaspore 18 Pollination Pollination- transfer of pollen grains from anther to stigma; plants depend on pollinators to transfer pollen. The majority of pollinators are biotic agents such as insects (like bees, flies, and butterflies), bats, birds, and other animals. Other plant species are pollinated by abiotic agents, such as wind and water. Fertilization- takes place inside the ovary when the nucleus of pollen grain fuses with the nucleus of an ovule to produce a zygote Types of Pollination Self-pollination Cross-pollination pollen from the anther is deposited on the stigma of the transfer of pollen from the anther of one flower to the same flower, or another flower on the same plant stigma of another flower on a different individual of the same species. leads to the production of plants with less genetic leads to greater genetic diversity because the diversity, since genetic material from the same plant is microgametophyte and megagametophyte are derived used to form gametes, and eventually, the zygote. from different plants. 19 Steps Involved in Pollination and Fertilisation of a Flowering Plant A. After pollen has landed on the stigma, it grows a pollen tube down through the style to the ovary. B. The nucleus of the pollen grain travels down the pollen tube and fertilises the nucleus in the ovule. C. The fertilised ovule develops into a seed. The seed contains the plant embryo, which contains genetic material from both parents. The ovary develops into the fruit. A B C 20 Double Fertilization After pollen is deposited on the stigma, it must germinate and grow through the style (long and slender stalk that connects the stigma and ovary) to reach the ovule. Microspores, or the pollen, contain two cells: o Pollen tube cell- grows into a pollen tube through which the generative cell travels, it travels through the style to reach the embryo sac, it enters the ovule sac through the micropyle, pollen tube is guided by chemicals secreted by the synergids present in the embryo sac o Generative cell- divides to form two sperm cells, one sperm fertilizes the egg cell, forming a diploid zygote; the other sperm fuses with the two polar nuclei, forming a triploid cell that develops into the endosperm Endosperm- tissue produced inside the seed as a product of double fertilization, provides nutrition in the form of starch 21 References 1. Alcamo E, Warner J (2010) Schaum’s Outline, Microbiology 2e, McGraw Hill Company 2. Clark MA, Choi J, Douglas M (2020) Biology 2e. Rice University, OpenStax 3. Madigan M (2012) Brock Biology of Microorganisms 13e, Pearson Company 4. Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB (2014) Campbell Biology 10e, Pearson 5. Talaro K, Chess B (2012) Foundations in Microbiology 8e, McGraw Hill Company 22