Plant Form and Function BIOL 1306 PDF

6/21/23 Living Things Are Organized and Studied at Different Levels • Cells are the smallest unit of life • Similar cells group together to form tissues • Multiple tissues come together to form organs Plant Form and Function BIOL 1306: Biology 1 for Majors Jenifer Gifford, Ph.D. [email protected]...

6/21/23 Living Things Are Organized and Studied at Different Levels • Cells are the smallest unit of life • Similar cells group together to form tissues • Multiple tissues come together to form organs Plant Form and Function BIOL 1306: Biology 1 for Majors Jenifer Gifford, Ph.D. [email protected] • Organs with related functions are grouped together into organ systems • Organ systems work together to support the organism. • At each level, the structure determines the function 0 1 Survival of the Fit Enough Structure Determines Function at all Levels Correlations between structure and function begin at molecular level: • Protein shape correlates with their roles as enzymes, structural components of cell, or transporters. Similar correlations between structure and function occur at the cellular level: • Example: Cells that secrete digestive enzymes contain a lot of rough ER and Golgi compared to non-secretory cells 2 • Inherited physical structures are adaptations that enhance a plant or animal’s chances of survival and reproduction • Structures are often just “good enough” to function and are not necessarily perfect in design • Overarching themes of biology: – Structure determines function – Structures/functions often support survival and reproduction 3 1 6/21/23 Learning Goals 1. Compare and contrast the structures of monocots vs. dicots 2. Describe the overall structure of a plant (roots, shoots, and leaves) including information regarding the diversity within these structures and the function of each major component 3. Explain the importance of surface area to absorption 4. Describe the structure and function of epidermal, ground, and vascular tissues 5. Describe which structures within a plant are responsible for primary vs. secondary growth 4 Introduction to Angiosperms • Flowers are the distinguishing characteristics of plants classified as angiosperms; All fruits come from flowers • Angiosperms have dominated the earth for 100+ million years; 250,000 species of flowering plants • A few hundred domesticated species provides most of our food: beets & carrots; apples, nuts, berries, squashes; peas, peanuts and beans (legumes); wheat, rice and corn (grasses) 5 Two classes of angiosperms: Monocots and Dicots • Angiosperms are characterized broadly by the number of leaves that appear upon sprouting. • These leaves are called cotyledons Two classes of angiosperms: Monocots and Dicots Monocots and dicots differ in: – number of cotyledons (seed leaves) – pattern of leaf venation – arrangement of stem vascular tissue – number of flower parts – root structure Arabidopsis Dicots 6 Arabidopsis Grass Grass Monocots 7 2 6/21/23 Monocot or Dicot? PLANT FORM AND FUNCTION: FLOWERS AND SEEDS ARE DESIGNED FOR REPRODUCTIVE SUCCESS 8 9 The Flower is the Organ of Sexual Reproductive Plant Lifecycles 10 Flowers typically contain four types of modified leaves called floral organs. 1. Sepals enclose and protect a flower bud. 2. Petals: colorful and fragrant, advertising the flower to pollinators. 3. Stamens consist of a filament Stamen Anther tipped by an anther, which contains sacs where pollen Filament is produced. 4. Carpels: long slender style with a sticky stigma at its tip. • Stigma is a landing platform for pollen. Petal • Contains the ovary and one or more ovules, each containing a Ovary (Ovules) developing egg and supporting cells Stigma Style Carpel Ovary Sepal 11 3 6/21/23 Types of Fertilization Some plants are Male or Female Self Fertilization Cross Fertilization 12 13 The Development of Pollen/Ovules Results in Reproduction Pollen may be carried by wind, water, and animals. Pollination is the transfer of pollen from anther to stigma. After pollination, the pollen grain germinates on the stigma. – Its tube cell gives rise to the pollen tube, which grows downward into the ovary. – When the pollen tube reaches the base of the ovule, it enters the ovary and discharges two sperm near the embryo sac. Double Fertilization: One sperm fertilizes the egg; the other contributes its nucleus to the large diploid central cell of the embryo sac. This becomes the endosperm. 14 15 4 6/21/23 The Ovary Develops into a Fruit The Ovule Develops into a Seed • Post-fertilization: ovule begins developing into a seed. • Seed stockpiles proteins, oils, and starches. • Embryonic development: zygote divides into two cells. Ovule • Cell division produces a ball of cells that becomes the embryo. • A thread of cells anchors the embryo to the parent plant and pushes the embryo into the endosperm (food storage). • Embryo develops in the ovule to become a mature seed. • Near the end of its maturation, the seed loses most of its water and forms a hard, resistant seed coat. Zygote Cotyledons Endosperm Seed coat Two cells • While the seeds are developing from ovules, hormonal changes triggered by fertilization cause the flower’s ovary to grow, thicken, and mature into a fruit. • A fruit is a mature ovary that acts as a vessel, housing and protecting seeds and helping disperse them from the parent plant. • Although a fruit typically consists of a mature ovary, it can include other flower parts as well. Shoot Embryo Root 16 Seed 17 Seed Dispersal Fruits are Just Plant Ovaries 18 19 5 6/21/23 The Flower is the Organ of Reproduction In the life cycle of a generalized angiosperm: 1. Fertilization occurs in an ovule within a flower. 2. The ovary develops into a fruit and the ovule develops into Pollen the seed containing the embryo. The fruit protects the seed Ovary and aids in dispersing it. Embryo 3. Completing the life cycle, sac Fertilization within ovule the seed then germinates Ovule (begins to grow) in a suitable habitat. Fruit (from ovary) Mature 4. The embryo develops into Seed (from ovule) plant a seedling, and the Embryo seedling grows into a mature plant. Plant Tissues Develop from Meristem and Form the Major Plant Organs Germinating seed 20 21 Review: Plant Cells Although eukaryotic cells share many key features, plant cells have several features not found in animal cells: – Plant cells are surrounded by cellulose-rich primary cell wall – Some plant cells have a rigid secondary cell wall – Cytoplasm of adjacent plant cells are connected by plasmodesmata – Chloroplasts are the site of photosynthesis – Large central vacuole: • Contain aqueous solution called cell sap and store waste, water, and nutrients 22 Early Plant Growth When a plant embryo first develops, the first cells are called meristem cells. • Meristem cells are undifferentiated cells are able to divide indefinitely and give rise to many types of differentiated cells 23 6 6/21/23 Dermal Tissue Early Plant Development Even after development, apical meristems tissue exists at the tips of stems and roots in adult plants. It produces the three types of meristem, which produces three specialized tissues in the plant: 1. Epidermal tissue forms the outer protective covering 2. Ground Tissue fills the interior of the plant 3. Vascular Tissue transports water and nutrients within the plant and also provides support 24 • Dermal tissue system consists of dermal tissue: – Tissue is also called epidermis – Epidermis is outermost layer of cells – In shoots, primary function is to protect the plant – In roots, primary function is absorbing water and nutrients • Epidermis is made up of several different cell types and thus represents a complex tissue 25 Ground Tissue Dermal Tissue Structures • The Cuticle is a waxy layer that forms a continuous sheet on surface of leaves and stems. It minimizes water loss and forms a barrier to protect plant from viruses, bacteria, and spores from parasitic fungi Ground tissue is responsible for - photosynthesis - carbohydrate storage at the roots - structural support • Stomata are pores that allow CO2 to enter and O2 to exit photosynthetically active tissues • Root Hairs increase the surface area of the roots in order to increase water uptake • Trichomes are hair like structures that can serve as defensive or glandular structures 26 27 7 6/21/23 Vascular Tissue Ground Tissue Vascular tissue system is made up of two complex tissues: xylem and phloem – Xylem conducts water and dissolved nutrients from the root system to the shoot system – Phloem conducts sugars, amino acids, hormones, and other substances from roots to shoots and from shoots to roots Most photosynthesis and carbohydrate storage takes place in the ground tissue system 1. Parenchyma contains chloroplasts or starch granules 2. Collenchyma provide flexible structural support to actively growing parts of the plant 3. Sclerenchyma contains tough, rigid lignin as well as cellulose Parenchyma Collenchyma Xy HIGH Phlo LOW 28 29 Vascular Tissue: Phloem Vascular Tissue: Xylem There are two types of waterconducting cells in Xylem: 1. The xylem of all vascular plants contains tracheids with pits through which water moves 2. In angiosperms, xylem also contains vessel elements with perforations for water transport They form chains with overlapping ends that create tubes within vascular tissue 30 Phloem contains two types of specialized cells: 1. Sieve-tube elements are long, thin cells with perforated ends called sieve plates 2. Companion cells maintain the cytoplasm and plasma membrane of sieve-tube elements 31 8 6/21/23 Bringing the Tissues Together PLANT FORM AND FUNCTION: ROOTS, SHOOTS, AND LEAVES 32 33 Nutrient Absorption Structure Influences Nutrient Acquisition • For photosynthesis to occur efficiently, plants need large amounts of light, CO2, and water • Both the root and shoot systems function in absorption • Roots absorb water soil nutrients and shoots absorb light • Plants that are most efficient absorbers have a large surface area compared to its volume • Additionally, for synthesis of necessary biomolecules, plants need nitrogen, phosphorus, potassium, magnesium, and other nutrients • Two systems can be used to acquire resources: • Shoot system harvests light and carbon dioxide from atmosphere to produce sugars • Root system anchors plant and takes in water and nutrients from soil 34 35 9 6/21/23 Root Systems Roots, Shoots, and Leaves are Diverse Plant diversity can be analyzed on three levels: 1. Morphological diversity among species 2. Phenotypic plasticity, or changes in structure in individual’s root system in response to the environment. Genetically identical individuals may have very different systems/structures in different environments 3. Modified structures that are specialized for unusual functions 36 • Many root systems have taproot and fibrous roots • There are many key functions of the root system: – Roots anchor plant to the soil – Roots absorb ions and water from soil – Roots conduct water and ions to the shoot system – Roots obtain energy from the sugar in the shoot system – Roots store material produced in the shoot system for later use 37 Modified Root Systems Phenotypic Plasticity of Root Systems Example of Phenotypic Plasticity: • Spruce trees tend to have root systems less than a meter deep in waterlogged soil • Wet soil lacks oxygen, so their roots are shallow • Same tree in drier soil would have deeper root system 38 Adventitious roots grow from shoot system: – In ivy, adventitious anchor roots act to anchor the plant – Prop roots of corn brace the plant – Pneumatophores—specialized lateral roots in genus Avicennia: • Function in gas exchange • Oxygen in atmosphere can diffuse into root system through pneumatophores Biennial plants, such as carrots and beets have storage roots that are a thick taproot that stores carbohydrates during plant’s first two growing seasons 39 10 6/21/23 Shoot Systems The shoot system contains one or more stems and leaves • Stems: • Vertical aboveground structures • Consist of nodes where leaves are attached, and internodes, or segments between nodes Types of stems: • Herbaceous Stems: Exhibit only vertical growth. There is no bark Found in herbs, most standard flowering plants (dandelions, roses, tulips etc). Outermost surface is covered in a cuticle • Woody Stems: Exhibits both vertical and outward growth (bark). Found in trees. bushes and shrubs 40 Primary Growth Lengthens the Roots and Shoots Apical meristems are found at the tips of roots and in the buds of shoots and results in primary growth, which allows roots to push downward through the soil and shoots to grow upward, increasing exposure to light and CO2 The apical meristems of root tips are covered by a root cap. • Root growth occurs behind the root cap in three zones. 1. Zone of cell division, which includes the apical meristem and cells derived from it. 2. Zone of elongation, where cells lengthen by as much as 10 times. 3. Zone of differentiation, where cells differentiate into dermal, vascular, and ground tissues, including the formation of primary xylem and primary phloem. 41 Secondary Growth Thickens the Diameter Secondary growth is an increase in thickness of stems and roots and occurs at Lateral Meristems/Cambium • Cambium differs in location from an apical meristem. It forms a cylinder that runs the length of the root, trunk, or branch. Cambium cells divide to increase the width of the plant • There are two types of cambia in plants: 1. Vascular cambium is located between secondary xylem and secondary phloem 2. Cork cambium is located near the outer perimeter of the root, trunk, or branch 42 Secondary Growth Thickens the Diameter Vascular cambium produces: 1. Secondary xylem which produces wood toward the interior of the stem. 2. Secondary phloem produces the inner bark toward the exterior of the stem. Cork cambium produces cells in one direction, the outer bark, which is composed of cork cells. 43 11 6/21/23 Secondary Growth Thickens the Diameter You hammer a nail into a tree trunk 2 meters above the ground. The tree is currently 5 meters tall and grows taller at a rate of 1 meter per year. How far above ground level will the nail be in 10 years? A. 2 meters B. 5 meters C. 15 meters D. 20 meters 44 45 A tree will die if the bark is stripped off around the entire circumference of the tree. Why is this so? A. Water-conducting cells in xylem are removed, and the tree can no longer conduct water and minerals up the trunk to the leaves. B. Phloem cells are removed, sugars can no longer be transported from the leaves to the roots, and the roots will die. C. The apical meristems are removed, preventing any further increase in height. Oxygen is lethal to the inner wood of tree trunks. D. 46 Phenotypic Plasticity of Shoot Systems Morphological Diversity and Phenotypic Plasticity • Shoot systems range in size • Size and shape of a plant’s shoot system can vary based on variation in growing conditions • Variation in size and shape of shoot system of various species minimizes competition for light: – Silversword plants native to Hawaii have shoot systems that are particularly diverse – Lush environments and competition for light favors taller shoot systems – Dry, windblown habitats favor short stems that are more anchored to the soil 47 12 6/21/23 Modified Shoot Systems Genetically identical plants look different based on the environment they’re grown in Shoot System Plasticity However, genetics is still an important factor for the phenotype, as genetically different plants are phenotypically very different in the same environments. 48 49 Phenotypic Plasticity of Leaves Leaf Structural Diversity • Vast majority of photosynthesis occurs in leaves: – Leaf’s relatively large surface area available for absorbing photons and supporting photosynthesis • Simple leaf has two main structures: Expanded blade and a Stalk called petiole • Arrangement of leaves on stem may vary • Although leaves do not grow continuously, they do exhibit phenotypic plasticity • Oak tree leaves vary depending on amount of sunlight they are exposed to: Shade leaves: • Relatively large and broad, providing high surface area to maximize photon absorption Sun leaves: • Have relatively small surface area, reducing water loss in areas of body where light is abundant 50 51 13 6/21/23 Modified Leaves sometimes look like flowers Modified Leaves • Onion bulbs store nutrients • The leaves of succulents store water • Tendrils enable vines to climb • The bright red leaves of poinsettias attract pollinators • The tubelike leaves of the pitcher plant trap insects • Cactus spines protect the stem 52 53 54 14