Plant Science Plant Structures Instructional Materials Service Texas

Plant Science Plant Structures Instructional Materials Service Texas A&M University - 8384 - 1

Plant Structures • • • Parts of a Vascular Plant Root Structure Stem Structure (External) Leaf Structure Parts of a Complete Flower 2

Parts of a Vascular Plant 3

Plant Organ Functions • Roots support the plant and supply it with water and nutrients. • Stems connect the root and leaves. • Leaves capture energy from the sunlight and use it to make food for the plant. • Reproductive structures attract pollinators and produce seeds and fruits. 4

• All living organisms consist of cells. Groups of cells with similar functions form tissues. Tissues with similar functions form organs. 5

Plant Organs Plant organs include their roots, stems, leaves, and reproductive structures. Each plant organ performs a specialized task in the life of a plant. • Roots, stems, and leaves are all vegetative structures. • Flowers, seeds, and fruits make up reproductive structures. 6

• The cell is the basic structural and functional unit for all living organisms. Organelles within a cell perform specialized functions. 7

Organelles with common functions in both plant and animal cells include: • Nucleus – synthesizes ribosomes and RNA and stores DNA • Endoplasmic Reticulum (ER) – prepares protein for export; synthesizes steroids; regulates calcium levels; and breaks down toxins • Mitochondrion – converts energy from organic compounds to energy for cellular activities 8

• Ribosomes – organize protein production • Microtubules – contribute to cell support and division • Golgi Complex – processes and packages substances made by the cell • Cell membrane – semi-permeable structure that separates the cellular contents from the outside • Lysosomes – digest old organelles and foreign substances 9

• Three organelles that are found only in plant cells are plastids, vacuoles, and the cell wall. Plastids contain DNA, store starches and fats, and contain pigments involved in photosynthesis. Vacuoles store metabolic wastes and often occupy as much as 90% of a cell’s volume. The cell wall is composed of cellulose fiber and gives plant cells a very defined shape. 10

Root Structure Zone of Differentiation Epidermis Cortex Root Hairs Phloem Tubes Zone of Elongation Xylem (water transport) Root Cap Meristem 11

The Epidermis The epidermis is the outermost layer of cells surrounding the root. The cells of the epidermis are responsible for absorbing water and minerals from the soil 12

The Cortex The cortex is a layer of tissue between the epidermis and the vascular tissue. Cortex cells function in the movement of water and in food storage. 13

Root Hairs Root hairs are found along the main root and perform much of the actual work of water and nutrient absorption. Root Hairs Most plants produce root hairs that only live a few days or a few weeks. As a plant grows, new root hairs form. 14

Xylem is the supporting and water conducting tissue of vascular plants. Xylem 15

Phloem is the food conducting tissue of vascular plants, made up of sieve tubes and other cellular material. 16

Meristem The meristem is at the tip of the root and is responsible for manufacturing new cells. This is the area where cell division and growth occur. Meristem 17

PLANT TISSUE SYSTEMS • A plant tissue is an organized mass made up of similar types of cells. Three classifications of tissues based on their origin, structure, and physiology are: dermal tissue, ground tissue, and vascular tissue. 18

• Dermal tissue forms the outer layer, or epidermis, of the plant. This type of tissue is responsible for a plant’s environmental interactions including light passage and gas exchange. In some types of plants, this tissue often has environmental adaptation features that regulate water loss from the plant and the exchange of carbon dioxide and oxygen from within the plant. 19

• Ground tissue consists of three types of cells that function in storage, metabolism, and support. Parenchyma cells have thin, primary cell walls and highly functional cytoplasm. These types of cells are the most common and abundant type of cells in plant tissues, making up the fleshy parts of fruits, roots, and tubers. 20

• Collenchyma cells are elongated cells with thick cell walls. These types of cells contain cellulose, which provides “flexible” support for plant stems and leaves. Sclerenchyma cells develop extensive secondary cell walls that contain lignin, suberin, and/or cutin. The longevity of these types of cells is short because the rigidity of their cell walls prevents them from exchanging the necessary components needed for active metabolism. 21

• Vascular tissues consist of xylem and phloem. Xylem consists of trachids and vessels, which function to conduct and transport water and minerals from the soil up through the plant. Phloem consists of sieve elements and companion cells, which function in the transport of sugars, amino acids, and other small molecules from the leaves to other parts of the plant. 22

PLANT ORGANS • Dermal, ground, and vascular tissues within a plant associate to form the plant’s organs, which include the roots, stems, leaves, and flowers. 23

Roots • The root is the first plant structure to emerge from a seed during germination. • Roots are mostly found below the soil surface and represent about 50% of a plant’s weight. • The primary functions of roots are to absorb water and nutrients from the soil and to support the plant in an upright position. 24

Root Functions • Roots distribute the food energy produced in the leaves to the rapidly growing areas found at the root tips. • Some plants use their roots as a specialized food storage reserve. • The first root to emerge from a seed is the primary root, or radicle. • Based on the relative sizes of primary and secondary roots, classifications of root systems include taproot, fibrous, and adventitious. 25

Roots (taproot) • Plant root systems are classified based on the relative sizes of their primary and secondary roots. • Plants such as dandelions, carrots, turnips, and most trees have a taproot. • In taproot systems, the primary root thickens and becomes the dominant root. 26

Roots (fibrous) • In fibrous root systems, the primary and secondary roots are of similar diameter. • They remain fairly close to the soil surface. • Fibrous root systems help to prevent the erosion of topsoil during heavy rains. • Plants such as onions, grasses, and corn have fibrous root systems. 27

Root Types Tap Root Fibrous Roots 28

Zones of root growth and differentiation include the: • Meristem – area of active cell division and growth (root tip) • Zone of elongation – nutrient and water absorption occurs causing cells to increase in size • Zone of differentiation/maturation – cells undergo changes to become specific tissues (epidermis, cortex, and vascular tissue) 29

• Root hairs located along the main root form as an outgrowth of the epidermal cells. Their primary function is to absorb water and nutrients from the soil. The root cap, located at the outermost tip of a root, covers and protects the root’s growing region. It also directs root growth through the soil. 30

• A plant’s stems serve as supportive structures for the plant’s leaves. They also function in the transport of water and nutrients from the roots to the leaves and in the transport of food energy created in the leaves to other plant parts. 31

The internal anatomy of a woody stem consists of: • Xylem and phloem – to conduct water, nutrients, and food reserves • Cambium – the site of cell division and active cell growth (meristematic tissue) • Pith – the parenchyma layer at the center of a stem 32

Structures making up the external anatomy of woody and herbaceous stems include: • Terminal buds – growing points located at the tips of stems • Axillary buds – growing points located in the leaf axils • Node – the point of leaf attachment to the stem • Internode – the area of the stem located 33 between nodes

• Some plant stems have developed modifications for protection and to store additional food and water. • Examples of above-ground stem modifications include thorns, prickles, stolons, spurs, pseudobulbs, and cladophylls. Rhizomes, tubers, corms, and bulbs are examples of below-ground stem modifications. 34

• The leaves on a plant function to capture sunlight for the plant processes of photosynthesis. • Plant leaves contain stomata that allow for gas exchange and transpiration. 35

The internal anatomy of a leaf consists of the: • Cuticle – a thin film covering the outer layer of the leaf to protect it from excessive temperatures and water loss • Epidermis – cell layer on the upper and lower sides of a leaf that protects the inner cell layers and contains the guard cells to regulate stomatal opening and closing • Mesophyll – innermost cell layers that contain the palisade parenchyma cells for photosynthesis and the spongy parenchyma cells for gas exchange 36

Leaf Structure Vein Midrib Expanded Portion of Blade (Lamina) Axillary Bud Node Bladestalk (Petiole) Internode Base of Leaf 37

Midrib & Veins Vein Midrib The midrib is the most prominent, central vein in a leaf. Lateral veins are secondary veins that branch from the midrib. Both midribs and lateral veins contain vascular tissue. 38

Leaf Blade (Lamina) The expanded flat portion of a leaf is the leaf blade, or lamina. 39

Petiole (Bladestalk) The petiole attaches the lamina to the plant stem. Petiole 40

Axillary Bud An axillary bud exists on the stem just above the point where the leaf petiole attaches to the stem. 41

• The flat portion of a leaf is the leaf blade (or lamina). The petiole attaches it to the plant stem. Stipules located in the leaf axils function as food manufacturing structures. 42

Stem Structure (External) Terminal Bud Growing Point Young Leaf Axillary Bud Nodes Petiole Internode Abscission Layer 43

Stems function as supportive structures. They hold a plant’s leaves up toward the sun so the leaves can capture energy from sunlight. Stems transport water and nutrients from the roots to the leaves, and food energy from the leaves to the roots. 44

• Flowers are the plant organs that function in plant reproduction. Flowers vary in size, structure, and composition among plant species. 45

Parts of a complete flower include the: Calyx – leaf-like structures that form an outer ring around the base of a flower and function to enclose and protect the flower bud before it opens Corolla – often colorful and/or scented to attract specific pollinators to the flower Pistil – the female reproductive organs (stigma, style, ovary) Stamen – the male reproductive organs (anther, filament) 46

Flower types based on the presence or absence of the four floral parts include: • Perfect complete – contains all four floral parts • Perfect incomplete – lacks only petals and/or sepals • Incomplete – lacks one of the four floral parts • Pistillate – has a pistil, but no stamens (imperfect incomplete flower) • Staminate – has stamens, but no pistil (imperfect incomplete flower) • Sterile – lacks both pistil and stamens 47

• A monoecious plant is one in which staminate and pistillate flowers exist on the same plant. • Dioecious plants are those in which the male (staminate) and female (pistillate) flowers exit on completely separate plants. 48

Parts of a Flower Pollen Grains Stigma Filament Style Anther Petal Pollen Tube Ovule Embryo Sac Microphyle Ovary Sepal Integuments Receptacle 49

Sepals are leaf-like structures that form an outer ring around the base of a flower. Sepals enclose and protect a flower bud before it opens. Sepals The complete ring of sepals is called the calyx. 50

Petals are often the bright and colored part of a flower. Petal colors and scents attract specific pollinators. Petals 51

Stamens Anther Filament The stamen contains both the filament and the anther. The filament is a stalklike structure that holds the anther. Stamens are the male reproductive parts of a flower. 52

Pistil Stigma The pistil includes three parts: 1. Stigma 2. Style 3. Ovary Style Ovary 53

Pistil 1. Stigma The stigma is a sticky, flattened surface that projects upwards towards the pollinator. Birds and insects collect nectar from previously visited plants and brush against the sticky surface of the stigma. 54

Pistil 2. Style The style is a supportive structure that holds the stigma in a position to maximize the chances of pollination. Style 55

Pistil 3. Ovary Pollen Tube Ovule Ovary The ovary is an enlarged structure that contains the female sex cells, or ovules. The pollen tube grows through the ovary and into an ovule. 56

Receptacle The enlarged part of the pedicel where it joins the flower is the receptacle. Receptacle 57

Pedicel The pedicel (flower stalk) supports the flower. Pedicel 58

Acknowledgements Kristi Falco, Graduate Assistant, Instructional Materials Service, researched and developed the information used in this Power. Point Presentation. Christine Stetter, Artist, Instructional Materials Service, developed and illustrated this Power. Point Presentation. . Keith Zamzow, Curriculum Specialist, Instructional Materials Service, edited and reviewed this Power. Point Presentation. Vickie Marriott, Office Software Associate, Instructional Materials Service, edited this Power. Point Presentation. 59

ALL RIGHTS RESERVED Reproduction or redistribution of all, or part, of this presentation without written permission is prohibited. Instructional Materials Service Texas A&M University 2588 TAMUS College Station, Texas 77843 -2588 http: //www-ims. tamu. edu 2006 60