Plant Structure and Organization - 1

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Edwin Daniel
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1 Plant Structure and Organization - 1 In our first unit of Biology 203 we will focus on the structure and function of the higher plants, in particular the angiosperms, or flowering plants. We will look at how plants solve the many problems of life in ways that are similar to and in ways that are different from the animals with which you are now familiar. It may be helpful at first to review some of the characteristics of life from the context of how plants approach life and living. Principles of Plant Biology Structure and Support Living organisms have an organized structure, and exhibit increasing levels of complexity from molecules, to cells and tissues, to integrated systems of organs. This is evident in the cellular structure and organization of plants and repeated over and over in the development of shoot and flower buds and root primordia. Energy Needs Living organisms require energy to survive. Virtually all plants do photosynthesis, providing their own chemical energy, which is then stored as carbohydrate fuel. All living organisms are dependent on this photosynthetic product for their energy source. Plants must do cellular respiration, the process that converts the fuel molecules to the energy needed to do cell work, just as all organisms must. These chemical pathways are virtually the same in all organisms. Dependence on Water All life on earth depends on water. Plants metabolic dependence on water equals that of other organisms. Plants have means of conserving water as do animals. Plants use water pressure (turgor) to maintain strength in soft tissues Plants use water pressure to promote elongation and cell growth (increase in cell dimension). Water is the transport medium for plant nutrients throughout the plant body. Reproduction Plants have great reproductive versatility. Many plants reproduce both asexually and sexually. As plants evolved, dispersal via seeds versus spores (single-cell structures) provides an energy head start for establishing new plants as well as protection for the embryonic plant. In addition, plants have evolved means to ensure successful sexual reproduction in the absence of mobility and means of dispersing young to new locations.

2 Plant Structure and Organization - 2 Growth and Development Living organisms have growth and development. These processes are dependent on the instructions coded in molecules of DNA, the genetic molecule of life. Molecular biology is changing how we know about plant processes just as it is how we know about animals. In particular, the tiny Arabidopsis, often studied in growth and inheritance experiments in the laboratory, is proving to be an excellent genetic tool to look at the molecular events of plant development. Regulation As with animals, hormones (regulatory chemicals) control much of plant metabolism. In addition, environmental cues such as light, touch and gravity are important to plant growth and development. Response to Stimuli Living organisms respond to stimuli, both external and internal. Some plants close their leaves when they are touched; others track the sun's path. Wound tissue forms when branches are broken from trees and chemical signals are relayed from one area of a plant to other areas in response to stimuli. For example: Stomata open and close in response to water stress. Plants respond structurally to conditions of their environment. Tree ring analysis reveals both past and current climate information. Trees grow directionally in response to wind. Defense Plants may have more need to defend against potential predators and competitors than many animals. Most plants lack motility and are fixed in space once germinated. They have evolved a delightful array of physiological (secondary metabolite) defenses as well as structural defenses to deter potential predators. Plants and Ecology Plants form the foundation of the environment s food chain. Without plants and photosynthesis, and the evolution of land plants, we would have no terrestrial ecosystems (at least as we know them). Plants are critical to mineral cycling and maintaining stability of ecosystems. The vast diversity of plants provides diverse habitats on earth for all other organisms in virtually all climates. Plant Value to Human Economy and Esthetics We interact with plants daily. They provide us with food, clothing, shelter, fuel, paper, drugs (medicines), spices and the oxygen we breathe. In the Pacific Northwest, many have employment opportunities in forestry and National Parks (as well as landscaping, nurseries and floristics, not to mention golf courses). Plants decorate our surroundings and stimulate our senses with shape, color and smell. We may have privacy from our neighbors and reduction from stress because of plants in our environment. A walk in the woods or time spent in one s garden restores sanity in a frantic life.

3 Plant Structure and Organization - 3 As we progress through our Biology 203 experience this term we will be addressing how plants meet the challenges of living organisms. We shall start with the process of reproduction and development of flowering plants followed by plant structure and organization and continue with how plants function. First, a brief review of the organization of the flowering plant body may be useful. Plant Organization The basic plant body plan is organized along an axis - with growth originating from both ends (or tips) of the axis. This growth takes place in special cell division regions of the plant called apical meristems. Meristems consist of a few cells called the meristem initials and a set of derivative meristems. Tissues derived from the apical meristems are known as primary growth and result in increase in plant dimension or length of the primary plant body. Plants, in general, exhibit open growth, or continuous growth from their meristems of embryonic origin until they die. At all times the tips of plants are essentially embryonic, with active meristems, while other regions of the same plant may be thousands of years old. Plant development is comprised of three processes: growth, morphogenesis and differentiation. Cell position in the meristem region is critical to plant development. Growth consists of cell division and increase in size. Shape and form of plants (morphology) depends to a large extent on the pattern of cell division and cell enlargement, and the planes of division in meristem regions. Microtubule alignment is critical in determining the plane of cell division. Asymmetrical separation of cytoplasm is also common. The specialization of cells for particular functions is the process of differentiation. Differentiation in plants is related to its position within the plant body, and is ultimately controlled by gene expression in the individual cells. As stated, we will be looking primarily at the structure and function of the angiosperms, or flowering plants. The most distinctive features of flowering plants are their reproductive features. The reproductive organ is the flower. Following reproduction, the embryo and seed are enclosed within a fruit, which develops from the ovary and surrounding tissues of the flower. Flowering plants are divided into two broad groups, the Monocotyledons (Monocots) and the Euicotyledons (Dicots), as well as several smaller ancestral alliances. The monocot and dicot differences are important in our study of plant anatomy. It will make your understanding of plant structure a little easier if you have this introduction first.

Plant Structure and Organization - 4 Two Major Groups of Flowering Plants: Monocotyledonae Dicotyledonae Flower parts in 3's Flower parts in 5's (4's) Leaves with parallel veins Leaf venation palmate

4 Plant Structure and Organization - 4 Two Major Groups of Flowering Plants: Monocotyledonae Dicotyledonae Flower parts in 3's Flower parts in 5's (4's) Leaves with parallel veins Leaf venation palmate or pinnate No true cambium Cambium usually present One cotyledon (seed leaf) Two cotyledons (seed leaves) Scattered vascular bundles Vascular bundles in a ring (cylinder) Sheathing leaf bases Leaves usually have a petiole All of this should make more sense when we look at plant structure during the next week or so. Plant Life span and Sturdiness of Plants Plants are either herbaceous or woody. Woody plants (shrubs and trees) have significant woody (or tough) parts above the ground that persist year after year. Herbaceous plants do not have such strong, woody parts that persist year after year, and are rarely as large as the woody plants. Plants can complete their life cycle in from one to several growing seasons. Annuals are plants that germinate, grow, reproduce and die in one growing season. Biennials grow vegetatively in their first growing season and reproduce and die in a second growing season. Perennials grow for several seasons. They may reproduce year after year, once reaching sexual maturity (polycarpic), or in the case of some plants, grow vegetatively for a number of seasons, then reproduce once (monocarpic) and die. Perennials can be herbaceous or woody. Some woody perennials, such as the Bristle cone pine, live for thousands of years.

Plant Structure and Organization - 5 Plant Systems There are two major systems in the typical plant: Root System Growth toward gravity Generally below ground Consists of roots Shoot System Growth

5 Plant Structure and Organization - 5 Plant Systems There are two major systems in the typical plant: Root System Growth toward gravity Generally below ground Consists of roots Shoot System Growth away from gravity along axis Generally above ground Consists of stems and leaves Flowers are modified shoot systems Roots, stems and leaves are the organs of plants, just as we have organs in animals. We will spend considerable time looking at these structures in the next few weeks, once we learn the cells and tissues from which they are constructed. Leaves, stems and roots are organized into regions, and plant tissues are located in precise ways within these regions. This actually makes learning about plant structures pretty straightforward.

Plant Structure and Organization - 6 Root (From outside to interior) Epidermis Cortex Stele (Vascular tissue)

Cortex o Vascular Tissue (Discreet bundles in rings in primary growth) o Pith (With pith rays between the

Dicot o Upper Epidermis o Palisade mesophyll o Veins (Vascular tissue) within mesophyll areas o Spongy mesophyll

6 Plant Structure and Organization - 6 Root (From outside to interior) Epidermis Cortex Stele (Vascular tissue) Pith in Monocots only; Dicots have a central stele General Dicot Root General Dicot Stem Stem Dicot o Epidermis o Cortex o Vascular Tissue (Discreet bundles in rings in primary growth) o Pith (With pith rays between the vascular bundles) Monocot o Epidermis o Cortex o Vascular Tissue (Discreet bundles scattered throughout) Leaves Dicot o Upper Epidermis o Palisade mesophyll o Veins (Vascular tissue) within mesophyll areas o Spongy mesophyll o Lower epidermis Monocot o Upper Epidermis o General mesophyll o Veins (Vascular tissue) within mesophyll area o Lower epidermis

Plant Organization. Learning Objectives. Angiosperm Tissues. Angiosperm Body Plan

Plant Organization. Learning Objectives. Angiosperm Tissues. Angiosperm Body Plan Plant Organization Learning Objectives 1. List and give the major function of the three main types of plant tissues 2. Identify a monocot verses a eudicot plant by observing either root, stem, leaf, or