Overview of Plants & Plant Structure Botany: Part I Overview of Plants & Plant Structure This is the first in a series of four PowerPoints for the AP Biology Redesign Botany Unit.

The Study Of Botany Derives Components From Each Of The Four Big Ideas In Biology Big Idea 1: The process of evolution drives the diversity and unity of life Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow to reproduce & to maintain dynamic homeostasis Big Idea 3: Living systems store, retrieve, transmit, and respond to information essential to life processes Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties. Big Idea 1: Land plants evolved from algae. The selective pressures of living and reproducing on land drove the evolution of plants from simple nonvascular plants to modern flowering plants. Big Idea 2: Many examples of plant concepts reside here: photosynthesis; C and N cycles; role of cell walls; respond to changes in environment; homeostasis; immune responses; timing of seed germination; phototropism; photoperiodism Big Idea 3: Communication between plant cells via plasmodesmata and/or plant hormones; sexual reproduction in plants (details of each cycle not required) Big Idea 4: Organelles interact, including plant specific ones – chloroplasts, central vacuoles; interactions between organ systems (root, stem and leaf); food chains and webs; primary productivity; plants as invasive species; affect of diseases on plants, especially on native species vs. invasive ones.

Characteristics of Land Plants Eukaryotic Autotrophs Cell Wall - cellulose Alternation of Generations Embryophytes – protected embryo Review the meaning of both eukaryotic and autotrophs, relating plants to photosynthetic organisms with chloroplasts. The cell wall composed of cellulose is specific to plants. Alternation of generations will be explained further, but is essentially the alternation between a haploid (gametophyte) and a diploid (sporophyte) generation. All land plants have a protected embryo at some stage in their life cycle.

Photosynthetic Autotrophs Students should have some prior knowledge of photosynthesis. This is a good time to see what they recall about the process.

Alternation of Generations Alternation of Generations is not specifically mentioned in the new Curriculum Framework, but it is clearly important to understanding how plants function and how they differ from other organisms. This is a generic slide representing a complex life cycle. It is important that students recognize where mitosis and meiosis occur and that gametophytes produce gametes and sporophytes produce spores. It is very helpful to have students draw their own representations of the alternation of generations in plants. It is also helpful to explicitly point out that plants do not produce gametes by meiosis, but rather use meiosis to produce haploid spores for the diploid sporophyte. Their haploid gametes are produced by mitosis within a haploid generation of the plant. It is also a good time to have students discuss, again, the importance of meiosis in producing genetic variety and its importance in evolution.

Alternation of Generations Key Haploid (n) Diploid (2n) Spore dispersal MEIOSIS Sporangium Mature sporophyte (2n) Sporangium Sorus Here we use the fern life cycle as a specific example of alternation of generations in plants. No specific plant life cycles are required knowledge on the AP exam, so do not feel you have to teach life cycles for mosses, ferns, gymnosperms and angiosperms. Feel free to insert a different example here if you prefer. Talk through the next three slides of the life cycle of a fern and allow the students to explain the sequence of the cycle to their neighbor. Here we start with a mature sporophyte (diploid) with sori (plural for sorus which is a cluster of sporangia) on the underside of its reproductive leaves. (You may want to have samples of sori on fern leaves to show your students.) In the sporangium, cells undergo meiosis and become haploid spores. When the sporangium matures it ruptures and the spores are released. A review of the meaning of diploid and haploid may be appropriate for your students. Fiddlehead (young leaf)

Alternation of Generations Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Rhizoid Underside of mature gametophyte (n) Sporangium Sperm Archegonium Mature sporophyte (2n) Egg Sporangium FERTILIZATION Sorus The released spores develop into photosynthetic gametophytes (n). Each gametophyte develops sperm-producing organs called antheridia and egg-producing organs called archegonia. Notice that only mitosis is occurring as these structures develop and produce gametes. The sperm use flagella to swim to eggs in the archegonia (challenge students to explain how this limits the range of habitats for ferns). When the egg and sperm unite upon fertilization, the diploid condition is restored. Fiddlehead (young leaf)

Alternation of Generations Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Rhizoid Underside of mature gametophyte (n) Sporangium Sperm Archegonium Mature sporophyte (2n) Egg New sporophyte Sporangium Zygote (2n) FERTILIZATION Sorus The zygote (2n) develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. Whether you are discussing fern, moss, roses, or pecan trees the general theme of alternation of generations remains the same. Gametophyte Fiddlehead (young leaf)

Four Groups Bryophytes Ferns Gymnosperms Angiosperms From the simplified phylogenetic tree, students should recognize that these four groups of plants are monophyletic, meaning there is a unique common ancestor that all four groups share amongst themselves that they do not share with any other organisms. They also show four evolutionary steps as plants moved from water onto land. (great examples of evolution producing adaptations to local environments; also examples of adaptive radiation)

Adaptations for Moving on To Land Prevention from dehydration-Evolution of waxy cuticle Method of gas exchange for photosynthesis-Evolution of stomata and lenticels. Method to obtain water and minerals-Evolution of roots Increase in size and support-Evolution of xylem fortified with lignin Method of reproduction without water-Evolution of pollen and pollination strategies. Method of protecting embryo from dehydration-Evolution of the seed Nonvascular land plants must live where water is readily available and will not be very tall due to the lack of vascular tissue. In these plants the sporophyte is nutritionally dependent on the gametophyte and remains attached.

Adaptations for Moving on To Land Prevention from dehydration-Evolution of waxy cuticle Method of gas exchange for photosynthesis-Evolution of stomata and lenticels. Method to obtain water and minerals-Evolution of roots Nonvascular land plants must live where water is readily available and will not be very tall due to a lack of vascular tissue. In these plants the sporophyte is nutritionally dependent on the gametophyte and remains attached. Graphics: http://www.squidoo.com/plants-lessons, http://en.wikipedia.org/wiki/Stoma, http://utsa.edu/sombrilla/fall2009/story/plastic-surgery-plants.html

Bryophytes Nonvascular land plants Mosses, liverworts and hornworts Gametophyte (n) is photosynthetic , dominant generation Typically ground-hugging plants (Why?) In this picture the photosynthetic gametophyte is green and the mature sporophyte with sporangium appears brown. Ask students to explain why these plants cannot grow very tall.

Ferns Seedless vascular plants Horsetails and ferns Sporophyte (2n) is dominant generation Most common in damp areas due to flagellated sperm that must swim to reach eggs Ferns and horsetails are in the Phylum Pterophyta and commonly referred to as pterophytes. These plants can grow very tall, but still live in moist environments – why? (vascular tissue for growth, but swimming sperm require water for reproduction) Be sure to mention that the seedless vascular plants that formed the Carboniferous forests eventually became coal.

Gymnosperms “Naked” seeds not enclosed in ovaries Conifers, ginkgos, and cycads Sporophyte (2n) is the dominant generation Seeds are exposed on modified leaves that usually form cones Gymnosperms (the name means “naked seed” and refers to the fact that they do not possess an ovary) are vascular, non-flowering, seed-bearing plants that we typically associate with cones, e.g. pine trees. The ovules of gymnosperms are not protected by the ovary or fruit tissue. A change in anatomy enabled seed plants to grow to great heights. (Lignin! – a term not on the AP exam, but is another example of adaptation to local environment and the resulting adaptive radiation it made possible) The adaptations first appearing in Gymnosperms, pollen and ovules, diminished the requirement of water for fertilization (wind-blown pollen! vs. swimming sperm); allowing these plants to reproduce under a broad range of conditions. The development of seeds with protective coats is a major reason for the success of seed plants. The giant sequoia is one of the largest and oldest living organisms. Some are estimated to be between 1,800 and 2,700 years old.

Angiosperms Flowering plants Pecan trees, roses, peach trees, tomatoes Sporophyte (2n) generation is dominant Flowers and fruit Most abundant of all plant species Angiosperms have reproductive structures in flowers and seeds enclosed in fruits. The name means “seed in a vessel” referring to the presence of an ovary that encloses the seed. The hallmark of angiosperm life cycles is double fertilization. Flower parts are modified leaves and these have diversified to attract animal pollinators, provide food, and prevent self-fertilization. Angiosperms have coevolved with animals. Fruits develop from the ovaries after fertilization and serve to protect seeds and aid in dispersal. Recap the connection between bryophytes, ferns, gymnosperms, and angiosperms focusing on their distinguishing characteristics as plants moved from water to land. You should include a discussion of the great reduction in the gametophyte stage as plants moved onto land.

Plant Structure and Function A simple body plan underlies the diversity of plant forms that exist today. Plants have two vegetative organ systems, the root system and the shoot system. Apical meristems can produce new tissue throughout the plant’s life. Most cells are totipotent, so plants can repair damage. Growth patterns are established in the embryo. Apical meristems and the three tissue systems are established.

Hierarchy of Plant Organization Systems - root and shoot Organs – roots, stems, and leaves . Like animals, plants display a hierarchical organization. The basic anatomy of a vascular plants reflects their ability to draw resources from above and below the ground (the shoot and root systems). Plants rely heavily on both systems for survival. Discuss the interactions between these two systems. Roots are typically not photosynthetic but are dependent on the shoot system for sugars and carbohydrates resulting from photosynthesis. The shoot system is dependent on the root system for the water absorbed from the soil for photosynthesis.

Organ Systems: Another view of the plant organ systems. You do not have to teach the differences between monocot and Eudicot, it just makes a good discussion. Working down the hierarchy from the organismal level to the system level…plants have two vegetative organ systems, the root system and the shoot system. The root system is below the ground and the shoot system is above the ground. Root System – anchors plant, absorbs water and minerals, stores products of photosynthesis. Branching increases surface area for absorption. Shoot System – leaves are the main photosynthetic organs; stems hold leaves up to expose them to sunlight and connect the roots and leaves. Ask students to hypothesize some fundamental similarities and differences between these two systems based on their location above and below the ground.

Organs: Roots Roots – anchor a vascular plant to the soil, absorb minerals and water, and often store carbohydrates

Root Adaptations Each of these evolutionary root adaptations increase plant survival in a given environment. Interesting examples of root adaptations. These are not required knowledge, so you do not have to teach these, but they again make great examples of adaptations to local environments produced via natural selection and are just plain interesting! Prop roots – aerial roots of Hala trees support the tall, top-heavy trees which are found in sandy, unstable soils Storage roots – many plants store food and water in their roots; common beet Pneumatophores – air roots, such as these found on mangroves allow the root system to obtain oxygen which is lacking in the thick mud of intertidal swamps Ask students to hypothesize the purpose of the adaptations from the picture. This information is pretty specific, but these are great examples of evolutionary adaptations allowing success in a given environment. Encourage the students to pick a favorite and be able to explain it in an evolutionary sense.

Organs: Stems the main photosynthetic organs Stems – lift leaves and reproductive structures

Stem Adaptations Some plants have stems with additional functions, such as food storage and asexual reproduction. These are examples of modified stems. None of these are required knowledge, but again, they are pretty interesting  Rhizome – horizontal shoot that grows just below the surface of the ground; vertical shoots emerge from axillary buds Stolon – horizontal shoots that grow along the surface of the ground; “runners” allow asexual reproduction as plantlets form at nodes Tubers - enlarged ends of rhizomes or stolons specialized for storing carbohydrates; “eyes” of potatoes are clusters of axillary buds Bulbs – vertical underground shoots consisting of enlarged bases of leaves that store carbohydrates; note the layers of modified leaves Again, encourage students to adopt a favorite.

Organs: Leaves Leaves – the main photosynthetic organs These are examples of different leaf arrangements. Simple Leaf – single, undivided blade, some are deeply lobed Compound Leaf – blade consists of multiple leaflets, a leaflet has no axillary bud at its base Doubly compound Leaf – each leaflet is divided into smaller leaflets Note the petiole and axillary bud on each of these diagrams Leaves – the main photosynthetic organs

Types of Leaves These are examples of different leaf arrangements: Simple Leaf – single, undivided blade, some are deeply lobed Compound Leaf – blade consists of multiple leaflets, a leaflet has no axillary bud at its base Doubly compound Leaf – each leaflet is divided into smaller leaflets Note the petiole and axillary bud on each of these diagrams

Leaf Adaptations Some plant species have leaves with adaptations that function in support, protection, storage, or reproduction in addition to photosynthesis. Once again, not required, but more examples of evolution are always good to include. Tendrils – cling to support this pea plant; tendrils are typically modifies leaves, but some are modified stems as in grapevines Spines – the spines of this prickly pear are actually leaves, photosynthesis is carried out by the fleshy stem Storage leaves – found on succulents for the storage of water Reproductive leaves – produce adventitious plantlets which fall off the leaf and take root in the soil Bracts – often mistaken for petals, surround a group of flowers; these brightly colored leaves attract pollinators

Transport water and products of photosynthesis Plant Tissues Tissue Components Function Dermal Epidermis Periderm Protection Prevent water loss Ground Parenchyma Collenchyma Sclerenchyma Metabolism Storage Support Vascular Phloem Xylem Transport water and products of photosynthesis Students do not need to memorize the different tissue systems or the names of their component cell types (no test questions about parenchyma, collenchyma, etc.), but the general layout of a plant and how these various systems interact would be good to understand. To that end, we provide the next few slides: There are three types of plant tissue; dermal, ground, and vascular. As in animals, dermal tissue is associated with covering and protection and therefore easy to identify. Likewise, vascular tissue is associated with transport. The materials needing special vessels for transport in plants are water and the sugars produced during photosynthesis. Ground tissue comprises those tissues that can not be identified as either dermal or vascular. It is in the ground tissue that life processes take place in a plant.

Location of Tissue Types Which tissue type in most abundant in plants? How is this representative of “form fits function”? Allow students to study the location of the different tissue types and infer the function of the different tissues. Ground tissue is the most abundant. This is the tissue where photosynthesis, food storage, regeneration, support, and protection take place. In other words, the processes of life occur in this tissue. The dermal and vascular tissues are dependent on the ground tissue. The emphasis here should be on important interactions between these systems, rather than on memorizing the system names themselves.

Dermal Tissue Forms epidermis, usually one cell layer Some cells differentiate: Stomata – pores for gas exchange Trichomes – leaf hairs, protect against herbivores and damaging solar radiation Root hairs – increase root surface area Epidermal cells of the shoot system secrete a waxy cuticle that limits water loss, reflects damaging solar radiation, and form a barrier against pathogens Once again, structure reflects function. The opening formed by the two guard cells, the stomata, allows gas exchange. Ask the students if they have had any experience with trichomes. How do they help protect a plant from herbivores? The increased surface area afforded by the root hairs allows greater absorption. Ask students what resources were needed by this radish seed for it to germinate. Are the functions of root hairs similar to those of lateral roots and taproots? No, roots function in anchorage and root hairs function in absorption.

Ground Tissue Ground tissue is the most abundant tissue Cells differentiate: Parenchyma – most abundant, carry out photosynthesis, store protein and starch Collenchyma– elongated, thick cell walls, provide support Sclerenchyma– thick cell walls reinforced with lignin, programmed cell death, cell walls remain to provide support Knowing and being able to identify the specific cell types is not essential, but a brief overview of the differentiation of these cells is foundational. Simply understanding that cells differentiate and that their resulting structure matches their function is important. We will not test on the specific cell types and/or their individual functions. Just make students aware that cells differentiate and these are good examples of such differentiations.

Vascular Tissue Transport System Xylem – carries water and minerals from roots to rest of plants, composed of dead cells Phloem – is composed of living cells, moves carbohydrates from production sites to where they are either used or stored Xylem and phloem are the two transport vessels in vascular plants. They are composed of differentiated cells which are specialized for their function.

Created by: Jackie Snow AP Biology Teacher and Instructional Facilitator, Belton ISD Belton, TX