Slide Show on Plants1—BSC 1005 L
Prepared by William H. Outlaw Jr.
SLIDE 1: Attributes of Plants.
This is the master slide for the slide presentation and it will appear several times. The lecture will focus on these six points. As the saying goes, “redundancy is the mother of learning.”
SLIDE 2: Attributes of Plants. “Evolutionary Relationships” is bold; the other attributes are faded.
This slide sets the general pattern for the style of the presentation. The slides following the highlighted attribute will focus on that attribute.
SLIDE 3: Evolutionary Relationships of Plants (Part A).
This is the first of two slides on the evolutionary relationships of plants.
The first major point is the definition of a plant, which is given on the slide: “A multicellular 3-D photoautotroph with complex reproductive structures; sexual reproduction by alternation of generations.” Several of these words will be new, and I would suggest that you go over the definition slowly, defining and elaborating. Remind students that all organisms are composed of one or more cells and, by definition, plants are multicellular. Then, stress the importance of three-dimensional structures—some organisms grow only in one dimension (i.e., a filament) and they “know how” to divide in only one dimension. Other organisms (e.g. Ulva, the sea lettuce) essentially grow only in two dimensions and form a sheet. Plants are capable of cell division in any plane and, thus, can grow into a complex shape. Plants are photoautotrophs—that is, they use light (“photo”) themselves (“auto”) to grow (“troph”). In a later slide (Mode of Nutrition), this point will be discussed again, but it is nevertheless useful to introduce the idea here. Plants also have complex reproductive structures, meaning that a number of sterile cells (i.e., cells that themselves do not undergo meiosis or syngamy) are dedicated to sexual reproduction. Finally, the means by which plants carry out sexual reproduction is designated “alternation of generations.” This point will be emphasized also, on another slide (Sexual Reproduction). At present, just note that the complete sexual cycle involves alternation between a haploid phase of growth and a diploid phase of growth. [Alternate means to switch back and forth between two options. However, popular usage of the word has changed somewhat, to be essentially a synonym of alternative. E.g., the runner up in a contest is designated an alternate. Because of this confusion in words, it is a good idea to explain the basic concept.]
Next, briefly go over the evolution diagram. As this slide presentation will follow that on fungi, this figure gives the TA a good chance to emphasize that animals and fungi are more closely related to each other than either is to plants. Examples of Protista—in no particular order—may be mentioned as a way of explaining that Protista is a “grab-bag” kingdom and many Protistans are not closely related. In this same vein, mention that whereas many Protistans (all the algae) are photoautotrophs, only one group—the green algae—are related evolutionarily to plants. Then, go over the lines of evidence—or points of similarity—that support the idea that green algae and plants share an evolutionary history.
SLIDE 4: Evolutionary Relationships of Plants (Part B).
The evolution of plants has to be considered in the context of adaptation to a terrestrial life style.
Aquatic and marine environments moderate temperature extremes and the rate of change of temperature As examples, plants have developed morphological features (e.g., heat reflection) and biochemical features (e.g., accumulation of stress proteins) to gain access to land.
Water insufficiency is a major problem, and water is usually the resource that is most limiting for growth of a terrestrial plant. As examples, plants have developed morphological features (e.g., a surface of wax that retards water loss) and developmental features (e.g., the seed, which germinates only under permissive conditions) as means of tolerating or avoiding water insufficiency.
As fresh biomass and water have approximately the same density, support tissues generally are limited in algae. In contrast, air has a very low density, indicating plants require support tissues. Support tissue and transport tissues often occur in the same location, and, indeed, in cases, some cells function both in support and transport. Thus, in marine and aquatic photoautotrophs, nutrients are absorbed locally and photosynthesis generally occurs throughout the body, and—generally—support tissues are not present.
UV light is destructive to plants (as it is to animals). Plants are sessile (i.e., they can not move to the shade), unlike many terrestrial animals. Plants have developed several means (e.g., UV-absorbing compounds in the epidermis) to cope with the solar UV flux.
SLIDE 5: Attributes of Plants. “Body Plan” is bold; the other attributes are faded.
Again, this slide will appear each time to separate the foci and attract attention to the discussed attribute.
SLIDE 6: Body Plan of Plants.
The body plan of plants is, logically, a reflection of the specialized regions.
The leaf is specialized for the conversion of solar energy into chemical energy, which can be used in the construction of chemical building blocks (e.g., sugars, amino acids) for growth or for making compounds (e.g., sugars, lipids) that are simply sources of energy for subsequent use.
The stem is specialized for supporting the leaves—often, a means of positioning leaves in an unshaded area where they function best. The stem also contains transport tissues of two types. One type transports water and soil nutrients to aerial portions of the plant, particularly the leaves. A second type of transport tissue removes products of photosynthesis from leaves and transports these products to parts of the plants, such as roots, that do not conduct photosynthesis.
The root is specialized for acquiring soil nutrients and water, and for anchoring the plant.
SLIDE 7: Attributes of Plants. “Mode of Nutrition” is bold; the other attributes are faded.
SLIDE 8: Nutritional Mode.
Light is a form of energy, and energy may be converted from one form to another. From your own experience, provide examples of other forms of energy. E.g., the potential energy in the chemical bonds in gasoline is converted to kinetic energy and heat by an engine. The sugar you eat may be converted to heat, motion, other chemical energy . . . . Thus, heterotrophs convert chemical energy into other energy. Plants (e.g., leaves during darkness or roots, which are not photosynthetic) also convert chemical energy to other energy, just as you do. Photoautotrophs are special: they have the ability to capture light energy and convert it into chemical energy.
Photosynthesis is a two-part process. First, plants harvest light, converting the energy in light into high-energy chemical intermediates (NADPH and ATP). Second, the high-energy-chemical intermediates are used to convert energy-poor CO2 into products such as sugars and other chemicals that are used in the synthesis of the plethora of compounds found in plants. Alternatively, the high-energy-chemical intermediates may be used in the required conversion of simple salts (e.g. NO3-, SO42-) into compounds such as amino acids.
Heterotrophs, of course, cannot harvest light energy and use it to reduce CO2 to organic form. Higher animals and many other heterotrophs are also unable to use energy-poor NO3- and SO42-. Humans, for example, require many amino acids in their diet. Emphasize that heterotrophs not only depend on autotrophs for carbon sources, but also for sources of other elements in usable form.
SLIDE 9: Attributes of Plants. “Sexual Reproduction” is bold; the other attributes are faded.
SLIDE 10: Sexual Reproduction.
As mentioned in the slide show for fungi, it would require too much time to develop the concepts of life cycles in any detail. However, most students will know from the previous units on genetics that animals and plants derive traits from parents in a virtually equal way. I.e., haploid gametes combine to form the diploid, which is the familiar organism, like a man or a woman. Thus, mammals are diploid organisms, forming gametes by meiosis and gametes are the only haploid cells. In contrast, (with exceptions) fungi are essentially haploid organisms and have no diploid phase, except the zygote, which is the single-cell product of fertilization. Thus, fungi form gametes by mitosis.
Plants have both a haploid multicellular phase of growth and a diploid multicellular phase of growth, hence the appellation, “alternation of generations,” which is short for “alternation of a haploid generation with a diploid generation.” Read the text on the right of the slide, and coordinate this text with the graphic.
SLIDE 11: Attributes of Plants. “Classification and Examples” is bold; the other attributes are faded.
SLIDE 12: Classification and Examples.
For most students, plants will be more familiar than fungi. I suggest that you make use of this fact and your own knowledge to drive much of the discussion. Thus, far fewer examples of plants are given, than was the case for fungi.
In the case of fungi, discrete differences in sexual reproductive structures provided the basis for separating these organisms into one of three taxa (or four, if chytrids are included). Of course, these differences in sexual reproductive structures are only one of a host of characteristics that fungi of particular taxa share, to which I alluded.
Sexual reproductive structures or features also provide a primary basis for classification of plants. In flowering plants, the number of seed leaves, the number of petals, the position of insertion of the perianth (sum of petals and sepals), the fusion of parts and so forth all play a role in classification. However, when one looks broadly at plants, it is not the choice of alternative structures (as the case, for example, with ascomycetes [spores in ascus] vs. basidiomycetes [spores in basidium]) that one examines. Instead, it is usually the presence or absence of an analogous structure that is used to place a plant into one of the four major taxa.
The horizontal bars at the top of this slide show the major criteria that are used to place a plant in one of the four major taxa of plants. These criteria are intended to complement other information presented on previous slides. Thus, go over these criteria first, and these look at the small photos of organisms that fit into each category. For absolute clarity, I note that bryophytes lack all the attributes, whereas flowering plants have vascular systems, produce seeds, and have flowers. Seeds and flowers are, of course, generally familiar to everyone, so play up on this general knowledge.
SLIDE 13: Example of Bryophyte Unidentified moss (North Leon County).
As these are relatively unimportant organisms, I would suggest that you move quickly through this slide. With that said, try and inject something of general interest into the show—e.g., the dead remains of mosses are highly absorbent and are used in potting mixtures. Before the modern era, the absorbent properties were used to advantage to make bandages and as a sanitary aid during menses.
SLIDE: 14: Example of vascular non-seed plant Psilotum nudum (Botanical Garden, University of Tübingen).
This plant, commonly known as whisk fern, is fairly common in Florida. Lacking roots and leaves, it is an ancient plant.
SLIDE 15: Example of vascular non-seed plant Cyrtomium falcatum (north Leon County).
Commonly known as the holly fern (as are species of Polystichum), these natives of the orient are grow outdoors in mild climates, but they grow indoors well also, being little affected by low humidity. This photograph shows the lower surface of the leaf, where clusters of spore-forming structures are obvious.
Although seedless vascular plants do not play a major role in the current biosphere, their importance should not be dismissed. During the Carboniferous, they dominated the landscape and their remains serve us as fossil fuels. Most students will be surprised to learn that the foliage industry in Florida is worth hundreds of millions of dollars!
SLIDE 16: Example of seed-bearing non-flowering plant (Gymnosperm) Sequoiadendron giganteum (Yosemite National Park).
The giant sequoia, though slightly shorter than the coastal redwood, is the most massive organism on Earth.
SLIDE 17: Example of seed-bearing non-flowering plant (Gymnosperm) Taxodium distichum (FSU campus).
If anything, the bald cypress is a hallmark of Florida’s swamps. However, as this slide shows, it is well adapted to upland locations, where its growth is much faster than in its native flooded habitat.
Cypress can live for a long time—one on the boat cruise at Walkulla Springs is estimated to be 600 years old! Old-growth cypress are famous as a natural source of durable wood and logging operations about 75-100 years harvested most old trees, some of which reached 6-8 feet in diameter.
Cypress and the redwood are related. In the Southeast, pine trees are the most common gymnosperms and are an important economic asset.
SLIDE 18: Example of flowering plant (dicot) Rose laevigata (north Leon County)
Dicots are one of the two categories of angiosperms (flowering plants). Although I do not think that you should ask students to distinguish dicots and monocots on the basis of this slide show, you should know the general characteristics in order to field questions (two seed leaves, flower parts in multiples of 4 or 5, net venation in leaves).
The Cherokee rose (in slide) is an exotic that originated in China. Being widely planted and weedy, it is an invasive species that has become feral. Depending on your own experiences, you may wish to discuss briefly the hazards of invasive exotics (such as Brazilian pepper in the Everglades).
Roses are an important plant family. Examples of roses include apples, pears, peaches, plums, apricots, as well as minor fruits such as mayhaws, blackberries, and loquats.
SLIDE 19: Example of flowering plant (monocot) Brassio lealiacattleya, tri-generic hybrid (Orchid from the collection of the late Lena Belle Outlaw).
Monocots are second of the two categories of angiosperms. They have one seed leaf, flower parts in multiples of 3, and parallel venation in leaves.
Orchids are the largest family of monocots and the second largest family of plants in terms of the numbers of different species. (Composites [e.g., sunflower] are dicots and the largest family of angiosperms). Orchids have enormous esthetic appeal and provide minor quantities of consumables (e.g., vanilla flavoring).
SLIDE 20: Attributes of Plants. “Role in the Biosphere” is bold; the other attributes are faded.
SLIDE 21: Role in the Biosphere.
Plants play many roles in the biosphere. For example, they provide shelter, they represent a reservoir of nutrients, they stabilize soil... Given the nature of this presentation, however, only one role will be emphasized—photosynthetic reduction of CO2. Your students will already be familiar with the role, and it has been the focus of much of this slide presentation, so you have the chance to make several summary statements.
Put CO2 reduction in the context of human society—virtually all our food and fiber and much of our energy and shelter are derived directly or indirectly form plants, wither living or as fossil fuels. Virtually all our food is produced in an agronomic context and our continued reliance on wild species (e.g., ocean fish) must be in question. From your own knowledge, try and develop an interesting anecdote about consequences of the disruption of plant CO2 fixation (e.g., the Irish potato famine).
1 Thanks to D. K. Sakole for able assistance in a variety of ways, particularly for developing the tutorial website that complements this presentation.
Thanks to L.L. LeClaire for the identification of the orchid (Brassia laeliacattleya).