BIO112.02 Laboratory Guide #5
DIVERSITY OF THE PLANTS
INTRODUCTION
Plants are photosynthetic autotrophs that capture radiant energy from the sun and convert it to chemical energy in the bonds of carbohydrates. All plants are multicellular eukaryotes with chlorophyll a and chlorophyll b as their photosynthetic pigments and cell walls made of cellulose (unlike the chitinous cell walls of fungi). They also store their carbohydrates as starch, which helps differentiate them from some of the algae to which they are related. Plants are most closely related to the green algae, Division Chlorophyta, which also use starch for food storage; indeed, the three groups of algae (Chlorophyta, Rhodophyta, Phaeophyta) are sometimes classified not as protists but in Kingdom Plantae. True plants differ from algae in three major ways: 1) all are multicellular (some algae are single-celled), 2) they are terrestrial (except when they have secondarily evolved an aquatic lifestyle, e.g., water lily), and 3) plants are embryophytes, meaning their embryos are enclosed in protective maternal tissue.
Another feature that unites the Kingdom Plantae is an aspect of their life cycles: all plants exhibit alternation of generations, the alternation between distinct, multicellular, diploid and haploid phases of their life cycle. The diploid phase, called the sporophyte, produces haploid spores, which then grow into the gametophyte. The gametophyte then produces gametes (eggs and sperm) that unite in fertilization to form a diploid zygote. The zygote is once again the sporophyte generation. There is thus an alternation between the sporophyte and gametophyte stages. A generalized life cycle for plants is illustrated in the figure below:
In this lab you will learn the details of the life cycles of four representative plants: moss, fern, pine, and lily. All exhibit alternation of generations, but the details differ, as well as the relative sizes and independence of the gametophyte and the sporophyte (the larger phase is said to be “dominant”). Most of the differences in the life cycles of the various plant divisions can be related to the evolution of traits that permit greater terrestriality and independence from water.
This laboratory exercise gives an overview of the eleven divisions in the kingdom Plantae. These divisions occur in four groups with similar characteristics:
1) Nonvascular plants:
Hepatophyta (liverworts)
Anthocerophyta (hornworts)
Bryophyta (mosses)
2) Ferns and fern allies (seedless vascular plants):
Lycophyta (club mosses and quillworts)
Pterophyta (ferns, whisk ferns, and horsetails)
3) Gymnosperms (seed plants with “naked seeds”):
Ginkgophyta (ginkgo)
Cycadophyta (cycads)
Gnetophyta (gnetophytes)
Coniferophyta (conifers)
4) Angiosperms (seed plants with seeds enclosed in fruits):
Anthophyta (flowering plants)
In this exercise, we will see many of the above shared characteristics, as well as those characteristics which differ among the eight major vertebrate classes: the Myxini, Cephalaspidomorphi, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia. We will use a traditional "phenetic" taxonomy for the vertebrates. However, you should recognize three things about the taxonomy of vertebrates:
1. There is no universally accepted taxonomic scheme for the vertebrates. The taxonomy presented here is a widely used classification scheme, but not the only one in common use.
2. Traditional "phenetic" taxonomies are based almost exclusively on morphology. They do not reconcile very well with the actually phylogeny (evolutionary history) of the vertebrates. As an example, birds are phylogenetically a subset of the dinosaurs, which are themselves a subset of the reptiles. However, traditional taxonomy artificially elevates birds to the level of a class, while relegating dinosaurs to a mere order in Class Reptilia. Similarly, traditional taxonomies totally miss the rather close phylogenetic relationship between the birds and the crocodilians; crocodilians are in many ways anatomically and physiologically more similar to birds than to any other reptiles.
3. The alternative "cladistic" taxonomies which rely strictly on monophyletic groups are prohibitively cumbersome to use because they are not strictly hierarchical and they define many logical modern vertebrate groups by exclusion; e.g. dinosaurs become "non-avian dinosaurs". We will use a traditional taxonomy because it is more convenient, straightforward and familiar. We will also study only extant (living) groups of vertebrates, while recognizing that the vast majority of vertebrate species and the majority of higher taxa are, in fact, extinct.
After completing this laboratory you should be able:
1) To list the distinguishing characteristics of members of the kingdom Plantae.
2) To identify and outline the major features of the natural history of the major groups of Plants.
3) To draw and label the life cycles of four representative plant species (moss, fern, pine, lily) and relate these to the the evolution of terrestriality in plants.
Materials
Materials at stations arranged on the lab benches. These consist of fresh materials
and live specimens as well as preserved specimens, prepared microscope slides,
and other written and illustrated materials.
Microscopes, slides and cover slips, forceps, lens paper.
Dissecting stereo microscopes.
Procedure
1. Starting at any station, read about the materials in your lab manual and observe the specimens on the lab benches. You may be asked to make a wet mount of a specimen, or examine a prepared slide, or look at an entire specimen, depending on the station.
2. Be able to recognize all specimens as well as their distinguishing characteristics.
3. In your lab notebook, create and fill in tables to summarize the key features of the different groups of plants. The layout of these tables is specified in the text below.
4. Make detailed diagrams of the life cycles of the moss, fern, pine, and lily. Use your text, the photographic atlas, the life cycle posters, and live and preserved materials to help you construct the diagrams.
5. Dissect a lily flower and draw a picture of its parts. Learn all the parts of a flower.
Study Suggestions
1. Make sketches and detailed notes on specimens. This will help you to observe the specimens more carefully, as well as help you study later.
2. Plan to view the specimens once or twice more before the lab test. Test yourself by attempting to identify the specimens without first looking at their labels.
Key Features of the Major Plant Groups
For each of the four major groups of plants (nonvascular plants, ferns and fern allies, gymnosperms, and angiosperms) determine which characteristics it possesses and summarize this information in a table in your lab notebook. Use the following labels for the columns:
Dominant generation? (Sporophyte or Gametophyte)
Do sperm require free-standing water for fertilization? (Yes or No)
Vascular system present? (Yes or No)
Seeds present? (Yes or No)
Flowers and fruits present? (Yes or No)
Examples (i.e., name some representative species)
At each of the following stations, use the Dichotomous Key to the Plant Divisions to identify the specimens and help reinforce the characteristic features of each plant division.
A Dichotomous Key to the Plant Divisions
All of the following groups are eukaryotic, photosynthetic autotrophs with chlorophyll a and cellulose-rich cell walls. They are all multicellular embryophytes.
1. Nonvascular plants; gametophyte generation dominates over sporophytegenration Mosses and Moss Allies
2. Plants low-growing with stemlike and leaflike appendages; sporophyte
usually a capsule atop a slender stalk BRYOPHYTA
2. Plants low-growing, flat, sheet-like and lobed; sporophyte umbrella-likeor horn-like
3. Lack stomata; sporophytes associated with umbrella-like structures;may have gemmae cups for asexual reproduction HEPATOPHYTA
3. Stomata present; sporophyte an elongated hornlike capsule;gemmae absent ANTHOCEROPHYTA
1. Vascular plants; sporophyte generation dominates over gametophyte
generation
2. Seedless plants; reproduce by spores only Ferns and Fern Allies
3. Plant apparently just a green stem, lacking leaves; if with scalybranches, these arise in whorls from nodes of hollow,
jointed, silica-rich stem
4. Plant with stem and flattened branches only; dichotomouslybranched; simple spore-producing structures (sporangia) at
tips of stems PTEROPHYTA, in part (Psilotum nudum)
4. Plant with silica-rich, round, jointed, hollow stem; may havescaly branches arising in whorls from nodes of stem; "cone"
(strobilus) of sporangia present at tip of stem PTEROPHYTA,
in part (Equisetum sp.)
3. Plant with true leaves and leafy appearance
4. Plant with leafy fronds; low-growing to tree-sized; sporangiaeither in clusters (sori) on underside of leaf or borne entirely on
specialized "fertile" fronds PTEROPHYTA
4. Leaves various (either moss-like or scaly (Lycopodium,Selaginella), or quill-like if an aquatic plant (Isoetes);
all low-growing; sporangia borne in strobilus at stem tip,
or in leaf axils, or at fleshy base of leaves (Isoetes)
LYCOPHYTA
2. Seed plants
3. Flowers absent; seed naked, not enclosed in ovary (or fruit)Gymnosperms
4. Trees (sometimes shrubs); either broad-leaved or with needle-likeor scale-like leaves
5. Seeds usually borne in woody cones; leaves needle-like orscaly; usually evergreen CONIFEROPHYTA
5. Seeds with ill-smelling, fleshy coat; deciduous tree withfan-shaped leaves with parallel veins GINKGOPHYTA
(Ginkgo biloba)
4. Shrubs or trees; leaves palm-like, or in the shrub Ephedra,leaves small and scaly and stem photosynthetic.
5. Shrub with many branches; leaves scale-like and stemsphotosynthetic and jointed (not hollow as in Equisetum);
desert habitats GNETOPHYTA (Ephedra)
5. Shrubs or trees with distinct trunk or with stem mostlyunderground; leaves palm-like; tropical or subtropical
habitats CYCADOPHYTA
3. Flowers present; seed enclosed in ovary, maturing into fruit:Angiosperms ANTHOPHYTA
NON-VASCULAR PLANTS MOSSES AND MOSS ALLIES
There are three divisions of nonvascular plants: Hepatophyta (liverworts), Anthocerophyta (hornworts), and Bryophyta (mosses). Members of this group are nonvascular and lack true leaves and roots. They absorb water and nutrients directly through their surfaces and are therefore restricted to moist habitats. They also require water to complete their life cycles, since the sperm swim from the antheridium to the archegonium. The gametophyte (haploid) generation is dominant over the sporophyte (diploid) generation.
Examine live specimens of the various species under the dissecting microscope.
Study the poster of the moss life cycle, which is representative of the life cycles of the bryophytes. Use the preserved mount of the moss life history: can you identify the capsule, gametophyte generation, sporophyte generation, and operculum? Also look at microscope slides of moss antheridia, archegonia, and sperm.
In your lab notebook, make a detailed diagram of the moss life cycle, labeling all key stages and structures.
Compare the moss life cycle to the preserved mount of the Marchantia (liverwort) life history: can you find the thallus, gemmae cups, antheridia, and archegonia?
VASCULAR SEEDLESS PLANTS - FERNS AND FERN ALLIES
The two divisions that make up the ferns and their allies are seedless vascular plants with the sporophyte generation dominating over the gametophyte generation. As with the bryophytes, the sperm are free-swimming, meaning that water must be present at some point in the life cycle of these plants for them to prosper in a given habitat. Lacking seeds, they propagate via air-borne spores. View living specimens and various preserved plants.
Lycophyta: club mosses and quillworts
Lycopodium, Selaginella, Isoetes are the three genera. Shown here is a real fossil of Lepidodendron, a tree-sized lycopod. These species made up the “coal forests” during the age of dinosaurs. The Carboniferous was their heyday.
Pterophyta: ferns
See the prepared slides of fern antheridia and archegonia on the prothallium, young fern sporophyte on prothallium, and fern sporangium. Study the poster of the fern life cycle, which is representative of the life cycles of the seedless vascular plants.
Division Pterophyta also includes the horsetails and scouring rushes, which are distinctive enough that they sometimes classified in their own division (Sphenophyta). Equisetum is the only genus. These plants are high in silica, so their stems are not good for the teeth of herbivores. View the prepared slide of horsetail strobilus (l.s.).
The whisk ferns were likewise formerly in their own division (Psilophyta), but are now considered to be true ferns. Only one species (Psilotum nudum) occurs in the U.S.; it can be found along the Georgia coast. Characteristics include dichotomous branching, and lack of true leaves or roots.
In your lab notebook, make a detailed diagram of the fern life cycle, labeling all key stages and structures.
GYMNOSPERMS
The uniting feature of this group is the presence of a seed, but with no ovary enclosing the seed. Thus the name gymnosperm, which means “naked seed”. Because there is no ovary, technically these plants have no true fruits, though some (e.g., ginkgo, red cedar) have fleshy coatings on the seeds.
Ginkgophyta: The ginkgo.
A very ancient lineage, with just one remaining species: Ginkgo biloba, a common ornamental tree species. Female trees are not widely planted because their seeds have a foul-smelling fleshy coat, but there is a female ginkgo on campus, to the northwest of Tate Hall.
Cycadophyta: The cycads.
One species (Zamia pumila) is native to the U.S.; it occurs in Florida and southern Georgia. See the living specimen as well as cycad cones and seeds on display.
Gnetophyta
Ephedra is the only species native to the U.S. It is found out west in arid habitats.
Coniferophyta: The Conifers.
Cone-bearing, needle-leafed trees and shrubs. Lots of species native to Georgia, including bald cypress (Taxodium), red cedar (Juniperus) and pines (Pinus), altogether representing three families. Study the poster of the pine life cycle and the preserved and live materials that accompany it.
In your lab notebook, make a detailed diagram of the pine life cycle, labeling all key stages and structures.
ANGIOSPERMS
Angiosperm means “vessel seed” which refers to the protective ovary enclosing the seed. The ovary develops into the fruit. These plants are called the flowering plants because they are the only group that possesses true flowers. This is the most species rich group of all plants, with almost 90% of all species. This group arose about 130 million years ago, according to the fossil record.
Anthophyta. Flowering Plants
This division has two classes: Monocotyledones (monocots) and Dicotyledones (dicots). The monocots include grasses, lilies, orchids -- they are primarily herbaceous (exceptions being the palms and bamboos).
What are the differences between dicots and monocots? Consult your text and photographic lab atlas to discover how these two classes differ in terms of leaf venation, number of flower parts, the arrangement of vascular bundles, and number of cotyledons (seed leaves).
Study the flowering plant life cycle as exemplified by the Lily (Lilium). See poster.
Also see slides of Lilium anthers and pollen tetrads, 8-nucleate embryo sac (= “mature female gametophyte”), stigma and pollen tubes. Be sure you understand the concept of double-fertilization.
In your lab notebook, make a detailed diagram of the lily life cycle, labeling all key stages and structures.
FLOWERS AND FRUITS
A. Anatomy of a flower.
Identify the following structures on a diagram and actual specimen of a flower, beginning with the innermost whorl of the flower and working outwards.
Pistil (or carpel) of the flower contains the female reproductive cells.
The narrow neck of the pistil is the style, which is topped by the stigma, the sticky
surface that receives the pollen during pollination.
The swollen base of the pistil is the ovary, which contains one or more ovules within.
The ovules have the egg cells within them; when the egg is fertilized and matures into an
embryo, the ovule becomes the seed. The mature ovary, enclosing one or more seeds, is
the fruit.
Stamens are the pollen producing structures. They consist of an anther borne atop a
slender filament.
Petals are the often brightly colored structures surrounding the pistil(s). They are
attractive to pollinators. Collectively, all of the petals are called the corolla.
Sepals are the outermost whorl of the flower. They are usually green and enclose the
flower when it is in a bud. Collectively, all of the sepals are called the calyx.
B. Fruit structure and function.
View the preserved and fresh specimens of different fruit types. Try to identify the seeds, ripened ovary, and perhaps even the style and calyx of the original flower.
