Lab 10: Bryophytes 1 Name: ______________________________________ Date/Lab time: _________________ Lab 10:NONVASCULAR PLANTS: (Bryophytes) Supplies: Moss with “sexual” organs Compound microscope Prepared slides showing moss archegonia Dissection scope and antheridia Slides and coverslips Prepared slides showing liverwort archegonia Liverwort with sexual organs and antheridia?? Slide of liverwort sporophyte Vocabulary to know: Alternation of generations, Antheridia, Archegonia , Diploid, Gametangia , Gametes , Gametophyte , Gemmae cup, Haploid, Protonema, Rhizoids , Sporangium , Sporophyte, Terrestrial, Vascular tissue LAB SYNOPSIS: We will compare and contrast the available non-vascular plants in lab We will examine the morphology and anatomy of the vegetative and reproductive organs of the non- vascular plants. Bryophytes - Non-vascular plants. There are 4 phyla of plants that fit the above definition of bryophytes: Kingdom Plantae Phylum Bryophyta (mosses) Phylum Hepaticophyta (liverworts) Phylum Anthocerophyta (hornworts) Introduction: The Kingdom Plantae is within the domain Eukarya. We will be looking at the nonvascular plants, commonly called the bryophytes during this lab. Tracheary elements are water conductive cells, which these plants lack. Nonvascular plants also lack nutritive conductive cells of the phloem. All land plants (the non-vascular plants and the vascular plants) probably evolved from aquatic green algae over 425 million years ago. In contrast to most algae, the liverworts and mosses have become adapted to a terrestrial existence. Members of these groups are green and have rhizoids (root hair like structures). Members are found in a wide range of habitats including Arctic and desert environments but, since they lack true vascular tissue, growth is restricted to times when surface moisture is available. During dry conditions, the body desiccates (dries) until water again becomes available. Non-vascular plants also require water for successful sexual reproduction. The sperm are mobile and need water to swim to the egg. The plant body may be flattened (liverworts), or it may be erect and radially symmetrical (mosses). The reproductive organs, in contrast to those of the algae, are multicellular. As with the algae, the members of this group reproduce both sexually and asexual. In contrast to the algae (Kingdom Protista), all non-vascular plants are within the Kingdom Planta and thus have a well-established alternation of generation , consisting of an independent multicellular gametophyte (haploid )(1n) phase and a mostly dependent multicellular sporophyte (diploid )(2n) phase. Gametes (1n) (sperm and egg) are produced in 2 separate gametangia that are multicellular, the archegonia (female) and the antheridia (male). Lab 10: Bryophytes 2 In addition to alternation of generation, all plants share the following characteristics Plantae characteristics 1. Are multicellular photosynthetic eukaryotes 2. Plant embryos are protected by tissues of the parent plant 3. Cell wall- cellulose 4. Chlorophyll a and b 5. Starch as carbohydrate storage *Recall that diploid (2n) refers to a cell that has pairs of homologous chromosomes (2 sets). Like you, one set of chromosomes come from your mother the other set comes from your father. Meiosis is a type of cell division that separates the two sets of chromosomes. In humans this happens in the testicles (males) and the ovaries (females). During meiosis homologous pairs of chromosomes are separated resulting in cells containing a single set of chromosomes. These cells are haploid (1n). These would be like your sperm or egg. In the alternation of generations in plants, the product of meiosis is a haploid cell (spore). This 1n cell undergoes cell divisions producing a multicellular haploid organism (gametophyte). This gametophyte (1n) will produce 1n gametes (either sperm or egg). (We do not do this. We humans do not have a multicellular haploid phase). The 1n plant’s 1n sperm is released and ultimately swims to and fertilizes an egg cell (1n) producing a 2n zygote. The zygote undergoes mitotic cell division resulting in a multicellular diploid organism (sporophyte). It is this 2n sporophyte that will produce the new 1n spore, via meiosis, thus continuing the life cycle. Classification of Currently Living Plants Phyla PHYLUM COMMON NAME CHARACTERISTICS Non-vascular plants Hepaticophyta Liverworts No filamentous stage; gametophyte flat Anthocerophyta Hornworts Embedded archegonia; sporophyte grows basally Bryophyta Mosses Filamentous stage; sporophyte grows apically (from the tip) Non-seed Vascular plants Psilotophyta Whisk ferns No true leaves; roots absent Lycophyta Club mosses Simple leaves in spirals; sporangia in leaf axils Equisetophyta Horsetails Simple leaves in whorls; stems jointed Polypodiophyta Ferns Complex leaves; sporangia on underside of leaves Seed plants (Gymnosperms) Cycadophyta Cycads Compound leaves; swimming sperm; seeds on modified leaves Ginkgophyta Ginkgo Deciduous; fan-shaped leaves; swimming sperm Gnetophyta Gnetophytes Vessels in vascular tissue; opposite, simple leaves Pinophyta Conifers Seeds in cones; needlelike or scale-like leaves Flowering Seed plants (Angiosperms) Magnoliophyta Flowering plants Endosperm; carpels; much reduced gametophytes; seeds in fruit Lab 10: Bryophytes 3 PHYLUM BRYOPHYTA - MOSSES Mosses differ from the liverworts in that the gametophyte (1n) of the moss begins as a filamentous, branching structure (protonema) and the mature gametophytic plant body is differentiated into “stem- like” and “leaf-like” parts. In addition, the sporangium (capsule ), contains a highly complex series of tooth-like structures that facilitate the dispersal of its spores. (see figure below) circle parts identified as you precede through the lab. The above figure illustrates the alternation of generation in moss. A. The Moss Gametophyte (1n)- Gamete Producing Generation of Moss When you are looking at moss, you are seeing a multicellular haploid organism. Recall: in the seed plants this part of the life cycle (gametophyte) is microscopic. The main body of all other groups of plants is the sporophyte. PROCEDURE- Observation and drawing 1. Examine fresh samples or prepared slides of an early moss gametophyte (1n) (protonema). Note its similarity to filamentous algae. Look for small bud-like structures along the length of the filament. These will mature into "leafy" gametophytes (1n). 2. Using a dissection microscope, examine the "leafy" part of the moss. This haploid gametophyte is the long-lived photosynthetic generation in the moss life cycle. The mature gametophyte consists of whorls of "leaves", a stem, and rhizoids. Although mosses and other non-vascular plants have true stems (note the nodes and internodes), they lack true leaves and true roots. Water and nutrients are taken in by rhizoids. Rhizoids are simple root-hair-like extensions from the epidermis. Lab 10: Bryophytes 4 3. Moss lacks true leaves. True leaves protect the shoot apical meristem during early growth. Moss “leaves” do not form in this way. Record your observation in your Plant Forms Table, noting that this is the gametophyte generation! 4. Using the dissection microscope examine the upper side of a "leaf" for the presence of a waxy cuticle that protects the plant from excess water loss. Sketch the gametophyte (1n) generation of the moss. Label the “leaves”, stems and rhizoids. 5. Using a dissecting microscope, try to locate gametangia “gamete sacks” at the very tip of the "leafy" gametophyte (1n). This is where antheridia (male gametangia) or archegonia (female gametangia) are located. Sperm production: Many cells in the antheridia undergo cell divisions to produce the male gametes (sperm). Egg production: Only a single cell in the archegonia develops into the female gametes (egg). (No meiosis is required in these gametangia- remember the cells are already haploid). 6. Examine prepared slides of moss antheridia and archegonia and locate the sperm and the egg. Note the differences in appearances (good test question:). Sketch moss gametangia (label location of sperm and egg) Antheridia Archegonia Fertilization : One egg within the archegonia will be fertilized by one sperm resulting in the diploid zygote. The zygote will undergo cell division producing the diploid sporophyte generation (note this in the fern life cycle figure). Lab 10: Bryophytes 5 B. The Sporophyte (2n) Spore Producing Generation of Moss PROCEDURE- Drawings and descriptions (refer to life cycle figure) 1. Examine the available specimens of common mosses that consist of both the gametophytic and sporophytic generations. The diploid sporophyte is easily distinguishable since it sticks up out of the gametophyte and consists of a terminal sporangium (capsule) (often covered by a pointed cap termed the “ calyptra ”). A slender leafless stalk (seta) and a foot that is embedded in the tissue of the "leafy" gametophyte. The relatively large (up to ~5cm) leafy gametophyte is photosynthetic and supports the nutrition of the sporophyte, which only lives a short time. 2. Use a dissection microscope; Draw and label the sporophyte (2n) generation of moss available in lab. Label the calyptra and capsule. Note the calyptra often falls off the mature sporophyte. 3. Under a dissection microscope, carefully separate the moss sporophyte (2n) from the gametophyte (1n). Note that the capsule often has a covering (the calyptra). Remove the calyptra (the calyptra is actually part of the gametophyte’s archegonia that gets ripped off