Supergroup Archaeplastida, part 1 – Lab Exercises
Please choose one live specimen or prepared slide to image. Take a picture under the microscope and submit via Canvas. Make sure that your picture is appropriately centered, cropped, and focused. Add a scale bar.
Rhodophyta (Red Algae)
Exercise 1.1: Examine Polysiphonia
Polysiphonia is a highly branched filamentous red alga that grows by an apical cell. It has an isomorphic alternation of generations (gametophytes alternating with tetrasporophytes). Reduced carposporophytes grow epiphytically on female gametophytes Make a fresh mount of the filamentous red alga Polysiphonia. Observe and draw a small portion of an individual.
Exercise 1.2 – Examine Porphyra
Examine a prepared slide of the multicellular marine red alga Porphyra. Porphyra is farmed and marketed as nori (used in Japanese cuisine). Draw a small portion of an individual.
Exercise 1.3: Examine red algal seaweeds
Examine available specimens of calcareous and non-calcareous seaweeds on the pressed herbarium sheets.
Chlorophyta (Green Algae)
Exercise 2.1: Examine Chlamydomonas
Chlamydomonas is a unicellular biflagellate green alga. Make a fresh mount of Chlamydomonas. Are the cells swimming? Can you see two flagella? Note the large cup-shaped chloroplast and the two contractile vacuoles at the base of the anterior flagella. Draw a few cells. Two mating strains were mixed several hours ago. Make a wet mount and find a pair of mating cells. Chlamydomonas forms isogametes (gametes that are morphologically identical to each other). In this type of reproduction, vegetative cells of different mating strains act as gametes when the cells enter the sexual phase. Chlamydomonas has a zygotic cycle. Observe and draw a cell. Observe and draw a pair of mating cells.
Exercise 2.2: Examine Pandorina
Make a fresh mount of Pandorina. Pandorina is a close relative of Chlamydomonas. A small group (8, 16, or 32) of Chlamydomonas-like biflagellate cells forms a small spherical colony. Observe and draw a mature colony.
Exercise 2.3 – Examine Volvox
Volvox is a large, hollow, spherical colony of small biflagellate (Chlamydomonas-like) cells that are interconnected by narrow threads of cytoplasm. Make a fresh mount of Volvox. Observe the colonies rolling about, driven by the flagella of the member cells. Fusion of gametes results in new colonies that develop within the hollow center of the original colony. Breakup of the parental colony will release the young colonies. Observe and draw a mature colony.
Exercise 2.4: Examine Oedogonium
Oedogonium is a filamentous green alga that anchors itself to the substrate by a “foldfast.” Oedogonium forms reproductive cells within oogonia (which form egg cells) and antheridia (which form sperm). Observe the prepared slide of macrandrous Oedogonium. Reproduction is oogamous (flagellated sperm and non-flagellated egg cell). Sperm are formed within antheridia, and egg cells are formed within oogonia. Observe holdfast, antherida, and oogonia, if present. Draw a representative portion of a filament.
Exercise 2.5: Examine Scenedesmas
Scenedesmas forms a short filament of four flattened cells with short spines at either end. Make a fresh mount of Scenedesmas. Reproduction is by non-flagellated isogametes (sexual) or autospores (asexual) to form new individuals. Draw an individual
Exercise 2.6: Examine green algal seaweeds
Examine available specimens of green algal “seaweeds” on the pressed herbarium sheets.
Exercise 3.1: Examine Spirogyra
Spirogyra is a filamentous alga that was formerly placed in the Chlorophyta. Make a wet mount of Spirogyra. Individuals have a single large chloroplast that is shaped like a flattened ribbon wound around the inside of the cell. Reproduction in Spirogyra is by conjugation. Filaments of opposite mating types line up and form conjugation tubes between aligned cells. The protoplast (i.e. the portion of the cell within the cell wall) from one filament migrates through the conjugation tube to fuse with the cell of the other filament. The zygote undergoes meiosis (zygotic cycle) resulting in flagellated haploid spores that are released, swim away, and form new filaments. Observe and draw a small portion of a filament with spiral chloroplasts. Draw a small portion of conjugating filaments, if observed.
Exercise 3.2: Examine desmids
Desmids, like Spirogyra were formerly classified in the Chlorophyta. Make a fresh mount from the desmid mix. Each desmid consists of one cell consisting of two halves (semicells) separated by a groove (sinus) and connected by an isthmus. The nucleus resides in the isthmus. Reproduction is usually asexual and occurs by the separation of semicells. Draw one or two desmids.
Exercise 3.3: Examine Chara
Chara is notable for its complex macroscopic organization with stem-like and whorled leaf-like portions (branchlets) at the nodes. Chara is common in mineral rich freshwater ponds and lakes (including those of our local mountains). They encrust their cells with calcium carbonate, so appear chalky white when dried out. Examine the available specimen of Chara. Use the prepared slides to observe the reproductive organs (oogonia and antheridia) of Chara. Sketch the central axis, branchlets, and male and female organs of an individual.
Exercise 4.1 Examine the available specimens of living mosses.
Examine the available mosses. Identify the gametophyte and sporophyte (if available) features for each specimen:
Gametophyte features: – thallus divided into leaf-like and stem-like portions
– are these mosses erect (acrocarpous) or prostrate (pleurocarpous)?
Sporophyte features: – foot, seta, capsule
– is a calyptra present?
– is the peristome visible?
Draw one gametophyte:
Draw one sporophyte:
Exercise 4.2: Examine a prepared slide of Mnium Antheridial Head l.s.
Moss antheridia are ellipsoidal and borne on a stalk. The cells that will develop into sperm are surrounded by a jacket of sterile cells. Observe and draw a moss antheridium (the slender appendages observed are paraphyses).
Exercise 4.3: Examine a prepared slide of Mnium Archegonial Head l.s.
Moss archegonia are borne on a long stalk. Each consists of swollen chamber (the venter) that contains the egg cell and an elongate neck with a neck canal that connects the venter to the outside, permitting swimming sperm to reach the egg by swimming down the neck canal. Observe and draw a moss archegonium (note the paraphyses, as above).
Exercise 4.4: Examine a prepared slide of Mnium Archegonia w.m.
Archegonia viewed in l.s. (as above) may be difficult to view, depending on how the archegonial head was sectioned. View a whole mount of an archegonium for comparison.
Exercise 4.5: Examine a prepared slide of a moss capsule l.s.
Observe and draw the capsule. Label (if visible) the spores, columella, peristome, annulus and operculum.
Exercise 5.1: Examine the available specimens of living liverwort gametophytes.
Examine the available liverworts. Distinguish between thalloid and “leafy” liverworts (if available). Which of these is similar in appearance to moss gametophytes? Identify the following gametophyte features (if available):
– thallus, gemmae cups, antheridiophores, archegoniophores
Draw a liverwort gametophyte:
Exercise 5.2: Examine a prepared slide of a Marchantia thallus c.s.
Observe a cross sectional view of a Marchantia thallus. Note the rhizoids on the lower surface of the thallus – many of these form a wick-like bundle that runs parallel to the thallus. Observe air chambers on the upper surface of the thallus. These are connected to the outside of the thallus by a pore and contain groups of photosynthetic cells called “cactus cells.” Draw a small portion of a thallus, including rhizoids and air chambers with cactus cells.
Exercise 5.3: Examine a prepared slide of Marchantia gemmae c.s.
Gemmae are multicellular, asexual spores that are formed by mitosis of the liverwort. These are located in cup-like structures (gemmae cups). They are dispersed as rain drops strike the cups, ejecting and scattering the scores away from the parental thallus. Observe and draw a gemmae cup.
Exercise 5.4: Examine a prepared slide of Marchantia antheridiophore l.s.
Liverwort antheridia are similar to those of mosses. Observe and draw an antheridium.
Exercise 5.5: Examine a prepared slide of Marchantia archgoniophore l.s.
Liverwort archegonia are similar to those of mosses. Observe and draw an archegonium.
Exercise 6: Examine a prepared slide of an Anthoceros sporophyte w.m.
Observe and draw a young sporophyte. Label the foot, seta, and sporangium. Are elaters visible?
Exercise 7.1: Examine the available specimens of living and preserved lycopods.
Observe both club mosses (Lycopodiaceae) and spike mosses (Selaginellaceae). Are these plants sporophytes or gametophytes? Note microphyll-type leaves, stems, and roots (if visible). Are sporophylls visible? What is the location of the sporangia on the sporophyll? Are sporophylls clustered into a strobilus (= cone)? Draw one lycopod.
Exercise 7.2: Make and examine a wet mount of a Selaginella or Lycopodium stem c.s.
If material is available (do not use potted specimens!), use a razorblade to make a thin section of a lycopod stem. Stain with the available stain, and view. Is xylem and/or phloem visible? Draw.
Exercise 7.3: Examine a prepared slide of a Lycopodium strobilus l.s.
Observe a Lycopodium strobilus. Draw one sporophyll.
Exercise 7.4: Observe the rehydration of Selaginella lepidophylla (resurrection plant).
Selaginella lepidophylla (like many mosses) is a poikilohydric plant that is able to withstand nearly complete desiccation during times of environmental drought without dying. These plants are able to rehydrate and become metabolically active in a matter of hours. This is a very rare attribute in vascular plants. Conversely, poikilohydric mosses are common, and many are able to rehydrate and become metabolically active in a matter of minutes. Observe the Selaginella at half hour intervals and make note of any changes in the plant.
Exercise 8.1: Examine the available specimens of living and preserved ferns.
Are the observed plants sporophytes or gametophytes? Note the megaphyll-type leaves, stems, and roots (if visible). Draw a fern frond. Are any of the leaves sporophylls? On which surface of the sporophyll are the sporangia located? Are sporangia present? If so draw a sorus.
Exercise 8.2: Examine the three genera of water ferns.
The water ferns are heterosporous – what does this mean? Draw one of the three water ferns: Azolla, Salvinia, or Marsilea.
Exercise 8.3: Examine a prepared slide of a fern sorus c.s.
Observe a fern leaf cross section showing a sorus on the lower (abaxial) leaf surface. Observe the sporangia (this type of sporangium is called a leptosporangium). The cluster of leptosporangia are protected by a flap of tissue called an indusium. Draw a sorus including sporangia and an indusium.
Exercise 8.4: Examine a prepared slide of a monoecious fern prothallium w.m.
Monoecious fern gametophytes (prothallia) form both antheridia and archegonia. Observe and draw a fern gametophyte noting both the antheridia and archegonia.
Exercise 8.5: Examine the fern gametophytes.
Examine growth of fern gametophytes. Have any of them given rise to sporophytes?
Exercise 9.1: Examine the available specimen of living Psilotum nudum.
Observe and draw a portion of the sporophyte. Note the bifurcating pattern of branching, non-vascularized leaf-like prophylls, and synangia (formed by fusion of three sporangia). Draw a small portion of the plant.
Exercise 9.2: Examine a prepared slide of a Psilotum synangium c.s.
Observe and draw a synangium.
Exercise 10.1: Examine the available specimens of living or preserved Equisetum.
Note the differences between the available specimens of horsetails. Some Equisetum species have unbranched photosynthetic stems, some of which bear strobili. Other species are dimorphic, with branched photosynthetic stems that don’t form strobili, and unbranched non-photosynthetic stems that bear strobili. All species have hollow stems that bear fused rings of tiny leaves at each node. The stems are rough and abrasive due to a surface layer of SiO2 crystals. Draw a representative stem and strobilus.
Exercise 10.2: Examine a prepared slide of Equisetum strobilus l.s.
Observe a strobilus in longitudinal section. Note the sporangia borne on the inner surface of a sporangiophore. Draw a sporangiophore with sporangia.