Lab Week 10
In lab week ten, we looked at deuterosomes, and phyla Echinoderma and Chordata. Review materials for this lab can be found here. Deuterosomes are embryologically distinct from protostomes in that, early in development, the blastopore forms the anus, not the mouth. In this lab, we dissected sea stars and trout, and observed the dissection of a tunicate.
- Echinodermata: Echinoderms are marine organisms that exhibit pentamerous (sections in multiples of five) radial symmetry as adults, but bilateral symmetry in their larval stage. They have a spiny surface with an underlying endodermis, a unique water vascular system (which is actually a system of tubes involved in movement in feeding), a short but complete digestive system, and separate sexes (they are dioecious). In class, we looked at two microscope slides of sea stars, focusing on pedicellaria (small pinchers on the aboral surface of the sea star to prevent algae growth), and a cross section of the arm that showed a water vascular system andtube feet. Key structures of the sea star dissection include the oral surface, aboral surface, pedicellaria, spines, pyloric caecum, tube feet, ring canal, radial canal, stone canal, madreporite, and gonads. Through cross sections of the starfish ray, we also observedossicles, the radial canal, and tube feet.
- Chordata: Chordates include a diversity of organisms; unique to all chordates, however, is the presence of a dorsal hollow nerve chord, notochord, pharyngeal gill slits, and post-anal tail, at some point in development. Subphyla included in Chordata include Urochordata(tunicates), Cephalochordata (lancelets), and Vertebrata (vertebrates).
- Urochordata: In examining the subphylum Urochordata, we looked at an adult sea squirt, and a tadpole larva of sea squirt. On the tadpole larvae we were able to observe the four distinguishing characteristics of all chordates. On the adult tunicate, we observed structures under the dissecting scope, including the incurrent & excurrent siphon, pharyngeal basket, and gill slits.
- Cephalochordata: We looked at both slides and specimens of the lancelet (the old name for this was Amphioxus, though now it is Branchiostoma). Under the dissecting scope we observed structures including the rostrum, oral opening, pharyngeal basket & slit, notochord, anus, atriopore and nerve chord; in the cross section, we found the notochord, nerve chord, pharynx, and myomeres.
- Vertebrata: As a representative of vertebrata, we dissected a fresh rainbow trout. Important structures that we observed included the operculum, dorsal fins, swim bladder, liver, kidney, gills, spleen, heart, intestine, and (in some very rare cases) ovaries or testes.
Lab Week 9
Lab week nine continued our study of the animal kingdom with a look at more protostomes. These protostomes that we looked at were the Ecdysozoans, which form a clade that is genetically differentiated from the Lophotrochozoans. Like most animals, organisms in Ecdysozoa are bilaterally symmetrical, and have tissues; all of these organisms also share the feature of ecdysis(shedding of an exoskeleton at some point in development). The two Phyla of Ecdysozoans that we looked at included the Arthropods and the Nematodes. In this lab, we dissected a crawfish (an Arthropod), and an Ascaris worm (a Nematode). An overall review of the material can be foundhere, and a review of the crawfish dissection can be found here.
- Nematoda: Nematodes share the features of major organ systems and tissues, bilateral symmetry, and pseudocoeloms; they have a complete digestive system with both a mouth and anus. We looked at both the dissection of an Ascaris worm, as well as a cross-section, and students should be familiar with the structures in both of these mediums of observation. We also looked at some live Nematodes in the soil of the Marchantia we studied previously in week four. We noted the thrashing motions in which these worms moved as, unlike the earthworm studied in week eight, Nematode worms lack muscles in the body wall, and have only longitudinal muscles. Students should recall that not all Nematodes are free-living. TheAscaris worm we dissected lives in the small intestine of vertebrates, and Trichinella spiralis, discussed in the slides, lives in muscle tissue.
- Arthropoda: Arthropods include a remarkably diversity of life on earth, comprising over half of the known species on the planet. These animals share the characteristics of having tissues, bilateral symmetry, and, like all Ecdysozoans, they shed their exoskeleton, which is composed ofchitin. Arthropods also have segmented bodies and jointed appendages. They have complete digestive systems, open circulatory systems, and are mostly dioecious (have separate sexes). In lab, we looked at the Subphyla Chelicerata, Crustacea, and Uniramia (Hexapoda). We dissected a crawfish, and made use of a dichotomous key to determine the orders of different insects.
- Chelicerata: This group included both spiders and horseshoe crabs that we observed. The first appendages of these organisms, the chelicera, are modified for catching prey and defense, whereas the second appendages, the pedipalps, are used for manipulation. Important external structures that we observed in the Chelicerata include: Cephalothorax, abdomen, telson, coupound eyes, ocelli, chelicerata, pedipalps, spinnerets, spiracles, and the epigynum.
- Crustacea: This group includes a large diversity of the marine food chain; crustaceans have mandibles, antennae, compound eyes, and branched appendages. We looked at barnacles under the dissecting scope, and likewise observed Daphnia. We spent a great deal of time on the crawfish dissection, and noted both external and internal structures of the organism. Important external structures include the telson, swimmerets, copulatory swimmerets (if male), and compound eyes. Internal structures observed include the green gland, heart, stomach, digestive glands, extensor muscles, flexor muscles, and intestine.
- Uniramia: We had a myriad of different organisms on display representing the Subphylum Uniramia, including several pinned organisms, and slides of mosquito and a human flea. We looked at the external anatomy of a grasshopper, and noted antennae, compound eyes, wings, spiracles, femurs, tibias, and the tarsus of individuals. Student should also know the body regions of the organism (head, thorax, abdomen), and be able to use a dichotomous key.
Lab Week 8
Lab week eight began our study of the animal kingdom. We looked at protostomes; during the first block of lab we examined the Phyla Porifa, Cnidaria, Nematoda, and Platyhelminthes. The second block of lab examined the Lophotrochozoans, including the Phyla Ectoprota (AKA Bryozoa), Annelida, and Mollusca, and we focused on the dissection of an earthworm and squid. We also looked at the morphological features of a clam. Resources for looking at the first block of phyla can be found here, and phyla of the second block can be reviewed here. Students should know the morphology of these groups well, and be able to classify these organisms as acoleomates (no true body cavity), pseudocoleomates (a body cavity not lined with muscle tissue), or coleomates (a body cavity lined with muscle tissue), and know whether the morphologies of these organisms are asymmetrical, radially symmetrical, or bilaterally symmetrical. Marching through the phyla:
- Porifera: These are the sponges; characteristic of this Phylum is an asymmetrical body plan, with no tissues present. Structures of a sponge do include a hollowed out area called thespongocoel, the opening to which is called the osculum. Further body organization of the sponge includes the following structures:
- Pinacoderm: The outer layer of the sponge, which includes porocytes (tubular cells forming channels into the spongocoel.
- Mesophyl: The gelatinous middle layer of the sponge. This layer has calcium carbonatespicules that support & protect the sponge; spicules are produced by amoebocytes, which can also become gametes. A protein called spongin may also be used for support.
- Choanocytes: Unique to sponges, these are flagellated cells that perform the function of bringing water through porocytes and into the spongocoel (the water then exits through the osculum). Choanocytes engulf particles and circulate gasses and waste.
- Sponges lack a body cavity (the spongocoel is not a body cavity); they feed off of suspended debris, and digest the debris in the lysosomes of cells. More information on sponges can be found on page 246 of the Dolphin lab book.
- Cnidaria: This phylum includes jellyfish, and the hydra that we looked at in lab. Unlike sponges, Cnidaria have well-defined tissues. They are radially symmetrical, but have no coelom, and no complete digestive system. Unique to Cnidaria are stinging cells, called cnidocytes. The morphology of Cnidaria includes an outer epidermis, and an inner lining of the digestive tract, called the gastrodermis, both held together by a gelatinous mesoglea. Students should note that cnidarian species can have one or both of two types of body plans in their life histories; these body plans include a Polyp stage, and a Medusa stage. The hydra that we looked at in lab has only the polyp stage in its lifecycle, and the jellyfish we looked at has only the medusa stage. More information on Cnidarians can be found on page 248 of the Dolphin lab manual.
- Platyhelminthes: In this phylum, we see the development of major organ systems, and have our first example of an organism that exhibits bilateral symmetry. Like the Porifera and Cnidaria, however, these organisms are acoelomic. Examples of this phylum that we examined included:
- Turbellaria, or free-living Planaria. We had live Planaria in lab, and also looked at cross-sections of the organism. We noted the sensory organs of the Planaria, including eyespotsand auricles (chemoreceptors).
- Trematoda, or flukes, are parasites of vertebrates such as ourselves. Through slides, we were able to observe oral suckers, a gastrovascular cavity, a uterus, and testes.
- Cestoda, or tapeworms, is another parasitic flatworm. We looked at a preserved specimen in lab, and looked at slides, which included the scolex of the organism, which attaches to the inner intestine of the worm's host.
- More information on Platyhelminthes can be found on page 252 of the Dolphin text.
- Ectoprocta (Bryozoa): We looked briefly at a slide of Cristatella, and a detailed picture of the body plan can be found on page 263 in the Dolphin lab manual. Most of these animals are colonial, and all are bilaterally symmetrical, with a well-defined body plan. Students should know what a lophophore is (the crown of ciliated tentacles used in filter feeding).
- Annelida: This Phylum includes the segmented worms. Characteristics of Annelids include segmentation, a complete digestive system, excretory organs, a (ventral) nervous system, and a closed circulatory system that runs dorsally. Annelids have a true, fluid-filled coelom, with both circular and longitudinal muscles. Annelids are also monoecious, or hermaphroditic, though they do not fertilize themselves. Ecologically, these organisms are important as both predators and prey in marine environments; terrestrial annelids, such as the earthworm, turn over soil, helping plant root growth, and the breaking down of organic detritus. We dissected earthworms in lab; some of the important features observed include the:
- Cuticle, Setae, Excretory pores, Clitellum (which secretes a cocoon around eggs), Intestine, Hearts (there were five), Seminal vesicles, Seminal receptacles, Gizzard (grinds food), Crop (stores food), and Dorsal blood vessel.
- Mollusca: We examined five Classes of the Phylum Mollusca, and these are discussed in the Dolphin text on page 270. We looked at two representatives of this Phylum in depth in dissecting a squid, and observing a clam. Mollusks are coelomates, though their body cavity is often reduced. The body is divided into three regions, including a muscular foot, a mantle, and a visceral mass; a shell may also be present, reduced, or absent altogether. Ecologically, the Phylum is very diverse, with some species feeding as herbivores, others as detritivores, and others as predators. Classes that we examined include:
- Polyplacophora: These were the chitons, which were flattened, and had eight dorsal plates.
- Gastropoda: This class includes snails and slugs; we saw some preserved specimens of these, and had some live freshwater snails.
- Scaphopoda: Representatives of this class included some tusk shells in small dishes.
- Cephalopoda: This classes includes squid (we dissected one), and octupi; we also observed anautilus shell. Some of the important morphological structures that we looked at on the dissected squid included:
- Tentacles, Arms, Fin, Mantle, Eye, Collar, Mouth, Horny Beak, Gill, Kidney, Systemic Heart, Siphon, Ink Sac, Liver, Cecum, Gonads, Stomach, and Pen.
- Bivalvia: This class included clams, oysters, and muscles, and we observed a plastomount of a dissected clam. Some of the important structures observed on this mount included:
- Mouth, Abductor Muscle, Intestine, Heart, Anus, Gill, Mantle, Foot, and Palp.
Lab Week 7
We had a lab practical on week seven covering all the material before fungi.
Lab Week 6
In this lab we explored some of the diversity in the fungi kingdom. We focused on members of Phyla Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota, and we looked at the two interesting fungi associations of lichens and mycorrhizae.
Resources for looking at the different phyla we studied can be found here, and pictures for lichens and mycorrhizae are here. Students should also consider reviewing the lifecycle of fungi, a diagram of which can be found on page 218 of the Dolphin lab book.
Fungi are eukaryotic, and heterotrophic, with a body made up of filamentous hyphae. These hyphae combine to form a mycelium, the vegetive part of the fungus, and many arecoenocytic, that is, they have many nuclei in the cytoplasm of cells, with no nuclei between these cells. Some have septae (partitions) between cells and a single nucleus in the cell cytoplasm. With the exception of the Phylum Chytridiomycota, nuclei are haploid (1N), and the only diploid (2N) cell is the zygote. In the life-cycle of fungi, we also find dikaryotic (also called heterokaryotic) cells (n+n). These cells have two distinct haploid nuclei in them.
Fungi feed by secreting digestive enzymes on their food; their food then breaks down, and fungi absorb the nutrients. This feeding process is performed by the mycelium of the fungi; what we generally think of when we picture fungi (mushroom stalks and caps) is actually the fruiting body of the fungi, which produces spores.
In class, we looked at five phyla of fungi in detail:
- Glomeromycota: This is a relatively new Phylum, established by DNA evidence.
- Chytridiomycota: These can be found on pages 216-217 in the Dolphin lab manual. In class, we looked at some live material in a a wet mount slide, and drew some observations on some of the hyphae found. These fungi are unique in that they have flagellated zoospores.
- Zygomycota: This group can be found in pages 217-219 of the lab manual. In class, we looked at Rhizopus culture. We observed hyphae, mycelial mats, sporangia, and zygospores. We also made a wet mount of the zygospore to examine (these were the black areas of the hyphae). Some things to note about this phylum:
- These fungi are mostly terrestrial decomposers, some of them mutualists with other species.
- They reproduce both sexually and asexually, though not with a distinct sperm and egg.
- Zygospores are diploid, and the result of two different mating types (remember we don't have male and females in fungi; we have types, usually + or -). Zygotes can divide meiotically to produce haploid cells, which become sexual spores.
- Asexual spores also exist, and they are produced by mitosis, in the asexual phase of the fungi.
- Hyphae in this phylum are coencytic.
- Ascomycota: This group can be found on pages 220-222 in the lab manual. The group includes mildews, such as the powdery mildew we saw on the lilac leaf. In the mildew we located ascocarps (fruiting bodies) of the fungi. Asci (a singular ascus) produces haploid spores. Some ascomycotes that we had on display included:
- Basidiomycota: Also known as club fungi, this Phylum includes somewhere around 30,000 different species of decomposers, parasites, and mutualists. All of them have basidia, club shaped structures that produce four spores. They do not have ascus, zygospores, or sporangium, but they do have fruiting bodies, basidiocarps, which are commonly eaten. Their hyphae are also always septate (cells are separated). We dissected an Agaricusmushroom, and looked for the spores within it.
In addition to these five Phyla, we also looked at fungal associations including
lichens and
mycorrhizae. Lichens include fungi that occur in a symbiotic relationship with an algae or cyanobacterium. The vast majority of the lichens involved in these symbioses are ascomycota, though a few algae include basidiomycota. Lichens are very slow growing, but can survive in very extreme environments (e.g., on rocks, trees, within soil).
In lichens, we noted the difference between crustose, foliose, and fruticose morphologies.
We looked at mycorrhizae, which includes fungi that have a mutualistic symbiosis with plants; over 95% of vascular plants have such a relationship with a fungi of the phylum Glomeromycota, Basidiomycota, or Ascomycota.
Students should know the lifecycle of fungi, and know the ploidy level (2N, N, N+N) of the different specimens looked at in the lab.
Lab Week 5
In lab week five, we studied biological diversity among seed producing plants. These plants included the angiosperms and gymnosperms and the angiosperms. Gymnosperm ("naked seed") plants are characterized by producing seeds from an exposed ovule, and angiosperm ("receptacle seed") plants are characterized by flowers bearing an ovary that holds ovules and develops into a fruit.
Again, in this lab, we stress the difference between haploid and diploid tissue. We noted that all of these plants contain vascular tissue containing lignin, which provides the plant support. For all of these plants, the "predominant" stage of the plant's life is the sporophyte (2N, diploid) stage, with the gametophyte stage being greatly reduced (down to three cells in angiosperms). As with the seedless plants discussed in lab week four, it is important to remember that sporophytes are always diploid, and produce haploid spores through meiosis. In contrast, gametophytes, which grow from spores, are haploid, and undergo mitosis to produce gametes, which then fuse together to produce another sporophyte. Students should be familiar with the details of this process in both angiosperms and gymnosperms.
In contrast to seedless plants, spores are retained in the sporophyte, and gametophytes that develop from these spores are either retained inside the sporophyte ovule (in the case of female gametophytes), or dispersed as pollen (in the case of male gametophytes). What we call pollen is really just the male gametophyte stage of the plant. Pollen is carried via wind or animal dispersal to another plant; this is pollination. Pollination is distinct from fertilization, the latter being the fusion of sperm and egg, which takes place after sperm travel down the pollen tube to the ovule. An important thing to remember about this process in the seed plants is that no water is needed for fertilization (as opposed to the seedless plants). Thus we can see seed plants' adaptation to a more terrestrial lifestyle in pollination. A fertilized egg will develop into a zygote within the ovule; amature ovule is a seed.
We looked at both gymnosperms and angiosperms independently in week five's lab. Gymnosperms that we observed included conifers (mostly from around our campus), cycads, and ginkos. We looked at a cross section of a pine needle, and saw vascular tissue, epidermis, a waxy cuticle (protecting the pine from desiccation), and resin ducts. We also examined staminate (male) cones, which produce pollen and are smaller and more short-lived than the female cones. Male cones are located lower on the tree than female cones; this is believed to be an adaptation to avoid self-pollination. Students should be able to:
- Distinguish between sporophytes and gametophytes, and describe what these stages look like.
- Explain how pollination and fertilization happens in gymnosperms.
- Compare and contrast the life-cycle of gymnosperms with that of seedless plants, such as ferns.
Angiosperms include all of earth's flowering plants. These plants are the most diverse group of plants today, producing both flowers and fruits. Students should be able to label all parts of a flower, and be able to describe the functions and ploidy levels (haploid or diploid) of these parts. Students should be aware that a fruit is the enlargement of the ovarian wall that holds seeds. Thusa fruit is a mature ovary. After this lab, students should be able to compare and contrast the life stages of gymnosperms and angiosperms, and provide hypotheses as to why angiosperms might have characteristics such as bright showy flowers and edible fruits.
Excellent review slides for angiosperms and gymnosperms, as well as topics of previous labs, are available on the Darwin server, a link to which can be found on the current student resource page at Iowa State.
Lab Week 4
In week four's lab, we looked at Seedless Plants, and the Chlorophyta (a protist) Nitella. Seedless plants observed include Bryophyta and Pterophyta. Chlorophyta were included in this lab because they are believed to be the most closely related algae to plants.
The transition from an aquatic to a terrestrial environment that was made by ancestors of plants required several adaptations for living on land including:
- Adaptations to minimize water loss
- New methods of obtaining water and nutrients
- Ways to transport water and nutrients to different plant cells
- New means of support to grow tall and compete for sunlight
- New dispersal mechanisms
- A means of reproduction that allowed for outcrossing (as opposed to inbreeding).
After leaving this lab, students should be familiar with the life cycle of plants, including what phases of the plants we looked at are
haploid, and which are diploid, and what both these terms mean. A good illustration of this, which uses a fern such as the ones we looked at as an example, can be found
here. Students should note that the green structures on this diagram are diploid (2N), and the gray structures are haploid (N). Another illustrative diagram is shown in Dolphin's text.
Good terms to know also include
isogamy and
anisogamy (a.k.a. heterogamy). If students know which of the organisms we looked at have which form of sexual reproduction, that's great, and if students can come up with hypotheses as to why different types of organisms may have isogamy vs. anisogamy, even better! Also, students should note that
oogamy is a special case of anisogamy.
Structures of the organisms we looked at should also be known, and most are found in the Dolphin text. Terms include, but are definitely not limited to: rhizoid, antheridium, archegonium gemmae, thallus, sori, oogonia, gametangia, etc. Students should also know the classification of the species we looked at, and be able to spell the scientific names.
A lot of good material for study can be found on the Iowa State website from the links at the top, repeated
here and
here.
Lab Week 3
In week three's lab, we discussed:
Our coverage of bacterial diversity was limited, but images of what we did see can be viewed in the link above, as well as in Lab Topic 14 of Dolphin (2008). We also covered the use of an ocular micrometer; scopes in our lab are calibrated as such:
- At 4X magnification, 1 ocular unit (OU) = 25 micrometers
- At 10X magnification, 1 OU = 10 micrometers
- At 40X magnification, 1 OU = 2.5 micrometers
Our coverage of protists was much more involved, and included several
clades that we observed.
Protists are different from bacteria in that they are
eukaryotic. Eukaryotic organisms have complex structures that have membranes, including a nucleus, which holds most of the genetic material in a cell. A large number of protists are single-celled, but there are also colonial (e.g.
Volvox) and multicellular (e.g.
Oedogonium) protists. Terms regarding the cellularity of organisms are good to know:
- Unicellular: Organisms that are composed of only one cell.
- Colonial: Organisms composed of more than one undifferentiated cells.
- Multicellular: Organisms composed of more than one different types of cells.
Protists carry out about 50% of the photosynthesis on earth, and are thus a critical component of the biosphere. Some of these organisms clarify water through filter feeding, others are eaten by larger animals. Some protists (e.g. Trypanosoma) are parasitic to other species, including humans.
Most protists are free-living; many are photosynthetic, and almost all of them live in water. They get around with
pseudopodia,
flagella, or
cilia.
After leaving this lab students should be able to:
- Differentiate between unicellular, colonial, and multicellular organisms under the microscope.
- Know what clades are photosynthetic.
- Know what clades are heterotrophic/autotrophic.
- Know what protists are parasitic, and describe the life-cycles of these protists.
- Know how mobile protists are able to move around.
- Understand the difference between mitosis and meiosis.
- Explain sexual and asexual reproduction in green alga.
- Know what organisms are isogamous/anisogamous.
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