1 cell comparison lab
Examination of Prokaryotic Cells
- Examine a slide of bacterial types under high power (400 X). The slide contains spherical cells (cocci), rod-shaped cells (bacilli), and spiral shaped cells (spirilla). Draw several cells. The rod-shaped bacteria on the slide are attached end-to-end forming threadlike filaments. If you look carefully, you can seed the individual cells that compose the filament. Write the magnification used next to your diagram. Note the size of these cells compared to eukaryotic cells.
- Cyanobacteria are photosynthetic prokaryotes and may be connected in chains or filaments. Examine a slide of cyanobacteria such as Anabaena under high power (400X). Draw representative cyanobacteria in your notebook.
Below: Typical bacilli (rod shaped), typical spirilla, and anabaena (400X).
Examination of Eukaryotic Cells
We will examine pond water as an example of a eukaryotic cell.
- Prepare a slide using a dropper to obtain a sample from the bottom of the culture jar.
- Identify the organisms you find
- Draw them in your notebook and indicate the magnification used.
Below: Amoeba proteus, 200X. The second photograph was taken several minutes after the first. Click on the photographs to view enlargements.
Example - Paramecium
The pellicle (outer covering) of paramecium is covered with hundreds of cilia.
They have numerous organelles including a gullet (oral groove) and an anal pore.
Below: Paramecium caudatum X 100
Ciliates have a large macronucleus and a smaller micronucleus.
The micronucleus is involved in sexual and asexual reproduction. Other nuclear activities are handled by the macronucleus.
The macronucleus is polyploid (approximately 860 N in Paramecium aurelia) and the micronucleus is diploid..
During reproduction, the macronucleus disintegrates. Later, a micronucleus will develop into a macronucleus.
Most reproduction is asexual (mitosis). Sexual reproduction is by conjugation.
Below: Conjugation in Paramecium X 200
Observation of a Living Plant Cell
- Prepare a wet mount of an Elodea leaf. View the cell under low and high power. Use the fine focus to focus up and down on a cell. Cells above and below your cell may interfere with your viewing. Identify the cell wall, and chloroplasts. If your specimen is fresh, you should be able to see the chloroplasts moving within the cell.
- Notice that there are few chloroplasts in the center of the cell. This space is occupied by the central vacuole.
- Draw an Elodea cell and state the magnification used.
Below: Elodea 100X and 400X.
Animal Cells
- If you have not observed human cheek cells in a previous laboratory exercise prepare a wet mount by using the following procedure.
- Scrape the inside of your cheek with a toothpick and rub it on a dry slide.
- Add one drop of methylene blue to stain the cells. This will make them easier to see.
- Place a cover slip on the slide as described above and observe the cells under low power then high power.
- Identify the nucleus.
- How do these animal cells differ from the Elodea (plant) cells? See your drawings of typical plant and animal cells to help with the answer to this question.
- Draw a cheek cell.
Below: Human cheek cells 100X.
Lichens
Lichens are structures made up of two different species: 1) a fungus and 2) either a cyanobacterium or a green algae.
The photosynthetic cells are contained within the middle layer.
The photosynthetic cells provide photosynthesis for the lichen. It was thought that the relationship was mutualistic because the fungus prevented the algal cells from desiccation. Recent evidence indicates that the photosynthetic cells may grow faster when separated from the fungus. Perhaps the fungus is parasitizing the photosynthetic cells.
Below: Lichen thallus (cross-section) X 200. The algal cells are a lighter color. They are surrounded by and held in place by fungal hyphae.
Reproduction is asexual. Fragments are produced that contain fungal hyphae and photosynthetic cells.
Lichens derive most of their water and minerals from rainwater and air. This allows them to survive on bare rock, tree trunks, inhospitable places.
Below: Lichens growing on a rock. Below: Lichens growing on trees.
Lichens are so efficient at absorbing nutrients from the air that they can be used to monitor air quality because some kinds do not survive in polluted air.They play an important ecological role: breaking down rocks and starting the process of soil formation.
Mycorrhizae
A mycorrhiza is a mutualistic relationship between a fungus and a plant rootThe fungus functions like a root by growing into the soil and absorbing nutrients for the plant. The plant provides the fungus with products of photosynthesis (sugar).Many plants do not do well or do not grow at all without the fungi. Approximately ninety percent of all plants develop mycorrhizae.
Ectomycorrhizal Fungi
Ectomycorrhizal fungi form a dense network of hyphae around plant roots. The hyphae may penetrate the root, but they do not penetrate the root cells. Ectomycorrhizal fungi are common in cool, northern climates.
Ectomycorrhizal fungi have been described as the "dominant nutrient-gathering organs in most temperate forest ecosystems" because nearly every tree in temperate and northern forests form these associations with fungi.
Arbuscular Mycorrhizal Fungi
The hyphae of arbuscular mycorrhizal fungi (endomycorrhizal fungi) penetrate the plant root cell walls but not the plasma membranes. The portion of hyphae within the plant cell forms a highly-branched type of haustorium called an arbuscule, which aids in the transfer of nutrients between the two species.
Arbuscular mycorrhizal fungi are common in grasslands and tropical ecosystems. They are found in eighty percent of all terrestrial plants.
Example: Rhizopus (black bread mold)
Asexual reproduction involves mycelia producing sporangia that produce haploid spores by mitosis. The spores produce new mycelia.
When environmental conditions deteriorate, sexual reproduction may occur. Hyphae from opposite mating types produce structures that contain several haploid nuclei. Fusion of two of these structures from opposite mating types results in a heterokaryotic zygosporangium. A thick wall develops that functions to protect the zygospore until environmental conditions become favorable. When conditions are favorable, nuclear fusion (karyogamy) occurs within the zygosporangium producing diploid nuclei. This is followed by meiosis. The zygosporangium then germinates to produce a sporangium which releases haploid spores.
Rhizopus Sporangia X 40. Rhizopus Zygosporangia X 40.
Phylum: Ascomycota (Sac Fungi)
Examples: Yeasts, molds, morels, truffles
Ascomycetes are important in digesting resistant materials such as cellulose (found in plant cell walls), lignin (found in wood), and collagen (a connective tissue found in animals). This group also includes many important plant pathogens.
Many, perhaps half of the species of ascomycota form lichens- a symbiotic relationship between a fungus and a photosynthetic cell such as a green algae or a cyanobacteria. The fungal component of most lichens is an Ascomycete.
Morels (left) are sac fungi. Photo courtesy of Michael Lawliss Below: Peziza cross section X 200. Asci with ascospores can be seen in the photograph below.
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Examples of Sac Fungi
Morels and truffles are gourmet delicacies.
This group includes many important plant parasites such as Dutch elm disease, chestnut blight, leaf curl fungi, and Claviceps.
An ergot is the hard, purple-black fungus Claviceps purpurea. It contains toxic alkaloids, including LSD. When infected rye is made into bread, the toxins are ingested and cause vomiting, muscle pain, feeling hot or cold, hand and foot lesions, hysteria and hallucinations. Historians believe that those that accused their neighbors of witchcraft in Salem may have been suffering from ergotism. Claviceps is used to stimulate uterine contractions and to treat migraine headaches.
Yeast are single-celled members of the sac fungi.
Most reproduction is asexual; a small cell pinches off from a larger cell. This type of mitosis where a smaller individual grows from a larger individual is called budding.
Yeast (Saccharomyces) budding X 1000. Click on the images to view enlargements.
Yeast
During sexual reproduction, the fusion of two cells results in the formation of an ascus.
Schizosaccharomyces octosporus X 1000
The elongated cell in the upper left part of the photograph contains ascospores.
Cells in the lower left part of the photograph contain ascospores.
Yeast are important in leavening bread by CO2 production and in producing ethanol for alcoholic beverages.
Phylum: Basidiomycota (Club Fungi)
Some examples of basidiomycetes are mushrooms, puffballs, shelf fungi, birds nest fungi, and stinkhorns.
This group includes some serious plant diseases such as rusts and smuts.
Below: Mushrooms.
Shelf fungi are particularly important in breaking down wood.
Below: Shelf fungi.
Below: Basidia and basidiospores X 1000.