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Lab 1 summary CC-BY-NC

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Summary of Lab 1 for BIOL 112 (Winter 2011). Week of Jan 10, 2011. This lab is mandatory to confirm registration. There is no pre-lab flow chart or quiz for this lab. Note that this lab is basically equivalent to the first lab in BIOL 111, so if you've taken BIOL 111 you'll probably be allowed to leave early.

There will be a post-lab quiz on the material presented in this lab during the next lab, so it might be a good idea to take notes or otherwise pay attention.

Topic: The microscope: plant and animal cells.

1Safety in the lab

  • Lab coats and safety goggles with side shields should be worn in the lab at all times
  • No contact lenses
  • Material Safety Data Sheets (MSDS) available for chemicals used in lab exercises
    • Headings (probably don't need to know this, but just in case): product information, information on the preparation of the MSDS, hazardous ingredients, physical data, fire and explosion hazards, reactivity data, toxicological properties, preventive measures, first aid measures
    • Classes (same as the above): compressed gas, flammable and combustible material, oxidizing material, poisonous and infectious material (divisions 1 (immediate toxic effects), 2 (other toxic effects), and 3 (biohazardous infectious materials)), corrosive material, and dangerously reactive material

2The compound microscope

  • Allows us to see at the level of micrometres instead of millimetres
  • Microscopes are expensive instruments, so don't, say, use them as makeshift baseball bats
  • They aren't really suited for hitting home runs, anyway
  • The one we use in this lab is called the Zeiss compound microscope

2.1Parts of a microscope

  • 10x eyepieces, mounted on the binocular head; differences between left and right eyepiece can be adjusted by the dioptry adjustment collar on the left eyepiece
  • Body tube (where the image is formed), leading to the revolving nosepiece where the four objective lenses are mounted:
    • scanning objective: 3.2x
    • low power objective: 10x
    • high power objective: 40x
    • oil immersion objective: 100x (requires the cover slide to be immersed in oil, with the tip of the objective submerged in the oil as well)
  • Mechanical stage that holds the slide against a metal frame; the slide and the stage can be moved using the stage movement knobs
  • Condenser that converges light rays coming from the light source; two lenses:
    • main lens: the main lens
    • front (top) lens: smaller, use only for the 10x, 40x, 100x objectives; tilt it down for the scanning objective
  • Condenser diaphragm: controls the amount of light that reaches condenser
  • Illuminator in base of microscope; intensity controlled by a knob on the base
  • Field diaphragm for adjusting the amount of light coming from the illuminator

2.2Using a microscope

  • It's a good idea to focus and centre on the slide using low power before switching to high power
  • The coarse and fine knobs should be used for the 3.2x and 10x objectives; for the higher power objectives, use only the fine focus kob
    • Using the coarse focus knob with the high power objectives may cause the objective to hit and break the coverslide lol
  • Oil immersion: place a small drop of oil on the coverslide, start with 40x, focus on the specimen (fine focus only obviously)
    • Afterwards, wipe the objective lens with a dry Kimwipe, and the slide with a Kimwipe with a dab of Slide Brite
  • Wet mounts: put some water on top of the specimen, cover with a cover slide (try to get no air bubbles)
    • Can use 3.2x and/or 10x to find, then view on 40x

3Magnification formula

Total magnification formula: magnification of eyepiece x magnification of objective x magnification of binocular tube

4Examination of plant cells

  • Hopefully you know what cells and tissues and organs are by now so I won't go into that
  • Elodea leaf: first examine, then stain with iodine and examine again
    • Elodea: freshwater plant, important in lake ecosystems blah blah
    • View on 10x then 40x
    • May be able to view cytoplasmic streaming (chloroplasts moving around the cell)
    • Draw the iodine through the leaf - place a drop at one side of the coverslide, place a Kimwipe on the other side
    • The iodine solution will then magically travel to the other side as if it were irresistibly attracted to the Kimwipe or something
    • The iodine solution kills the leaf (lol), but you will be able to see pyrenoids (starch-containing bodies) more clearly
    • Description of drawing: cells with cell walls, a nucleus and little chloroplasts streaming around happily within each cell
  • Cross sections (perpendicular to the main axis) vs. longitudinal sections (parallel to the main axis)
  • Selective staining: allows us to distinguish between different materials in the cells
    • Because different materials take up different stains etc
    • Lignified cell walls --> safranin (red), typical of thick-walled supportive cells
    • Cellulose cell walls --> fast green (guess)
    • Starch grains --> crystal violet (purple)
  • Ranunculus acris (buttercup) root: prepared slides
    • Drawing: an inner circle with a star-shaped gathering of lignified cells with thick red walls, and an outer circle with a cluster of thin-walled green cells with purple starch grains (probably where the food is kept)

5Examination of animal cells

  • While plant cells have a thick cellulose cell wall, animal cells have no such thing
  • All cells have a thin plasma membrane around the cytoplasm though
  • Human epithelial cells, from the cheek:
    • Use a toothpick to put some on a slide, cover with coverslide
    • Stain with methyl green solution
    • Drawing: should look like a bunch of balls with nuclei in the middle
  • Small intestine of Amphiuma (cross section)
    • Prepared; stain is haematoxylin-eosin, nuclei are purple, cytoplasm is pink, plasma membranes are stain-less
    • Drawing of cross-section: sort of like a tomato that has gone splat; villi projecting into the lumen, that's it mostly
    • Drawing of epithelial cells: each has a nucleus, line the outside of the villi
  • Kidney tubule (nephron) of Amphiuma (cross-section)
    • Same stain as above, also prepared
    • Drawing: like hooded figures with really large hoods bordering the inside of an ellipse; those hooded figures are the epithelial cells
    • These cells have nuclei which enclose nucleoli, as well as a cytoplasm

6Introduction to controls

  • A series of parallel experiments, each changing a single variable
  • Allows you to either confirm or discount a variable as either sufficient or necessary to produce an outcome
  • A way of eliminating alternate explanations for your results, and making sure that it was the tested variable that accounted for the results
  • For example, let's say you want to determine if spraying yourself with Axe will attract more girls to you than spraying yourself with cooking oil
  • So you set up an experiment with both negative and positive controls, and of course actually test axe as well
  • Negative controls: make sure that something does NOT do something
    • Ensuring that the procedure is not observing an unrelated effect
    • To avoid false positives
    • So you go out into the world without spraying anything on yourself
    • Do you attract any girls? Hopefully you don't, because that will make the controls of this experiment simpler to explain
  • Positive controls: make sure that something DOES do something
    • Ensuring that the procedure is competent in observing the effect
    • To avoid false negatives
    • So you go out into the world with Axe sprayed liberally all over your body; this should cause many girls to flock to you
  • And then you spray yourself with cooking oil and compare to the controls
    • If you still attract a flock of girls, then you know that it was the cooking oil and not, say, your charming personality that caused it
    • And if you don't attract any girls, then it just means that the cooking oil is not as effective as Axe at attracting girls, and perhaps logically so
    • In any case, either way you've managed to narrow it down to your usage of Axe and cooking oil
    • Plus, with your positive control, you've shown that Axe should attract girls, and so for cooking oil to be as effective, it ought to do the same
  • A probably better experiment (I think it was in the lab manual) would have to do with flour and flour substitute in a cake
    • Negative control = neither flour nor flour substitute
    • Positive control = flour only
    • Experiment = flour substitute
    • The negative control experiment will have a pretty bad cake, confirming that without flour, cake = bed
    • The positive control experiment will have a pretty awesome confirm, confirming that with flour, cake = good
    • And since you want to see if the flour substitute will be as good as flour, you perform the experiment
    • This will probably show you that the flour substitute is not as good as flour in terms of making a good cake
    • However, you will have learned the basics of using controls, so no harm done really

7Drawings

  • An Elodea thorn cell and two adjacent cells
  • Representative cells of Ranunculus root
  • A small group of cheek cells
  • Either epithelial cells of Amphiuma intestine or tubule cells of Amphiuma kidney