Lessons 7–8 · 2 lessons · A. Zikiryayev, A. To‘xtayev, I. Azimov, N. Sonin. Biology. Basics of Cytology and Genetics, Grade 9, revised and expanded 5th edition. “Yangiyul Poligraph Service”, Tashkent, 2019
8
Laboratory work 1: viewing a bacterium and a blue-green alga under the microscope
Textbook: p. 28
GoalLearn the procedure and results of observing a hay bacillus and a blue-green alga under the microscope.
The laboratory work is done under the teacher’s guidance. To prepare a hay infusion, pieces of hay are boiled in water, filtered and left at 20–25 °C for several days; boiling is done only by adults or the teacher. Then a drop from the thin film on the surface is placed on a slide, covered with a cover slip and stained with methylene blue. Under the microscope, first on low and then on high power, you see rod-shaped, motile bacteria and shiny oval spores. A mount of a blue-green alga (for example Oscillatoria) shows blue-green filaments of small cells with no nucleus and no chloroplasts, which sway back and forth. Afterwards wash your hands with soap and dispose of slides as the teacher instructs.
Worked examples
A result note: “Hay bacillus: rods, motile; some have a shiny oval spore. Magnification: 400×.”
An Oscillatoria filament is made of similar cells and no nucleus is visible because the cell has no formed nucleus; the filament sways.
Class activity
“Microscope rules”. In pairs put cards in the right order: set the light, low-power lens, focus, high-power lens, drawing. Do not touch the lenses with fingers.
Practice
1
How can a mount be stained to observe bacteria?
Methylene blue (a blue dye) is dropped under the cover slip.
2
What do you see in a hay bacillus mount under the microscope?
Motile rod-shaped bacteria and shiny oval spores.
3
Why is the low-power objective used first?
It gives a wider field of view, makes finding and focusing the object easier, and protects the slide and lens.
4
What does it show that Oscillatoria cells can be called nucleus-free?
It belongs to prokaryotes: there is no formed nucleus, the genetic material lies in the cytoplasm.