1. Microscopes II
Mmmmmm onions

2. Learn how to make a wet mount Look at an onion cell Lab questions
October 31st 2017
Agenda
Review microscopes
Learn how to make a wet mount
Look at an onion cell
Lab questions
Learning Goals
Students will be able to create a wet mount
Students will be able to focus microscopes to observe plant cells

3. You are little monsters
Take 5 minutes to explain class Dojo

4. Compound Light Microscope
Scanning Electron Microscope
CLM:
Function: Uses visible light to illuminate a thin section of sample
Maximum magnification:Approximately 2000x School light microscopes that do not use oil immersion have a magnification range of x
Best for: Looking at some living things (for example, a single cell layer)  Looking at cells and tissues (preparation steps are less critical than for electron microscopy) Getting an overview of a sample
Disadvantages: Low resolution compared to electron microscope
SEM:
Function: Lets you look at the surface of objects at high resolution.
Maximum magnification:Approximately x
Best for: Looking at surfaces of objects Looking at objects in 3D
Disadvantages: Resolution often not as high as the transmission electron microscope Can’t be used to look at living things (samples need to be dried and coated in metal before visualising) Costly to run
TEM:
Function: Lets you look at a very thin cross-section of an object (such as a cell)
Maximum magnification:Approximately x
Best for: Looking at internal structure of objects Looking at objects at very high resolution Looking at relationships between structures at high resolution
Disadvantages: Can’t be used to look at living things (samples need to be prepared extensively before visualising) Costly to run

5. Compound Light Microscope vs. Electron Microscope Image
Light Microscope Electron Microscope
2D image D image
Low resolution (blurry image) High resolution (very clear image)

6. Compound Light Microscope Image of a Fruit-Fly

7. Electron Microscope Image of a Fruit-Fly

8. The Size of Cells
The majority of cells are microscopic and cannot be seen with the unaided eye (without a microscope)
1 micrometer (µm) = one millionth of a meter
Interactive Cell Size and Scale:

9. RULES to Remember When Using the Microscope
Bring object into focus using the low power lens.
Do not allow the lens to touch the slide!
Switch to medium power lens. Use the fine-adjustment knob to focus.
Switch to high power lens. Only use the fine-adjustment knob to focus (NEVER the coarse-adjustment knob to focus at high magnification. You risk breaking your slide or lens, or both! Use the fine adjustment knob at high magnification.)
If you lose view of your object, switch back down to a lower magnification.
Always return to low power lens before removing the slide.

10. LOOKING AT CELLS: Making a Wet Mount
Place slide flat on table.
Add a drop of water to center of slide.
Place specimen in the drop of water.
Holding the cover slip with your thumb and forefinger at 45°, place one edge of the cover slip on the slide.
Support the outer edge of the cover slip with a needle/forceps, and gently lower the cover slip, allowing the air to escape.
Avoid air bubbles! Air bubbles have a black periphery under the microscope.

11. Making a Wet Mount

12. Water bubbles appear to have a thick dark border

13. BIOLOGICAL DRAWINGS
Biological drawings are made to illustrate objects seen under the microscope.
A biological drawing illustrates what you see, NOT what you think you see.

14. Drawing Use blank paper.
Use a sharp, hard pencil (e.g. H or 2H); DO NOT USE PEN!
Draw at least one half of your page.
Should be composed of one to two cells.
Leave space for labels on the right side of the drawing.
Note details and proportions of your specimen.
Draw what you see, NOT what you think you see.
Do not sketch. Draw firm, clear lines, including only relevant details that you can see clearly.
Do not colour. Darker area should be shaded by dotting.
Use double lines to indicate thick structures.

15. LABEL your drawing Labels: Must be written neatly.
Do not label directly on the drawing; should be outside of your drawing
Label lines:
Use a ruler to draw; lines should never cross
Must be horizontal and from the structures being identified to the label
Title:
Use the name and part of the specimen
Underline the title

16. LABEL your drawing Magnification of the lenses
Ocular lens x objective lens used to view the specimen
Must be recorded on the lower right-hand side of the drawing.
How to Find Magnification:

17. Example

18. CHECKLIST FOR BIOLOGICAL DRAWING
Use plain, blank (unlined) paper and a sharp, hard pencil.
Draw as large as necessary to show details clearly.
Do not shade or colour.
Draw label lines that are straight (using a ruler) and run outside your drawing.
Include
a title or caption,
labels, and
magnification of the microscope you are using.