✅ 1. Required Practical: Onions Under Microscope (B1) Flashcards
Safety Measures in Microscope RP
- Take care when handling glass slides as they are very fragile.
- Avoid getting iodine solution on your skin
- Wear eye protection
- Take care not to break the slide by moving the objective lens too far downwards.
Equipment needed for the Microscope RP
- Light Microscope with low and high power objective lenses
- Microscope slide and cover slip
- Selection of samples: onion, Elodea, filamentous algse
- Dilute iodine solution
- Dropper pippette
- Scalpel, Scissors, Foreceps
- Mounted needle
- Blotting paper or filter paper
- Range of prepared animal cells including cheek cells and red blood cells
- Range of prepared plant cells including onion epidermal cells and leaf palisade cells.
Microscope RP Method
- Collect a small of the cell you want to observe
- Remove the inner skin or a layer of onion using foreceps, or a thin layer of Elodea or filamentous algae using the scalpel
- Place the thin slice onto a clean glass slide. Use your foreceps to keep the onion skin flat on the glass slide.
- Using a pilette, add one or two drips of dilute iodine solution on tip of the onion skim or slice of algae plant.
- Hold the coverslip by its side and lay one edge of the cover slip onto the microscope slide near the specimen.
- Lower the cover slip slowly so that the liquid spreads out.
How to Set Up the Microscope in a Microscope RP
Before you can look at the cells on the slide, you will need to set up your microscope.
Most microscopes will have a built-in light source, but if the one you are using does not, then you need to arrange a mirror found underneath the stage sl that light is directed through the lens system.
- Move the stage to its lowest position.
- Place a prepared slide on the centre of the stage and fix it in plsce using the clips.
- Select the objective lens with the lowest magnification.
- Look through the eyepeice and turn the coarse focus adjustment until the cells come into view.
- Turn the fine focus adjustment to adjust the focus so the cells can be clearly seen.
The Total Magnification Calculation Formula for Microscope RP
Total Magnification = Eyepiece Lens Magnification x Objective Lens Magnification
How to Calculate Cell Size in Microscope RP
- At a low magnification, place a transparent rule across the microecope stage.
- Measure the width of the field of view using the ruler markings.
- Place the slide to be virwed into position. Increase the magnification until individual cells can be viewed.
- Calculate the new width of the field of view at this magnification, using the formula:
Field of view = (Original Magnification/New Magnification) x Original field of view - Count the number of cells visible across the field of view
- Calculate the elngth of a single cell using the following formula:
Length of cell = Field of view/Number of Cells.
How do you Calculate the Actual Size and Image Size of a Specimen and also the Magnification?
Magnification = Image Size / Actual Size of Specimen
In a Triangle I is at the top, A and M are on the bottom, which creates an ‘I AM’ triangle.
Parts of the Microscope:
- Eyepiece -Fine Focus
- Objective Lens -Coarse Focus
- Stage -Fine Focus
- Slide -Light
What is Resolution
Resoltion is the ability to distinguish between two seperate points. The resolving power of a microscope affects the level of detail it can show.
Max Resolution and Max Magnification of Light, Transmission Electron and Scanning Electron Microscopes:
(Type of Microscope: Max Resolution - Max Magnification)
(Type of Microscope: Max Resolution - Max Magnification)
Light: 200nm - x1,500
Electron: 0.2nm - x 2,000,000
Example Question: You are looking at onion cells under a microscope. The cells on the slide appear to measure 5 mm with a magnification of ×200. What is the actual size of the cell in micrometres (μm)?
For this question you first need to find the correct formula from the ones given above (the I AM triangle). You are trying to find the specimen size and so the formula you need is:
size of real object = Size of Image/Magnification
size of real object = 5/200 = 0.025 mm
This answer is in mm, where 1 mm = 1000 micrometres (μm) To convert to μm: 0.025 × 1000 = 25 μm
Why it is important to add a scale or magnification to a drawing or a photograph.
It is crucial to add a scale of magnification to a drawing or photograph because then you are able to differenciate between the image size and make a relation to the actual size of the object in view.
What are the difference between Transmission Electron and Scanning Electron microscopes
Transmission electron microscopes give 2D images with very high magnification and resolution. Scanning electron microscopes give dramatic 3D images but at lower magnifications.
