Using a microscope Flashcards
what is the field of view
This is the lit circle when looking through the ocular lens. it refers to how much of the sample you can see when magnified
what is the smallest field of view
The smallest field of view is when using the highest magnification objective lens.
what is the largest field of view
The largest field of view is when using the lowest magnification objective lens
what can an optical microscope be used to view
Living organisms such as Paramecium and Amoeba
Smear preparations of human blood and cheek cells
Thin section of animal, plant and fungal tissue, such as bone, muscle, leaf, root or fungal hyphae.
what happens if specimens are viewed with a high magnification
not everything is in sharp focus, this shows the specimen has depth
describe the art of focusing
Step 1 – Obtain a slide and place it on the stage over the central hole
Step 2 – Rotate the nosepiece so that low power objective is in line with the body tube
Step 3 – Raise the body tube using the coarse focussing knob
Step 4 – To begin to focus on low power, use the coarse focussing knob. When the specimen comes into view, then use the fine focussing knob to bring the specimen into sharp focus.
Step 5 – Adjust the diaphragm (amount of light) to get the most detailed view.
Step 6 – Increase to a higher magnification by rotating the nosepiece until the objective click into place
Step 7 – use only the fine adjustment knob to focus images on medium and high power.
why does the orientation of a specimen appear reversed/upside down
The lens system, particularly the objective lenses and ocular lens, flips the image both horizontally and vertically. This means that the image you see through the microscope is a mirror image of the actual specimen.
what happens when you move the slide or adjust the focus
the direction of movement is opposite to how it appears through the eyepiece
how do we prepare a dry mount sample (for e.g. hair)
Solid specimens are viewed whole or cut into very thin slices with a sharp blade, this is called sectioning. The specimen is placed on the centre of the slide and a cover slip is placed over the sample.
how do we prepare a wet mount sample (for e.g. aquatic samples)
Specimens are suspended in a liquid such as water or an immersion oil. A cover slip is placed on from an angle.
how do we prepare a squash slide (for e.g root top squashes)
A wet mount is first prepared, then a lens tissue is used to gently press down the cover slip. Depending on the material, potential damage to a cover slip can be avoided by squashing the sample between two microscope slides. Using squash slides is a good technique for soft samples. Care needs to be taken that the cover slip is not broken when being pressed.
how do we prepare a smear slide (for e.g. blood)
The edge of a slide is used to smear the sample, creating a thin, even coating on another slide. A cover slip is then placed over the sample.
what is the advantage of making a temporary mount of cells
they are quick to prepare and can be observed while they are alive
why should the specimens used be thin
to allow light to pass through them, which is necessary for viewing the details of the specimen under a microscope.
why should the cover slip be placed on a wet mount at an angle
to reduce or prevent air bubbles from being trapped under the cover slip, which can interfere with the clarity of the image.
why are biological specimens often difficult to distinguish
they are often colourless
what is a stain
coloured chemicals that bind to specific molecules in or on the specimen enhancing visibility. some stains bind to specific cell structures, allowing different structures to be distinguised within a single preparation.
how does staining the specimen help
Staining enhances the visibility of these structures by binding coloured chemicals to specific molecules, making it easier to observe and differentiate various components.
give three examples of how stains can be used
- increase contrast so different parts of a cell can be distinguised.
- to observe the location of certain chemicals in a cell
- differentiate between organisms that can be difficult to tell apart
what is differential staining
using two different stains. this helps distinguish between different types of organisms or organelles within a sample
name two types of stains
methylene blue and iodine
how to prepare a cheek slide
1) Add a very small drop of sodium chloride solution to the microscope slide. This is to ensure the sample remains hydrated.
2) Use a sterile spatula or toothpick to obtain a sample. Rub it gently inside your cheek to collect cheek cells.
3) Place the specimen into the drop of sodium chloride solution on the slide by swirling the end of the spatula or toothpick in the solution. Dispose of the used spatula or toothpick properly as it is a biohazard.
4) Add a drop of methylene blue stain to the sample. This stain is used because cheek cells and epithelial cells are very transparent and need to be coloured to be visible under the microscope.
5) Carefully place the cover slip on top of the stained sample. Hold it at a right angle to the slide and gently lower it to avoid air bubbles.
6) If there is too much liquid and it seeps out from the sides of the cover slip, use a paper towel to blot away the excess. Treat the paper towel as a biohazard and dispose of it properly.
how to prepare an onion slide
1) Peel off a thin, transparent layer of onion cells from the onion. This layer is the epidermal cells.
2) Use a pair of tweezers to transfer the onion cell layer onto the microscope slide. 3) Spread the layer out gently to prevent it from folding or curling. Alternatively, you can peel the layer directly onto the slide.
4) Apply a few drops of iodine stain to the specimen. This will wet the mount and stain the cells, making them more visible under the microscope.
5) Carefully place the cover slip on top of the stained sample. Hold the cover slip at a right angle from one side and gently lower it to avoid trapping air bubbles.
why did the onion cell need to be stained
To observe the cells. nuclei and cell walls absorb the stain more strongly, so that they can be distinguished.
