"Use a microscope to observe the living world around you (1)" Tiny World PPT Courseware 4

"Use a microscope to observe the living world around you (1)" Tiny World PPT Courseware 4

In 1663, the British scientist Robert Hooke made a very remarkable discovery. He used a homemade compound microscope to observe the structure of a cork sheet and found that they looked like small rectangular rooms, so he named them cells.

Observe onion epidermal cells

Preparation before observation

There are certain requirements for observing objects under a microscope. The object must be prepared as a slide specimen before its fine structure can be observed under a microscope.

Materials and Tools

Materials required for the experiment: onion, knife, water, dropper, iodine, absorbent paper, slide, cover slip, microscope, tweezers

How to prepare slide specimens

Place a drop of water in the middle of a clean glass slide and set it aside for later use.

Use a knife to lightly score "#" on the inner epidermis of the onion; use tweezers to remove the onion epidermis within the "#" and place it in the center of the water drop on the slide. Note that the specimen should be unfolded flat and not folded.

Cover the specimen with a coverslip at an angle. When placing the coverslip, place one end first, and then slowly lower the other end. Be careful not to have air bubbles.

Finally, use a dropper to take a few drops of iodine, use a paper towel to absorb the excess dye, and the onion epidermis slide specimen is completed.

How to use a microscope correctly?

1. Hold the frame arm with one hand and support the lens base with the other hand, place the microscope on a flat table facing the light; (Placement)

2. Turn the converter and turn the low-magnification objective lens to the bottom of the tube;

3. Adjust the reflector under the stage and look down from the eyepiece to see a bright aperture; (Light alignment)

4. Adjust the coarse focus screw to lift the lens barrel so that the low-magnification objective lens is about 2 to 3 cm away from the stage. Place the slide of the specimen you want to observe on the stage and clamp it with a slide clamp so that the specimen is exactly in the center of the light hole on the stage; (mounting the slide)

5. Adjust the focusing screw and lower the lens barrel so that the low-magnification objective lens is just above the glass slide;

6. Look down from the eyepiece, adjust the focus screw, slowly lift the lens barrel until the specimen appears in the field of view, and adjust the light so that you can see the specimen as clearly as possible; (focus adjustment)

7. Move the slide slowly and observe each part of the specimen. Note that the direction of movement is exactly opposite to the direction seen through the eyepiece. (observe)

maintainance:

The microscope must be kept clean at all times to prevent oil and dust from adhering to it. If the lens is dirty, wipe it gently with lens cleaning paper. If there is any oil stain, first dip the lens cleaning paper in a little xylene and wipe it off.

When observing fresh specimens, a cover slip must be added to prevent the specimen from drying and deforming due to evaporation or from contaminating and corroding the objective lens. At the same time, the surface of the specimen can be evened and the light can be concentrated, which is conducive to observation.

The small room-like structures we observe on the onion epidermis are onion cells.

Communicate and show the cells of the onion epidermis that everyone has drawn. What else can we discover?

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