Questions about onion epidermal cell experiments

1. Cell membrane, the resolution of the optical microscope is limited, the cell membrane is very thin, and the cell membrane cannot be clearly observed Answer supplement The cell membrane is a bilayer structure, with a thickness of only a few molecules, so the optical microscope is not clear Answer supplement There is no thread in the lens, can you express it more clearly? I'm a student of biology and I make observations a lot, so I don't know what you mean Answer supplement The two eyepieces are not threaded, in an optical microscope, the eyepieces are removed and replaced at any time, without threads, and the objective lens is on a converter and is locked by threads.

Observe the procedure of onion epidermal cells with a microscope.

1) Have your microscope ready.

2) Cut the onion and break off a tender scaly leaf; Use a blade to lightly scratch a "well" on the surface of the scale leaf, and use tweezers to gently tear off the epidermis of an onion scale leaf in the middle of the "well".

3) put a few drops of water on the slide; Clamp the onion epidermis with forceps and place in water on the slide and flatten; Clamp the coverslip with forceps and cover, without air bubbles.

4) Drop a drop of diluted iodine on the left side of the coverslip, and use absorbent paper to suck the iodine solution on the right side of the coverslip and dye the onion skin.

5) Place the sections prepared through the above steps on the stage of the microscope and clamp them.

6) Observation with a low magnification.

Transparent, just one layer, easy to observe, purple onions do not need to be dyed.

1. Purple onions are generally used, because they are purple, they can be used in the light microscope without dyeing.

See the cells below.

2. His epidermal cells are relatively large.

3. The arrangement of his cells is neat and regular, and it is like a graphite molecule, layer by layer, so the light transmittance is good and easy to see.

4. Flush out the sedan car in something with the above benefits, **cheap.

Permeability. Also known as solute dispersion, it is due to the presence of solute particles, which reduces the free energy of water.

Therefore, its water potential is lower than that of pure water, which is expressed as a negative value. At standard pressure, the permeation potential of the solution is equal to the water potential of the solution because the pressure potential of the solution is zero. The permeability potential of the solution is determined by the total number of solute particles in the solution, and the permeability potential of the cell is mainly affected by the concentration of the cell cavity, so all factors that can affect the cell concentration will affect the cell permeability potential.

1. Introduce the onion to the topic.

Remove a piece from its inner epidermis, and make a specimen of onion epidermal slide.

1) Drop a drop of water in the middle of a clean glass slide;

2) Use a knife to draw a "well" on the inner wall of the onion scale leaves, and use tweezers to remove the water droplets from the inner epidermis of the onion in the "well" and put it on the glass slide**, pay attention to the specimen to be flat and not folded;

3) Cover the specimen with a coverslip at an angle, and when placing the coverslip, first put one end and then slowly lower the other end, taking care not to have air bubbles. If the water is insufficient, drop along the edge of the coverslip; If there is too much water, you can use absorbent paper to absorb it;

4) Drop a drop of diluted iodine from one side of the coverslip and tilt the slide slightly, and then use absorbent paper on the other side of the coverslip to absorb the excess water;

5) Onion epidermal slide specimens can be made for observation.

2. Students make their own slide specimens in groups (it is best to make three copies of the slides to facilitate the comparison and observation below.)

3. Observe onion epidermal cells.

1. Observe the onion skin with the naked eye and draw what you see on the scientific record book.

2. Then use a magnifying glass to observe the onion skin and draw what you see into the scientific record book.

3. What do students observe with the naked eye and a magnifying glass? How do they differ?

4. Use a microscope to observe onion epidermal cells.

1) Show the microscope, guide the students to understand the microscope, introduce the name, function and use method of each part, and the students are familiar with the microscope in a group of 5 people.

2) The onion epidermal cells were observed by microscope in each group. (Division's operation demonstration: placement - light alignment - loading - focusing - observation.) Follow the operation step by step. ）

3) Students observe, record, and trace onion epidermal cells. Teachers inspect and guide, and the leader of the experiment team of each group supervises whether the operation of the group members is standardized, and everyone is required to operate, observe, and communicate the observation results. The team leader draws the findings under the microscope onto the scientific notebook.

Name of the experiment: Observation of onion epidermal cells.

1. The purpose of the experiment: 1. Make temporary transfer of plant cells, and learn the basic method of making temporary transfer of plant.

2. Understand the basic structure of plant cells.

3. Practice drawing cell structure diagrams.

2. Teaching focus: make temporary mounting, summarize the structural characteristics of plant cells.

3. Teaching difficulties: making temporary films; Practice drawing the structure of a plant cell.

4. Materials and utensils: onion scale leaves, filial piety saline, dilute iodine solution, tweezers, blades, droppers, gauze, absorbers, glass slides, coverslips, microscopes.

Process: 1) Enter the Qiaoqinghu laboratory and sit in groups first. Each group quickly took out the microscope and turned it on to a good light. The teacher reviews the use of the microscope and answers the question.

With a microscope, in addition to the light, adjusting the focus, placing and moving the slide specimen, it is also necessary to allow visible light to penetrate the object being observed so that the object can be seen clearly. Therefore, the material to be observed must be thin and transparent. In order to do this, the material being observed needs to be processed to make a slide specimen, which is then observed.

There are three commonly used slide specimens:

Slicing – made from thin slices cut from living organisms (usually made from solid materials);

Smear – made from liquid biological material (e.g. yeast fluid, blood, etc.);

Sheeting – made with a small amount of material (e.g., onion scales, cabbage leaves) torn or picked from an organism

All three types of slide specimens can be made permanent (for long-term storage) or temporary (not for long-term storage).

2) Methods and steps for making onion epidermal cells for temporary mounting:

Preparation: 1. Wipe the slides and coverslips with clean gauze. (RUB).

2. Put the slide on the experimental table and use a dropper to drop a drop of normal saline on the slide. (drops).

Making Temporary Installations:

3. Use tweezers to tear a small piece of transparent film from the inside of the onion scales - the inner epidermis. (tear or take).

4. Insert the torn inner epidermis into the water droplets on the slide and flatten it with tweezers. (Exhibition).

5. Pick up the coverslip with tweezers, so that one side of it first touches the water droplets on the slide, and then slowly lowers it and covers the material to be observed, so as to avoid the appearance of bubbles under the coverslip and affect the observation. (Cover).

Staining: 6. Place a drop of dilute iodine solution on one side of the coverslip. (dyeing).

7. Attract the other side of the coverslip with absorbent paper so that the stain solution infiltrates the whole specimen. (Suck).

3) Practice drawing a diagram of cell structure.

4) After the observation is completed, put the microscope back in its original place.

Objective: To illustrate that the plant body is made up of cells.

Materials: microscope, onion, tweezers, dropper, water, glass slides, needles, covers, absorbent paper, gauze.

Methods: (1) Wipe the slides and coverslips with gauze.

2) Use a liquid tube to drop a drop of water on the slide.

3) Tear off a small piece of epidermis from the onion scale leaf with tweezers.

4) Place the peeled epidermis into a droplet of water on the slide and place it with a needle.

5) Clamp the coverslip with tweezers, first put the water droplets touching the slide on one side, and then slowly lay the coverslip flat to make a temporary section.

6) Put the temporary slice on the microscope, adjust the position of the microscope and the temporary slice, and organize the students to observe in order.

Note: (1) Try your best to choose a thinner onion skin and make temporary slices.

2) For clear reading, red ink can be used for staining. This is done by placing a drop of red ink onto the edge of the coverslip. Use absorbent paper to absorb water on the other side. The red ink is sucked through, and the epidermis is stained.

3) Since the onion skin is temporarily sliced and needs to be made before class, it is necessary to replenish water frequently and keep enough water under the coverslip.

Onions, microscopes, water, sucrose solution, tweezers, glass slides, coverslips, absorbent paper, Petri dishes.

01 First of all, use tweezers to take the outer skin of the onion, pay attention to the purple skin, it does not matter the size, but it must be very thin and thin.

02 Then put the dry and clean glass slide, drop a drop of water on the glass slide, put the peeled onion into the water, it must be a layer, and then cover the coverslip.

03 Adjust the microscope first, then put the finished loading on the microscope, observe with a low magnification, and move the loading until you find the purple large leaf vesicle.

04 Then take off the temporary mounting, add sucrose solution dropwise on one side of the slide, and attract it with absorbent paper on the other side. Wait three minutes to see the changes in the cells.

05 After the observation is completed, drop water on one side of the tablet, and also attract it with absorbent paper on the other side, and observe the changes of the cells after about three minutes.

1) Take the cleaned glass slides and coverslips.

2) Use a dropper to aspirate a drop of distilled water to a glass slide**.

3) Tear off a small piece of the onion epidermis with tweezers and immediately put it into the water droplet of the glass slide, the material should not be too large (never beyond the scope of the coverslip), and do not overlap or shrink the material, and can be carefully flattened with forceps or dissecting needles.

4) Take the coverslip with forceps so that one side of the coverslip touches the water droplets of the slide first, and then slowly lower the coverslip to prevent bubbles. If bubbles remain, use forceps or a dissecting needle to raise the coverslip slightly and then lower it. Do not press the coverslip with your fingers.

5) After adding the coverslip, if you find that the coverslip or material is floating on the water droplet, you can use absorbent paper to absorb part of the water from the side of the coverslip, so that the coverslip is close to the slide; If you find that the water does not cover the bottom of the coverslip, and there is too little water, you can use a dropper to fill the edge of the coverslip with a small amount of water until the water covers the bottom of the coverslip.

6) Finally, use absorbent paper or gauze to dry the water around the coverslip, and the loading is complete.

To see more cells in the field of view, the magnification should be minimal.

The magnification of microscope A is 10 20 = 200 times and the magnification of microscope B is 5 10 = 50 times 50 200, that is, microscope B is selected.

The correct steps are 2 1 4 3 5 which can be abbreviated as: rubbing, dripping, tearing, spreading, covering, and dyeing.

Option B. Because the size of the field of view is constant, the larger the cell magnification, the smaller the number of cells in a certain range. Therefore, if you want to see more cells, you should choose a microscope with low magnification.

The correct step is: 21453

First of all, you need to know:

a. Magnification = objective eyepiece.

b. The larger the magnification, the smaller the field of view, that is, the smaller the range of view, so choose B.

Step 21453

Microscope magnification = eyepiece specification multiplied by objective lens specification, so choose a; 21453

B (the smaller the magnification, the more cells are seen).

A microscope should be chosen.

Correct step 21435

B - The magnification is larger than that of A.

Wipe - drip - tear - cover - dye.