Onion Skin Epidermal Cells: How to Prepare a Wet Mount Microscope Slide

Summary

This educational video demonstrates the process of preparing a wet mount slide of stained onion epidermal cells. The presenter explains how to select and peel the thin, transparent layer of cells from an onion bulb, transfer it onto a microscope slide, and apply iodine for staining. The video also covers techniques for placing a cover slip to minimize air bubbles and adjusting the microscope's light levels for optimal viewing. Finally, the presenter shows the cells magnified under different objective lenses, highlighting the cell walls, nuclei, and the importance of staining for visibility.

Takeaways

• 🔬 The video demonstrates how to prepare a wet mount slide of stained onion epidermal cells.
• 🧐 The process begins with selecting a smooth and shiny layer of onion bulb for obtaining the specimen.
• 🔎 A thin, transparent layer of cells is peeled off the onion layer using tweezers for use as the specimen.
• 📍 An alternate technique mentioned is peeling the onion skin directly onto the slide for a larger, flatter specimen.
• 💧 Iodine is used as the wet mount solution, which also serves to stain the cells for better visibility.
• 🏷️ A cover slip is applied by holding it at a right angle and allowing it to drop onto the slide, minimizing air bubbles.
• 🔭 The specimen is first examined under a 4X objective lens, magnifying the cells 40 times actual size.
• 🔍 The video explains that a compound microscope is parfocal, allowing for easy transition between different magnification levels.
• 🌑 Adjusting the light level by using the dimmer dial or iris diaphragm can improve contrast and visibility of the specimen.
• 🔬 The final examination is done under a high dry lens at 400 times actual size, revealing detailed cell structures.

Q & A

What is the purpose of the video?

The purpose of the video is to demonstrate the process of preparing a wet mount slide of stained onion epidermal cells.

What type of specimen is used in the video for the wet mount slide?

The specimen used is a thin, transparent layer of onion epidermal cells obtained from the inner layer of an onion bulb.

How does one identify the correct layer of onion epidermal cells?

The correct layer is identified by its smooth and shiny appearance compared to the rough and matte side of the onion layer.

What technique is shown for obtaining the onion epidermal cells?

The technique involves breaking the onion layer towards the shiny side and gently peeling apart the two pieces to obtain the thin layer of cells.

How should one handle the thin layer of onion epidermis to place it on the slide?

The thin layer should be torn off with tweezers and then carefully spread out on the slide to avoid it folding over on itself.

What alternative method is suggested for transferring the onion skin to the slide?

The alternative method is to peel the layer of onion skin directly onto the slide, allowing it to wrap around the slide like Saran Wrap.

What staining agent is used in the video for the wet mount?

Iodine is used as the staining agent, which provides both the wet component and stains the cells for better visibility.

How is a cover slip applied to the specimen on the slide?

The cover slip is held at a right angle to the slide and then dropped, allowing it to fall and push the air out, creating fewer air bubbles.

What magnification is used to initially examine the onion epidermal cells?

The initial examination uses a 4X objective lens, magnifying the specimen 40 times actual size.

How can the contrast of the specimen be improved if the stain is not taken up well?

The contrast can be improved by adjusting the light level, either by using the dimmer dial on the microscope base or by opening or closing the iris diaphragm.

What is the highest magnification used in the video to view the onion epidermal cells?

The highest magnification used is with the high dry power objective lens, which magnifies the specimen 400 times actual size.

Outlines

00:00

🔬 Preparing a Wet Mount Slide of Onion Epidermal Cells

This paragraph describes the process of preparing a wet mount slide of stained onion epidermal cells. The presenter starts by selecting a microscope slide and obtaining a specimen from the onion bulb. The bulb has a rough matte side and a smooth shiny side, and the goal is to peel off the thin transparent layer of cells from the shiny side. The presenter uses tweezers to tear off a piece of the onion epidermis and places it on the slide. The delicate layer of cells may fold over, so it needs to be spread out. The presenter also mentions an alternative technique for transferring the onion skin directly onto the slide. For staining, iodine is used, which serves as both the wet mount and staining agent. A cover slip is applied by holding it at a right angle and letting it drop onto the slide to minimize air bubbles. The specimen is then examined under a 4X objective lens, which magnifies the cells 40 times. The cells are described as misshapen bricks, and the video shows a microscopic view of the onion epidermal cells.

05:03

📸 Enhancing Microscopic Image Contrast and Viewing Techniques

In this paragraph, the focus is on enhancing the contrast of the specimen when viewing under a microscope and adjusting light levels to improve visibility. The presenter demonstrates how to adjust the light by using the dimmer dial on the microscope base or by opening and closing the iris diaphragm, which controls the amount of light shining through the specimen. After focusing the specimen at low power, the presenter switches to a high dry power lens, which magnifies the specimen 400 times. The video shows examples of onion epidermal cells viewed at this higher magnification, where the cell walls and nuclei are more clearly visible. The presenter also suggests visiting Science Prof Online for more educational content.

Keywords

💡Wet Mount Slide

A wet mount slide is a type of microscope slide preparation where a small piece of biological material is placed in a drop of liquid on a slide. In the context of the video, the liquid is iodine, which serves to both wet the specimen and stain it for easier viewing under a microscope. The process involves placing a thin layer of onion epidermal cells onto the slide and then covering it with a drop of iodine to prepare for microscopic examination.

💡Onion Epidermal Cells

Onion epidermal cells refer to the outermost layer of cells of an onion bulb, which are used as a specimen in this video. These cells are thin, transparent, and serve as a model system for demonstrating cell structure under a microscope. The video describes how to carefully peel these cells from the onion layer to prepare a wet mount slide, highlighting their importance in the process.

💡Microscope Slide

A microscope slide is a small glass or plastic plate used to hold a specimen for examination under a microscope. In the video, the microscope slide is where the onion epidermal cells are placed and prepared for staining and viewing. The slide is an essential tool in microscopy, providing a stable platform for the specimen.

💡Iodine

Iodine is a chemical element used in the video as a staining agent for the onion epidermal cells. It not only provides the 'wet' part of the wet mount slide by adding moisture but also colors the cells, enhancing their visibility under the microscope. The use of iodine is crucial for making the cell structures stand out clearly.

💡Cover Slip

A cover slip is a small, thin piece of glass placed over the specimen on a microscope slide to protect the sample and provide a smooth surface for viewing. In the video, the cover slip is carefully applied to the iodine-wetted onion epidermal cells to prepare the wet mount slide for microscopic examination. Proper application of the cover slip is demonstrated to minimize air bubbles.

💡Objective Lens

The objective lens is the lens of a microscope that is closest to the specimen. It is used to magnify the image of the specimen. In the video, the presenter uses a 4X objective lens to initially examine the onion epidermal cells, providing a lower magnification view before moving to higher magnifications. The objective lens is a key component in determining the level of detail visible in the microscope.

💡Magnification

Magnification in microscopy refers to the increase in the apparent size of an object due to the use of a microscope. The video mentions magnification levels of 40 times and 100 times actual size, achieved by using different objective lenses. Magnification is essential for observing the fine details of the onion epidermal cells that are not visible to the naked eye.

💡Compound Microscope

A compound microscope is a type of microscope that uses multiple lenses to achieve higher magnification and resolution. The video discusses the use of a compound microscope to view the onion epidermal cells at different magnifications. The compound microscope allows for the observation of cellular structures that are not possible with the naked eye.

💡Parfocal

Parfocal is a term used to describe the ability of a microscope to maintain focus when switching between different objective lenses. In the video, the presenter mentions that the microscope is parfocal, which means once the specimen is in focus with one objective, it will remain relatively in focus when switching to another, requiring only minor adjustments.

💡Light Adjustment

Light adjustment refers to the process of modifying the intensity and distribution of light to optimize the viewing conditions in microscopy. The video demonstrates how adjusting the light level, using the dimmer dial and iris diaphragm, can improve the contrast and visibility of the onion epidermal cells under the microscope. Proper lighting is crucial for achieving clear and detailed images.

💡Cell Wall

The cell wall is a rigid outer layer that provides support and protection to plant cells, including onion epidermal cells. In the video, the presenter notes the presence of thick cell walls in the onion epidermal cells when viewed under higher magnification. The cell wall is an important structural component of plant cells, contributing to their shape and function.

Highlights

Introduction to preparing a wet mount slide of stained onion epidermal cells.

Selection of a microscope slide for the specimen preparation.

Obtaining a specimen from the smooth, shiny side of an onion bulb layer.

Technique to gently peel apart the onion layer to access the epidermal cells.

Method to tear off a thin layer of onion epidermis using tweezers.

Spreading the delicate onion epidermis layer on the slide.

Alternate technique for transferring onion skin directly onto the slide.

Use of iodine as a staining agent for the wet mount.

Procedure for applying a cover slip to the specimen to avoid air bubbles.

Examination of the specimen under a 4X objective lens for initial magnification.

Description of onion epidermal cells appearing like misshapen bricks under the microscope.

Explanation of the compound microscope's parfocal property for ease of focus adjustment.

Observation of onion epidermal cells at 100x magnification for a closer look.

Technique to improve contrast by adjusting light levels for better visibility.

Demonstration of using the dimmer dial and iris diaphragm to control light.

Switching to high dry power for 400x magnification to observe cell details.

Observation of thick cell walls and cell nuclei in the onion epidermal cells at high magnification.

Promotion of additional educational resources available at Science Prof online.

Transcripts

in this video I'm going to show you how

to prepare a wet Mount slide of stained

onion epidermal

cells here's my microscope slide I want

to have that out and

ready I can obtain my specimen from one

layer of onion bulb if I look at this

layer one side is kind of rough and

matte and the other side is smooth

smooth and

shiny I need to break my onion layer

towards this shiny side and then very

gently

peel the two pieces apart there's a thin

transparent layer of cells holding these

two pieces of the onion layer together

that's the layer of epidermal cells that

I'm looking for for my

specimen now I need to obtain a piece of

that onion epidermis to place on my

slide I can do that by tearing it off

with a pair of

tweezers this is a very delicate thin

layer of ss and they'll fold over on

themselves uh so when you place that

onto the slide once you get it off your

tweezers you're going to need to spread

it out a little bit the little piece of

onion epidermis can easily get all

watted up and that makes it very

difficult to see this

sounds while filming in the lab I forgot

to include an easier alternate technique

for getting that onion skin onto the

slide so I'm going to show it to you

here in my dining room with my two

helpers the best way to get a large flat

sheet of these onion epidermal cells is

to peel that layer of onion skin off

directly onto the slide it's very thin

it'll wrap right around the slide just

like Saran

Wrap so apparently I've lost my helpers

because onions are way too stinky so we

might as well head back to the lab

for this wet Mount I'm just going to use

iodine this will provide the wet part of

the wet Mount and it will also stain the

cells and make them easier to

see now I'm going to obtain a cover slip

a clear square that I'm going going to

place on top of my specimen on the

slide the best way to apply that cover

slip is to hold it at a right angle to

the slide at one side of your specimen

and then let it drop let it fall as it

falls it will push the air out and

you'll have fewer air bubbles this way

here's my finished prepared specimen

here's a closer look at the application

of that cover slip again I hold it at a

right angle to the slide I let it drop

that pushes the air out sometimes I'll

give it a little tap and now I'm all

set I'm now going to examine my specimen

using the 4X objective lens that will

magnify the specimen 40 times actual

size here's my first look

microscopically at the onion epidermal

cells magnified 40 times these cells

look kind of like misshapen bricks a

whole bunch of

them the compound microscope is par

focal what that means is once I get my

specimen in focus at one power in this

case the scanning power I can switch to

the next higher objective the low power

in this case and my specimen will still

pretty much be in Focus I'll only have

to adjust the focus a little bit to get

it

crisp here are my onion epidermal cells

magnified 100 times actual

size so this is a closer look at that

specimen we just looked at under 40

total magnification the specimen that

did not stain so

well we stained the specimen to increase

the contrast to make it more visible and

since the stain wasn't taken up that

well there are other ways to improve the

contrast of our specimen when viewing

this specimen and taking this picture I

adjusted the light level I turned it way

down and that helped me see the cells

much more distinctly and

clearly here's just a reminder of the

different ways you can adjust the light

level shining up through your

specimen the first way is to use the

dimmer dial on the base of your scope

that dial will make the light shining up

from the base brighter or

dimmer you can also adjust the amount of

light shining up through your specimen

by opening or closing the iris diaphragm

that's directly beneath the stage it

looks and feels like a camera lens you

twist it and you can let more or less

light through the

stage once the specimen is clearly in

focus at low power that yellow banded

lens I can switch the objective to the

high dry power that's the blue banded

lens and it will magnify my specimen a

total of 400 times actual size here are

a couple examples of onion epidermal

cells viewed at 400 times actual size

through that high dry lens these samples

have stained a little better than the

ones I showed you previously I can see

the thick cell walls and these elongated

cells in this picture I can see a cell

nucleus in the second cell below the

pointer more seriously nerdy amazing

free stuff at science Prof online.com go

there