onion cheek cell experiment

Onion Peel Cell Experiment

The onion peel cell experiment is very popular for observing a plant cell structure. Onion is a eukaryotic plant that contains multicellular cells. We know that the cell is a structural and functional unit of life that builds up living structures.

The bulb of an onion is formed from modified leaves . Like plant cells, onion cells have a rigid cell wall and a cell membrane enclosing the cytoplasm and nucleus.

Onion epidermal cells exist as a single layer that serves as a protective skin. It separates the thick, juicy scale leaves of the onion. Thus, the bulb of onion is formed from modified leaves.

The epidermal cell of an onion bulb is simple and transparent. Its microscopic observation introduces the general view of plant anatomy to the students.

Firm and medium-sized onions are generally used to visualize the onion’s epidermal cells. This post explains the theory, requirements, and procedure of the onion peel experiment. Also the observation, result and precautions of the experiment are also discussed.

Content: Onion Peel Cell Experiment

Requirements, observation, precautions.

The main objective of performing the onion peel cell experiment is to observe the arrangement and structural components of the onion epidermis. The following facts about the onion peel cell experiment play a significant role in educating students:

• The epidermis of the onion bulb is a single layer of tissue that is easy to separate. For this reason, onion peel is best for educational and experimental purposes to study the structure of plant cells.
• Due to the large size of onion cells, the cells can be examined under low magnification.
• It is also a simple experiment that the students can efficiently perform, plus they can practice how to use a microscope.

We need the following glassware and reagents to prepare a temporary slide of an onion peel.

Materials required to separate onion skin

• Medium-sized onion

Materials needed to stain and mount the onion peel

• Petri Plate
• Distilled Water
• Clean glass slide
• Blotting paper
• Compound microscope

An onion is a multicellular plant. The presence of a rigid cell wall and a large vacuole is a characteristic feature of a plant cell. Thus, onion being a plant, comprises features common to plant cells. Like plant cells, onion cells consist of a cell wall and cell membrane surrounding the cytoplasm, nucleus and a large vacuole.

• The cell wall is a rigid, protective coat covering the cell membrane, including all the internal components. The rigid cell wall maintains the shape of onion cells and contributes to the compact arrangement of the epidermal cells in onion.
• The cell membrane is interior to the cell wall surrounding the cytoplasm, including all the internal structures.
• The cytoplasm is the cell’s inner space that appears jelly-like. It moves the cytosolic material around the cell through cytoplasmic streaming.
• The nucleus is present near the periphery of the cytoplasm. It is the control centre of the cell and the largest organelle in the cell.
• The vacuole is large and prominently seen at the centre of the cell. It stores solid and liquid contents. The basic shape or size of a vacuole differs depending on the needs of the cell.

Video: Onion Peel Cell Experiment

Procedure of Onion Peel Cell Experiment

The steps to perform the onion peel cell experiment are as follows:

Steps to separate an onion peel

A. Take an onion, separate its outermost peel and chop it into two equal halves.

B. Then, take one fleshy scale leaf of a chopped onion bulb and split it into two.

C. Then carefully pull a thin, transparent epidermal peel from the convex surface of the scale leaf using forceps.

D. Then, wash the separated peel in the Petri plate containing water. You can cut the onion peel into small rectangular pieces using a blade.

Steps to stain and mount an onion peel

E. After that, transfer the onion peels into the Petri plate containing diluted safranin stain. Leave the peels undisturbed for about 3 minutes.

F. Finally, rinse the extra stain of the peel by again dipping it in the Petri plate containing water.

G. With the help of a brush or forcep, transfer the peel to the centre of a clean glass slide.

H. Then, to mount the onion peel, add a drop of glycerine over the centre of the slide. Glycerine prevents the peel from drying up.

I. After that, carefully mount a cover slip over the centre of the prepared slide by slowly lowering it with a needle. During this stage, you need to avoid the entry of any air bubbles.

J. Using a piece of blotting paper, remove extra glycerine from the margins of a cover slip.

K. Observe the temporary slide under the compound microscope.

• First, turn on the microscope’s light and ensure the low objective lens is in line with the optical tube. Then, place the prepared slide on the stage of a microscope.
• Looking from the side (not through an eyepiece), lower the tube using the coarse focus knob until the end of the objective lens is just above the cover glass. During this stage, do not crack the cover glass, or the objective lens may get damaged.
• Now look through the eyepiece and adjust the smaller, fine focusing knob to move the optical tube upwards until an image comes into focus.
• Then, swap the objective lens to a high objective lens so that you can notice the cells at greater magnification.
• Prepare an observation table for the cells as seen under a microscope and note the features listed in the observation table.
• Shape of cells: Rectangle
• Arrangement of cells: Compact
• Inter-cellular spaces : Absent
• Nucleus : Present (at the cell’s periphery)
• Stained portions : Cell wall and nucleus are darkly stained with less-stained cytoplasm
• Unstained portions : Cell membrane and Vacuole

• Do not overstain the onion skin.
• Avoid the folding of the peel.
• The glass slide and cover slip should be dry and clean.
• Put a coverslip carefully to avoid any air bubbles.
• Using blotting paper, remove the extra glycerine.

Therefore, the onion peel cell experiment is an engrossing activity that can help a student to observe and study the plant cell structure . Students can prepare the temporary slide and observe the differences between the slide with stained onion skin and the slide without any stain. The microscopic observation of onion peel cells will allow students to closely examine each component of onion cells.

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Onion Cells Under a Microscope ** Requirements, Preparation and Observation

How to obtain a thin layer of onion cells, how to prepare a wet mount slide, observations.

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The Human Cheek Cell var pfHeaderImgUrl = '';var pfHeaderTagline = '';var pfdisableClickToDel = 0;var pfHideImages = 0;var pfImageDisplayStyle = 'block';var pfDisablePDF = 0;var pfDisableEmail = 0;var pfDisablePrint = 0;var pfCustomCSS = '';var pfEncodeImages = 0;var pfShowHiddenContent = 0;var pfBtVersion='2';(function(){var js,pf;pf=document.createElement('script');pf.type='text/javascript';pf.src='//cdn.printfriendly.com/printfriendly.js';document.getElementsByTagName('head')[0].appendChild(pf)})();

1. Put a drop of methylene blue on a slide. Caution: methylene blue will stain clothes and skin.

2. Gently scrape the inside of your cheek with the flat side of a toothpick. Scrape lightly.

3. Stir the end of the toothpick in the stain and throw the toothpick away.

4. Place a coverslip onto the slide.

5. Use the SCANNING objective first and use the coarse adjustment knob to bring the slide into focus. Cells will appear very tiny at this magnification.

6. Switch to LOW POWER and use the coarse adjustment knob. Cells should be visible, but they will be small and look like nearly clear purplish blobs. If you are looking at something very dark purple, it is probably not a cell.

7. Once you think you have located a cell, switch to HIGH POWER and focus using the fine adjustment knob. (Remember, do NOT use the coarse adjustment knob at this point.)

Observations:

Sketch the cell at low and high power. Label the nucleus , cytoplasm, and cell membrane of a single cell . Draw your cells to scale.

1. Why is methylene blue necessary?

2. The light microscope used in the lab is not powerful enough to view other organelles in the cheek cell. What parts of the cell were visible.

3. List 2 organelles that were NOT visible but could be found in cells if you had a microscope with a better magnification.

4. Keeping in mind that the mouth is the first site of chemical digestion in a human. Your saliva starts the process of breaking down the food you eat. Keeping this in mind, what organelle do you think would be numerous inside the cells of your mouth?

Other Microscope Resources

Introduction to the Microscope  – E Lab – explore how to use a light microscope ( Letter E Slides )

Observing Plant Cells   –  microscope observation of onion and elodea

Comparing Plant and Animal Cells  – compare onion cells to human cheek cells

Investigation: Banana Starch and Plastids  – compare a ripe banana to a green banana by viewing plastids stained with iodine

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Cheek Cell Lab

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• Page ID 20319

• Shannan Muskopf
• Granite City School District via Biology Corner

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• Put a drop of methylene blue on a slide. Caution: methylene blue will stain clothes and skin.
• Gently scrape the inside of your cheek with the flat side of a toothpick. Scrape lightly.
• Stir the end of the toothpick in the stain and throw the toothpick away.
• Place a coverslip onto the slide
• Use the SCANNING objective to focus. You probably will not see the cells at this power.
• Switch to low power. Cells should be visible, but they will be small and look like nearly clear purplish blobs. If you are looking at something very dark purple, it is probably not a cell
• Once you think you have located a cell, switch to high power and refocus. (Remember, do NOT use the coarse adjustment knob at this point)  

The Human Cheek Cell

1. List the 3 parts of the Cell Theory

2. Describe or define each of the following

• cell membrane

3. Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell membrane. Draw your cells to scale.

4. Why is methylene blue necessary?

5. The light microscope used in the lab is not powerful enough to view other organelles in the cheek cell. What parts of the cell were visible?

6. List 2 organelles that were NOT visible but should have been in the cheek cell. 7. Is the cheek cell a eukaryote or prokaryote? How do you know? 8. Keeping in mind that the mouth is the first site of chemical digestion in a human. Your saliva starts the process of breaking down the food you eat. Keeping this in mind, what organelle do you think would be numerous inside the cells of your mouth?

Experiment 4 - Onion and Cheek Cells

By grade 10 students.

Learning Objective:

To prepare stained temporary mounts of a) onion peel and b) human cheek cells, and to record observations and draw labelled diagrams

Materials Required:

An Onion Bulb

1 Pair of Forceps

2 Watch Glasses

Glass Slides

A (Paint) Brush

1 Blotting Paper

Safranin (red stain) / Methylene blue

Compound/light/low power microscope

Safety Precautions:

1. HANDLE GLASSWARE WITH CARE AS IF BROKEN, SHARP SHARDS CAN CAUSE INJURIES

2. HANDLE THE NEEDLE WITH CARE

Experimental Accuracy:

1. Use a paintbrush to transfer specimen

2. Prevent air bubble formation in the slide

3. Place most promising region in the centre of the slide for observation

4. Don’t use too much/little stain

Methodology:

General Preparation of a Temporary Mount:

1) Place a one cell thick layer of cells on the slide

2) Add a drop of water or stain

3) Lower a coverslip onto the drop(carefully so as to prevent the formation of air bubbles)

4) Place the slide inside folded paper towel/blotting or filer paper to drain excess fluid. Press on the coverslip lightly/gently from the outside of the paper towel

Preparation of Stomata

Take a fleshy, membranous peel from an onion cell. Break it into two, and use a pair of forceps to pull a membranous epidermal peel from the inner surface of the leaf

Cut the leaf peels obtained into smaller pieces, so as to allow them to fit onto the microscope slides, using a blade or scissors.

Transfer the pieces to a watch glass of water. Use a paintbrush to do so(so as to prevent cell damage, while ensuring the epidermis doesn’t dry up).

Prepare a second watch glass, by mixing a small amount of water with 1 to 2 drops of methylene blue solution or Safranin. Transfer the peels to this watch glass. Leave the peel in the watch glass for 2-3 minutes before dipping them in water to remove excess stain

Take the peels out, and place them on clear, glass slides using a brush. Add glycerine using a dropper, before gently placing a coverslip on the slide. Place the coverslip using a needle to prevent air bubble formation

Drain excess glycerin/stain using blotting paper

Place the slides under the objective lens, on the stage of the microscope. Use the stage clips to stabilize the slide. Examine the cell.

Preparation of Cheek Cells

Use a toothpick to gently obtain cell samples from the inside of your cheek. Place the cells on glass slides containing water. Mix and spread the mixture using a needle.

Add Methylene blue solution using a dropper, After 2-3 minutes, remove any extra water or stains from the slide by drying it using blotting paper/filter paper.

Add glycerine using a dropper, before gently placing a coverslip on the slide. Place the coverslip using a needle to prevent air bubble formation

Observation - Onion Cells:

The epidermis of the leaf is observed. It consists of compact cells, with the general characteristics of plant cells. The stained features are the cytoplasm, whereas the cell wall and nucleus remain unstained. The nucleus(in the periphery) , cell walls(around the perimeter), and large vacuoles(in the center) are distinct features of each cell(it is important to emphasize on the cell walls being distinct).

Note: we’ll have to include a labelled cell diagram separately as drawing cells is also a part of the syllabus for this experiment(even for the onion cheek cells).

Cheek Cells:

The characteristic features of plant cells are observed. The cells are large, flat and irregular in shape. They lack cell walls and large vacuoles however contain thin cell membranes(around their perimeters) and deeply stained nuclei(in their centres).

Overall Observation:

We can elucidate that cheek cells are animal cells whereas onion peel cells are plant cells based on the cellular features we in them observe through microscopic examination.

Experiment in Context:

Basics of Microscopy:

Here are some key points to consider when observing specimen using a light microscope: Focusing/Choosing Magnification

1) Always focus on lower power first, regardless of whether higher power magnification will be more suitable(to find the specimen in the first place before zooming in)

2) Use the large coarse knobs first to focus. Once you nearly have the image, make it sharp by using the smaller fine-focusing knobs

3) Place the most promising region of the slide exactly in the middle of the region of the stage through which light enters

4) Before increasing magnification, perform step one to ensure that the most promising region is exactly in the middle of the FOV(field of view). Then change to a higher magnification

Taking care of your microscope

Focus by moving the specimen and lens away from each other, never closer to towards other.

Ensure that the slide is clean and dry prior to using it.

Don’t touch the surface of the lens.

While carrying your microscope, ensure you carry it by the armpiece and base, not the body.

Step wise Projection

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Experimental Preparation of Temporary Mounts of an Onion Peel

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Experimental Preparation of Temporary Mounts of an Onion Peel !

Experiment:

Objective :.

To prepare a stained temporary mount of an onion peel and to record observations and draw labeled diagrams.

Apparatus and materials required :

An onion, glass slide, watch glass, coverslip, forceps, needles, brush, blade, filter paper, safranin, glycerine, dropper, water, and a compound microscope.

All living organisms are made up of cells. The shape, size and the number of these units vary in organisms. The three major components of a cell are the cell membrane, cytoplasm and nucleus. In a plant cell, a cell wall surrounds the cell membrane.

Procedure :

1. Take an onion and remove its outermost peel.

2. Now cut a small part from an inner scale leaf with the help of a blade.

3. Separate a thin, transparent peel from the convex surface of the scale leaf with the help of forceps.

4. Keep this peel in a watch glass containing water?

5. Add two drops of safranin stain in the watch glass to stain the peel.

6. Take a clean slide and put a drop of glycerine in the centre of the slide.

7. With the help of a brush and needle transfer the peel on the slide. Glycerine prevents the peel from drying up.

8. Carefully cover it with a coverslip and avoid any air bubble from entering interring the coverslip.

9. Remove any excessive glycerine with a filter paper.

10. Observe the prepared mount of the peel under the low and high magnification of a compound microscope.

Observations :

A large number of rectangular cells are visible. These cells lie close to each other with intercellular spaces between them. These cells are surrounded by distinct cell walls. These cells have a dark stained nucleus and a large vacuole in the centre.

Precautions :

1. Overstaining and understaining should be avoided.

2. Folding of the peel should be avoided.

3. Clean and dry glass slide and coverslip should be used.

4. Coverslip should be put carefully avoiding any air bubbles.

Experiment 1.2 :

To prepare a stained temporary mount of human cheek cells and to record observations and draw labelled diagrams

Toothpick, slide, coverslip, filter paper, needles, brush, watch glass, methylene blue, dropper, glycerin, water and a compound microscope

Animal cells are usually irregular in shape. They do not have a cell wall. They are surrounded by a cell membrane and contain cytoplasm and nucleus.

1. With the help of the flat end of a washed toothpick gently scrape the inside of your cheek.

2. Place the scrapings in the centre of a clean glass slide.

3. Add a drop of water arid a drop of methylene blue.

4. After one minute remove the extra water mixed with methylene blue by slightly tilting the slide.

5. Put a drop of glycerine over the stained scrapings and cover it gently with a coverslip.

6. Remove the excessive glycerine using filter paper.

7. Observe the scrapings under the low and high magnifications of a microscope.

Observations:

Many flat, oval or irregular cells are seen. The cell membrane encloses hyaline cytoplasm and an oval, dense nucleus. The cell wall is absent as in all animal cells.

Precautions:

1. The cheeks should be scraped gently avoiding any injury.

2. Over-staining and under-staining of the cells should be avoided.

3. Coverslip should be placed carefully avoiding the entry of air bubbles.

4. A dry and clean glass slide and coverslip should be used.

5. The cheek cells should be spread properly to avoid their folding.

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• Smear or Cells: Preparation and Fixation
• Experiment to Observe Temporary Mount of a Leaf Peel to Show Stomata
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Recording Observations for Onion Cheek Experiment

In this activity, activity overview, template and class instructions, more storyboard that activities.

• This Activity is Part of Many Teacher Guides

As students learn about basic plant and animal cells, doing a hands-on experiment is a great way for them to observe the differences in real things. The Onion-Cheek Experiment is a simple introductory experiment to help students practice using the microscope while they examine the differences and similarities between cells.

Students will use this worksheet to record their hypothesis, observations, and any conclusions they can make about basic cells. It is set up for just observing onion cells and cheek cells, but can be added to include additional cells for observation.

Clicking "Use This Assignment" will copy the worksheet into your teacher account. Feel free to make any adjustments to instructions or the items on the worksheet to tailor it for your students and the way you'll be conducting the experiment.

Materials Needed

• Glass Slides & Covers
• This Worksheet

Experiment Instructions

• Create a hypothesis about plant and animal cells and write it into the hypothesis box on the worksheet.
• Cut the onion into the thinnest slice you can (this part may be done by the teacher).
• Put a drop of iodine on one glass slide.
• Lay the onion slice on the slide and cover it.
• Observe the slice under the microscope at 100x and 400x.
• Record observations and draw what the cell looks like.
• Rub the toothpick on the inside of your cheek.
• Rub cheek cells onto a new glass slide.
• Add iodine to the slide and cover it.
• Observe the cheek cells under the microscope at 100x and 400x.
• Formulate a conclusion and write it into the conclusion box on the worksheet.

(These instructions are completely customizable. After clicking "Copy Activity", update the instructions on the Edit Tab of the assignment.)

Student Instructions

• Click "Start Assignment".
• While observing each type of cell, jot down notes and sketch what you see.
• Come up with a conclusion and write it at the bottom of the worksheet.
• Save and Exit

Lesson Plan Reference

Grade Level 6-8

Difficulty Level 3 (Developing to Mastery)

Type of Assignment Individual, Partner, or Group

Type of Activity: All Worksheet Templates

How to Guide Elementary Students in Hypothesis Formation for the Onion Cheek Experiment

Introduce the concept of a hypothesis.

Begin by explaining what a hypothesis is in simple terms. Use examples relevant to the students' everyday experiences to illustrate the idea of making an educated guess based on observations. Discuss the importance of a hypothesis in scientific experiments, emphasizing that it's a starting point for discovery and learning.

Familiarize Students with the Onion Cheek Experiment

Introduce the Onion Cheek Experiment, explaining the process in a way that is easy for young students to understand. Show them the materials they will be using, like the onion, microscope slides, and microscopes. Describe what they might expect to see, such as the different shapes and structures of cells. Avoid giving too much detail to encourage their own observations and guesses.

Guided Hypothesis Formation

Lead a brainstorming session where students can share their ideas about what they think they might observe in the onion and cheek cells. Encourage every student to contribute, fostering a supportive and inclusive environment. Guide them through refining their ideas into clear hypotheses. For example, if a student suggests they will see “circles” in the onion cells, help them articulate this into a more structured hypothesis, like “I think the onion cells will be round in shape.”

Documenting and Sharing Hypotheses

Provide students with worksheets where they can write down their hypotheses. These worksheets can have prompts or sentence starters to help them articulate their thoughts. Have students share their hypotheses with the class. This not only builds confidence but also allows them to hear different perspectives and ideas, which can be a valuable learning experience in itself.

Frequently Asked Questions about Recording Observations for Onion Cheek Experiment

What precautions should be taken while handling microscopes and biological samples.

When handling microscopes and biological samples, such as onion and cheek cells, certain precautions are essential. Firstly, microscopes are delicate and should be handled with care; always carry them with both hands, one holding the arm and the other supporting the base. Ensure the lens is clean and avoid touching the glass with fingers. When preparing slides, use clean slides and cover slips to avoid contamination. For cheek cell samples, use a sterilized toothpick or swab and avoid sharing these between students to prevent cross-contamination. It's also important to handle all biological samples as potential biohazards; after the experiment, dispose of the samples appropriately and sanitize the work area. Wearing gloves and washing hands before and after the experiment can further minimize the risk of contamination.

How Do Environmental Factors Affect Onion and Cheek Cells?

Environmental factors can significantly affect both onion and cheek cells. Variations in temperature, humidity, and light exposure can cause observable changes in the cells. For instance, extreme temperatures might damage cell structures or affect their visibility under a microscope. High humidity can lead to condensation on slides, obscuring the view, while low humidity might cause the cells to dry out and shrink, altering their appearance. For onion cells, light exposure can impact the process of photosynthesis, potentially affecting cell health and appearance. Therefore, when preparing and observing these cells, it’s crucial to consider and control environmental factors to ensure accurate and consistent observations.

What Are the Key Differences Between Onion Cells and Cheek Cells?

The key differences between onion cells (plant cells) and cheek cells (animal cells) are primarily due to their distinct structural characteristics. Onion cells have a rigid cell wall made of cellulose, providing structural support, which is absent in cheek cells. Inside onion cells, large vacuoles are prominent, which store water and nutrients, whereas cheek cells have smaller, more temporary vacuoles. One of the most notable differences is the presence of chloroplasts in onion cells, the site of photosynthesis, which are not found in animal cells like those from the cheek. Furthermore, the shape and arrangement of these cells differ; onion cells are generally more uniform and rectangular, while cheek cells are irregular and rounder. These differences are fundamental in teaching students about the diversity of cell types in different organisms.

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• Visualizing Onion and Human Cells
• In this experiment you will prepare different types of cells from a plant and animal, onion and human respectively, and then visualize them under a microscope. HYPOTHESES: The experimental hypothesis is that the cells will appear different in overall shape and membrane structure, but there will be some shared similar structures, like nuclei, in both cells. The null hypothesis of the experiment is that there will be no difference in structure between the two cell types.
• First, to prepare an animal cell slide, start by pouring 30 mL of distilled water into a beaker.
• Then, use a glass dropper to place 2 - 3 drops of the water onto the center of a clean microscope slide.
• Next, take a clean toothpick and scrape the inside of your cheek to gather cells. CAUTION: Do not scrape your cheeks too aggressively. The scraping should not cause discomfort or bleeding.
• Put the end of the toothpick with the cheek cells onto the wetted area of the slide and mix the water and cheek cells together.
• Next, add two drops of methylene blue staining solution to the wetted area of the slide and mix it in with a clean toothpick.
• Let the mixture sit at room temperature for 3 minutes.
• After 3 minutes have passed, use a glass dropper to add a drop of glycerol to the mixture.
• Carefully, place a cover slip over the mix on the slide by first standing one end of the cover slip vertically and aligning it along to one side of the mixture. Then, carefully lower the other end of the cover slip down until the mixture is completely covered.
• Finally, remove any excess liquid with blotting paper.
• Next, prepare a slide of plant cells by placing five drops of distilled water into a clean watch glass.
• Then, with forceps, take a thin strip of onion and place it into the water.
• Apply 5 drops of safranin solution to another watch glass.
• Now using a pair of forceps transfer the piece of onion from the distilled water into the safranin.
• Allow the onion to soak for 30 seconds.
• Then, again with forceps, move the onion back into the distilled water.
• Now, place 3 drops of glycerol onto the center of a glass microscope slide.
• Using the forceps again, transfer the onion into the glycerol on the slide.
• Gently place a cover slip over the onion on the slide and blot away any excess liquid with a piece of blotting paper.
• Next, you will visualize the slides you have prepared using a compound microscope. First, turn on the scope and set the objective lens to the lowest level of magnification. NOTE: A compound microscope typically has two levels of magnification.
• Place the cheek tissue slide onto the stage of the microscope and bring the cells into focus by adjusting the stage and using the coarse adjustment knob.
• When the cells are in focus, observe the individual cells and draw what you see. Repeat these observations at medium and high magnifications adjusting the focus with the fine adjustment knob. IMPORTANT: Do NOT use the coarse adjustment knob at high magnifications.
• Next, rotate the nose piece so that the oil lens is almost in place.
• Place a drop of immersion oil on top of the cover slip of the cheek cell slide.
• Use the oil lens to view the cheek cells and record your observations.
• Repeat these steps to view the onion plant cell, moving again from low to medium, high, and oil lenses (steps 20 – 24).
• Record all of your observations and note the differences you see between animal and plant cells.
• When you are finished, place the cheek cell slide and toothpicks into a diluted bleach solution. Dispose of the cover slips into a glass waste container.
• Finally, turn off the microscope and clean the lenses with lens cleaning paper.
• Calculate the total magnification for each of the viewing levels. Remember to account for both the eyepiece magnification and the objective lens magnification. NOTE: Eye piece: 10X magnification, Objective lens: 4X, 10X, and 40X magnification
• Then, identify the structural differences between plant and animal cells using the observations made under the microscope.
• Label the nuclei in both cell types and then highlight or note any differences that you see between them.

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Microscope Cell Lab: Cheek, Onion, Zebrina

• Microscope Cell Lab: Cheek, Onion,…

Introduction

The purpose of this lab was to use the microscope and identify cells such as animal cells and plant cells. This subject is important because in Biology, we will be using the microscope many times during different laboratory exercises. The microscope is used for looking at many specimens that cannot be seen with the naked eye.

Humans only have a resolution, the ability to separate or distinguish two or more objects that are close together, of 0.1 millimeters. The average microscope has a resolving power of up to 0.2 micrometers. In this lab, we adjusted the resolution on the microscope to have a better look at the specimens that were observed. In addition, we needed to look at the contrasts of some specimens in this lab.

Contrast is defined as being able to see different parts of the specimen at hand. In this lab, in order to increase the contrast of some specimens, we stained the samples using Methylene Blue and Water. The main hypothesis of this lab was, can we use the compound microscope to look at samples that we normally cannot see with our unaided eyes?

Materials, Methods, and Results

In this laboratory exercise, our main instrument was the compound microscope. In order to prepare the samples for observation certain materials were used. I used tools such as:

• Compound Microscope
• Cover slips
• Methylene Blue
• Razor blades
• Zebrina stem
• Laboratory Exercise Manual

There were three mini-lab procedures carried out during this lab. The first lab exercise was observing animal cells, in this case, my cheek cells.

The second lab exercise was observing plant cells, in this case, onion epidermis.

The third lab exercise was observing chloroplasts and biological crystals, in this case, a thin section from the Zebrina plant.

The first thing that was done in this lab exercise was gather materials. I worked with two other classmates that sat at my table.

Observation of animal cells (squamous epithelium of a cheek)

Using a toothpick, I carefully scraped the inside of my cheek to get the cells. I then spread it across the slide, added the Methylene Blue solution, and then covered the slide with a coverslip. I placed the slide in the center of the stage and made sure it was secured with the stage clip.

The objective lens was already at 10X magnification, so I switched it to 40X magnification. I moved the stage closer up using the Coarse Adjustment. The specimen wasn’t exactly in the middle, so I had to move the slide around using the X-Y stage control so that I was looking directly at the sample.

I also adjusted the lighting of the microscope using the diaphragm. I then switched the magnification to 40X. I adjusted the Fine Adjustment to get a sharper image of the cell. I was able to see the cheek cell correctly. I was able to see the Cytoplasm, Nucleus, and Cell Membrane.

Observation of plant cells (onion epidermis)

For this observation, a plant cell was to be seen. An onion bulb was retrieved. Using the forceps, I removed a small slice of the onion and carefully and quickly put it on the slide. I also added water to ensure that the onion slice would not dry out.

I adjusted the lighting again using the diaphragm, to contrast the compartments of the cell. I moved the stage closer up using the Coarse Adjustment and switched the magnification to 10X. I was able to see the Nuclei and Cell Walls between each cell.

Observation of chloroplast and biological crystals

For this observation, I looked at a small section from the Zebrina stem. The stem was gotten from the bucket in front of the classroom.

The small section was obtained by slicing a tiny amount of the stem using the razor blade. It was placed on the slide, followed by the water. When first observed, nothing clear could be seen.

It appeared to be that the Zebrina stem was cut too thick. The stem had to be cut once more, and this time much thinner, but not too thin. The same procedure was repeated again, adding water, placing the coverslip, putting the slide on the stage, adjusting the stage, and making the image sharper.

The second sample proved to be much better. The magnification was already positioned at 10X magnification, which made the cell much clearer to see. The Cell Walls, Cytoplasm, Nucleus, Chloroplasts, and Crystals were able to be seen.

• Calculate the resolving power of the lenses on your microscope.

To find the resolving power for each of the lenses on the compound microscope, I used the Abbey equation. I plugged in the appropriate numbers into the variables, where d = resolution (nm), 0.612 was given, l = wavelength of light used (550 nm), and NA = numerical aperture. I repeated this equation for each magnification, getting the resolving power for each of the lenses.

• Will this resolution be attained with each sample you look at? What will be some of the interfering factors?

Each resolution for each sample is different. Some samples will require you to choose a higher magnification or lower magnification. Some interfering factors can be using contaminated samples such as dirty slides, using the wrong stains or dyes, using the incorrect sample, broken slides, and many more.

Other interfering factors could be for using incorrectly using the equipment or broken equipment such as broken objective lens, broken illuminators, the light might be too high or too dim, and many more.

• What happens to resolving powers as the NA increases?

When the Numerical Aperture increases, the resolving power will decrease.

• What differences can you observe between animal cells (cheek epithelium) and plant cells (onion epidermis)? Think of the size, shape, and cellular components.

The onion epidermis cell is the only cell that has a cell wall. In addition, it is the only cell that has a chloroplast, where photosynthesis can happen. The cheek epithelium cell is the only one that has centrioles, the barrel-shaped organelle that is responsible for helping organize chromosomes during cell division.

Furthermore, the presentation of the onion cells was positioned right next to each other, on top of each other, below each other, like a checkerboard. The cheek cells were bunched up together at some areas, almost overlapping each other. The onion cells almost looked rectangular-shaped, whereas the cheek cells look oval-shaped.

• How many chloroplasts would you estimate are in each cell of Zebrina?

From looking at the Zebrina slide, I would estimate that there was about 50 chloroplasts.

• What function do you think the calcium oxalate crystals have?

Calcium oxalate is a calcium salt of oxalic acid. It forms crystals known as raphides, which appears to be what I saw when l looked at the Zebrina sample. Interestingly enough, while reading about calcium oxalate, I discovered that it is a major constituent of human kidney stones, founded in the urine.

From observing the calcium oxalate crystals, it looks like spikes/needles. From what I know about spikes, they serve as a weapon. So my assumption is that these crystals are used as a defense of some sort.

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Onion and Cheek Cell Lab Experiment - Organelles

Subject: Biology

Age range: 14-16

Resource type: Visual aid/Display

Last updated

23 August 2016

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