Activity Overview

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

  • Microscope
  • Glass Slides & Covers
  • Iodine
  • Onion
  • Cheek
  • Tooth Pick
  • Dropper
  • This Worksheet

Experiment Instructions

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

Template and Class Instructions

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

Student Instructions

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

Lesson Plan Reference

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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