The Arizona STEM Acceleration Project

Observing and Measuring Specimens by Using Microscopes

Observing and Measuring Specimens by Using Microscopes

A 7th Grade STEM Lesson

Georgina Matzkin

March 2023

Notes for Teachers

• Context: This lesson takes place in a classroom for four hours.
• Students may work in small groups of 2-4.
• An emphasis should be on correctly using the microscope when focusing as well as measuring the specimen in millimeters.
• Another emphasis is on explaining the relationship between plant cells and animal cells and their functions.

List of Materials:

Depending on class size and the group size, you will need:

• 1 microscope per four students.
• 1 prepared slide with the letter “e” per four students.
• 1 prepared slide with tissue paper fragment per four students.
• 1 empty glass slide per four students.
• Hair strand (student’s own) with tape
• Salt (2-3 crystals per group)
• 1 prepared slide with paramecium (animal cell) per four students.
• 1 prepared slide with corn roots tip (plant cells)
• 1 prepared slide with a grid (used for measuring specimen) per four students.
• 1 handout per student for drawing and measuring specimens and writing observations.
• Optional - observe living organism found in pond water. These microorganisms will need to be ordered a week before students start using the microscopes to insure, they are ready to be used. Students can also observe fruit flies that the teacher can catch in backyard by leaving a container with a rotten banana or orange. Teacher would need to freeze container after removing the fruit, so the fruit flies are available to use.

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Arizona Standards

Science Standards:

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7.L1U1.9 Construct an explanation to demonstrate the relationship between major cell structures and cell functions (plant and animal).

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Science and Engineering Practices:

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• use mathematical and computational thinking
• engage in argument from evidence
• obtain, evaluate and communicate information

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Writing Standard:

• 7.W.1-Provide a concluding statement or section that follows from and supports the argument presented.

Speaking and Listening Standards:

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• 7.SL.1-Engage effectively in a range of collaborative discussions (one‐on‐one, in groups, and teacher‐led) with diverse partners on grade 7 topics, texts, and issues, building on others’ ideas and expressing their own clearly.

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Mathematical Practices

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5. Use appropriate tools strategically.

6. Attend to precision.

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Objective(s):

I will be able to correctly name the parts to the microscope and focus the specimen.

I can correctly calculate the total magnification given the microscope objectives and eyepiece.

I can correctly focus the specimen at 40X and 100X.

I can draw the specimen and describe in writing what I am seeing under the microscope.

I can measure specimens in millimeters (length & width) by using a grid on the slide.

Agenda

(150 minutes or 3 days of instructional time with each period being 50 minutes)

Day 1- Students will be shown the parts of the microscope and the teacher will explain what each part does.

-Students will practice using the microscope and focus the letter “e” slide. Students will see that the letter “e” is seen backwards when placed on the stage.

-Students will draw the letter “e” with their naked eye, calculate the magnification they are using and then write the observations they see.

-Students will then measure the letter “e” with the grid slide. Students will place the grid on top of the letter “e” and measure how many grid squares the letter covers.

Day 2 - Students will draw the salt cubes using their naked eye. Students will then focus the salt specimen and calculate the magnification at 40X and 100X. Students will also write observations and measure the salt cubes with the grid.

-Students will draw the tissue paper using their naked eye. Students will then focus the tissue paper specimen and calculate the magnification at 40X and 100X. Students will also write observations and measure the tissue paper with the grid.

-Students will draw the hair strand using their naked eye. Students will then focus the hair strand specimen and calculate the magnification at 40X and 100X. Students will also write observations and measure the hair strand with the grid.

-All students need to take turns with the microscope and write their information.

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Day 3 - Students will observe the plant cell (corn roots tip or any other plant cell) and animal cell today (paramecium or any other single animal cell).

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-Students will draw the plant cell using their naked eye. Students will then focus the plant cell specimen and calculate the magnification at 40X and 100X. Students will also write observations and measure the plant cell with the grid.

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-Students will draw the animal cell using their naked eye. Students will then focus the animal cell specimen and calculate the magnification at 40X and 100X. Students will also write observations and measure the animal cell with the grid.

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-All students need to take turns with the microscope and write their information.

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Day 1

Day 2 �Handout�made to be �used and �glued in�student’s�Interactive�Notebook.

Day 3

Hands-on Activity Instructions

• In groups of 2-4, students will work together and take turns using the microscope.
• Students must first learn the parts of the microscope and how to use the microscope. Teacher needs to review this and point to a part of the microscope and students need to say the part and explain what it is used for.
• Students will also need to learn how to calculate the magnification they are using. Students need to multiply the eyepiece and the objectives together to find the total magnification.
• Students will also learn how to measure specimens in millimeters by using a grid on a slide when looking through the microscope.
• Students will view several specimens but the main slides that students will view are the plant cell and animal cell.
• Students can also view live microorganism in pond water, but the teacher will need to buy them.

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Letter “e”- upside down

Paramecium-prepared slide

Plant cell- root

YouTube video that shows how to measure using grid (video not created my me):

https://www.youtube.com/watch?v=xGWljZC5GzY

Glass slide

How can we observe and analyze something so small that our naked eyes can’t see?�

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Yes! The microscope (Some students might say telescope.)

In the next few days, we will learn how to use the microscope, calculate the magnification of what you are observing, draw and write your observations, as well as measure your specimen.

We will then observe an animal and plant cell and make comparisons. How are the cells different? The same?

Let’s explore what your naked eye can’t see!

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Assessment-�Teacher will assess student’s work. See slides 8 and 9.

Students will be assessed on their drawings and observations.

Is the drawing a replicate of the field of view?

Are the magnifications correctly calculated?

Are the specimens correctly measured in millimeters?

Are students able to see the differences and similarities of animal and plant cells?

Differentiation

Teacher will walk around the room helping those group of students that are having difficulty focusing or measuring.

Strategically pair students as needed.

Create a word wall with key vocabulary and images.

Remediation

Extension/Enrichment

Students that can focus and measure without any difficulties will be given other specimens to observe and measure, like fruit flies or other prepared slides the teacher has.

These students can also walk around the room helping students who are struggling.

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