Lesson 3 of 6
Objective: SWBAT accurately represent what they see when examining slides using a microscope.
Microscopes are design for one person to see the magnified object on the stage. But how do you know what others are seeing? How do you know if you are seeing the same thing other see when they look at the same object?
Great scientists accurately document what they see when using the microscope so they can share their discoveries with other scientists.
Before students use a microscope to examine cells, they will take a look at common objects and record what they see so we know they are seeing what we intend for them to see.
This lesson prepares students to use the microscope to examine cells. In the next lessons we use the microscope to look at onion cells and cheek cells.
But how do we know students are accurately seeing what we know they've been given? Students will practice using the microscope by examining everyday items. Their detailed drawings tell us if they are using the microscope correctly. Once we've gotten students successfully practicing their microscope skills, we can move on to cells. The student performance indicator for this lesson is (MS-LS1-1 Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells.) We are preparing students to tackle the standard - LS1.A: Structure and Function - All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular).
When students are using the microscope, they should be asking the question, what does __________ look like if I magnify it to see it better? And, what else can I investigate using the microscope? (SP1 - Asking questions and defining problems).
Students will be collecting data about things they may not have considered what they look like under a microscope. Students are always in awe of the comics they see under the microscope. How the printer makes any color out of only four colors of ink (cyan, magenta, yellow and black) is not a question students have asked before now. (SP3 - Planning and carrying out investigations)
Students will compare salt and sugar under the microscope. Two substances that look the same without a microscope but are easily distinguished with a microscope. Students will also understand why cotton feels cooler to wear and why wool can be scratchy. (SP4 - Analyzing and interpreting data)
Recording exactly what they see is a learning goal for students in the lesson. Student observations can be evaluated for their attention to detail as they view the objects and their precision as they draw the representations to be shared with other scientists. (SP8 - Obtaining, evaluating and communicating information)
The preparation time for this lesson depends on the number of slides created for students to view. I created the "e" slides by using a label maker with clear tape. I printed the letters with the smallest font and then stuck the sticky clear label to a microscope slide.
At the fabric store I was able to secure small samples of cotton and wool fabrics.
The comics are from the Sunday newspaper and I happen to have salt and sugar in the science lab.
I make my own slides for the sugar, wool, cotton and salt. The slides are recycled file folders cut to the size of a standard glass slide. A hole is punched in the center. The objects to be view are secured with clear tape. Salt and sugar stick easily to the tape.
A complete materials list can be found in the resources section.
Students in Action
Students in Action
We begin this lesson with a projected image of the microscope. With student contributions we are able to identify the essential parts of the microscope. This, I tell the students, will facilitate our conversation if they are having trouble with the microscope. The expectation is that you will use the appropriate vocabulary when asking for help.
I use a document camera to facilitate the labeling. I ask for student input. They have a word list on the sheet. The parts we are labeling are obvious to the students with a little thought. We label the eyepiece, arm, revolving nose piece, stage, stage clip, coarse focus, fine focus and light source.
Students will place this document in their science journal to reference as they work with the microscopes. Student groups are not permitted to transition to a microscope until they have successfully labeled the parts. I will move about the room and check to see if students have completed the first page before allowing them to proceed to a microscope. I initial their page. I have a pretty difficult signature to duplicate so this is an effective indicator that I have checked the students' journals. When I visit student groups as they work with the microscopes, students are expected to use the appropriate vocabulary. They can reference their notes. Often I will quiz them on the parts as i talk with each group.
Several microscopes are setup around the classroom for student use. If possible we limit the number of students at each microscope to two.
I visit each group of students as they are looking at the selected objects asking to let me see what they are seeing so I know the microscope is in focus and the slides are properly placed over the light source.
Some student try to turn the letter "e" upside down so the image is projected right side up. I correct the placement of the slide and let them know that the point of the lesson is for them to see that the microscope has inverted the image.
As students look at the wool slide, I ask them if they can see why sometimes wool feels itchy next to our skin. The wool is different than the cotton. When you look at wool under the microscope you see loose fibers. These are irritating to some people and cause their skin to itch.
The cotton samples have an open weave. I point out to students that the spaces in the open weave is one of the reasons cotton feels cool. This is where I see students pull the hem of their shirts up to the microscope to look at the fabric. Sportswear have an interesting texture as well.
Even though sugar and salt appear similar without the microscope, they are very different under the microscope. Students are surprised by this revelation. They are also surprised to find out that neither salt nor sugar is actually white.
Students know that there are only four colors used by printers. Many have changed the cartridges themselves. The colors are black, magenta, cyan and yellow. So students are again surprised when they look at a comic with the color orange under the microscope. They see tiny dots of yellow and magenta.
I check for the accuracy of student drawings and encourage details. For instance the comic colors should be represented with dots, not solid colors.
In this short video, I share the purpose of the tasks selected for microscope practices.
Connecting the Learning
I use this time to get a feel for student success with the microscope.
I ask students what surprised them most in this microscope lesson? Students offer a variety of examples, just about all the experiences are new to them.
When you used high power, did you see the same amount of the object? The students should indicate that they see less of the object.
Can you share an example? Students usually share the millimeter markings on the the ruler. Using low power the students see more marks than they do on high power. The lone marking on high power is magnified.
In the next lesson we will look at plant cells, specifically onion cells and animal cells, specifically your cheek cells. What do you expect to see? Students answers vary. They expect to see more than we will actually see. The concept of how small the cells actually are is still not clear to students.