LESSON PLAN
Teachers: Jennifer Park
Title of lesson: Microscope Mania
Length of lesson: 60 minutes
Name of course: Biology
Grade level: 9th grade
Honors or regular or magnet: Regular
Source of the lesson:
- http://sun2.science.wayne.edu/~gk12/lessons/LabSkills/Lesson%20Plan-Basic%20Skills%20of%20Microscopy.doc
- http://sciencespot.net/Media/microparts.pdf
- http://sciencespot.net/Media/micropuzzle.pdf
- http://www.l-spioneers.org/hschool/teachers/pitts/bio/un9/cellobservations.htm
TEKS addressed:
(1) Scientific processes. The student, for at least 40% of instructional time, conducts field and laboratory investigations using safe, environmentally appropriate, and ethical practices. The student is expected to:
(A) Demonstrate safe practices during field and laboratory investigations
(2) Scientific processes. The student uses scientific methods during field and laboratory investigations. The student is expected to:
(B) Collect data and make measurements with precision
(5) Science concepts. The student knows how an organism grows and how specialized cells, tissues, and organs develop. The student is expected to:
(A) compare cells from different parts of plants and animals including roots, stems, leaves, epithelia, muscles, and bones to show specialization of structure and function;
Concept(s)
Many organisms and biological structures are too small to be seen with the naked eye. Biologists often use a light microscope to observe such specimens. A light microscope is used to magnify the specimen and magnification is usually accompanied by improved resolution (being able to distinguish two points as two separate and distinct points). We will examine the functions of the primary parts of the microscope and learn how to use it to observe and identify differences and similarities between plant and animal cell parts.
Performance or learner outcomes
Students will be able to:
· Identify and describe the function of the basic parts of the microscope
· Become familiar with basic skills of light microscopy, including how to carry a microscope, focus a microscope, prepare a slide, and determine the magnification.
· Use a microscope to identify cell parts.
· Compare and contrast plant and animal cells
Resources, materials and supplies needed
· Compound microscope (one for each group of four)
· Classroom set of slides (about 16 clean slides per group)
· Thick crayon
· Cover slips
· Class set of scientific prepared slides
· Toothpick
· Onion
· Water
· Iodine
· Methylene blue
· Disposable pipettes
· Gloves
Safety Considerations
Students should be careful in handling the slides and while working with the microscopes. Students should also handle the iodine and methylene blue with much care since they may be harmful if swallowed, inhaled, or in contact with skin (students should be wearing gloves when working with these chemicals). They may also cause eye irritation. Students should alert the teacher if there is any spillage of the chemicals.
Supplementary materials, handouts
- Parts of the Light Microscope transparency
- Parts of the Light Microscope worksheet
- Lab worksheet
- Microscope Mania word search and make-a-word challenge worksheets
|
Engage: Teacher Does
Show pictures of images that can only be observed through the microscope, such as epithelial cells, bacteria, etc.
Tell the students that today they will be learning how to use microscopes to see organisms and structures that are too small to be seen with the naked eye.
Time: __5__minutes |
Probing Questions
Can you tell me what this is an image of?
What are several things that are common with all these images?
|
Student responses/ Misconceptions
Cells, bacteria, etc. (most students may not know exactly what they are)
They are all small, cannot be seen with naked eye, etc. |
|
Explore: Teacher Does
First, go over the Parts of the Light Microscope worksheet with the students (with the transparency on the overhead). Save the section over the power of magnification for later.
Go over the safety rules of handling microscopes, slides, and especially iodine and methylene blue before beginning the lab. Stress that students need to wear gloves in order to continue with the lab.
Start the lab and walk around the classroom, monitoring each group’s progress.
*Note: If it looks like the class will run out of time before completing the lab exercise, half of each group prepare and examine the onion cells while the other half works on the cheek cells. Then at the end, students can exchange and explain their observations to each other.
Time: __40_minutes |
Probing Questions
What is the function of the coarse adjustment knob? eyepiece? etc.
How should you carry the microscope?
What should you do if you break a prepared slide/spill the chemicals/come in direct contact with the chemicals?
When should you wear gloves?
Where should you begin examining the slides?
Which knob do you turn to move the stage away from the objective?
Which scientific prepared slide did you choose?
What do you find most interesting in the slide you are observing?
Describe the general shape of the onion/cheek cells.
What is the purpose of staining the onion cells?
Which parts of the onion cells were more visible after the staining?
Describe the similarities and differences you see between the onion and cheek cells.
How do you calculate the total magnification?
|
Student responses/ Misconceptions
Moves the stage up and down for focusing; contains the ocular lens, etc.
By holding onto the arm and supporting the base.
Notify the teacher and do not touch it.
Before beginning step 10 in the lab instruction.
At the lowest power objective.
Coarse adjustment knob
Various responses (E. coli, Salmonella, etc.)
Various responses.
Various responses
To make the parts of the onion cells more visible.
Various responses
Onion and cheek cells both have a nucleus and cytoplasm. Onion cells have cell walls and chloroplasts while cheek cells do not (instead have cell membranes).
Multiply the magnification of ocular lens with magnification of objective lens. |
|
Explain: Teacher Does
Teacher will go over the lab worksheet to make sure all of the students carrying out their lab work correctly.
Go over how to calculate magnification. The magnifying power of each objective is etched on the side of the lens (e.g. 4x, 10x, or 40x). The ocular is the lens that you look through and usually magnify the image 10 times. So to calculate the total magnification, you would multiply the magnification of the ocular lens with the objective lens.
Time: __15__minutes |
Probing Questions
1. Describe what you observed in the scientific prepared slides. (Pick and choose the questions on the lab worksheet that you want to go over)
What is the magnification of the ocular lens?
What are the magnifications of the objective lenses?
How do you calculate the total magnification?
For instance, what is the total magnification for a plant cell observed under 40X objective? Explain answer. |
Student responses/ Misconceptions
Various responses.
10X
4X, 10X, 40X
Multiply magnification of ocular lens with magnification of objective lens. 400X because 10X times 40X equals 400X. |
|
Extend / Elaborate: Teacher Does
If students are done before the time for lab is up, have them working on the Microscope Mania word search and word puzzle.
Time: __0__minutes |
Probing Questions
|
Student responses/ Misconceptions
|
|
Evaluate: Teacher Does
Students will turn in their lab worksheets for evaluation.
Time: __0__minutes |
Probing Questions
|
Student responses
|
Name:
Date:
Basic Skills of Microscopy
Materials:
· Compound microscope
· Thick crayon
· Glass slides
· Cover slips
· Set of scientific slides to examine
· Toothpick
· Onion
· Water
· Iodine
· Methylene blue
· Disposable pipettes
Procedure:
1. Remove the microscope from its cabinet and carry it upright with one hand grasping the arm and the other hand supporting the microscope below its base. Place the microscope onto the workstation.
2. Make sure the objective is clicked in the “low power” (4x or 10x) position. Do this by rotating the nosepiece until the low power is in line with the body tube.
3. Always begin examining slides in the low-power objective.
4. Rotate the coarse adjustment knob located on the side of the microscope to move the stage 1cm away from the objective.
5. Write a normal sized letter “e” on the slide with the crayon and place it right-side up onto the stage and clip it in place. Make sure the “e” is on top of the light source so you could be able to see light shine on the “e” through the microscope.
6. Now, while you are in the low-power objective, turn the coarse adjustment until you can focus. You should see your letter magnified. If you don’t, move your slide carefully on the stage until the letter is surrounded by light.
7. Focus up and down to receive the best image.
8. Now, take a scientific, prepared slide and examine it. Always try to have the most clearest image. Draw what you see on your data sheet. This step is up to your teacher.
9. When you get the clearest image, find the total magnification of that image by multiplying the magnification of the objective lens and the ocular lens together. The ocular lens is 10x so just multiply 10 times the magnification of the objective lens.
10.
WEAR GLOVES NOW
BEFORE CONTINUING WITH THE LAB.
Prepare a wet mount of the onion membrane.
a. First take a thin layer of onion skin off the onion.
b. Put it flat on a slide.
c. Using the pipette, put a drop of iodine stain on it.
d. Carefully put on a cover slip remembering to angle it.
e. Examine the cells under low, then medium power, and then carefully
move the objective lens to high power.
f. Draw a few cells showing what you observed on high power.
11.
Next,
prepare a wet mount of your cheek cells.
a. Using a
toothpick scrape the inside of your mouth.
b. Place it
carefully on the center of the slide.
c. Using the
pipette, place a drop of methylene blue stain on it.
d. Repeat
steps d-f from onion skin directions.
Data Sheet
Scientific prepared slide
_______ (name of organism you observed)
Total magnification: _____
Onion and Cheek Cells
Label the following structures if present on your drawings:
1. Cell Walls: Plants have thick cell walls to strengthen the plant stem.
2. Cell Membranes: Animals have thin membranes because they have other forms of skeletons. Plants have cell membranes just underneath their cell walls.
3. Chloroplasts: Plants have green colored structures that produce food by photosynthesis.
4. Nucleus: Both plants and animals have these; they control heredity and cell division.
5. Cytoplasm: Both plants & animals have clear liquid/gel where most of the cell's life functions occur.
|
Onion Cell |
Cheek Cell
|
Answer the following questions from your observations:
- Describe what you observed in the scientific prepared slides.
- Describe the general shape of onion cells.
- Which parts of the onion cells became more visible after staining?
- In which way were the cheek cells similar to the onion skin cells? How did they differ?
- What are the functions of the cell wall?
- Since the plant cell has a cell wall and a cell membrane, what is the advantage to the plant over just a cell membrane? What are the disadvantages?