Physiology Box

5. Slimy cells

Summary
To solidify students’ conceptualization of cells, students build a model of a cell in a ziplock bag using polyvinyl alcohol slime as cytoplasm. So far, students’ experience with cells has been 2 dimensional – diagrams and microscopic slides. The 3 dimensional nature of cells comes to life as students use everyday objects to represent the many parts of a cell. In addition, students can use this activity to develop a sense of scale, calculating how big a human would be if the ziplock bag cell model were really the size of a cheek cell.

4. Seeing Cells - Sources

Sources
Blank cell coloring diagrams can be found at:

  • Shannan Muskopf’s Biology Corner website has great simple animal cell and plant cell line drawings.
  • In my classes, I adapted the plant and animal cell diagrams from The Biology Coloring Book by Robert D. Griffin.

The best resource for this lesson is the fabulous Biology Corner website of Shannan Muskopf. In Biology 1 and 1A, Chapter 3, she provides:

4. Seeing Cells - Assessment

Assessment

  1. Have students turn in their labeled diagrams and conclusion questions.
  2. Provide an unlabelled cell diagram for them to correctly label and describe the function of each part.
  3. Assign a cell quiz. Use the one attached to this lesson, use the one at Shannan Muskopf’s Biology Corner website, or create your own.

4. Seeing Cells - Lesson Plan

Lesson Plan

  1. Ask students to free associate what comes to mind when you write the word “cell”. In addition to biological cells, they may come up with prison cells, cell phones, a terrorist cell and more. In all these uses, a “cell” is a single functioning unit or compartment that is part of a larger whole. That too is what a cell is in biological terms, the building block upon which all living things are built.
  2. Show students pictures of cells. Have students tell you what they see and notice. Emphasize both the diversity of different cell shapes and sizes and also how all cells share certain features.
  3. Give students the cell coloring diagrams. Lead your students in coloring the diagrams and describe the job of each cell part as you go. You may want to have students write the job of each part of the cell beside the name of the part.
  4. Now that students have learned a little bit about cells, they will now get a chance to look at some real cells through a microscope. If students have not used a microscope before, go over the parts of a microscope and how to properly use it.
  5. Demonstrate how to make each type of slide (see the directions on the Seeing Cells student handout, one of the attachments at the bottom of the main summary page).
  6. Answer any questions then let students begin work on the lab in groups of two. By the end of the activity, students should have 2 labeled drawings of each type of cell, one at 40x and one at 400x.
  7. Assist students with making slides, using the microscopes, and bringing cells into focus. The human cheek cells are often difficult to find and get into focus since they are much smaller and more disperse than the onion and Elodea cells. Many will need help locating these cells on the slide.
  8. When all student have completed the drawings, review what they saw using the Cell Images transparency.
  9. Point out the cell parts that can be seen through a light microscope (cell membrane, cell wall, cytoplasm, nucleus, and chloroplasts).
  10. Discuss why it is that other cell parts could not be readily observed (they are too small or need special dyes to be able to see them).
  11. Discuss the differences between plant and animal cells (plants have cell walls and chloroplasts) as well as the difference between the elodea and onion skin cells (only leaf cells have chloroplasts).

4. Seeing Cells - Getting Ready

Getting Ready

  1. Make copies of cell coloring diagrams. Make one copy on a transparency so that you have one to color in along with your students.
  2. Make copies of Seeing Cells Lab handouts.
  3. Make transparency of the Cell Images and any other images of cells you found.
  4. Set up microscopes.
  5. Set out stations for students to make slides. Each station should include glass slides, cover slips, iodine, methylene blue, tap water, eye droppers, several pieces of red onion, one Elodea stem, and clean toothpicks.

4. Seeing Cells - Background

Animal cell: Image created by Mariana Ruiz VillarrealAnimal cell: Image created by Mariana Ruiz Villarreal Plant cell: Image created by Mariana Ruiz VillarrealPlant cell: Image created by Mariana Ruiz Villarreal Bacterial cell: Image created by Mariana Ruiz VillarrealBacterial cell: Image created by Mariana Ruiz Villarreal

4. Seeing Cells - Logistics

Time
45-75 min introduce the parts of a cell and their functions
Optional: 10-15 min discuss microscope parts and usage
5-10 min demonstrate proper procedures for making slides
45-90 min make slides, look at cells, create diagrams, and answer questions
10-15 min discussion and review

Grouping
Teams of 2.

Materials

4. Seeing Cells

Summary
The invisibly small world of the cell comes to life as students look at plant and animal cells through a microscope. Students create wet-mount slides of onion skin, elodea leaf, and human cheek cells. They learn some of the gross differences between plant and animal cells (cell walls are present in plant but not in animal cells), and even some of the differences between different plant cells (chloroplasts are found in the leaves but not in the roots). It is suggested that this lesson take place after students learn the parts of a cell and their functions. Resources for good cell diagrams are provided in the Sources section. This lesson may be used in conjunction with the Pond Water activity for students to get a sense of the diversity of microscopic life, both single celled and multi-celled.

Life on Mars - Sources

Sources
This lesson was inspired by a workshop by Steve Ribisi of the University of Massachusetts and Mission 10 from the Life in the Universe curriculum, published by the SETI Institute.

To learn more about the Mars Rovers, go to the NASA/JPL website. The following are some of the highlights from this site that may be used in conjunction with this lesson:

Life on Mars - Going Further

Going Further

  1. See the Imax movie “Roving Mars”. The animation is absolutely incredible. Sadly, little of the scientific discoveries on Mars itself are discussed in the movie but the engineering that went into designing the rovers and getting them to Mars is clearly and dramatically shown.
  2. After completing this activity, bake the soil samples at 200 degrees for 30 minutes, or microwave them on high for 5 minutes, to kill the yeast. Then do the activity again. The nutrient milkshake and agar plate tests should now show negative results but the protein test should still detect the presence of the yeast.
  3. Study other aspects of Mars such as its size, gravitation, planetary history, etc. NASA provides an extensive list of Mars-related lesson plans.
  4. Investigate what the “blueberries” really are – beads of hematite. Bring in samples of hematite and test some of its physical properties using methods described in the History of Rock activity. Hematite stats:
    • Hardness - 6.5, comparable to pyrite
    • Color – reddish grey, reddish brown, grey, dark grey
    • Density - 5.3
    • Luster – metallic
    • Streak – reddish brown
    • A neodymium magnet will show a weak attraction for hematite, regular magnets will not.