• While students are performing the lab activity, you should circulate around the room, assessing proper techniques in making a wet mount slide. You should also view their slides and drawings.

• Generally assess student understanding during lecture and the Jigsaw activity.

• Collect Observation Sheets for individual assessment.

Day 1: Observing Eukaryotes under a Light Microscope

Safety Precautions:

• It is helpful to go through the lab yourself before conducting the lesson.

• Students should wear goggles and gloves to protect skin and eyes from iodine and Methylene blue.

Show students the glass marble and use it like a magnifying glass. Ask students, “How does the glass marble allow me to see things differently?” It magnifies the things you see through it.) Explain that: “In 1673, Anton van Leeuwenhoek published the first drawings of small creatures that he saw with his homemade microscope. The lenses were tiny spheres of glass, much smaller than the marble and it is suspected that he possessed a microscope that could magnify 500X although the only lenses from him that still exist magnify only 230X. How do you think scientists know that?” (His drawings probably show objects magnified 500X.) “It’s interesting that in 1610, Galileo observed the moons of Jupiter, but it took more than 60 years after that to see tiny things here on earth. Why do you think it took so long?” (It took the development of better stains and microscopes for the world of microbiology to be discovered.)

Lab Activity—Observing Eukaryotic Cells

Display the Prokaryotic and Eukaryotic Cells diagram to students (S-B-3-2_Prokaryotic and Eukaryotic Cells Poster.doc). Ask them to pay attention to the differences present in the eukaryotic cell and field any student questions. Ask, “What differences do you observe?”

Hand out copies of the Eukaryotic Cells Observations Sheet and KEY (S-B-3-2_ Eukaryotic Cells Observations Sheet and KEY.doc). Tell students that they will be observing cells that van Leeuwenhoek might have observed with his microscope: “Today, you will prepare wet mount slides for the onion peel and an elodea leaf.” For instructions, visit www.indiastudychannel.com/projects/1509-Making-Temporary-Mount-Of-Onion-Peel-Cell.aspx.

Demonstrate how to pull the peel of the onion from the fleshy part of the bulb for making a wet mount. If necessary, demonstrate or have a student demonstrate how to make a wet mount slide and stain the sample. CAUTION: Iodine stains skin and clothes. Wear goggles to protect the eyes from iodine.

While students are observing the onion leaf cell, point out the structures that they should see: a vacuole, the nucleus, cell membrane, cell wall, and possibly, mitochondria. Have students draw and label their observations.

Have students view the prepared slides of human cheek cells. Tell students what to expect when viewing a cheek cell. They are much smaller than the onion cells, but they should still recognize the cell membrane and the nucleus.

Have students pinch the leaf off an elodea plant and make a wet mount slide of the leaf. Do not stain. Students should be able recognize the cell wall and membrane, and they should see the chloroplasts moving within the cell. Explain that the pigment in chloroplasts allows it to be seen with the light microscope. Ask students: “What is missing from the cell?” (The nucleus.) Have students draw the stain under the cover slip by dropping one or two drops of iodine to one side of the cover slip and using edge of a paper towel on the opposite side to absorb the water and pull the stain through. Students should be able the view the nucleus with the iodine stain.

After the activity, ask students how these cells differed from the prokaryotic cells (found in yogurt) that they viewed. (Students should say that these cells are much bigger. They may mention that these cells have a nucleus, a vacuole, mitochondria, and chloroplasts.) Ask students: “Do you think van Leeuwenhoek could have seen prokaryotic cells with his microscope?” (Not with 230x magnification or they may have looked like dust particles.) Then ask, “What structure was found in all of the cells viewed today?” (A nucleus.)

Day 2: The Structure and Function of the Eukaryotic Cell

Remind students that cells are living organisms and must carry out all the same functions of a large organism. Eukaryotic cells have specialized structures called organelles, which carry out those functions. Have students brainstorm the functions organelles would need in order to keep the cell alive. On the board, write the functions that the students listed, and relate as many as you can to the common characteristics of living things.

Activity: Jigsaw Organelle Functions

Tell students: “You will be working in groups to ‘jigsaw’ the functions of the organelles. The groups should be ready to present in about twenty minutes.” (See the Jigsaw Classroom link in Related Resources for an explanation of the jigsaw technique.)

Assign each expert group one or two structures/organelles to research. To become an organelle “expert,” the student will need to know:

• the name of the organelle,

• its function,

• where it is located in cell, and

• whether it is found in a plant or animal cell, or both.

Make sure students are writing important information about the function of the organelle or structure. After the groups finish their research, students will re-form into new groups, each with one student from each expert group. The new groups should have one “expert” represent all the organelles found in eukaryotic cells. Have students label cells and write the functions of the organelles in the handout, Organelles of Eukaryotic Cells (S-B-3-2_Organelles of Eukaryote Cells and KEY.doc).

To close, go back to the list of functions that were hypothesized by students at the beginning of class. Ask students, “Which organelle/organelles fulfilled each function? Were there any functions that a cell performs, that you missed? Why are those functions necessary?”

Day 3: Comparing Eukaryotic and Prokaryotic Cells

Explain to students that the term nucleus is Latin for “kernel” or “core” and that eukaryote is a Greek word that means “true kernel” (Eu-true and karyote-kernel). Remind students that prokaryote means “before the nucleus.” Ask students: “What assumption are biologists making by using the names prokaryote and eukaryote?” Biologists are assuming that prokaryotic cells are more primitive than eukaryotic cells.

Activity: Venn Diagram

Have students work individually or in pairs to create a Venn diagram comparing prokaryotic cells and eukaryotic cells (S-B-3-2_Venn Diagram Prokaryotic and Eukaryotic Cells and KEY.docx). It may be helpful to use poster paper for this activity, since there will be many items included in the diagram. After the activity, have students share any questions remaining about how the types of cells compare and make corrections to the Venn diagrams as needed.

Extension:

• Students who may be going beyond the standards can do one of the R.A.F.T. activities listed below, or have students make their own.

  Role of Writer	Audience	Format of Writing	Topic with Strong Verb
  Nucleus	Ribosomes	Memo to company	Get back to work
  Chloroplast	Organelles	Editorial	If it weren’t for chloroplasts, life on earth wouldn’t exist.
  Bacteria	Lysosome in a macrophage	Letter	Pleading for your life

• Students who may require extra practice with the standards can make flash cards to assist in vocabulary development. Have students use the cards to make a concept map. Use string or yarn to connect the ideas.