Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Set up the eight compound microscopes at eight separate lab stations.
2. Using a note card, label each of the lab stations U1–U4 according to the slide which will be displayed there.
3. Cut a blank notecard into eight squares. Tape one square over each microscope slide label and number each slide according to the key.
4. The slides do not need to be focused prior to students attending the lab. Allow students to focus the image to practice proper microscope technique.
5. Assign students to a lab station and instruct students how to rotate through the stations so that every group of students visits each station U1, U2, U3 and U4.

Safety Precautions

This laboratory activity is considered nonhazardous. Remind students to follow all standard laboratory safety guidelines.

Disposal

The materials used in this lab may be saved for future use. Store slides in their original container to prevent breakage.

Lab Hints

• Refresh students’ memory on the proper method to focus a microscope before beginning this activity.
• If students are using immersion oil, remind them to clean the slide and 100X objective with lens paper before rotating to the next lab station.
• So what really happened? Shadow actually spotted a loose frog hopping down the street (a rare occurrence in winter). The neighbor boy Timmy, was taking his pet frog to school for show-and-tell in a glass jar with a cork lid containing leaves from a family house plant. He too slipped on the icy sidewalk cutting his cheek and dropping the jar in the snow. The cork popped off and Hoppy took off. Unfortunately for Hoppy—Shadow caught him and ate him for breakfast.

Teacher Tips

• If possible, it is best to have U1–U4 on one side of the laboratory and the other identical U1–U4 set on the other side of the laboratory. Instruct students if they were originally assigned to the right side of the classroom they should rotate on the right side only.
• If the classroom has access to microscope accessories capable of displaying images on a television screen, display the slides on the television after everyone has completed the lab. Have a classroom discussion and invite students to share their observations and their method of determining the origin of the cell sample.
• Allow each student approximately 2 minutes at each lab station.

Answers to Prelab Questions

Sample Data

Answers to Questions

1. What is the function of a chloroplast? Why are chloroplasts found in plant cells and not animal cells?

   Chloroplasts are only found in plant cells because they are not necessary for animal cell life—animals do not undergo photosynthesis. The process of photosynthesis converts light energy to chemical energy.

2. Describe the general shape of the animal and plant cells examined in this laboratory. Name an organelle that is unique to animal cells and explain its function.

   Animal cells are round in shape, but not often perfectly spherical. They contain a nucleus which floats around the middle. It is not dead center nor is it attached to the cell membrane. Lysosomes, which are digestive organelles, are unique to animal cells.

3. Many organelles are too small to be seen with a classroom compound microscope. List three important organelles in plant or animal cells that are not visible and explain their function in the cell.

   Student answers will vary. Example: Ribosomes are a nonmembranous organelle that makes protein.

4. Based on the information in your textbook as well as laboratory observations, how were the cells observed under the microscope different from those pictured in the Prelab Activity Worksheet? Why does this difference occur?

   The observed cells were not as idealistic as those pictured in the textbook. The pictures in the textbook revealed several organelles that were not visible under the microscope at 100X such as the golgi apparatus and the smooth endoplasmic reticulum. In textbook and worksheet pictures of the cell, several organelles appear just as large as the nucleus so one would think they should realistically be able to observe the pictured organelles. However, some non-visible organelle membranes and structures are thinner than the resolution of the microscope and therefore are not visible.

References

Campbell, Neil A. Biology. Pearson Benjamin Cummings; San Francisco, 2005. Seventh Edition, p 100–101.

Introduction

Mrs. Kruse and her dog Shadow stepped out the front door for their usual morning walk on a blustery December morning. The next thing she knows—she is lying at the bottom of the icy steps and bleeding from her hand. Examine various slides of tissue samples collected from the scene to figure out the rest of the story!

Concepts

• Microscopy
• Plant vs. animal cells
• Cellular characteristics
• Organelles

Background

In order to determine the cause of an accident or solve a crime, investigators rely on many factors, including witnesses, physical evidence, logic and forensic science. In examining any tissue samples for example, a preliminary step would be to investigate the type of cellular structure and organelles found in the cell. How can you determine if the sample is from a plant or an animal?

Most cellular features are too small to be viewed with a classroom compound microscope. The cell wall or cell membrane is visible as a boundary between cells. The nucleus will be visible inside the cell, although it may not be in the “center” of every cell. Plant and animal cells have many organelles in common, including the nucleus, nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum, Golgi apparatus, ribosomes (free and attached), cell membrane and mitochondria.

Some organelles found in plant cells are not found in animal cells and vice versa. Centrioles, which help organize cell division in animal cells, do not occur in higher order plant cells. Vacuoles serve as sites for the storage of food molecules, breakdown of waste products and hydrolysis of macromolecules in plant cells. The enlargement of plant cell vacuoles is a major mechanism of plant growth.

Experiment Overview

Mrs. Kruse has a concussion and cannot remember how she wound up injured at the bottom of the stairs. A neighbor informed police that she saw Mrs. Kruse’s dog barking and chasing after a hopping object around the time in question. With the icy winter conditions it is possible that this incident was nothing more than an excited dog and icy stairs. In order to rule out foul play, however, evidence was collected from the scene. The purpose of this lab activity is to examine four unlabeled slides obtained from the staircase and front yard and to determine if the slides contain plant cells or animal cells.

Materials

Prelab Questions

Complete the Prelab Activity Worksheet before beginning this laboratory activity. Use a reference source, such as a textbook or the Internet, to review the types of cell structures in plant and animal cells.

Safety Precautions

This laboratory activity is considered nonhazardous. Follow all standard laboratory safety guidelines.

Procedure

1. You will be assigned to one of the compound microscopes set up throughout the classroom.
2. Each microscope is labeled U1–U4 and contains the corresponding unknown slide. Note: Microscopes with the same label contain the same unknown slide.
3. Focus the image on the slide using the 4X objective. Adjust the coarse and fine focus knobs as needed to clearly view the cells.
4. Once the image is focused, switch to the 10X objective. Adjust the coarse and fine focus knobs as necessary.
5. Switch to the 40X objective to view the smaller components of the cell and adjust the fine focus knob to view the image clearly.
6. After viewing with the 40X objective, continue with the oil immersion objective if available. Note: The fine focus knob should be used to clarify the image when the objectives are changed to 40X and 100X.
7. Record observations of each cell on the Plant and Animal Cells Mystery Worksheet. Be as specific as possible describing the shapes of cells and organelle, morphology, etc. Identify each cell as plant or animal based on the observations.
8. Return microscope to 4X objective, lower the microscope stage, and, if necessary, wipe clean all objective lenses and the prepared microscope slide using lens paper.
9. Rotate through the workstations as designated by your instructor (the slides may be viewed in any order). Repeat steps 1–7 with the three remaining workstations.

Student Worksheet PDF

10898_Student.pdf