Materials Included In Kit

Additional Materials Required

Safety Precautions

Wear chemical splash goggles. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information. Follow all normal student laboratory safety rules.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All solutions may be disposed of according to Flinn Suggested Disposal Method #26b. The other materials used in this activity may be saved or disposed of according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in two 50-minute class periods. The pre-laboratory assignment should be completed before coming to lab.
• A prepared animal cell and a prepared plant cell slide are included in this kit. Students may alternate and look at these slides or they may be shown to the students through a digital microscope or through a document camera if desired.
• There has been concern expressed about the classic activity in which students remove cheek cells from the inside of their mouths. The procedure described in this activity eliminates the potential dangers inherent in collecting cheek cells from the mouth. The cells secured from the wrist will be easy to find. Students are likely to be amazed at how easy it is to remove cells from the surface of the skin. The simple removal technique illustrates the fact that the skin is continually shed. Microbes and other organisms are shed along with the skin thus helping in the fight against microbe invasion.

Teacher Tips

• The tape used for this activity should be as sticky as possible and it must be clear—not opaque. Clear, box-sealing tape works well.

• Have students explore what happens when a plant is overwatered and cells expand to the point of bursting. Place stalks of rhubarb in a bowl of water and leave them there for at least a day. The ends of the stalk will split and curl showing that cells with too much water expand and burst open.
• Have students make their own models of plant and animal cells. Flinn Scientific’s CellGel™ works great for this type of activity.
• Have students hold hands and form a circle to represent a cell membrane. Have some students stand inside the cell mem¬brane and others outside the cell membrane. Designate different students as items such as water, oxygen, wastes and viruses. Discuss and have students that are able to pass through the cell membrane do so.
• Single-celled plants belong to the Kingdom Protista. Have students observe cell slides from the Kingdom Protista and discuss how they are similar and different than the cells of plants.
• Have students compare and contrast other prepared plant and animal cell slides. Discuss how cells from different parts of plants and animals compare.
• Have students replicate Robert Hooke’s original experiment using a piece of cork. Slice a very thin layer of cork and prepare a wet mount by placing the cork on a microscope slide containing a drop of water. Place a cover slip over the piece of cork and have students make observations using a low power objective on the microscope.

Sample Data

Answers to Questions

1. Define the following terms. List whether or not these structures are found plants, animals or both.

Cytoplasm—The portion of the cell outside of the nucleus. Both.
Nucleus—The control center of the cell that contains nearly all of the cell’s DNA. Both.
Ribosomes—Small particles of RNA and protein found in the cytoplasm of the cell that are responsible for making protein. Both.
Endoplasmic reticulum—The site where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell. Both.
Golgi apparatus—Modifies, sorts and packages proteins and other materials for storage in the cell or for export out of the cell. Both.
Lysosomes—Digest lipids, carbohydrates and proteins into small molecules that can easily be used by the cell. Both.
Vacuoles—Saclike structures that store materials, such as water, proteins, salts and carbohydrates. Found in both, mostly plants.
Mitochondria—Organelles that convert the chemical energy that is stored in food into compounds that are more convenient for the cell to use. Both.
Chloroplasts—Structures found in plants that capture energy from the sun and convert it into chemical energy. Plants.
Cytoskeleton—Made up of protein filaments and is also involved in movement of the cell. Both.
Centrioles—Help to organize cell division. Animals.
Cell membrane—Regulates what enters and leaves the cell and also provides protection and support. Both.
Lipid bilayer—Gives cell membranes a flexible structure and forms a barrier between the cell and its outside surroundings. Both.
Cell wall—Provides support and protection for the cell. Plants.

2. What are the main differences between plant and animal cells?

Plant cells have cell walls, chloroplasts and large vacuoles. Animal cells lack cell walls and have centrioles. Plant cells are usually square and animal cells are more rounded.

3. What structures were able to be seen on the onion slide? What about the skin cell slide?

Answers will vary.

4. Why was stain added to the onion slice and skin cells?

Methylene blue stain was added to the cells so they could be more easily viewed.

5. What structures of the cells were stained the darkest?

Answers will vary. The nucleus should be darkly stained.

Introduction

Are animal cells actually different than plant cells? If so, how? In this activity, the various parts of animal and plant cells will be identified, labeled, compared and contrasted.

Concepts

• Plant cells

• Animal cells
• Cell structures

Background

The story of cells begins over 300 years ago with a Dutch naturalist named Antonie van Leeuwenhoek. Using a magnifying glass and primitive custom-made microscopes, Leeuwenhoek was the first to see single-celled life forms in blood and pond water. He called these organisms “antimacules.” Five years later an Englishman named Robert Hooke sliced a piece of cork and examined it under a microscope. He saw small empty spaces which he named cells or “small rooms.” It was not until 1839 that two German Scientists named Matthias Schleiden and Theodor Schwann determined that the cells that Robert Hooke and Antonie van Leeuwenhoek observed so many years before were the basic units of virtually all life forms.

Cells are divided into two distinct regions—the nucleus and the cytoplasm. The cytoplasm is a clear gel-like material found in the portion of the cell outside the nucleus. The nucleus is the control center of the cell and contains nearly all of the cell’s DNA. The nucleus is surrounded by a nuclear envelope. The nuclear envelope is composed of two membranes and contains thousands of nuclear pores that allow materials to move in and out of the nucleus. The nucleus also holds chromosomes (through which genetic information is passed from generation to generation) and the nucleolus. The nucleolus is the small dense region of the nucleus where the assembly of ribosomes begins.

Ribosomes are small particles of RNA and protein found in the cytoplasm of the cell that are responsible for making proteins. Cells that are active in protein synthesis are usually packed with ribosomes.

Endoplasmic reticulum, ER for short, is the site where lipid components of the cell membrane are assembled along with pro¬teins and other materials that are exported from the cell. The rough portion of the endoplasmic reticulum (rough ER) is involved in the synthesis of proteins. It is given the name rough ER due to the ribosomes that are found on its surface. A cell also contains smooth ER. Smooth ER lacks ribosomes and contains specialized enzymes that synthesize membrane lipids and detoxify drugs. Large amounts of smooth ER are found in liver cells.

Proteins produced in the rough ER move into a structure known as a Golgi apparatus. The Golgi apparatus modifies, sorts and packages proteins and other materials for storage in the cell or for export out of the cell. Lysosomes are small organelles filled with enzymes. They digest lipids, carbohydrates and proteins into small molecules that can easily be used by the cell.

Vacuoles are saclike structures that store materials, such as water, proteins, salts and carbohydrates. In many plant cells, there is a large vacuole filled with water that makes it possible to support heavy structures such as stems, leaves and flowers.

Mitochondria are organelles that convert the chemical energy that is stored in food into compounds that are more convenient for the cell to use. Mitochondria are enclosed by two membranes—an outer membrane and an inner membrane. The inner membrane is folded up in the mitochondria providing greater surface area for cellular respiration to occur.

Chloroplasts are structures found in plants that capture energy from the sun and convert it into chemical energy. This process is known as photosynthesis. Chloroplasts can be thought of as small solar power plants in the cell. Like mitochondria, chloroplasts are surrounded by two membranes. Inside the chloroplasts are large stacks of other membranes which contain the green pigment chlorophyll.

The components of the cell that helps support and maintain the structure of the cell are known as the cytoskeleton. The cytoskeleton is made up of protein filaments and is also involved in movement of the cell. Microfilaments and microtubules are the two main protein filaments that make up the cytoskeleton. Microfilaments are threadlike strands of protein that provide a tough, flexible, frame in the cell. Microtubules are hollow protein structures that are found only in animal cells that help maintain the cell’s shape and are used to form centrioles. Centrioles are located near the nucleus and help to organize cell division. The cell membrane of the cell regulates what enters and leaves the cell and also provides protection and support. The cell membrane is made up of a double layered sheet called a lipid bilayer. The lipid bilayer gives cell membranes a flexible structure and forms a barrier between the cell and its outside surroundings.

Cell walls are found in plants and lie outside of the cell membrane. The cell wall is porous enough to allow oxygen, water and carbon dioxide to pass through the cell. The main function of the cell wall is to provide support and protection for the cell. The cell wall of a plant remains intact even after a plant has died.

Experiment Overview

In this activity, the various parts of animal and plant cells will be explored, labeled, compared and contrasted.

Materials

Prelab Questions

1. Obtain the Exploring Plant and Animal Cells Worksheet.
2. Use the information from the background of this write-up and your textbook to label the structures in both the plant cell and the animal cell.
3. The second half of the Exploring Plant and Animal Cells Worksheet will be used in the procedure.

Safety Precautions

Wear chemical splash goggles. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all normal classroom guidelines.

Procedure

I. Plant Cell Observation

1. Obtain a piece of a raw onion.
2. Using a scalpel, slice the onion into rings that are about 6 mm thick.
3. Obtain a microscope slide.
4. Using a disposable pipet, place one drop of water on the middle of the slide.
5. Using forceps or your fingernail, remove the inner transparent membrane from the onion slice and place it on the drop of water on the slide.
6. Using a disposable pipet, place 2 or 3 drops of 1% methylene blue solution on the onion slice.
7. Use a dissecting needle to gently place a cover slip over the onion slice. Lower the cover slip down onto the onion cell and then remove the dissecting needle. This should help prevent staining your fingers. Caution: Use methylene blue carefully. It will stain most items including skin, clothing and tabletops.
8. Examine the slide under a microscope. Look for cells with lower power first and then switch to high power for more detail.
9. Record your observations of the onion cells by making drawings on Exploring Plant and Animal Cells Worksheet. Use your knowledge of the size of the microscopic field to estimate the size of the cells.

II. Animal Cell Observation

1. Wash the underside of a wrist that will be sampled for epidermal cells with soap and water.
2. Stick a clean piece of clear tape on the underside of the washed wrist.
3. Gently remove the piece of tape from the wrist being careful to avoid getting fingerprints on the tape. Forceps might help to remove the tape and avoid fingerprinting the tape.
4. Place the tape, sticky-side up, on a clean microscope slide.
5. Stain the top, sticky side of the tape with 2 or 3 drops of 1% methylene blue solution.
6. Use a dissecting needle to gently place a cover slip over the sticky tape. Lower the coverslip down onto the tape and then remove the dissecting needle. This should help prevent staining your fingers. Caution: Use methylene blue carefully. It will stain most items including skin, clothing and tabletops.
7. Examine the slide under a microscope. Look for cells with low power first, and then switch to high power for details.
8. Record your observations of epidermal cells by making drawings. Label your drawings with appropriate magnifications. Use your knowledge of the size of the microscopic field to estimate the size of the cells.
9. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10751_Student1.pdf