Exercise 2 - Diversity of Cell Types

Students observe prokaryotic and eukaryotic cells. Both living material and prepared slides should be available. Students will observe basic plant and animal tissue types and use simple staining methods.

EQUIPMENT	AMOUNT (Class of 24 with 8 groups)
Compound microscopes with oil immersion objectives, if possible	1/student
Microtome	Demonstration

MATERIALS

SOLUTIONS

PREPARATION

1. Supplies should be checked and replaced where needed. Purchase onions and yogurt and collect fresh and dry materials. Protozoa and blue-green algae cultures should arrive the day before lab. Keep algae in continuous, strong, but cool light.

2. Dye preparation:

   Neutral red

   0.5 g dye/100 ml distilled water

   Mix dye with water and store in several dropper bottles. Shelf life: one year

   1% methylene blue

   1 g dye/99 ml distilled water

   Add dye to water and mix well. Shelf life: one year
   This dye is optional and can be available for students to experiment.

3. IKI preparation:
   2.5 g I₂
   5 g KI
   50 ml distilled water

   Store in dropper bottles wrapped in aluminum foil. Shelf life: one month

1. Make a mixed culture by adding equal portions of the blue-green algae cultures to a large test tube. Set the tube in a rack with an empty tube next to it. For dispensing the culture, a Pasteur pipette should be placed in the empty tube with instructions to use only a small drop when making a slide.

2. Mix yogurt and water in a 1:3 proportion. Place in test tube. Use Pasteur pipette to dispense.

NOTES

CLASSROOM SUGGESTIONS

1. The time spent on this exercise can be decreased by viewing fewer specimens or increased by requiring drawings of all specimens.

2. A microtome can be set up for demonstration. Students can turn handle to get sections of approximately 10 micrometers. With an artists' paintbrush, students can then try removing sections of wax block, either singly or in a strip of four or five slices. If a flat bowl or pan of water is provided, they can transfer the slice(s) to the surface of the water and see how thin the slice(s) is. Usually embedded specimens can be obtained from plant or animal anatomists on the staff. Warn students about sharp blade.

3. Supply houses and audiovisual companies have good slides (35 mm) and films on structure of cells, types of bacterial cells, and comparison of plant and animal tissue. These audiovisuals can be used at the end of the laboratory to summarize the exercise.

4. A minimum homework assignment would be to hand in tables identifying structures in an electron micrograph.

5. Students can share prepared microscope slides, reducing the cost of offering this exercise.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. The prokaryotic cells and the eukaryotic organelles were similar in size. They are both membrane bound. The green color of the cyanobacteria and the green color of the chloroplast organelle is due to the presence of chlorophyll pigments.

2. Bone - matrix composed of mineral salts, primarily calcium carbonate and calcium phosphate, and collagen fibers.
   Cartilage - matrix composed of a dense network of collagenous fibers and elastic fibers embedded in a jelly-like substance (chondroitin sulphate).
   Loose connective tissue - matrix consists of collagenous, elastic and reticular fibers embedded in a semi-liquid intercellular substance.
   Blood - is considered a connective tissue as it consists of three cell lines suspended in a liquid matrix called plasma.
   Muscle - is not considered a connective tissue as an extracellular matrix is not a feature of this tissue. Its "connective" function is only as pertains to its attachment and insertion on bones.

3. The Papanicolaou stain (Pap smear) is used to detect cervical cancer. Tuberculosis is diagnosed using an acid-fast stain. Gonorrhea is diagnosed by the presence of intracellular, gram-negative diplo-cocci. Blood abnormalities, such as leukemias, can be detected by staining a blood smear with Wright's stain.

4. When the depth of field was restricted to the top of the chair, you would see only the back. When at the middle of the chair, you would see the end of the back, the start of the legs, and the seat. When at the bottom of the chair, you would see only the legs ending in the feet.

SUPPLEMENTAL MATERIALS

Cell Structure and Function, 25-minute video filmstrip. West Los Angeles, CA: Science Software Systems, Inc. #405-007

Introduction to the Bacteria, audio slide set. Burlington, NC: REX Educational Resources Company. #K3010

Kodachrome slides of various tissues can be ordered from Carolina Biological Supply.