Quiz Card Dissections
by Ernie Brown
Here’s a pdf version for download: Quiz Card Dissections
Do you hate to think about doing classroom dissections in biology because the students tend to get unruly? Does your room resemble a zoo more than a place where learning is taking place? Do you feel that your students really appreciate the inherent value of the life of the animal that they’re dissecting. Do they appreciate the fact that the animal they are dissecting died so that they might learn more about how it lived? Respect for life and learning more about how the organisms lived are important objectives for any dissection. Too often specimens are viewed simply as “pieces of meat” to glibly chop up and discard at the end of the class period. I have enjoyed great success with a “Quiz Card” approach to dissections for the last several years. I feel that the students learn the material better and appreciate the total functioning organism more completely when they have finished their dissection. The technique can be used with any textbook or lab handout that supplements your dissection activity.
While the students are reading the procedure for the dissection, make a list of all of the organs they are expected to locate and learn about on the chalkboard. Then, write the name of each organ on a separate 3 X 5 card and show the class your “deck of cards”. Have the students work in pairs, either determined by the teacher or by the students themselves. After the students have completed the dissection and are confident they know the location and functions of each of the listed organs on their own specimen, they sign up on the chalkboard indicating they are ready for their quiz over the material.
Beginning with the first pair of names on the list, take your 3 X 5 cards to their desk and “make a deal” with them for their quiz. I usually make the quiz worth 20 points total and have each student of the pair pull two cards (face down) from the deck. Each 5 point card identifies the organ that student must locate and discuss without help from his teammate. After the first student has completed his 10 point portion of the quiz, the second student then locates and discusses the two organs on the cards he has selected. Each member of the team receives the composite score from their individual quizzes.
You can vary this activity easily by making the quiz worth more or less than 20 points. You can let each pair of students make their own “deal” by picking any combination of cards/points that meet the total points for the quiz. Sometimes the students like to “go for broke” and pick one card for 10 points or pick five cards for two points each. When students realize that they are going to be required to locate and discuss specific organs in their specimen, they are much more diligent during the dissection. Procedures are read thoroughly and cuts are made carefully leaving organs in place as much as possible rather than being removed and piled on the dissecting tray.
It is the responsibility of each team to conduct the dissection and learn the organs by working together. Even if one member of the team doesn’t want to touch the specimen, he is still accountable for using a dissecting needle to point to the organs on his 3 X 5 cards. They can still be involved in the dissection by reading the procedure to the person actually conducting the dissection. By combining the individual quiz scores for a total team score, the students work together to teach each other much better since they each have an investment in the final quiz score.
Ernie Brown – Trego Community High School,Wakeeny, KS 67672
Clearing and Staining Small Vertebrates
By Ernie Brown
Here’s a pdf copy to download: Clearing and Staining Small Vertebrates
When teaching the skeletal system in anatomy class or comparing the structure of homologous organs, it is useful to be able to make comparisons between skeletal features of different vertebrate organisms. The bones to be studied can be carefully dissected away from the muscle tissue and then reassembled, requiring a great deal of teacher or student preparation time. By use of the clearing method, however, the entire skeleton can be studied in relation to the muscles, circulatory system, and other organ systems. After a little experience with the procedure, it is a simple matter to introduce modifications which will improve the quality of the preparations. At times, two specimens, treated in a similar manner, will respond differently.
Fresh specimens may be preserved in 10% formalin solution or 75% alcohol for a period of three to five days. Generally, specimens fixed in formalin are more easily controlled and require less watching. Formalin fixed tissues often require a longer time for the clearing process and the specimen may not clear as completely as alcohol fixed specimens. A little experimentation will provide the best results for the type of specimens you wish to clear.
Completely eviscerate the specimen if the skeletal system is to be demonstrated.
Place the specimen in 2% KOH (potassium hydroxide) or 2% NaOH (sodium hydroxide). This step will decolorize the tissue and make it jelly-like in consistency. Use the same clearing solution for both alcohol and formalin fixed specimens. You can control the rate of tissue maceration by adjusting the temperature of the KOH or the room temperature. As the pigments are dissolved out of the tissue, the solution may become discolored, in which case it should be changed as often as necessary.
Staining the skeleton begins after the flesh has become cleared and the bones are visible through the surrounding tissue. Alizarine red S is the dye recommended by most authors but others also have used indigo-carmine, Bordeaux red, alizarol black3G, and alizarine black SBB. Make a saturated stock solution of alizarine red S and add it to the 2% KOH solution to make it reddish in color. Cover the specimen with the dye solution and leave it to set.
The specimen will usually stain completely within two days but additional time may be required for larger specimens. After staining, the specimen is placed in clear 2% KOH solution and destained until the muscle tissue is again clear and the stain remains only in the bones. If the bones were not stained completely, repeat the staining process and clear as before.
When the specimen looks nearly transparent, place it in glycerine for storage. This will complete the clearing process. The change from 2% KOH to pure glycerine must be gradual for large specimens but is not important with smaller ones. A half and half mixture of pure glycerine and 1% KOH is recommended for those large specimens.
When clearing fish, the scales must be removed in order to see the skeleton. Scaling is best done after the fish has been stained since the scales will be red and easily visible. Some lizards must also be scaled. The scales may be easily removed by gentle scraping in a dish of water with a wire loop or other similar instrument. The hair of mammals and the feathers of birds may best be removed prior to staining.
• Davis, D. Dwight and V. R. Gore. Clearing and Staining Skeletons of Small Vertebrates. Chicago Nat. Hist. Mus. Technique Ser., 16p. 1947
• Evans, Howard E., Turtox News, Vol. 26, No.2, February 1948
• Mayorga, Horacio. A Rapid Method for Clearing and Staining Amphibian Skeletons Journal of The Ohio Herpetological Society, Volume 5, Number 1, May 1965