Frog Dissection SNC2P Grade 10 Science Applied Biology Tissues, Organs and Systems of Living Things Purpose To identify and examine the external and internal structures of the frog and compare them with those of other vertebrates Background Knowledge and Laboratory Goals You should reference the lessons we have covered previously in the Tissues, Organs and Systems of Living Things unit, regarding specialized tissues and organ systems. Look for both similarities and differences between Human organ systems and Bullfrog organ systems. Think about the major functions and specializations of both species and why these similarities and differences may have evolved. Remember, because of the preservation process, the limbs of the specimen will be very stiff, the tissue will be fairly tight and the colours of the animal will be partially bleached out. Materials Dissecting tray Dissecting kit (scalpel, forceps, dissecting scissors) Pins Preserved frog specimen (Rana catesbeiana) Large and regular sized paper Pen Camera Lab Safety Be extremely cautious when using scalpels, as they are very sharp. Wash hands thoroughly after laboratory completion. Refrain from touching mouth and eyes during laboratory, as the formalin solution is a mutagenic. Discard of specimen remains in appropriate bin. Do not pour formalin solution down the sink. If you feel faint or ill at any time, take a break and step outside for some fresh air. ***At any point in time, you must have one person reading directions while one person is cutting. Other group members may be observing or referencing books and diagrams. These group members should also be taking photos at several stages throughout the dissection, to reference to later during the lab reflection. Everyone should have a chance to rotate jobs.*** ******DO NOT WORK AHEAD WITHOUT READING INSTRUCTIONS******
Procedure Part 1: Approximate time - 10 minutes 1. Obtain dissecting equipment and preserved frog specimen. 2. Wash the frog under running water to remove preservative 3. Examine the overall shape of the animal, the position of the eyes and legs. Measure and record the length of the forelegs and hind legs. Compare the legs in terms of the number and structure of the digits (fingers and toes) Make a side-by-side drawing of a fore limb and a hind limb to illustrate their characteristics. 4. Pry open the mouth. Use scissors to carefully cut through the angle of each side of the jaw to allow of easier inspection. 5. Check for the presence of teeth by running your finger along both the upper and lower jaws. Record the dental pattern in the frog s jaw. 6. Carefully examine the frogs tongue. Describe the tongue, noting its attachment and shape ------------------------------------------------------STOP!------------------------------------------------------ Do not proceed without having your work checked. Part 2: Approximate time - 10 minutes 7. Pin the animal to the dissecting pan ventral side (belly) up, as in Figure 1. Figure 1. Incision patter through skin and body wall. 8. Run your fingers across the animal s chest at the level of the fore limbs to locate the pectoral bones and sternum. In the centre of the abdominal region, pinch the skin with the forceps (tweezers) and lift upward. Cut through the fold with the scissors to make a small opening in the skin. 9. Use the scissors to make a series of cuts in the skin only, as illustrated (A-B, C-D, and E- F), in order to make two flaps of tissue.
10. Pin the rectangular tissue flaps to the side, and the triangular tissue flaps upwards near the eyes (See Figure 2). 11. Using the scissors to carefully make a series of cuts through the muscle wall as you did with the skin. Lift upwards as you cut to avoid damaging the organs underneath. 12. Pin back the muscle flaps as you did with the skin flaps. The abdominal cavity and organs should now be visible. 13. Depending on the sex of your frog and time of year it was obtained, two different structures may be visible. Large, yellowish masses of fat tissue may be seen. If the specimen is female and it is the proper time of year, two very large masses of eggs, one on either side of the abdomen, may be observed. If masses of eggs are seen (small black eggs enclosed in a thin-walled ovary), these must be carefully removed before proceeding. Remove some fat tissue (if applicable) and place on large paper provided. Label the tissue on the paper. Remove the eggs (if applicable) and place on your paper. Label these as eggs or ova. Figure 2. Skin and Muscle flaps pinned to tray, exposing abdominal cavity and organs. ------------------------------------------------------STOP!------------------------------------------------------ Do not proceed without having your work checked. Part 3 Digestive System: Approximate time - 15 minutes 14. The lobed liver covers the upper portion of the abdominal region (Figure 3). 15. If you lift up the liver, the pea sized gall bladder is visible. A bile duct joins the gall bladder to the small intestine. Record on which side of the liver the gall bladder is found. 16. Under the liver lies the stomach. It is widest where it leaves the esophagus (which you will not see at this stage). How would you determine the precise point at which the stomach ends? What special structure is found here? 17. The pancreas is not easy to identify. It lies in the space between the stomach and the small intestine. Its tissue is flat. Do not confuse the pancreas with the spleen. The spleen is a round, hard, dark-coloured organ.
18. The small intestine fills the lower part of the abdominal cavity. Locate this pathway from the stomach until it joins with the large intestine. Trace the large intestine as far as possible. 19. Use scissors to carefully cut through the top of the stomach to detach it from the esophagus. Cut through the connective tissue (called the mesentery) and remove the stomach, then the small intestine, then the large intestine, from the abdominal cavity. Cut through the large intestine as low in the abdominal cavity as possible. Be carefully not to damage other organs. Spread out the system on the large paper. Label each section of the system. What is the longest portion of the gut? What is the advantage of its length? 20. Separate the stomach from the intestine and cut it open lengthwise to examine inside. 21. Using scissors, remove the liver, gall bladder, pancreas, and spleen (previously identified) and place intro separate boxes on the large paper. Label each organ. Part 4 Cardio/Respiratory System: Approximate time 10 minutes 22. Locate the sternum (breast bone) along the midline of the frog, which covers the heart region. Open the anterior (thoracic) region of the frog s body by lifting the sternum with the forceps and cutting to the anterior with the scissors, to the base of the throat. The pectoral bones must also be cut through. Remove all the tissue in order to expose the heart and the lungs. 23. The lungs are usually found low and on either side of the thoracic cavity, the heart lying between them (Figure 4). Remove the lungs and place on your paper in order to label. 24. The heart is enclosed by a thin membrane called the pericardium. Be sure to take a photo at this stage to review later. Remove the heart and place on your paper in order to label. Observe the structure of the heart. How does this heart differ from what you learned in previous classes? Part 5 Excretory and Reproductive Systems: Approximate time 10 minutes 25. The pair of flat kidneys lie against the back of the body. A kidney duct (ureter) runs from each kidney to the cloaca. 26. The bilobed bladder also empties into the cloaca, above the base of the large intestine. 27. Male Specimen: The testes are a pair of distinct, yellow-white, oval bodies closely associated with the kidneys. Ducts from the testes enter the kidneys and allow sperm to pass into the kidney ducts, then into the cloaca. Fat bodies are usually attached to the testes. Female Specimen: If there was a mass of eggs in each ovary, you may have already removed them. If not, the ovaries are attached to the body wall slightly above and to the side of the kidneys. In breeding season, the ovaries fill with ova, small black and whitish bodies. The ova exit the body via the oviducts. The openings of the oviducts are found at the base of the lungs. The long, coated tubes then lead to the cloaca. Fat bodies are usually attached to the ovaries. Remove the kidneys and place on your paper in order to label. Remove the testes and place on your paper in order to label. If you have not done so already, remove the ovaries and place on your paper to label.
Figure 3. Digestive System. Figure 4. Cardio/Respiratory Systems. By the end of the lab, you should have on your display paper the following organs and tissues: - Stomach - Small Intestine - Large Intestine - Liver - Gall Bladder - Spleen - Pancreas - Lungs - Heart - Kidneys - Bone Tissue - Skin Tissue - Muscle Tissue - Fat tissue - Eggs (Ova) or Ovaries or Testes Have the teacher look at your final paper of organs and tissues. Be sure the write the names of all group members clearly on the paper so they will show up in the photo. Take a final photo of your display paper and specimen to submit with your written reflection. Lab Instructions adapted from R. Ritter et al, Biology: A Canadian Laboratory Manual, 1987.
Lab Reflection Following completion of the Bullfrog dissection, answer the following questions through your preferred method from the provided list. Approved Methods: - 1 page written reflection plus pictures, 12 pt font, Times New Roman - 10 minute presentation - Blog post on the class website, equating to 1 page - 10 minute video presentation posted to the class website Questions: - What were some things that surprised you during the dissection? - What were some major similarities between what we learned about human organ systems and tissues and what you observed in the frog? - What were some major differences between human organ systems and frog organ systems? - Why do you think these similarities and differences exist? Think about the major needs and functions of each species and why these species would have evolved in such a way. Be sure to add photos you took during your laboratory activity, including proper figure titles to explain what the photo is showing. Lab Reflection Rubric Formatting Completion Communication Reflection is the proper length and structure (page formatting, video formatting, blog style etc.) Adequately answered each given question fully. Reflection includes photos taken during the lab activity, using appropriate figure captions. Student uses proper vocabulary regarding anatomy and dissection terms. 0 1 2 3 0 1 2 3 4 5 0 1 2 3 0 1 2 3 4 5 Knowledge and Understanding Student refers to various organs and tissues observed during the lab throughout the reflection Student clearly expresses an understanding of the connections between human systems and frog systems, including both similarities and differences, as well as why those exist. 0 1 2 3 4 0 1 2 3 4 5 Total /25