FROG DISSECTION LAB 100 points possible Purpose: The purpose of this lab is to enhance lab performance skills, develop dissection techniques, and compare and contrast the digestive system of a frog to that of a human. Materials: 1 Preserved frog, 1 dissection tray, 1 goggles, dissection kit (scalpel, forceps, scissors, pins, probe), 2 pairs of gloves (nonlatex), apron/lab coat, paper towels, plastic bag, plastic container, microscope, microscope slide, 1 straw, ruler Procedures PART 1 EXTERNAL OBSERVATIONS 1. Clear desk then gather materials. Put on apron/lab coat, gloves, goggles. 2. Follow instructions on the Frog External Anatomy Sheet to make observations. PART 2 INITIAL DISSECTION (See images below) 3. Place the frog on dissection tray (with belly facing up). 4. Pin each of the four limbs on dissection tray. 5. Use the forceps to lift the skin midway between the rear legs of the frog. Then, using the scalpel, make a small cut through the lifted skin. 6. Now, using the scissors, continue the incision up the midline all the way to the frog s neck. Do not cut too deeply. When you reach the frog s neck, stop. 7. Using the scissors, make horizontal incisions through the skin between the front legs. Repeat for the rear legs. 8. Separate the skin flaps from the muscles below it. Pick up flaps of skin with forceps and use scalpel to help separate the skin from the muscle. Then pin skin flaps to the dissection tray. 9. Use the forceps to lift the muscle midway between the rear legs of the frog. 10. Use the scalpel to start the incision in the direction of the chin. Then, using the scissors, continue the incision up the midline all the way to the frog s neck. Do not cut too deeply. The muscle is thin and you don t want to damage any organs. 11. VERY IMPORTANT: When you reach the point just below the front legs, turn the scissor blades sideways to cut through the bones in the chest. This will prevent damage to the organs. 12. Using the scissors, make horizontal incisions through the muscle between the front legs the repeat for the back legs. 13. Open the abdominal area by pulling back the muscle flaps with the forceps then use the scalpel to separate the muscle from the tissue. 14. Once the muscle flaps have been separated, pin them back. 15. Use Frog Organ Sheet to observe, identify, and record the frog s internal organs. 16. Remove a microscopic piece of tissues from different organs to view under the microscope. Make observations and drawings. GO TO PART 3 (OPTIONAL) OR PART 4 FOR POST LAB 1
PART 3 ADVANCED DISSECTION (Optional) 17. Try inflating the lungs by putting a straw in the frog s Eustachian tube and blowing. Be careful. Make observations. 18. Take a microscopic piece of any tissue and view it under the microscope. Make observations and drawings. 19. Continue to part 4. PART 4 POST LAB 20. Clean-up: Place all parts of frog back in plastic bag. Wash and dry all equipment and instruments. Return all materials to proper place, clean table. Wash your hands. Trash gloves. 21. Post Lab Reflection Answer the questions on the Frog Dissection Reflection sheet 2
Frog External Anatomy Sheet 1. Observe the dorsal and ventral sides of the frog. Dorsal side color Ventral side color 2. Examine the hind legs. How many toes are present on each foot? Are the toes webbed? 3. Examine the forelegs. How many toes are present? Are the toes webbed? 4. Use a ruler to measure your frog, measure from the tip of the head to the end of the frog's backbone (do not include the legs in your measurement). Compare the length of your frog to other frogs Your Frog (cm) Frog 2 Frog 3Frog 4 Frog 5Average Length 5. Feel the frog's skin. Is it scaley or is it slimey? 6. Other observations: 3
Frog Organ Sheet Locate each of the organs below. Put a check in the circle for each organ you find. o Liver The large structure of the body cavity. This brown colored organ is composed of three parts, or lobes. o Heart - at the top of the liver, the heart is a triangular structure. o Lungs - Locate the lungs by looking underneath and behind the heart and liver. They are two spongy organs. o Gall bladder--lift the lobes of the liver, there will be a small green sac under the liver. o Stomach--Curving from underneath the liver is the stomach. The stomach is the first major site of chemical digestion. Follow the stomach to where it turns into the small intestine. o Small Intestine--Leading from the stomach. o Large Intestine--As you follow the small intestine down, it will widen into the large intestine. The large intestine is also known as the cloaca in the frog. o Spleen--Return to the folds of the mesentery, this dark red spherical object serves as a holding area for blood. o Esophagus--Return to the stomach and follow it upward, where it gets smaller is the beginning of the esophagus. STOP! If you have not located each of the organs above, do not continue on to the next sections! Removal of the Stomach: Cut the stomach out of the frog and open it up. You may find what remains of the frog's last meal in there. Look at the texture of the stomach on the inside. What did you find in the stomach? Measuring the Small intestine: Remove the small intestine from the body cavity and carefully separate the mesentery from it. Stretch the small intestine out and measure it. Now measure your frog. Record the measurements below in centimeters. Frog length: cm Intestine length cm Kidneys - flattened bean shaped organs located at the lower back of the frog, near the spine. They are often a dark color. The kidneys filter wastes from the blood. 4
Testes - in male frogs, these organs are located at the top of the kidneys, they are pale colored and roundish. Oviducts - Oviducts are where eggs are produced. Bladder - An empty sac located at the lowest part of the body cavity. The bladder stores urine. 5
FROG DISSECTION DIAGRAM Directions: Accurately draw, color, and label all organs observed. 6
Frog Dissection Lab Scoring Guide 50 points possible Team Name: Score: Name: Name: Name: Name: Grade of a C Satisfactory behavior/cooperation. Demonstrated adequate lab skills (mostly everyone preformed their own job to complete the lab). Followed written/verbal directions most of the time. Acceptable clean up. But can use improvement. Grade of a B Group consistently showed good behavior/cooperation. Followed written/verbal directions the majority of the time. Very good clean up. Grade of an A Excellent behavior/cooperation (ex: NEVER played around/always got along/helped others without asking, etc.) Followed all written/verbal directions at all times (does not ask teacher to repeat already given/printed instructions, proactive and takes initiative) Excellent clean up (ex: leaves desk spotless, resupplies materials for next class, etc). Group exceeded all expectations. Comments: 7
Frog Dissection Reflection 25 points possible Directions: Answer the following questions thoroughly and in complete sentences. 1. Why did you do a frog dissection? 2. What was your job during the frog dissection? 3. Describe in detail what it was like when the frog was being dissected. 4. What did you find surprising or interesting about the frog? 5. What did you specifically learn by doing the frog dissection? 6. Explain what you would do differently to have the lab be more successful. 8
FROG/HUMAN DIGESTIVE SYSTEM OBSERVATIONS 25 points possible Directions: As you complete the frog dissection, draw (in detail) the digestive system of both the human and the frog. Then write a summary comparing and contrasting the digestive system of both. Be thorough and clear. 9