Name: Class: Date: Why are we dissecting a frog? Frog Dissection Pre-Lab Frogs and humans are vertebrates and they have very similar organ systems. Although all of the internal organs are not exactly the same, it is helpful to learn about anatomy through dissection. We will be looking at each body system and exploring the individual organs of the frog. We will be making comparisons between the frog and yourself. Some individuals argue that dissecting a frog is cruel. Dissection would be a cruel practice if the frogs were mistreated. The frogs that we use in lab for our dissection were bred in Mexico for the sole purpose of scientific study. The companies use a very safe preservative to make the frogs as safe as possible. The frogs we will be using in class have been prepared for dissection- all blood has been drained from their bodies. We still need to wear gloves and wash our hands while working with the frogs. Computers can be used to simulate a dissection. This method is very popular with some students. I do not believe that the computer experience is anywhere near as valuable as the actual dissection. But, I do think that it is a good tool. We will be going through a Virtual Dissection to help prepare for our actual dissection. The frogs we use, gave their lives for science. They are Organ Donors who would like us to learn more about them (and ourselves). In order to best use this opportunity to learn and show respect for the frog, we must follow all instructions and safety procedures. But, For our safety, we will be wearing gloves and goggles during the dissection. Aprons will be available for students. EVERYBODY must wash their hands before they leave the room. Hair should be tied back. No gum chewing or eating at all. 1. Why are we doing a dissection? What is the purpose of the lab? 2. What will we be doing in the lab to stay safe? Characteristics of amphibians Because their eggs are not in a shell, they must develop in a wet environment. Most amphibians do not have scales. Their skin is thin, smooth, and moist. They do not drink water! Instead, they absorb it through their skin. This is a major reason why most amphibians prefer to live in damp environments (or near water). Amphibians can breath through their lungs or through their skin. Ecological Indicators Amphibians are often called ecological indicators. When large numbers of amphibians begin to die or show deformities, this may indicate a problem with the environment. Sometimes deformities are caused by other living organisms. They are good ecological indicator because their skin is responsible for gas and water exchanges- and thus they are extremely sensitive to changes in air and water quality.
3. Frogs are amphibians, and do not drink water. How do frogs get their water? 4. Why are amphibians considered to be a good ecological indicator? Virtual Frog Dissection http://www.mhhe.com/biosci/genbio/virtual_labs/bl_16/bl_16.html Below you will find questions organized by section. Use the website above help you answer. Introduction 5. Why Dissect. Why are frogs a good model to use when studying the digestive system (as well as other systems)? 6. Natural History. Frogs and humans are both vertebrates. What does this mean they both have? 7. Dissection Tools. What tools are needed for a frog dissection? Click on Menu on the bottom at the bottom of the page when you are ready to move on to the next section External Anatomy 8. Orientation. Is it possible to tell if a frog is male or female by external appearance? 9. Skin. What does the mucus do for the skin? 10. Head. Where are the tympanic membranes (eardrums)? Do frogs have a pinna? 11. Cloaca. What materials would pass through a cloaca. 12. Legs. How many hind leg toes does a frog have?
Click on Menu on the bottom at the bottom of the page when you are ready to move on to the next section Internal Anatomy 13. The Initial Cut. Are you suppose to push the pins in at an angle or straight down? What is the benefit of pushing the pins in this way? 14. The Initial Cut. Describe the first cut you will be making. Include where you will be cutting and how deep. 15. The Initial Cut. Why are there so many blood vessels in between the skin and muscle layers? 16. Digestive System. Which organ is the pancreas located closest to? 17. Digestive System. The movie asks you to remove the intestines. What other organ(s) is/are removed with the intestines when you click on the tweezers? 18. Respiratory System. What does the skin do in frogs that it does not do in humans? 19. Respiratory System. Where are the lungs located in a frog (relative to the heart)? 20. Circulatory (Cardiovascular) System. How many chambers does a frogs heart have? 21. Circulatory (Cardiovascular) System What is a frogs heart missing when compared to a humans (what chamber)? 22. Circulatory (Cardiovascular) System Why is the three chambered heart not as efficient as a four chambered heart?
23. Reproductive System. In your own words, describe where are the testes located? 24. Reproductive System In your own words, describe where are the ovaries located? 25. Excretory System. What happens to blood that enters the kidneys? 26. Excretory System What organ connects the kidneys to the (urinary) bladder? 27. Nervous System. This video is long, and parts without sound. Please watch patiently. What makes up a frogs nervous system? 28. Muscular System. The upper leg muscles in a frog are responsible for moving which part of the frog s body? 29. Skeletal System. How many bones are found in the axial region? 30. Skeletal System. How many bones are found in the appendicular?
Follow-up. After you are done with the website portion of this pre-lab, complete the following questions: 31. Sketch the pattern of where you should cut to make the first incision on your frog (cut thru the integument). Draw directly on the picture to the right. Feel free to visit these additional sites for virtual frog dissections. 1. http://frog.edschool.virginia.edu/ 2. Digital Videos webpage. This page has video of dissection of sheep brain, frog heart, and crayfish brain. *WARNING* These videos are of live frogs. If you feel this will disturb you, then do NOT watch. This site is totally optional. http://www.wellesley.edu/biology/concepts/html/digitalvideos.html 3. Frog Dissection Video. Long video, but great step-by-step for what to expect when dissecting a frog. No Audio. http://www1.teachertube.com/viewvideo.php?video_id=155411&title=frog_diss ection_instructions