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Name:_____________________________________ Date:_________________________ FROG DISSECTION LAB MANUAL Prelab Discussion The common grassfrog, Rana pipiens, belong to the class Amphibia. Amphibians have adaptations for living in terrestrial as well as aquatic environments. Frogs are among the most commonly studied organisms in biology. Although many differences exist between humans and frogs, the basic body plans are similar. Humans and frogs both belong to the phylum Chordata. By studying the anatomy of a frog, you will be better able to understand your own body. In this investigation, you will examine the external features of a frog and identify parts of its external anatomy. In addition, you will dissect a preserved frog to observe its internal structure. Problem How is a frog structured for survival? Materials Apron (if desired) Dissecting pins Dissecting tray Forceps Gloves Hand lens Medicine dropper Paper towels Plastic bag Preserved frog Probe Scalpel Scissors Safety And Cleanup Wear gloves at all times. If you are allergic to latex, notify me immediately, before putting on gloves. Handle all instruments carefully. At end of lab, all instruments will be washed and dried thoroughly and placed back into the dissecting kit. The dissecting kits will be inspected for cleanliness and completion before and after each lab session. The lab bench will be washed and dried. If the frog will be used another day, wrap it in a wet paper towel and place it in a plastic bag with a label. If not, the frog will be discarded. Massachusetts State Frameworks: 4. Anatomy and Physiology Central Concepts: There is a relationship between the organization of cells into tissues and the organization of tissues into organs. The structures and functions of organs determine their relationships within body systems of an organism. Homeostasis allows the body to perform its normal functions. 4.1 4.2 4.3 4.4 Explain generally how the digestive system (mouth, pharynx, esophagus, stomach, small and large intestines, rectum) converts macromolecules from food into smaller molecules that can be used by cells for energy and for repair and growth. Explain how the circulatory system (heart, arteries, veins, capillaries, red blood cells) transports nutrients and oxygen to cells and removes cell wastes. Describe how the kidneys and the liver are closely associated with the circulatory system as they perform the excretory function of removing waste from the blood. Recognize that kidneys remove nitrogenous wastes, and the liver removes many toxic compounds from blood. Explain how the respiratory system (nose, pharynx, larynx, trachea, lungs, alveoli) provides exchange of oxygen and carbon dioxide. Explain how the nervous system (brain, spinal cord, sensory neurons, motor neurons) mediates communication among different parts of the body and mediates the body’s interactions with the environment. Identify the basic unit of the nervous system, the neuron, and explain generally how it works. 4.5 4.6 Explain how the muscular/skeletal system (skeletal, smooth and cardiac muscles, bones, cartilage, ligaments, tendons) works with other systems to support the body and allow for movement. Recognize that bones produce blood cells. Recognize that the sexual reproductive system allows organisms to produce offspring that receive half of their genetic information from their mother and half from their father, Procedure Part A – External Anatomy 1. Put on gloves and apron, if desired. 2. Obtain a dissecting kit. Obtain a dissecting tray and frog. Wash frog gently but thoroughly under running water to remove excess preservative. CAUTION: The preservative used on the frog can irritate your skin. Avoid touching your eyes while working with the frog. Dry the frog with paper towels and place it in a dissecting tray. 3. Identify the dorsal and ventral surfaces and the anterior and posterior ends of the frog. When you are ready to show that you have learned this section; call the teacher over to initial your demonstration of this. ________ dorsal __________ ventral __________ anterior __________ posterior 4. Locate the forelegs and hindlegs. Each foreleg, or arm, is divided into four regions: upper arm, forearm, wrist, and hand. Each hindleg also has four regions: thigh, lower leg, ankle, and foot. Identify the parts of the forelegs and hindlegs. Examine the hands and feet of the frog. If the hands have enlarged thumbs, the frog is a male. (check one) My frog is a _______________ male _________________ female 5. Locate the large, protruding eyes. Lift the outer eyelid using a probe. Beneath the outer lid is an inner lid called the nictating membrane. 6. Posterior to each eye is a circular region of tightly stretched skin. This region is the tympanic membrane, or eardrum. Locate the tympanic membranes on both sides of the head. __________ tympanic membrane 7. Anterior to the eyes, locate two openings called the external nares (singular, naris), or nostrils. ___________ external nares 8. Label the External Anatomy diagram. 9. Hold the frog firmly in the dissecting tray. Using scissors, make a small cut at each of the hinged points of the jaw, as shown below. CAUTION: To avoid injury, cut in a direction away from your hands and body. Open the mouth as much as possible. Under running water, rinse away any excess preservative if necessary. 10. The tongue is the most noticeable structure in the mouth. Observe where the tongue is attached and note the two projections at the free end. 11. At the back of the mouth, locate the large horizontal opening, the gullet opening. 12. Examine the roof of the mouth. Near the front center, are two small bumps, the vomerine teeth, and on either side of these, are the internal nares. The bulges behind the vomerine teeth are the eye sockets. Run your fingers along the top jaw. The teeth you feel are the maxillary teeth. The openings of the Eustachian tubes are on either side near the back of the mouth. Insert a probe into an opening of one Eustachian tube, and note where the probe stops. ________ internal nares __________ vomerine teeth __________ eustation tubes Part B - Internal Anatomy 1. Place frog on tray with ventral surface up (belly up). Securely pin the frog’s hands and feet to the bottom of the dissecting tray, as shown below. 2. With forceps, lift the loose skin of the abdomen. Carefully insert the tip of a pair of scissors beneath the skin. Cut away from your body. Cut along line AB as shown above. Continue cutting lines CD and EF. Be sure not to cut deeper than the skin. 3. With your fingers and the probe, separate the skin from the underlying muscles. Open the flaps of skin as far back as possible and pin them to the bottom of the dissecting tray. Note the muscles. 4. Carefully lift the abdominal muscles with the forceps. Cut a second AB incision. Keep the cut shallow so you don’t damage the underlying organs. You will need to cut through the pectoral bone (the rib cage of the frog). Then make second cuts of CD and EF. Open the abdomen as much as possible. You may need to re-pin. 5. Study the positions of the exposed organs. Most organs are held in place with a thin, tough membrane called mesentery. 6. If the frog is a mature female, the most obvious organs may be the ovaries, white sacs swollen with tiny black-and-white eggs. Carefully lift the ovaries and cut at the base of them to remove them. If they burst, the eggs will spill out in a big mess. ________ ovaries/eggs __________ no ovaries and eggs 7. The large reddish-brown organ in the upper part of the abdominal cavity is the liver. 8. With your fingers or a probe, lift and separate the lobes of a liver upward. Behind the middle lobe, look for a small greenish gland, the gallbladder. Cut out the liver and gallbladder, place it in your tray. The rest of the organs will be much easier to see with this cut out. ________ Liver __________ gallbladder DIGESTIVE SYSTEM 9. Locate the esophagus, which is a white tube leading from the mouth and connecting to the upper part of the white, muscular stomach. Notice the shape of the stomach. The stomach leads to the small intestine (long and coiled). Notice the mesentery that holds the intestines in place. Inside the first loop of the small intestine near the stomach, locate a thin, white organ called the pancreas (looks like a tongue with black spots on it – it makes insulin). Also in the intestinal mesentery, locate a brown bean-shaped organ called the spleen (makes blood cells, so it looks blue). 10. The small intestine ends in a large bag-shaped organ, the large intestine. The last organ of the digestive system is the cloaca, a saclike organ at the end of the large intestine. Undigested food leaves the frog’s body through an opening called the anus. Your teacher will, cut the esophagus near the stomach and then cut through the large intestine just above the cloaca. With his/her fingers, he/she will carefully remove the digestive system from the body and stretch out the digestive system so that you can measure it, and record this in the questions. 12. Open the stomach and examine its structure and contents. Dispose of the removed organs. Label the Digestive System diagram. ________ espohagus __________ stomach __________ small intestines __________ large intestines __________pancreas __________ spleen __________ anus Respiratory System 13. Locate the two lungs. They are small, spongy brown sacs that lie to the right and left of the heart. Look for the bronchial tubes that extend from the anterior part of the lungs and join with the trachea or windpipe. 14. Insert a dropper into the glottis of the frog. Pump air into the lungs and observe what happens. 15. With scissors and forceps, carefully remove the lungs from the frog’s body. Dispose of the lungs according to your teacher’s instructions. Circulatory System 16. Locate the heart. The heart is encased in a membranous sac called the pericardium. With the tip o f the scissors, carefully cut open the pericardium. 17. Note the vessel attached to the heart. The large artery on the ventral surface of the heart is the coronary artery. NOTE: If the frog has been injected with red and blue latex paint, the veins and arteries will be obvious. Urogential System 18. If your frog is a male, locate the testis; if your frog is a female; locate the ovaries. LAB PRACTICAL: Know each of the following EXTERNAL ANATOMY: Directional terms ______ anterior, ______ posterior ______hindlimb ______ foo, ______external nares ______ dorsal ______ ventral _______ hand ______ eye ______ tympanic membrane ______ nictating membrane. MOUTH: ______ internal nares ______ maxillary teeth ______openings to Eustacian tubes ______ tongue ______vomerine teeth ______ gullet opening DIGESTIVE: ______ esophagus ______ stomach ______ small intestine ______ liver ______ gallbladder______ pancreas ______ eye sockets ______ large intestine ______ anus UROGENITAL SYSTEM: (male): ______ kidney ______ fat body ______ urinary bladder ______ cloaca ______ trachea REFERENCE GUIDE ______ cloaca ______ testes (female): ______ kidney ______ fat body ______ urinary bladder ______ cloaca ______ ovary RESPIRATORY: ______ Lungs ______ forelimb ______ mouth QUESTIONS 1. Describe how the eyes of a frog close. 2. Describe how a frog jumps. 3. Are the hindlegs or forelegs more important in jumping? 4. Is the skin of the frog smooth or rough? Moist or dry? 5. Describe the color of the dorsal and ventral surfaces of the frog. 6. How many digits (fingers) are on each of the frog’s hands? 7. How many digits are on each of the frog’s feet? 8. Is your frog male or female? How can you tell? 9. Where is the nictating membrane attached? 10. Where is the tongue attached to the mouth? 11. How many lobes does the liver contain? 12. What is the shape of the stomach? 13. Describe the mesentery that holds the intestines. 14. Describe the general shape, or plan, of the frog’s digestive system. 15. How long (in centimeters) is the entire digestive system? 16. Describe the inside walls of the stomach. 17. Describe the contents of the frog’s stomach. 18. What happens when air is pumped into the lungs? 19. Describe the movement of the leg muscles as the leg is bent and straightened. ANALYSIS AND CONLCUSIONS 1. How are the feet of a frog adapted for swimming? 2. How is the coloration of the frog an adaptation to its habitat? 3. How is the location of the nares an adaptation to living in water? 4. How is the location of the nares and adaptation to living in water? 5. The tip of the tongue in a live frog is sticky. What would be an advantage of this? 6. Frogs are insect eaters. How is the frog’s tongue designed for the type of food it eats? 7. How does the length of the small intestine relate to its function in absorbing digested food? 8. List three adaptations that permit the frog to live on land successfully. a. b. c. 9. List three adaptations that permit the frog to live in water successfully. a. b. c.