Frog Dissection
Purpose
To observe the external and internal structures of a frog (amphibian).
Materials
Dissecting kit
Frog specimen
Dissecting tray
Frog specimen
Dissecting tray
Method
1. Place a frog on a dissection tray. To determine the frog's sex, look at the hand digits on its forelegs. A male frog usually has thick pads on its thumbs, which is one external difference between the sexes. Male frogs are also usually smaller than female frogs. Observe several frogs to see the difference between female and males.
2. Locate and identify the external features of the head. Find the mouth, external nars, tympani, and nictitating membranes.
3. Turn the frog on its back and pin down the legs. Cut the hinges of the mouth and open it. Locate and identify the structures inside the mouth. Use a probe to find the vomerine and maxillary teeth, internal nares, tongue, openings to the Eustachian tubes, esophagus, pharynx, and the slit-like glottis.
4. Look for the frog's cloaca, located between the hind legs. Use forceps to lift the skin and use scissors to cut along the cenre of the body from the cloaca to the lip. Turn back the skin, cut towards the side at each leg, and pin the skin back.
5. Lift and cut through the muscles and breast bone to open the body cavity. If your frog is a female, the abdominal cavity may be filled with dark-colored eggs. If so, remove the eggs on one side to see the organs underneath.
6. Locate and identify the organs of the digestive system: esophagus, stomach, small intestine, large intestine, cloaca, liver, gallbladder, and pancreas.
7. Identify parts of the circulatory and respiratory systems that are in the chest cavity. Find the left atrium, right atrium, and ventricle of the heart. Find an artery attatched to the heart and another near the backbone. Find a vein near one of the shoulders. Find the two lungs.
8. Use a probe and scissors to lift and remove the intestines and liver. Identify the parts of the urinary and reproductive systems. Remove the peritoneal membrane, which is connective tissue that lies on top of the red kidneys. Observe the yellow fat bodies attatched to the kidneys. Find the uterers, urinary bladder, testes, and sperm ducts if its a male; ovaries, ovaducts, and uteri if it is female.
9. Remove the kidneys and look for threadlike spinal nerves that extend from the spinal cord. Dissect a thigh and trace one nerve into the leg muscle. Note the size and texture of the leg muscles.
10. Dispose of the materials according to the directions from your teacher.
Analysis
1. Q: What is the function of the nictitating membrane?
A: To protect the eye and keep it moist while the frog can still see, instead of blinking like a human.
2. Q: A frog does not chew its food. What do the positions of its teeth suggest about how the frog uses them?
A: The frog uses the volmerine teeth to stab and secure its prey, while its maxillary teeth are used to crush the food before swallowing.
3. Q: Trace the path of food through the digestive tract.
A: The frog catches its food using its tongue. The food is pulled into the mouth, where it is crushed into smaller bits by the maxillary teeth and swallowed by the pharynx. The food travels down the esophagus to the stomach, where stomach acids digest the food. The food then enters into the small intestine, where the nutrients are absorbed into the bloodstream. The remaining food enters the large intesting, and travels to the cloaca, where wastes exit the body.
4. Q: Trace the path of blood through the circulatory system, starting at the right atrium.
A: Deoxygenated blood from the body enters into the right atrium. This blood mixes with oxygenated blood from the left atrium in the ventricle. This semi-oxygenated blood is sent out of the hearth through the main artery. The blood then either go to the lungs to gain more oxygen or throughout the body to the muscles.
5. Q: Trace the path of air through the respiratory system.
A: Air enters the frogs body in two ways. Firstly, air enters through the nasal cavities and travels into the lungs via the glottis in the mouth, travelling down the trachea. Air also enters through cuticles in the frogs skin where it is directly absorbed into the bloodstream.
6. Q: Trace the path of sperm in a male and eggs in a female.
A: A male frog has two testes, which are attached to its kidneys. Sperm travels through the kidneys into the ureters. Sperm is released directly through the cloaca onto the eggs of the female. In the female, the ovaries are located directly beside the kidneys. Eggs pass down through the pair of ovaducts and out of the cloaca.
7. Q: Trace the path of urine in both sexes.
A: Liquid wastes travel through the kidneys, where water is filtered from the wastes, and the water is sent back into the body. The waste travels down the ureters from the kidneys to the urinary bladder, where it is kept until it can exit through the cloaca.
8. Q: Which parts of the frog's nervous system can be observed in the abdominal cavity and hind leg?
A: The spinal nerves, which branch off of the spinal cord.
9. Q: Suppose in a living frog the spinal nerves extending to the leg muscles were cut. What ability would the frog lose? Why?
A: Since the frog uses the nerves to control its muscles, cutting the nerve would make the frog unable to move its leg at all, and anything after the cut.
10. Q: The abdominal cavity of a frog at the end of hibernation season would contain very small fat bodies or none at all. What are the functions of these?
A: The fat bodies act as insulation for the organs of the frog, especially for the reproductive organs. Since frogs aren't reproducing during their hibernation, they do not need the fat to insulate their gametophytes, they can instead use it to sustain themselves.
11. Q: Structures in an animals body that help it survive are called adaptations. How do the frogs powerful hind legs help it survive in water and on land?
A: In water, the webbed hind legs help the frogs swim faster to hunt and escape predators. On land, the legs allow the frog to hop very large distances. This can allow the frog to hop over large obstacles in its path. It also helps it to hunt by quickly surprising its prey, as well as to quickly escape predators.
12. Q: During one mating, the female lays between 2,000 and 3,000 eggs in water and the male sheds millions of sperm over them. How do these large numbers relate to the frogs ability to survive in water?
A: The large numbers of eggs and sperm means that there is almost a guarantee of fertilization, and with so many tadpoles, at least a few are bound to reach adulthood.
A: To protect the eye and keep it moist while the frog can still see, instead of blinking like a human.
2. Q: A frog does not chew its food. What do the positions of its teeth suggest about how the frog uses them?
A: The frog uses the volmerine teeth to stab and secure its prey, while its maxillary teeth are used to crush the food before swallowing.
3. Q: Trace the path of food through the digestive tract.
A: The frog catches its food using its tongue. The food is pulled into the mouth, where it is crushed into smaller bits by the maxillary teeth and swallowed by the pharynx. The food travels down the esophagus to the stomach, where stomach acids digest the food. The food then enters into the small intestine, where the nutrients are absorbed into the bloodstream. The remaining food enters the large intesting, and travels to the cloaca, where wastes exit the body.
4. Q: Trace the path of blood through the circulatory system, starting at the right atrium.
A: Deoxygenated blood from the body enters into the right atrium. This blood mixes with oxygenated blood from the left atrium in the ventricle. This semi-oxygenated blood is sent out of the hearth through the main artery. The blood then either go to the lungs to gain more oxygen or throughout the body to the muscles.
5. Q: Trace the path of air through the respiratory system.
A: Air enters the frogs body in two ways. Firstly, air enters through the nasal cavities and travels into the lungs via the glottis in the mouth, travelling down the trachea. Air also enters through cuticles in the frogs skin where it is directly absorbed into the bloodstream.
6. Q: Trace the path of sperm in a male and eggs in a female.
A: A male frog has two testes, which are attached to its kidneys. Sperm travels through the kidneys into the ureters. Sperm is released directly through the cloaca onto the eggs of the female. In the female, the ovaries are located directly beside the kidneys. Eggs pass down through the pair of ovaducts and out of the cloaca.
7. Q: Trace the path of urine in both sexes.
A: Liquid wastes travel through the kidneys, where water is filtered from the wastes, and the water is sent back into the body. The waste travels down the ureters from the kidneys to the urinary bladder, where it is kept until it can exit through the cloaca.
8. Q: Which parts of the frog's nervous system can be observed in the abdominal cavity and hind leg?
A: The spinal nerves, which branch off of the spinal cord.
9. Q: Suppose in a living frog the spinal nerves extending to the leg muscles were cut. What ability would the frog lose? Why?
A: Since the frog uses the nerves to control its muscles, cutting the nerve would make the frog unable to move its leg at all, and anything after the cut.
10. Q: The abdominal cavity of a frog at the end of hibernation season would contain very small fat bodies or none at all. What are the functions of these?
A: The fat bodies act as insulation for the organs of the frog, especially for the reproductive organs. Since frogs aren't reproducing during their hibernation, they do not need the fat to insulate their gametophytes, they can instead use it to sustain themselves.
11. Q: Structures in an animals body that help it survive are called adaptations. How do the frogs powerful hind legs help it survive in water and on land?
A: In water, the webbed hind legs help the frogs swim faster to hunt and escape predators. On land, the legs allow the frog to hop very large distances. This can allow the frog to hop over large obstacles in its path. It also helps it to hunt by quickly surprising its prey, as well as to quickly escape predators.
12. Q: During one mating, the female lays between 2,000 and 3,000 eggs in water and the male sheds millions of sperm over them. How do these large numbers relate to the frogs ability to survive in water?
A: The large numbers of eggs and sperm means that there is almost a guarantee of fertilization, and with so many tadpoles, at least a few are bound to reach adulthood.