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Dissection
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
Why Do Students Dissect Frogs?
BY KAITLYN BOETTCHER
There are many surgeons who say that they first discovered their life’s passion standing over a dissected frog
in a middle or high school biology class. But, apart from inspiring the medical professionals of tomorrow, what
is the purpose of dissection? And more importantly, why is everyone always dissecting those poor green
amphibians?
There are many reasons that students in biology classes are asked to perform dissections, and they have a lot
to do with understanding the body and the wider world. In dissecting an animal, students see, touch, and
explore the various organs in the body. Seeing these organs and understanding how they work within a
single animal allows students to understand how these systems work within many other animals, including
themselves. While there are various aspects that may differ between humans and other animals, many of the
organ systems in complex animals work in similar ways to those of humans.
One reason frogs are often chosen to be dissected is that their bodies provide a good overview of the organ
systems of a complex living thing. While the way their bodies work is nowhere near identical to a human’s,
there are many similarities. The organs present in a frog, and the way they are laid out in the body, are
similar enough to humans to provide insight for students about how their bodies work.
In addition to learning about themselves, students can learn about ecology and evolution through frog
dissection. Certain body structures and adaptations can be seen in frogs that illustrate how they evolved over
time and how they fill particular niches in the ecosystems they belong to. For example, the tongue of a frog
has adapted to have great length, strength, and speed in order to effectively catch insects in flight. The role
that this tongue allows the frog to fulfill—consuming insects as its primary food source—is important in the
balance of many ecosystems the frog is a part of.
There are practical advantages in using frogs, too. They're an appropriate size for dissection in the classroom
and make the process manageable for students and teachers. Also, frogs have a relatively short life span to
begin with, and while some species are rare in some places, others are abundant and are therefore prime
candidates for use in dissection. Bullfrogs, for example, are an invasive species in much of the United States.
While they naturally help to control insect populations, they are also threatening native populations of other
animals. This is especially the case when it comes to other frogs—bullfrogs are known to eat other frogs and
drive other frog species out of their natural habitats. Bullfrogs, while not the only frogs used for dissection, are
among the most common. The use of these frogs serves a dual purpose, controlling their populations and
providing a learning experience at the same time.
While it is true that many people, for many different reasons, oppose dissection in the classroom, and offer
alternatives like models or online options, dissection is still a valued educational tool thanks to its hands-on
nature. It is thought that if students see and feel these organ systems for themselves, they will take more out
of the lesson than if the teacher just lectured or assigned readings about it. Also, some teachers express the
hope that by learning about their own bodies through dissection, students will come to respect how their
bodies work, and think about how they treat them and what they put into them.
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All Name:_________________________________________ Study and Removal of the Frog's Brain Starting at the most anterior part of the head, the olfactory nerves connect to the nostrils and then to the olfactory lobes (A) where odors are processed. Just posterior to the olfactory lobes are two oval structurs, the cerebrum (B), and it is the frog's thinking center. Posterior to the cerebrum are the optic lobes (C), which function in vision. The ridge just behind the optic lobes is the cerebellum (D), it is used to coordinate the frog's muscles and maintain balance. Posterior to the cerebellum is the medulla oblongata (E) which connects the brain to the spinal cord (F). Brain Part Function Letter Cerebellum Cerebrum Olfactory Lobe Optic Lobe Medulla Oblongata Removal of the Frog's Brain: Turn the frog dorsal side up. Cut away the skin and flesh on the head from the nose to the base of the skull. With a scalpel, scrape the top of the skull until the bone is thin and flexible. Be sure to scrape AWAY from you, carefully chip away the roof of the skull to expose the brain. To receive extra credit for removing the brain, you must present it to me on a paper towel with all structures above visible.
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All FROG BONES The lower leg of the frog is a muscular leg that the frog uses for jumping. There are 3 main sets of bones in the lower leg. The femur is found in the upper thigh, and the tibiofibula is found in the lower part of the leg. The foot and ankle are made of the tarsals and metatarsals (toes). To expose the frog's leg bones you must remove the thigh muscle - the biceps femorus and the calf muscle - the gastrocnemius. You can leave the Achilles tendon intact (this tendon connects the muscle to the bone). The tarsals and metatarsals do not need to be exposed. To receive extra credit, clean your bones by removing the surrounding muscle. Bring the two bones on a paper towel. Good Luck! Label the leg bones: Femur, Tibiofibula, tarsals, metatarsals, pelvic girdle
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All PROCEDURE AND OBSERVATIONS: EXTERNAL ANATOMY
- Place the frog on its belly (ventral side) in the dissecting pan
- Examine the hind legs and front legs of the frog. The hind legs are strong and muscular and are used for jumping and swimming. The forelegs provide balance and cushion the frog when it lands after jumping. Notice the difference between the toes of the hind legs and those of the front legs. How many toes are on the front legs_______________. How many are on the hind legs__________________________. Label the hind and front legs on Figure 1.
- Locate the large, bulging eyes. The frog has 3 eyelids. The 2 outer ones are the color of the fog's body. They do not move. Locate the third eyelid. It is a transparent membrane the protects the eye while permitting the frog to see under water. It is call a NICTITATING MEMBRANE. Label the eye and the nictitating membrane on Figure 1.
- Behind each eye find the circular eardrum called a TYMPANUM. They locate the two openings into the nasal cavity. The nasal openings, are also call EXTERNAL NARES , found toward the tip of the snout will closes when the frog is under water. Label the mouth, tympanum, and the external nares on Figure 1.
- Feel the frog's skin. It is smooth, moist and thin. The frog can breathe directly through its skin as well as with its lungs. Turn the frog onto its ventral side and notice the color difference. Why does each sides color help protect the frog from predators? Coloration acts as camouflage
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All Figure 1. External Anatomy of the Frog: INTERNAL MOUTH STRUCTURES:
- Place the frog on its dorsal side in the dissecting pan and cut the corners of the mouth. CAUTION : Be careful when using scissors.
- Locate the TONGUE. Is it attached to the front or the back of the mouth?_____________Front___________ __________________________________________ _____In a live frog, the tongue is sticky and is used to catch insects. Pull on the tongue. Notice that it is still flexible.
- Feel the inside of the upper jaw ( maxilla ) and the lower jaw ( mandible ). The teeth you feel are the MAXILLARY TEETH. Locate the 2 VOMERINE TEETH on the upper jaw. They are located toward the front of the upper jaw and between the internal nares (internal nostril openings). What are the maxillary teeth and vomerine teeth used for? To hold onto prey
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All LOCATE and label THE FOLLOWING on Figure 2.
1. Vomarine Teeth : Used for holding prey 2. Internal Nares (nostrils ) breathing 3. Eustachian Tubes : equalize pressure in inner ear 4. Glottis : Tube leading to the lungs 5. Gullet: Opening leading to the esophagus 6. Tongue : Front attached, aids in grabbing prey 7. Tympanic Membrane : eardrum, located behind eyes 8. Nictitating Membrane: clear eyelid, protects the eye
- Maxillary Teeth : Used for holding prey
- Eye : vision Figure 2:
This material has been assembled together by Gulfside Art and Science Academy – GASA, but is not owned by GASA. All DISSECTING THE FROG:
- Place the frog on its dorsal side and secure it in place with dissecting pins through each of the legs.
- With your scissors make a cut ( through the skin only) along the midline of the belly from the pelvis to the throat.
- Now make transverse cuts through the skin below each of the fore limbs and above each of the hind legs. If needed you may pin the skin back. Notice the blood vessels under the skin. Why are there so many blood vessels? Closed- circulation, double-looped circulation, allows blood to reach all parts of the frog’s body
- Notice the abdominal muscles. Now cut through the muscle layer and repeat the incisions you mad in step 2 and 3. BE CAREFUL NOT TO CUT TO DEEP AND DAMAGE THE UNDERLYING ORGANS.
- You will have to cut through the sternum (breastbone). Open and re-pin the frog.
- If your frog is female, the body cavity maybe full of black eggs. You may have to remove one side in order to continue your dissection.
