SOURCE Lesson Plans Detail

Frog Dissection

Topic Anatomy
Program Brown Science Prep
Developed by Elizabeth Pon, Hunter Tabloff
Developer Type Brown students

Follow up


Supporting Web Information


(see above web information)

Pre Assessment Plan

quiz on frog anatomy

Post Assessment Plan

"practice test" from above assessment quizzes website

Overview / Purpose / Essential Questions

Purpose: introduce students to animal dissections and observe and learn about the major organ systems in the frog

Performance / Lesson Objective(s)

(see purpose)

Lesson Materials

preserved frog specimens

dissection instruments and trays
safety glasses

Lesson Motivation

Dissecting animals permits insight into general physiological characteristics, which enhances understanding of the human system.  These insights are relevant to students interested in systems biology, anatomy, physiology, and medicine.

Lesson Activities



External Anatomy

1. Observe the dorsal and ventral sides of the frog.

            Dorsal color:

            Ventral color:

2. Examine the hind legs.

            # of toes on each foot?

            Are toes webbed?

3. Examine the forelegs.

            # of toes on each foot?

            Are toes webbed?

4. Use a ruler to measure your frog, from tip of the head to the end of the frog’s backbone (do not include legs in measurement). Compare length to that of other frogs.

5. Locate the frog’s eyes. The nictitating membrane is a clear membrane that is attached to the bottom of the eye. Use tweezers to carefully remove the membrane. You may also remove the eyeball.

            Color of nictitating membrane?

            Color of the eyeball?

6. Just behind the eyes on the frog’s head is a circular structure called the tympanic membrane, which is used for hearing. Measure the diameter of the membrane.

            Diameter (cm):

7. Feel the frog’s skin.

            Is it scaley or slimey?

Anatomy of the Frog’s Mouth

1. Pry the frog’s mouth open & use scissors to cut the angles of the frog’s jaws open. Cut deeply enough so that the frog’s mouth opens wide enough to view the structures inside.

2. Locate the tongue. Move it around. You may remove it.

            Does it attach to the front or the back of the mouth?

3. In the center, back of the mouth is a single round opening. This is the esophagus. Use a probe (or blunt end of tweezers) to poke into the esophagus.

            To where does the esophagus lead?

4. Close to the angles of the jaw are two openings, one on each side. These are the Eustachian tubes, which the frog uses to equalize pressure in the inner ear while it is swimming. Insert a probe into the tube.

            To what structure does the Eustachian tube attach?

5. Just behind the tongue, before the esophagus, is a slit-like opening. (You may need to use a probe to open it up). This slit is the glottis, and it is the opening to the lungs. The frog breathes and vocalizes with the glottis.

            How does it compare to the esophagus?

6. The frog has two sets of teeth. The vomarine teeth are found on the roof of the mouth. The maxillary teeth are found around the edge of the mouth. Both are used for holding prey; frogs swallow their meals whole & do not chew.

            Run your finger over both sets of teeth & note the differences between them.

7. On the roof of the mouth, you will two tiny openings of the nostrils. Put your probe in these.

            To where does the nostril lead?

Internal Anatomy/Dissection

Dissection Instructions

1. Place the frog in the dissecting pan ventral side up.

2. Use scissors to life the abdominal muscles away from the body cavity. Cut along the midline of the body from the pelvic to the pectoral girdle.

3. Make transverse (horizontal) cuts near the arms and legs.

4. Lift the flaps of the body wall and pin back.

*If your specimen is a female, the body may be filled with eggs and an enlarged ovary. You may need to remove these eggs to view the organs.

Locate each of the organs below. Check the box to indicate that you found the organs.

1. Fat Bodies - Spaghetti shaped structures that have a bright orange or yellow color, if you have a particularly fat frog, these fat bodies may need to be removed to see the other structures. Usually they are located just on the inside of the abdominal wall.

2. Peritoneum - A spider web-like membrane that covers many of the organs. You may have to carefully pick it off to get a clear view.

3. Liver - The largest structure of the the body cavity.  This brown colored organ is composed of three parts, or lobes.  The right lobe, the left anterior lobe, and the left posterior lobe.  The liver is not primarily an organ of digestion, it does secrete a digestive juice called bile.  Bile is needed for the proper digestion of fats.

4. Heart - at the top of the liver, the heart is a triangular structure. The left and right atrium can be found at the top of the heart. A single ventricle located at the bottom of the heart. The large vessel extending out from the heart is the conus arteriosis.

5. Lungs - Locate the lungs by looking underneath and behind the heart and liver. They are two spongy organs.

6. Gall Bladder - Lift the lobes of the liver, there will be a small green sac under the liver.  This is the gall bladder, which stores bile. (hint: it kind of looks like a booger)

7. Stomach - Curving from underneath the liver is the stomach.  The stomach is the first major site of chemical digestion.  Frogs swallow their meals whole.   Follow the stomach to where it turns into the small intestine.  The pyloric sphincter valve regulates the exit of digested food from the stomach to the small intestine.

8. Small Intestine - Leading from the stomach.  The first straight portion of the small intestine is called the duodenum, the curled portion is the ileum.  The ileum is held together by a membrane called the mesentery.  Note the blood vessels running through the mesentery, they will carry absorbed nutrients away from the intestine.  Absorption of digested nutrients occurs in the small intestine.

9. 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.  The cloaca is the last stop before wastes, sperm, or urine exit the frog's body.  (The word cloaca means sewer)

10. Spleen - Return to the folds of the mesentery, this dark red spherical object serves as a holding area for blood.

11. Esophagus - Return to the stomach and follow it upward, where it gets smaller is the beginning of the esophagus.  The esophagus is the tube that leads from the frogs mouth to the stomach.  Open the frogs mouth and find the esophagus, poke your probe into it and see where it leads.

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

Urogenital System

The frog's reproductive and excretory system is combined into one system called the urogenital system. You will need to know the structures for both the male and female frog

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. Often the top of the kidneys have yellowish stringy fat bodies attached.

Testes - in male frogs, these organs are located at the top of the kidneys, they are pale colored and roundish.

Oviducts - females do not have testes, though you may see a curly-q type structure around the outside of the kidney, these are the oviducts. Oviducts are where eggs are produced. Males can have structures that look similar, but serve no actual purpose. In males, they are called vestigial oviducts.

Bladder - An empty sac located at the lowest part of the body cavity. The bladder stores urine.

Cloaca - mentioned again as part of the urogenital system - urine, sperm and eggs exit here.

Removal of the Frog’s Brain (optional)

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. With your scalpel held almost horizontally, carefully chip away the roof of the skull to expose the brain. Use scissors to cut away the heavier bone along the sides of the brain.

Understanding the 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 elongate bodies with rounded bases, this is the cerebrum (B), and it is the frog's thinking center. The cerebrum is the part of the brain that helps the frog respond to its environment. 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).


Wrap up / Conclusion

-search for the brain (notoriously difficult to find) and discuss how the brain operates as control center for rest of body functions

-discuss different parts of the brain and their unique functions

Alignment Info

Audience(s) High school students
STEM Area(s) Biology
Life Sciences (RI GSE) LS1.7-8.4b
Students demonstrate understanding of differentiation by… comparing individual cells of tissues and recognizing the similarities of cells and how they work together to perform specific functions.
Life Sciences (RI GSE) LS1.7-8.4c
Students demonstrate understanding of differentiation by… explaining how each type of cell, tissue, and organ has a distinct structure and set of functions that serve the organism as a whole.
Life Sciences (RI GSE) LS1.9-11.1a
Students demonstrate understanding of structure and function-survival requirements by… explaining the relationships between and amongst the specialized structures of the cell and their functions (e.g. transport of materials, energy transfer, protein building, waste disposal, information feedback, and even movement).
Life Sciences (RI GSE) LS1.9-11.1b
Students demonstrate understanding of structure and function-survival requirements by… explaining that most multicellular organisms have specialized cells to survive, while unicellular organisms perform all survival functions. (e.g. nerve cells communicate with other cells, muscle cells contract, unicellular are not specialized).
Life Sciences (RI GSE) LS1.9-11.1c
Students demonstrate understanding of differentiation by… comparing the role of various sub-cellular structures in unicellular organisms to comparable structures in multicellular organisms (e.g. oral groove, gullet, food vacuole in Paramecium compared to digestive systems in multicellular organisms).
Activity Type(s) Hands-on
Grade Level(s) High School
Version 1
Created 05/28/2013 09:42 PM
Updated 12/20/2018 11:52 AM