Download frog dissection study guide

Name:________________________________ Date:_______________________ Class:_______
Frog Dissection
Directions:
Throughout the entire dissection, refer back to the detailed frog packet on the placement of
the organs and how to cut in specific spots.
Objective:
To study the body structures of the frog and compare and contrast the frog body to the human
body structure.
Background Information
Frogs are classified as amphibians or “animals that live a double life.” The name is appropriate
because amphibians spend their immature lives in water and their adult lives primarily on land.
Tadpoles, or young frogs, are entirely aquatic. Adult frogs can live on land or in water. In this
investigation, you will dissect a frog.
Materials (per group)
Preserved frog, Pair of gloves, Dissecting pan, Dissecting pins, Scissors, Forceps, Pipette and
Colored Pencils/Markers
Pre-Lab Procedures:
You will start by coloring and labeling the frog diagrams below. You MUST use the color code
below. Refer to colored worksheets as a reference.
Fat body = yellow
Gall Bladder = green
Lungs = blue
Liver = purple
Stomach = orange
Spleen = gray
Small Intestine = dark blue
Pancreas = pink
Kidney = black
Large Intestine = brown
Heart = red
Dissection Procedures:
1. Place the frog on its belly (ventral side) in the dissecting pan.
2. Measure in centimeters the length and width of the frog.
Length: _________ cm (From head to the end of tail bone, do not include legs)
Width: _________ cm
3. Examine the back and front legs of the frog. Write an observation of the difference
between the toes of the back legs and the front legs.
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4. Locate the large, bulging eyes. The frog has three eyelids. Write an observation of any
similarities or differences between the frog’s eye and the human eye.
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5. Feel the frog’s skin. Write 3 observations of the skin that you see or feel. The frog can
breathe directly through its skin as well as with his lungs.
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6. Flip the frog over to examine his belly. Explain the difference in coloring between the
belly and the rest of the frog’s body.
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Internal structure:
1. Place the frog on its back (dorsal side) in the dissecting pan and pry open its mouth. If
you cut the corners of the mouth (about 1-2 cm) with scissors, the mouth will open
more easily.
2. Locate the tongue. Is it attached to the front or back of the mouth?
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In a live frog, the tongue is sticky and used to catch insects. You may play with it if you’d
like.
3. Gently run your finger along the inside of the upper jaw. The ridges that you feel are
maxillary teeth.
4. Find the gullet (throat), the wide opening that leads to the esophagus.
Now for dissecting:
1. Now you are ready to open the abdominal cavity. Place the frog on its back
(dorsal side) in the dissecting pan. Secure it by placing the pins through the
tip of the snout and each of its legs. (If needed)
2. First your incision will be made along the middle of the belly-from the pelvis to the throat
(bottom to the top). Begin by lifting the belly skin with forceps and inserting the point at the
midline near the pelvis. Carefully cut along the midline toward the throat. Note: Cut through
the skin only.
3. At the top and bottom of this incision, make transverse cuts towards
the forelegs and hind legs. Cut from B-C to D-E.
4. You are now ready to cut through the muscle layer. Repeat the incisions you made in
steps 2 and 3, this time cutting through the muscle layer. Work carefully.
CAUTION: Do not cut too deeply or you will damage the underlying organs.
5. The sternum, or breastbone, is located between the forelegs. Cut through this tough
structure. Fold back the muscle layer and secure it with pins.
6. If your frog is a female, the body cavity may be full of black eggs and ovary tissue. If they are
present, carefully remove the eggs and the tissue. Rinse out the body cavity with water.
Note: You may notice a lot of spaghetti shaped structures located just inside the abdominal
wall. These are fat bodies. You may remove them using the forceps so you can see the rest of
the organs.
7. The largest organ in the abdominal cavity is the reddish brown liver. Find it and count
the number of lobes and write it down ____________
8. Locate the greenish sac attached to the liver. This is the gall bladder. It stores bile,
which breaks down fats during digestion.
9. Beneath the liver, find the large, white stomach. It will be on the right side as you look
at the frog. The stomach connects to the small intestine. Separate some of the coils and
you will see that they are connected by thin, transparent membranes.
10. The small intestine eventually widens to form the large intestine. The large intestine is a
straight tube leading to the anus. Draw a diagram of the small and large intestine.
11. Two smaller organs are somewhat more difficult to find. Along the inner curve of the
stomach, locate the pinkish pancreas. In the coiled part of the small intestine, see if you can
find a small, reddish, spherical structure. This is the spleen. Did you find it? Circle Yes or No
12. Using scissors, carefully remove the liver. Cut through the upper end of the stomach and
the lower end of the large intestine. Then remove the stomach and intestines. Don’t throw
away.
13. Cut open the stomach and a section of intestine to examine the lining and internal features.
Respiratory System:
1. Locate the lungs, two reddish brown saclike structures.
2. OPTIONAL: Insert a clean pipette (with the bulb removed) down the frog’s glottis
(windpipe). Gently blow into the pipette and watch the lungs inflate. (put tissue where
you will place your mouth on the pipette)
Circulatory System:
1. Locate the heart between the lungs. Cut through the thin membrane that surrounds
the heart. This will expose the heart for closer examination.
2. The frog’s heart has three chambers. Find the two upper chambers-the right and left
atria (singular: atrium)-and the lower ventricle. Compare the thickness of the walls of
the atria and the ventricle.
Excretory System:
1. Find the two dark red kidneys attached to the back wall of the abdominal cavity.
2. Find the urinary bladder, which empties into the cloaca. The tubes leading from each
kidney to the bladder are called ureters.