Download External Anatomy

Name: ____________________________________ Due Date: __________________ Period: ________
To help you prepare for the dissection and to help you get the most out of it, you will be required to do some
independent work. The following is a list of tasks to help you learn about the frog. You must complete the
four required tasks (essentially these are just completing the lab) and two from among the 3 categories
(B=background, S=structure, F=function). This means you will complete 6 of the items below in total.
Initials
Category
Required
Task
Special Instructions
Read and highlight the lab procedures.
nd
B
B
Required
S
S
Required
F
F
Required
Read 1 frog article and rewrite it for a 2 grader:
www.exploratorium.edu/frogs/index
Find an article about frogs and print it out. Write
a 3-paragraph summary to explain it to the class.
Label the diagram included in the frog dissection.
Write a short poem or acrostic that uses the
names of some of the frog structures.
Make a short song that lists the path of food
through the frog from the mouth to the anus.
Complete the chart of functions included in the
dissection.
Make flashcards that have the structures on one
side and the functions on the other.
Create a crossword puzzle using organ functions
as clues.
Complete the Frog Dissection, Post-lab questions,
and conclusion.
Highlight structures in one color and
underline functions.
Include all the main ideas and be
careful not to plagiarize.
Be sure to organize it into 3 paragraphs
and be careful not to plagiarize.
Hint: The names are in the directions.
You have highlighted/underlined them.
Acrostics must use a word that is 6 or
more letters long.
Most of the functions are described in
the frog dissection.
Use graph paper or one a site linked by
your teacher. Include an answer key.
Answers in complete sentences;
conclusion in 3 paragraphs
External Anatomy
1. Place the frog in the dissecting pan ventral side up. Examine the hind and forelegs. The hind legs are
strong and muscular for jumping and swimming. The forelegs provide balance and cushion the frog
when it lands after jumping. Notice the toes on each.
2. Locate the large bulging eyes. The frog has 3 eyelids. The two outer ones are the color of the frog’s
body and do not move. The third is a transparent membrane that protects the eye while permitting
the frog to see under water. It also keeps the eye moist when the frog is on land.
3. Behind each eye, find the circular eardrum. Locate the two openings into the nasal cavity. These
external nares are found toward the tip of the snout, will close when the frog is under water.
4. Feel the frog’s skin. It is smooth, moist and thin. Because the skin is thin and moist, the frog can
breathe directly through the skin as well as with its lungs. Turn the frog over to examine its belly.
Notice the difference in coloring between the belly and the rest of the frog’s body.
5. While the frog is on its back (dorsal side), pry open its mouth, cutting it open at the corners. Locate
the tongue. Examine how it is attached in the mouth. In a live frog, the tongue is sticky and is used
to catch insects. Gently run your finger along the inside of the upper jaw. The ridges you feel are
maxillary teeth, used for grinding and crushing prey. Two vomerine teeth for catching prey can also
be found in the upper jaw, between and slightly behind the internal opening of the nostrils.
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6. Find the gullet (throat), the wide opening that leads to the esophagus. The esophagus transports
food from the mouth to the stomach, much like yours does. On both sides of the gullet, near the
jaw hinges are the openings to the Eustachian tubes; these tubes are auditory tubes for vertebrates.
Gently put your probe in these tubes to see where they lead on the outside of the frog.
Dissection
1. Place the frog on its back. Use scissors to lift the abdominal muscle
away from the body cavity. Cut along the midline of the body from
the pelvic to the pectoral girdle. Follow the diagram on the right.
2. Make transverse (horizontal) cuts near the arms and legs. Lift the
flaps of the body wall and pin back.
3. Repeat the cuts you made through the skin, this time cutting
through the muscles. Do Not cut too deep or you will damage the
organs below. The sternum or breastbone is between the forelegs.
Cut through this tough structure and fold back the muscles. Pin to
secure.
Internal Anatomy
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If your frog is a female, the body cavity may be full of black eggs and/or ovary tissue. If this is the
case, carefully remove this material and rinse the body cavity with water. Your frog should also have
fat bodies just under the abdominal wall. They are spaghetti shaped structures that have a bright
orange or yellow color. They may be large if your frog is larger.
The largest organ in the abdominal cavity is the liver. It is divided into several lobes-count them. The
liver has 2 main functions. First, it acts as a filter, removing poisons from the blood. It also produces
bile, a chemical that breaks down fats for digestion.
Locate the greenish sac attached to the underside of the liver. This is the gallbladder. It stores bile.
Posterior (behind) to the liver, find the large white stomach. It will be on the right side as you look at
the frog. The stomach is responsible for most of the mechanical breakdown of the food because
frog’s teeth only serve to hold prey in the mouth, not to break it apart. The stomach connects to the
small intestine, where the nutrients from food are absorbed into the bloodstream to be transported
throughout the body. Notice the thin, transparent membranes, called mesenteries that hold the coils
of small intestine together.
The small intestine eventually widens to form the large intestine. This straight tube leads to the anus
and functions to absorb water from waste materials before they leave the body. The very bottom
portion of the large intestine is called the cloaca. It is a cavity into which the digestive, urinary and
reproductive canals open. This area opens to the outside and materials that are sent here are voided
to the outside of the body.
Two smaller organs are somewhat difficult to find. In the mesentery, along the inner curve of the
stomach, locate the pinkish pancreas. This organ makes insulin which is used by the body to absorb
the carbohydrates from food into the blood. Also, in the mesentery see if you can find a small
reddish spherical structure. This is the spleen. The function of the spleen is to recycle red blood cells
and make white blood cells to fight disease.
Locate the lungs, two grayish saclike structures dorsal to the liver (above, towards the head). The
lungs take in air and facilitate the diffusion of oxygen in and carbon dioxide out of the blood stream.
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8. Locate the heart between the lungs. Cut through the thin membrane that surrounds the heart. This
will expose the heart for closer examination. The frog’s heart has 3 chambers. Find the two upper
chambers, the left atrium and the right atrium. The right atrium collects the oxygen depleted “blue”
blood as it comes back to the heart from the body. The left atrium collects oxygen rich “red” blood
flowing back from the lungs. Find the lower ventricle that squeezes the blood out to both the body
and the lungs. With the probe, examine these chambers to compare the thickness of the walls.
9. Find the two dark brown kidneys attached to the back wall of the abdominal cavity. Kidneys filter the
blood and remove nitrogen wastes (these make up the urine). Find the urinary bladder which holds
urine before it empties into the cloaca. The tubes between each kidney and the bladder are called
ureters.
10. Using your scissors, carefully remove the liver. Cut through the upper end of the stomach and the
lower end of the large intestine. This will allow you to remove the stomach and the intestines. The
intestines are the location of nutrient absorption for the frog. How long do you think the small
intestine is? Record your guess. Then stretch out the small intestine and measure it. Measure the
length of the frog and compare to the length of the intestine
Post Lab Questions
External 1. Describe the structural differences in the toes of the back and forelegs. Why are they different?
2. The frog’s sense organs are on the top of the head. How does this help the frog in the water?
3. Describe the difference in coloration between the belly of the frog and the rest of its body. How
does this color adaptation help the frog?
4. Describe the shape of the tongue and how it is attached to the mouth. How does this
adaptation help the frog?
5. Where do the Eustachian tubes lead?
Internal 6. How many lobes does the liver have?
7. Why is the gall bladder located where it is?
8. Which has thicker walls, the stomach or the small intestine? Explain why.
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9. Which has a thicker wall, the ventricle or the atrium? Explain why.
10. The membrane holds the coils of the small intestine together is called the ________________
11. How long was the small intestine? How does the length relate to its function?
Label the Diagram
A. __________________________________
B. __________________________________
C. __________________________________
D. __________________________________
E. __________________________________
F. __________________________________
G. __________________________________
H. __________________________________
I. __________________________________
J. __________________________________
K. __________________________________
L. __________________________________
M. __________________________________
N. __________________________________
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Organ
Function
Cloaca
Esophagus
Eustachian tubes
Fat bodies
Gall bladder
Kidney
Large Intestine
Left Atrium
Liver
Lungs
Mesenteries
Pancreas
Right Atrium
Pancreas
Small intestine
Spleen
Stomach
Teeth (maxillary & vomerine)
Ventricle
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Conclusion:
Sum up your work on the frog using the following prompt:
Paragraph 1:
 What is a vertebrate?
 What is an amphibian?
 Thesis statement (What is this conclusion about?)
Paragraph 2:
 Symmetry
 Organs/Systems
 Movement
 Endo/ectothermic
 Metamorphosis
Paragraph 3:
 How does form fit function in the frog?
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