Name(s):_________________________________
Date:____________
SNC 2D1 – Investigating Frog Organ Systems
Purpose: To investigate the primary function and organization of organ systems and to
observe the external and internal frog anatomy.
Introduction:
 As members of the class Amphibia, frogs may live some of their adult lives on
land, but they must return to water to reproduce. On the outside of the frog’s
head are two nostrils; two eardrums; and two eyes.
 Inside the mouth are two teeth in the middle of the roof of the mouth; and two
teeth at the sides of the mouth. Also inside the mouth behind the tongue is the
pharynx, or throat.
 In the throat, there are several openings: one into the esophagus, the tube into
which food is swallowed; one into the glottis, through which air enters the larynx,
or voice box.
 The digestive system consists of the organs of the digestive tract. From the
esophagus, swallowed food moves into the stomach and then into the small
intestine. Bile is a digestive juice made by the liver and stored in the gallbladder.
Bile flows into a tube called the common bile duct. The contents of the common
bile duct flow into the small intestine, where most of the digestion and
absorption of food into the bloodstream takes place.
 Indigestible materials pass through the large intestine and then into the cloaca,
the common exit chamber.
 The respiratory system consists of the nostrils and the larynx, which opens into
two lungs, hollow sacs with thin walls. The walls of the lungs are filled with
capillaries, which are microscopic blood vessels through which materials pass into
and out of the blood.
 The circulatory system consists of the heart, blood vessels, and blood. The heart
has two receiving chambers, or atria, and one sending chamber, or ventricle.
Blood is carried to the heart in vessels called veins. Arteries, which are blood
vessels, carry blood away from the heart.
Materials:
• safety goggles, gloves, and a lab apron
• dissecting kit
• preserved frog
• dissecting tray and paper towels
• plastic storage bag and twist tie
• string, magnifying glass, ruler
Name(s):_________________________________
Date:____________
Procedure:
1. Put on safety goggles, gloves, and a lab apron.
2. Rinse the frog in water and place it in a dissection tray.
Describe the appearance of the frog.
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Measure the total length of your frog in cm ___________
3. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. A
male frog usually has thick pads on its "thumbs," which is one external difference
between the sexes, as shown in the diagram below. Male frogs are also usually
smaller than female frogs.
4. Is your frog male or female? ______________________
5. Use the diagram below to locate and identify the external features of the head.
Find the mouth, external nares/nostrils, and eyes.
Name(s):_________________________________
Date:____________
How do the position of the frog’s eyes compare to those in humans?
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How is the positioning of the frog’s eyes an adaptive advantage for the frog?
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6. Turn the frog on its back and observe the feet and legs.
How are the feet and legs of a frog adapted for swimming?
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7. Cut the hinges of the mouth and open it wide. Use the diagram below to locate
and identify the structures inside the mouth. Use a probe to help find each part:
the vomerine teeth, the maxillary teeth, the tongue, the esophagus, the
pharynx/throat, and the slit-like glottis.
MAKING INCISIONS
8. Place the frog on its dorsal (back) side and tie the legs down as instructed.
Name(s):_________________________________
Date:____________
9. Use forceps to lift the frog’s skin between the rear legs. Use the scissors to cut
through the lifted skin in order to make the incisions noted in the diagram below.
Take care to cut only the skin.
10. Lift one flap from the skin with the forceps. Use scissors to help separate the skin
from the muscle layer below. Pin the flap to the dissection tray. Repeat with the
second flap of skin.
11. Make a vertical incision through the abdominal muscle. Begin by using the
forceps to lift the muscle layer between the rear legs of the frog. Make a small
cut with the scissors. Continue the incision up the midline to a point just below
the front legs.
12. Use scissors to cut through the chest bones. When you reach the point just
below the front legs, turn the scissors sideways so you only cut through the
bones in the chest. Be careful not to cut too deeply or you might damage the
heart or other internal organs.
13. As you did with incisions 2 and 3, use the scissors to make sideways incisions in
the muscle. Again, be careful not to cut too deeply.
Name(s):_________________________________
Date:____________
14. To separate the muscle flaps from the organs below, use the forceps to pull back
and hold the muscle flaps. Use the scissors to separate the muscle from the
organ tissue. Pin the muscle flaps back far enough to allow easy access to the
internal organs.
15. Use forceps to pick up the triangular flaps of skin and muscle just above the front
legs. Use scissors, if needed, to separate the muscle from the tissue underneath.
Pin the flaps back far enough to allow access to the body cavity.
INTERAL EXAMINATION
16. The first organs you will see are the liver and the heart.
17. The heart and the liver cover the organs below them. Use the forceps and probe
to pick up the liver and hold it to the side. Use the labelled diagram below to find
the organs of the digestive system.
18. Two organs secrete substances into the digestive system to aid in digestion.
These are the gall bladder and the pancreas. Hint: The pancreas is a thin,
yellowish ribbon.
Name(s):_________________________________
Date:____________
19. Trace the path of blood vessels to and from the heart. The vessels going to and
from the lungs may be hard to see. Notice that the frog has two atria, as humans
do, but only one ventricle.
20. Observe how small arteries are attached to the organs of the digestive system.
21. Observe the following digestive and circulatory organs in greater detail. (You may
need to cut out the liver to better access the organs underneath it)
a. Use the scissors to cut out the stomach. Cut it open lengthwise. You may
find the remains of the frog’s last meal. Notice the muscular walls of the
stomach.
b. Use scissors to cut out the small and large intestines. Unwind the small
intestine and stretch it out next to the large intestine. Notice how they
compare in size and shape.
c. Use scissors to cut out the heart. Notice how the frog’s heart is different
from a human heart.
22. Dispose of your frog properly, according to your teacher’s instructions.
23. Wash all equipment with soap and water. Dry completely with paper towels.