ACLC COLLEGE OF TACLOBAN

Senior High School Department

III. Science Department
Tacloban City
Name: ________________________________ Date: ________________________
________________________________ Block & Section: _______________
________________________________ Class Schedule:
________________
________________________________ Score: ________________________
________________________________ Rating: _______________________

ACTIVITY 4
(Group Activity)
I. TITLE: Frog Dissection

II. OBJECTIVE:

The dissection of frogs is an engaging introduction to vertebrate anatomy and mature body systems.
Exploring the anatomy of the frog allows discussions about adaptations and how anatomical
structures are related to their functions.

IV. MATERIALS
• Live frog**
• Dissecting kit (contents: dissecting pan/plate, scissors and/or scalpel blade, dissecting
knife, pin to fasten the specimen, pithing needle, forceps)
• Surgical gloves*
• Surgical mask*
• Laboratory gown*
• Tissue**
• Wet wipes**
• Garbage bag (for trash disposal)***
• Plastic cling wrap**
• Manila paper**
• Alcohol**
(Note: * individual, ** group, *** class)

IV. PROCEDURES:
V. 1st: Pithing
Before the experiment, you need to render the frog insensitive to pain. Pithing is one procedure
to accomplish this. Pithing will destroy the brain, which is located between the eyes. (For some
experiments, pithing will include severing the spinal cord.) Pithing is relatively painless to the
frog. Read the entire procedure before beginning so you can perform the procedure quickly.
1. Hold the frog facing away from your body, with the lower extremities extended.
2. Grasp the frog with your first two fingers: first finger on the nose, second finger under the
jaw. Flex the head forward (away from your body).
3. Move probe down midline until you come to the soft spot. Do not use undo pressure on
the frog skin. Frog skull is fairly hard cartilage; soft
spot is at the end of the skull.
4. Insert the probe quickly into the cranial vault and
sever the brain and spinal cord.
5. Move the probe into the cranial vault and move it
from side to side to destroy the brain. You can feel
inside
 the cranial vault, but the frog can’t feel anything. Without the brain, perception of any
sensory phenomena is impossible.
6. Test for reflexes to confirm that sensory perception has been destroyed and ensure that
the spinal cord is still intact, although it is now in shock.
7. Keep the frog moist. The frog will still be breathing because frogs breathe primarily
through the skin, not the lungs, so it is important to keep the frog moist.

VI. 2nd: External Frog Anatomy

1. Place the preserved frog on the dissecting tray with the dorsal surface facing up.
2. Observe the frog appendages that have evolved to adapt to terrestrial life. The frog uses 4
limbs to travel and move, making it a tetrapod. You will see that each forelimb includes
an upper arm, forearm, and hand. The frog’s hind limbs are divided into a thigh, lower
leg, and foot.
3. Looking at the head, identify the 2 external nares at the head’s tip. These function as a
means of respiration.
4. Find the round tympanic membranes that form the frog’s external sound receptors. You
will find these on the back side of the eyes.
5. Look closely at the eyes and attempt to find the frog’s third eyelid; this is the nictitating
membrane that moistens and protects the eye. As the frog is deceased, this will appear as
a cloudy eyelid attached at the bottom of the eye; however, it would appear clear in a
living frog.
6. Identify the cloaca, located at the specimen’s posterior end. The cloacal opening provides
the function of exit for all urinary, reproductive, and digestive systems.
7. Reposition the frog to lie on its dorsal side.
8. Carefully cut the jaw joints on each side of the
mouth to enable you to open the mouth wide.
9. Locate the glottis (leads to the lungs) and esophagus
opening (leads to the stomach). See figure at the
side.
10. Conduct a dental analysis. You will find 2 sets of
teeth. Firstly, locate the fine maxillary teeth lining
the upper jaw. Secondly, locate the two prominent
vomerine teeth located behind the mid-region of the
upper jaw.
11. On the sides of the roof of the frog’s mouth, you
should see 2 openings; the eustachian tubes that lead
to the tympanic membranes you identified earlier.
The function of these tubes is to aid in pressure
equalization.

VII. 3rd: Internal Frog Anatomy

1. Place the frog on the dissecting tray, ventral surface
facing up.
2. Using scissors, cut into the frog’s abdomen. To do
this, pinch the skin at the frog’s stomach and make a
small cut at the center.
3. Slice through the skin, keeping your cuts as straight
and clean as possible. Follow the cutting pattern (as shown
here).
4. Using the same pattern, Slice through the layers of muscle
until you reveal the internal organs beneath.
5. Locate the frog’s liver in the abdomen body cavity; it will be
comparatively large in size and brown. The largest internal
organ, the liver consists of 3 lobes.
 6. Reposition the liver lobes to reveal gallbladder beneath. The
gallbladder, which stores bile, will appear significantly smaller
and greenish.

4th: Maintain cleanliness. Make sure that the trash is disposed properly and clean all the
equipment used. The frog will still be used in the 5th part of this activity: Frog Bone
Preservation.

VIII. 5th: Bone Preservation

The process of preserving a skeleton can be tricky if you do not use proper care. It can also be
dangerous due to the risk of disease transmission when handling animal tissue and brains that
may be contaminated. However, if you are not squeamish about handling the carcass of an
animal and take a few simple precautions, you can clean and preserve a skeleton yourself,
allowing you to choose how to best display it.
1. Wear protective gloves. Remove as much flesh as possible using the skinning knife,
taking care not to scrape or damage the bones. The more flesh you can remove now, the
less work will be required later.
 2. Soak the carcass for six to eight hours in warm water. Straighten the wire coat hanger.
Bend one end into a loop. Feed the coat hanger into the brain cavity and use a stirring
motion to break apart the brain tissue. Rinse the brain cavity with warm water and repeat
the wire stirring to remove as much tissue as possible.
3. Fill the cooking pot with fresh water and heat it to approximately 90 degrees Fahrenheit.
Add 2 tbsp. of enzyme-based laundry detergent per gallon of water used in the cooking
pot. When the water is at the appropriate temperature, add the carcass.
4. Check the carcass every 15 minutes, removing flesh each time using the skinning knife
and picks or dental tools until the skeleton is clean. Strain the cooking water using a
colander or wire screen to catch any small bones or teeth that may detach from the
carcass.
5. Examine the bones for any sign of a white, waxy residue. If you find this residue,
degrease the bones using undiluted ammonia or a solution of dishwashing soap and
steaming (not boiling) water.
6. Prepare a solution of hydrogen peroxide and water. Soak the bones in this solution for up
to three days to bleach them.
7. Glue the bones together using clear-drying glue.

V. EVALUATION (by group):

Directions: Briefly answer the following questions below. Give what is asked.
For items 1-3, frogs belong under what…
1. Kingdom Animalia________________________
2. Phylum Chordata_________________________
3. Class Amphibian________________________
4. Why are frogs said to have “two lives?”
Answer: Frogs are said to have two stages of existence, due to the metamorphosis
that occurs in their life cycle. This process includes change in form and function
that happens from the aquatic tadpole stage to the adult stage on land. The tadpole
stage is considered as the initial phase of life, and the adult stage is known as the
second phase of life. This transformation is unique to frogs and some other
amphibians.

5. How are amphibians different from reptiles?

Answer: Amphibians and reptiles are both cold-blooded vertebrates, but they have
several key differences. One of the main difference is that amphibians have a two-
stage life cycle, with a larval stage (such as the tadpole) that is aquatic and a adult
stage that is terrestrial. This means that amphibians go through a metamorphosis
process, where they change from a aquatic organism to a terrestrial one, this
process is unique to amphibians. On the other hand, reptiles have a single
continuous life cycle, with no distinct larval stage, this means that they hatch from
their eggs and grow up gradually until they reach their adult form. This difference
in life cycle plays a big role in the ecological role of both groups, amphibians are
more dependent on aquatic habitats during their early stages and reptiles are more
flexible on their habitats.

6. What are 3 adaptations that frogs have that make them amphibians?
Answer: Frogs are amphibians that have unique adaptations that make them well-
suited for their environment. They have a dual life cycle where they begin their life
as tadpoles in water and then live as adults on land. Their gills are adapted for
obtaining oxygen from water and as they grow, they develop lungs that allow them
to breathe in open air on land. Additionally, as cold-blooded animals, they have
 behavioral adaptations such as laying on land in the sun to warm up internally.
Furthermore, they have backbones which is a common structure among
amphibians that gives them a central nervous system that is focused on the front,
allowing them to have sensory organs near the front and allowing a more complex
lifestyle.

7. List the ways in which tadpoles (immature frogs) and frogs differ from each other?
Answer:
Habitat: Tadpoles live in aquatic environments such as ponds, streams, and
swamps, while adult frogs can be found both in aquatic and terrestrial habitats.

Body shape and size: Tadpoles have a cylindrical, elongated body and a tail, which
is used for swimming, while adult frogs have a compact, terrestrial body shape and
no tail.

Respiration: Tadpoles use gills to extract oxygen from water while adult frogs have
lungs and can extract oxygen from the air.

Feeding: Tadpoles are herbivorous and feed on algae and aquatic plants, while
adult frogs are carnivorous and feed on insects, worms, and other small animals.

Limbs: Tadpoles do not have limbs while adult frogs have legs that they use for
swimming, jumping and moving around on land.

Metamorphosis: Tadpoles goes through metamorphosis which is a process of

changes in form and function during an organism's life cycle. Adult frogs do not go
through metamorphosis.

Heart: Tadpoles have three-chambered heart, Adult frogs have four-chambered

heart
Behavior: Tadpoles are mostly passive and are not able to move much, while adult
frogs are active and move around a lot.

External Anatomy
8. Dorsal means?
Answer: Dorsal refers to the back side of the animal. This is the side of the frog
that is opposite to the ventral side, which is the front or belly side of the frog.

9. Ventral means?
Answer: Ventral refers to the front or belly side of the animal. This is the side of
the frog that is opposite to the dorsal side, which is the back side of the frog.

10. Anterior means?

Answer: Anterior refers to the front or head side of the animal. This is the side of
the frog that is closest to the head, or the direction that the frog is facing or
moving. The anterior side of a frog's body is typically where the eyes, mouth, and
other sensory structures are located.

11. Posterior means?

 Answer: Posterior refers to the back side or tail end of the animal. This is the side
of the frog that is opposite to the anterior side, which is the front or head side of
the frog. The posterior side of a frog's body is typically where the spinal cord and
major muscles are located, which are important for movement and locomotion.

12. Frog lungs are poorly developed. How does this relate to their skin being thin and moist?
Answer: Frogs have underdeveloped lungs because they use their skin as a primary
means of breathing. The thin and moist skin allows for efficient exchange of gases,
making it unnecessary for them to have highly developed lungs.

13. How does the tympanic membrane work?

Answer: The eardrum, also called the tympanic membrane, is a delicate sheet of
tissue that separates the outer ear from the middle ear. The eardrum responds to
sound waves by vibrating, and these vibrations are amplified by three small bones
in the middle ear (the malleus, incus, and stapes). These vibrations are then
transmitted to the inner ear, where they are translated into electrical signals that the
brain can understand as sound.

14. Name 2 ways forelimbs are different than hind limbs.

Answer: Forelimbs are different from hind limbs in that they are typically more
specialized for grasping and manipulating objects and are attached to the
shoulders, while hind limbs are typically more specialized for locomotion and are
attached to the hips.

Critical Thinking Questions

15. The frog’s tongue is anchored in the very front – opposite to the orientation and
anchoring of humans. Why do you think this is so?

Internal Anatomy
16. Take a picture of the dissected frog, paste it in this section and label the parts.
Afterwards, write the specific organs in Column 1 as well as its corresponding function/s
in Column 2.

ORGAN FUNCTION/S
A.

B.
 C.

D.

E.

F.

G.

H.

Paste the printed photo here. Do not forget

.
to label the parts/organs. J.

K.

L.

M.