Name _________________________________________ Per. __________

BIOLOGY: FROG DISSECTION PACKET

Day 1: Frog External Anatomy, Muscles, and the Oral Cavity

1. Find each of the external labeled structures in the picture on your frog. Once you have identified the each part, put a check next to the name above.

2. Use a ruler to measure your frog. Measure from the tip of the head to the end of the frog’s backbone (do not include the legs in your measurement).

3. Examine the hind (back) legs. o How many toes are present? _________ o Are the toes webbed (attached to each other)? YES NO

4. Examine the forelegs (front). o How many toes are present? __________o Are the toes webbed (attached to each other)? YES NO

5. Do humans have any webbed fingers or toes? Why is there this difference between human and frogs?

6. Observe the dorsal and ventral sides of the frog. What color are they?

Dorsal side color: _________________________

Ventral side color: ________________________

7. What is the advantage to the frog of having different colors on the dorsal versus ventral side?

8. Explain how the differences between the dorsal and ventral sides feel on your frog?

Your Frog length (cm)

9. Feel the chest of the frog by pressing down on it. What does it feel like?

o What is different between the chest of the frog and the chest of humans?

o What benefit might this give to frogs to have a chest that feels this way?

10. Locate the frog’s eyes. There is a clear membrane that covers the eye and is attached to the bottom of the eyelid called the nictitating membrane. Use a probe to get underneath the nictitating membrane and use the probe to pull down the membrane and look at the eyeball.

o Why is the nictitating membrane clear(transparent)?

o Why do you think frogs require this membrane over their eyes? Relate this to the typical habitat they live in.

o Do humans have a nictitating membrane? Explain why or why not.

11. Just behind the frog’s eyes, locate the circular structure on the frog’s skin. This is called the tympanic membrane. The frog uses its tympanum to hear. Measure the diameter (distance across the circle) of the tympanum.

o Diameter of tympanum: ___________cm

12. What physical features suggest adaptation to life in water? List and explain below.

13. Why do you think its good for a frog to be slimy?

diameter

Anatomy of the Frog’s MouthProcedure:

14. Pry the frog’s mouth open and 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. You may be cutting through bone, so don’t be afraid to cut through something hard.

15. Identify all of the structures below on your frog. Be sure to answer the questions along the way. Put a check mark next to the bullet points below once you have found that structure.

The frog has two sets of teeth. The vomerine teeth are found on the roof top of the mouth. The maxillary teeth are found around the edge of the mouth. Use your finger to feel them. Both sets of teeth are used for holding prey. Frogs do not chew and swallow their meals whole.

Close to the angles of the jaw where you cut are two openings, one on each side. There may be junk inside of them, so use a probe to clean them out. These are the Eustachian tubes. They are used to equalize pressure in the inner ear while the frog is swimming.

o Carefully insert a probe into the Eustachian tube. It should poke through fairly easily to the outside of the frog’s head. What structure does the Eustachian tube attach to? (What structure does your probe come out of)? _________________________

On the roof (top) of the mouth towards the frog, you will find two tiny openings. If you put your probe into those openings, you will find they exit through the nostrils on the outside of the frog.

Locate the tongue. Touch tongue.

o Does the tongue attach to the front or the back of the mouth? ____________ o Is this the same or different than humans? Why do you think the frog’s tongue is

attached this way?

In the center of the mouth, toward the back is a single round (larger) opening. This is the esophagus. This tube leads down to the stomach.

Just behind the tongue and below the esophagus is a skinny, slit-like opening. You may need to use your probe to get it to open up. This slit is the glottis. It is the opening to the lungs. The frog breathes and vocalizes with the glottis.

Directions: Label each of the structures below on the frog’s mouth and complete the table.

Word bank:___Vomerine teeth___Maxillary teeth___Eustachian tubes___Tympanic membrane___Nostrils___Tongue___Esophagus___Glottis

Structure Function (What does it do?)

Vomerine teeth

Eustachian tubes

Nictitating Membrane

Tympanum

Esophagus

Glottis

Frogs can “breathe” through their skin, exchanging water and gases. What body system(s) would this function be a part of?

Day 2: Internal Anatomy (Digestive, Circulatory and Reproductive systems)

TIME TO OPEN UP YOUR FROG!Procedure: 1. Place Frog in Pan and Pin: Place your frog in the dissection pan. The frog should be lying on its dorsal side with the belly facing up. Place the pins through the hands and feet and into the wax to secure the four limbs to the pan.

2. Begin the First Skin Incision: Once the legs of the frog are securely pinned to the dissection tray, begin the first skin incision by using the forceps to lift the skin midway between the rear legs of the frog. Using the scalpel, make a cut along the center of the frog. MAKE SURE YOU HOLD THE SCALPEL CORRECTLY!

3. Continue the Skin Incision: Continue the skin incision by using the scissors to cut all the way up the frog's body to the neck (right past the front legs. Be very careful not to cut too deeply.

4. Make the Leg Incisions: Still using the scissors, make horizontal incisions just above the rear legs and between the front legs of the frog. Look at the picture to help.

5. Separate the Skin & Muscle: Now you need to separate the skin flaps from the muscle below. Pick up the flap of skin with the forceps, and use a scalpel to gently separate the skin from the muscle.

6. Pin Skin Flaps: Your frog should now look like the picture to the right. Pin the skin flaps to the dissection tray using several pins.

7. Begin the First Muscle Incisions: Now that the skin has been removed, use the forceps to lift the muscle midway between the rear legs of the frog. Next, use the scalpel to start a cut in the direction of the chin.

8. Continue the Muscle Incision: CAUTION. Using the scissors, carefully continue the incision up the midline of the frog, but do not cut too deeply, or you will damage the organs.

9. Turn Scissors Blades: This is very important. When you reach a point just below the front legs, turn the scissors blades sideways to cut through the bones in the chest. Turing the scissors partially sideways should prevent damage to the heart or other internal organs. When your scissors reach a point just below the frog's neck, you have cut far enough.

10. Make the Second Muscle Incisions: Next, using the scissors, make horizontal incisions through the muscle between both the front legs and above the back legs, so that you can open them up like you did the skin.

11. Separate Muscle & Organs: Use the forceps to hold the muscle flaps up, then use a scalpel to separate the muscle from the tissues below.

12. Pin the Muscle Flaps: Pin down the muscle flaps like you did for the skin. Your frog should now look like the picture to the right.

Now you are ready to look at all the organs that make up the important body systems!

Note: Your frog may have fat bodies. Fat Bodies are spaghetti shaped structures that have a bright orange or yellow color. Fat bodies store energy for hibernation.   If you have fat bodies, remove them now so you can see the other structures below.

Use the labeled picture and descriptions below to help you find the listed organs and body parts. Check them off in the boxes as you find them!

DIGESTIVE SYSTEM-Check off organs as you find them

Organs that help digestion even though the food doesn’t go directly through the m

Liver--The largest structure of the body cavity.  This red-brown colored organ is made of three parts, or lobes, and found in the middle of the body.  The liver stores food, helps to digest fat by making a juice called bile, and also removes wastes from the blood.

Gall bladder—Gently lift the lobes of the liver. Underneath you will find a small green sac.  This is the gall bladder, which stores bile made by the liver before the bile gets passed onto the small intestine. (Hint: it kind of looks like a deflated balloon.)

Pancreas – This organ is small and ribbon-like and lies above the curved end of the stomach. On preserved frogs it may not be easy to find, as the gland breaks down. The pancreas makes insulin, which is needed for the proper digestion of sugar.

Organs that help digestion that food pass directly through

Esophagus--Is the tube-like organ that carries food from the frog’s mouth to the stomach. Return to the stomach and follow it upward, where it gets smaller is the beginning of the esophagus.  Open the frog’s mouth and find the esophagus (big hole in the back of the mouth), poke your probe into it and see where it leads.

Stomach-- It is the oval, whitish sac curving from underneath the liver. 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. 

Small Intestine--Leading from the stomach.  The first straight portion of the small intestine is called the duodenum, the curled portion is the ileum.  A membrane called the mesentery holds the ileum together.  Absorption of digested nutrients occurs in the small intestine.

Large Intestine--As you follow the small intestine down, it leads to a wider tube called 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.) Locate the anus, which is where wastes exit the body.

Removal of the Stomach & IntestineCut the stomach out of the frog and open it up.  You may find what remains of the frog's last meal in there. 

o Describe what you found inside of the stomach, if anything.

o Look at the texture of the stomach on the inside. What does it look like on the inside?

o Note the ridges on the walls of the stomach called rugae. How do you think that rugae help the stomach break down and digest food?

Measuring the Small Intestine:  Remove the small intestine and stretch it out and measure it. 

Intestine length ________ cm

Compare that to the length of the frog you measured in Part 1.

Frog length:  ________ cm

Which is longer, the frog or the small intestine? Why do you think the small intestine is so long?

1. Below are diagrams of some of the internal organs of a human and of a frog. Label as many as you can using the word bank.

WORD BANKLungsHeartLiverStomachLarge intestineSmall intestine

WORD BANKLungsHeartLiverStomachLarge intestineSmall intestine

2. What are the similarities and differences between a frog digestive system and a humans digestive system?

3. How could you explain these differences between a frog and human digestive system? (ie food we eat and how we live).

Day 3 CIRCULATORY AND RESPIRATORY SYSTEMS

Heart – Find the reddish triangular heart in the middle of the upper body at the top of the liver. The heart has three chambers. The left and right atrium can be found at the top of the heart. They collect blood from the veins and pass blood to the ventricle. The single ventricle is located at the bottom of the heart and it pumps blood to the body through the arteries.

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

Arteries and Veins -- These carry blood throughout the body. Arteries move blood away from the heart and veins bring blood back to the heart.

Removal of the Heart and Lungs

Removal of the Heart: Using your scalpel, cut around the heart to break the right and left arteries. Lift the heart up and toward the head - use your scalpel again to cut the right and left veins. Remove the heart from the chest cavity.

o Label the heart picture below with RIGHT ATRIUM, LEFT ATRIUM, and VENTRICLE.

Human Heart

o How many chambers are in the frog heart? How does this compare to the human heart? Be specific.

o Red Blood mean oxygenated (has oxygen) Blue Blood means deoxygenated (no oxygen). Would the blood leaving the heart going to the lungs be oxygenated or deoxygenated? Why?

o Would the blood in the arteries leaving the heart to go to the rest of the body be oxygenated or deoxygenated? Why?

Removal of the Lungs: Cut out the lungs. Slice one lung open from the side.

o What do the lungs feel like?

o Look carefully at the arteries on the inside of the lungs. Why do you think there are so many of them? Hint: Think about the function of the lungs.

EXCRETORY AND REPRODUCTIVE SYSTEMS

1. Looking at your frog with the small intestine now removed, the two dark long organs embedded in the back wall are the kidneys. The kidneys filter waste from the body.

2. Remove the kidneys. What do they look and feel like?

3. Find the tube called the urinary duct that leads from each kidney to the bladder. The bladder is the flap-like structure that empties into the cloaca. This is where urine, eggs, and sperm are eliminated from the body.

4. What does the urinary duct look and feel like?

IS IT A BOY OR A GIRL???

FEMALE? If your frog is filled with eggs, it is a female ready for breeding. Eggs look like black

speckled masses. If your frog is a female that is not ready for breeding, the egg-producing ovaries appear as thin-walled gray folded tissues attached to the kidneys.

A coiled, white tube called an oviduct leads from each ovary and carries eggs to an ovisac -where the eggs are stored until a male squeezes the eggs from the female’s body.

MALE? If your frog has an enlarged thumb pad

then it is a male.

Why would it be an advantage for a male to have an enlarged thumb pad?

If your frog doesn’t have eggs or ovaries, it is a male. In a male frog, you will find the yellow bean-shaped testes attached to the kidneys. Sperm from the testes pass through the urinary duct into the cloaca.

Some male frogs have vestigial oviducts, which are small tube like structures to the sides of the kidney.

o Is your frog male or female? __________________

o Explain with at least 2 details how you know the sex of your frog.

o Describe 2 ways that the reproductive system in frogs is different from that in humans.

Internal Anatomy (Nervous system)

Procedure: 1. Remove ALL of the remaining organs as well as the connective tissue along the back of

the abdominal wall.

2. Locate the backbone – it is along the back surface of the frog. Run your fingers along to see what it feels like.

3. Inside of the backbone is the spinal cord. The backbone connects all the way up to the skull.

o Where does the spinal cord begin and end?

o Why do you think the spinal cord connects to the brain?

o What do you think frogs use their brains for?

Removal of the Brain

Procedure:

1. Turn the frog onto its ventral side, dorsal side facing upwards.2. Using the scalpel, cut through the bone on the head to get to the brain.  Use the diagram

below to show you where and in what order to cut.  

3. Try to pull the brain out in one piece.

o Draw a picture of what the brain looks like.

Cut through the bone here

Cut through the bone here. Be sure to do it at the back of the skull

Cut through the bone here. Begin to break apart the skull. Be very careful as the brain is right below the skull’s surface.

o What do you notice about the size of the brain? Why do you think it is this way? Compare it to what you know about a human brain.

4. Below is a picture comparing the frog brain to the human brain. Describe the differences between these two.

What differences in behavior or function of a frog and a human result from the differences in their brains? Give a specific example.

5. What is one new thing you learned about frogs during this dissection?

6. What is one thing you learned about frogs in this dissection that can apply to humans. State the thing you learned, as well as how it relates to humans.

7. How do you think this dissection was similar to doing surgery on a living human? How was it different?