Biology Investigation: Frog Dissection



Biology Investigation: Frog Dissection

Name:

Background Information

Amphibians are important indicator species for the health of ecosystems – amphibians live their lives in both aquatic and terrestrial ecosystems. Frogs are also vertebrates meaning they have a backbone containing a spinal cord and skull that protects the brain. Frogs may live some of their adult lives on land, but they must return to water to reproduce. Eggs are laid and fertilized in water. The amphibian you will dissect is the leopard, or grass, frog, Rana pipiens, which has a distinct metamorphosis.

On the outside of the frog’s head are two external nares, or nostrils; two tympani, or eardrums; and two eyes, each of which has three lids. The third lid, called the nictitating membrane, is transparent. Inside the mouth are two internal nares, or openings into the nostrils; two vomerine teeth in the middle of the roof of the mouth; and a ridge of maxillary teeth on the upper portion of the mouth. Also inside the mouth behind the tongue is the pharynx, or throat. 

In the pharynx, 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; and two into the Eustachian tubes, which connect the pharynx to the ear. The digestive system consists of the organs of the digestive tract, or food tube, and the digestive glands. 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. The pancreas also adds pancreatic juice. Most of the digestion and absorption of food into the bloodstream takes place here.

Indigestible materials pass through the large intestine and then into the cloaca, the common exit chamber of the digestive, excretory, and reproductive systems. 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 (humans have two ventricles). Blood is carried to the heart in vessels called veins. Veins from different parts of the body enter the right and left atria. Blood from both atria goes into the ventricle and then is pumped into the arteries, which are blood vessels that carry blood away from the heart. 

The urinary system consists of the frog’s kidneys, ureters, bladder, and cloaca. The kidneys are organs that excrete urine. Connected to each kidney is a ureter, a tube through which urine passes into the urinary bladder, a sac that stores urine until it passes out of the body through the cloaca. The organs of the male reproductive system are the testes, sperm ducts, and cloaca. Those of the female system are the ovaries, oviducts, uteri, and cloaca. The testes produce sperm, or male sex cells, which move through sperm ducts, tubes that carry sperm into the cloaca, from which the sperm move outside the body. The ovaries produce eggs, or female sex cells, which move through oviducts into the uteri, then through the cloaca outside the body.

The central nervous system of the frog consists of the brain, which is enclosed in the skull, and the spinal cord, which is enclosed in the backbone. Nerves branch out from the spinal cord. The frog’s skeletal and muscular systems consist of its framework of bones and joints, to which nearly all the voluntary muscles of the body are attached. Voluntary muscles, which are those over which the frog has control, occur in pairs of flexors and extensors. When a flexor of a leg or other body part contracts, that part becomes bent. When the extensor of that body part contracts, the part straightens. 

Helpful Diagrams

Frog Dissection Data Sheet

/10 K /20 T /24 C /10 A

Name:

/65 MARKS

Group Member(s):

Purpose - state in a full sentence (1 mark – Knowledge)

Materials – list in point form (2 marks – Knowledge)

Part A Procedure – Frog External Structures

1. Obtain the necessary dissecting equipment and a preserved specimen of the frog.

2. Examine the overall shape of the animal, the position of its eyes and legs, and the colour of the dorsal (back) and ventral (front) surfaces of the body. Don’t be afraid to examine the frog through touch!

3. Draw a biological diagram of the dorsal (back) side of the frog. Include the following labels: mouth, external nares, tympani, eyes, nictitating membranes, forelegs, hind legs, cloaca, toes, and digits.

(10 marks – Communication) Marks will be given for the correct labels (½ mark each x 10 = 5 marks), accurate diagram (1 mark), title (1 mark) neatness (1 mark), good use of space (1 mark) and correct labelling format (1 mark).

4. Describe the following features of the frog seen throughout the dissection. Use the helpful diagrams to locate these structures if necessary. There should be at least four details for the overall features, and two details for the structures of the head. (7 marks – Communication)

Overall Features

|Dorsal Side | |

|Ventral Side | |

Structures of the Head

|External Nares | |

|Tympani | |

|Eyes & Nictating Membrane | |

Part B Procedure: Frog Internal Structures

1. Place the frog in the dissection tray on its dorsal (back) side so that it is ventral side up. Look for the opening to the frog’s cloaca, located between the hind legs. Use forceps to lift the skin and use scissors to cut along the center of the body from the cloaca to the lip. Turn back the skin, cut toward the side at each leg, and pin the skin flat. The diagram above shows how to make these cuts. Take care to cut only the skin.

2. Below the skin is muscle tissue – note its appearance. Cut through the muscle in a similar fashion to the way you did the skin.

3. Use the helpful diagrams to locate and identify, as well as describe the organs of the digestive system listed below. There should be at least two details per structure. (5 marks – Communication)

Body Cavity & Digestive System

|Abdominal Muscle Tissue | |

|Stomach | |

|Small Intestine | |

|Large Intestine | |

|Liver | |

4. Refer to the helpful diagrams to identify and describe the parts of the circulatory and respiratory systems that are in the chest cavity listed below. There should be at least two details per structure. (2 marks – Communication)

Circulatory & Respiratory System

|Heart | |

|Lungs | |

5. Dispose of your materials according to the directions from your teacher, and clean up your work area and dissection utensils with soap, and wash your hands before leaving the lab.

Discussion Questions

Use the background information, helpful diagrams, and knowledge gained throughout the dissection to answer the following questions in full sentences.

1. What are three safety precautions that you followed throughout the lab? (3 marks – Knowledge)

a)

b)

c)

2. What type of frog were we dissecting? (1 mark - Knowledge)

3. What are three organs that humans have which frogs do not, based on what you saw in the dissection? (3 marks – Knowledge)

a)

b)

c)

4. Why do scientists study frogs in particular when determining whether an ecosystem is healthy or not? (1 mark – Thinking)

5. Describe the life cycle of a frog, and indicate at each stage whether it lives in the water or on land. (3 marks – Thinking)

6. Describe the pathway of food into and out of the body through the digestive system, including all organs. (2 marks – Thinking)

7. What is the third eyelid called, and what is its function? (2 marks - Thinking)

Eyelid:

Function:

8. What three systems use the cloaca as an exit pathway? (3 marks – Thinking)

1 -

2 -

3 -

9. How does the circulatory system in frogs compare to humans? Explain one similarity and one difference. (2 marks – Thinking)

10. Why do you think the tongue in a living frog would be sticky? (1 mark – Thinking)

11. Describe how a frog’s skeletal and muscular system work together to make movements. (2 marks – Thinking)

12. The abdominal cavity of a frog at the end of hibernation season would contain very small fat bodies or none at all. What is the function of the fat bodies? (1 mark - Thinking)

13. Structures of an animal’s body that fit it for its environment are adaptations. How do the frog’s powerful hind legs help it to fit into a life both in water and on land? (2 marks - Thinking)

14. Cold-blooded animals, such as frogs, are able to deliver blood to their cells once their bodies warm up. Predict when you think frogs are likely to be most active, and why. (1 mark - Thinking)

Conclusion (5 marks – Application)

Answer the following questions in a paragraph summary.

• Briefly describe what was done.

• Reflect on what went well and what could be improved upon if you had the chance to do it again.

• What did you learn?

• How does this dissection relate to the biology unit studied in class?

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