dissection of frog, perch, worm lab.pdf

Name: ____________________________________Ms. KiriakopoulosSNC2DInquiry Activity: The Digestive System of an AnimalAn animal is able to process and absorb nutrients in the food using its digestive system. Digestivesystems vary in animals. Biologists have found that particular animals, such as the earthworm, perch,and frog, are good representatives of the increasing complexity in digestive systems. In this activity,you will study these three digestive systems through dissection. You may do the dissection withpreserved specimens of an earthworm and perch or using a virtual dissection program. You maychoose to do only one dissection, or you may do all three to compare the systems.QuestionHow does the digestive system of the earthworm, the perch, and the frog accomplish the process ofdigestion?Materials & Equipment• paper towels• preserved specimens of earthworm, frog, perch• hand lens• scalpel or dissecting scissors• probe• dissecting tray• dissecting pins• forceps• virtual dissection program for earthworm, perch, and frog• pen and/or pencil• paperCAUTION: To avoid injury, use proper techniques when using the scalpel.ProcedurePart 1 — Digestive System of the Earthworm1. Since the organs are small, it is helpful if you are familiarwith their position in the earthworm before you begin yourdissection. Complete a diagram of the earthworm digestivesystem based on Figure 2.30. When you are finished withyour diagram, complete a virtual dissection of anearthworm by following the instructions in the program, orobtain a preserved specimen of an earthworm, dissectionFigure 2.30 The external and internal anatomyof the earthworm

Ms. KiriakopoulosSNC2Dtools, and dissection pan. Rinse your specimen with water and pat dry.2. Using the hand lens, examine the external structure of the earthworm so that you can identifythe prostomium, clitellum, setae, and anus. The prostomium is in front of the mouth. The clitellumlooks like a saddle and is on the dorsal side of the earthworm. The setae are tiny bristles found onthe ventral side. The anus is found on the ventral side of the last segment of the worm.3. Hold the earthworm in your hand so that the dorsal side is facing up. Using your scissors, make ashallow cut on the dorsal side from the clitellum to the prostomium.4. Separate the tissue and use dissecting pins to pin the body wall down to the tray. You may need tocut through the tissue that holds the body wall.5. Locate the mouth, esophagus, crop, gizzard, intestine, and anus using Figure 2.30.6. Clean up your work area. Make sure to follow your teacher’s directions for safe disposal ofmaterials. Wash your hands thoroughly.Part 2 — Digestive System of the Perch7. Complete a diagram of the perch digestive system based on Figure 2.31. When you are finishedwith your diagram, complete a virtual dissection of a perch or obtain a preserved specimen of aperch, dissection tools, and dissection pan. Rinse your specimen with water and pat dry.8. Observe the external structure of the perch. Note the position and number of fins. Find thelateral line, and locate the gill cover and anal opening.9. Examine the mouth of the perch.10.Create a flap through the muscle wall.Make an incision from the bottom of the gillcover along the ventral side to the analopening. Continue the incision up from theanal opening to the lateral line and thenalong that line to the head of the fish. Finishyour flap by extending your incision back tothe base of the gill cover.Figure 2.31 The external and internal anatomy of the perch

Ms. KiriakopoulosSNC2D11.Lift the flap of muscle wall to look at the organs of the perch. If you have a female perch, the areamay be filled with eggs. If this is the case, you should remove the mass of eggs before proceeding.If the perch is male, the testes will be smaller and lighter in colour. Locate the liver (light brown),gall bladder (olive colour), esophagus, stomach, pyloric caeca, and intestines.12.Clean up your work area. Make sure to follow your teacher’s directions for safe disposal of materials.Wash your hands thoroughly.Part 3 — Digestive System of the FrogMale or Female?1. Place a frog on a dissection tray. To determine thefrog’s sex, look at the hand digits, or fingers, on itsforelegs. A male frog usually has thick pads on its"thumbs," which is one external difference betweenthe sexes, as shown in the diagram below. Male frogsare also usually smaller than female frogs. Observeseveral frogs to see the difference between malesand females.What is the sex of your frog? _________Anatomy of the Frog’s MouthProcedure: Pry the frog’s mouth open and use scissors tocut the angles of the frog’s jaws open. Cut deeply enoughso that the frog’s mouth opens wide enough to view thestructures inside.1. Locate the tongue.2. In the center of the mouth, toward the back is a singleround opening. This is the esophagus. This tube leads tothe stomach. Use a probe to poke into the esophagus.3. Close to the angles of the jaw are two openings, one oneach side. These are the Eustachian tubes. They are used to equalize pressure in the inner ear whilethe frog is swimming. Find the Eustachian tubes.4. Just behind the tongue, and before you reach the esophagus is a slit like opening. (You may need touse your probe to get it to open up). This slit is the glottis, and it is the opening to the lungs. The frogbreathes and vocalizes with the glottis. Find the glottis.5. The frog has two sets of teeth. The vomarine teeth are found on the roof of the mouth. Themaxillary teeth are found around the edge of the mouth. Both are used for holding prey, frogs swallowtheir meals whole and do NOT chew. Locate both sets of teeth.6. On the roof of the mouth, you will find two tiny openings, if you put your probe into those openings,you will find they exit on the outside of the frog. These are the nostrils.

Frog Internal AnatomyMs. KiriakopoulosSNC2D1. Place the frog in the dissecting pan on its back (dorsal surface)2. Spread out the limbs3. Use T pins to fasten the frog to the wax in the tray.4. With forceps gently lift the lose skin away from the body Usingscissors, make a small cut in the middle of the abdomen5. Cut along the midline of the body from rear to the head.6. Make transverse (horizontal) cuts near the arms and legs.7. Life the flaps of the body wall and pin back.8. Repeat steps 5-7 but cut through the muscle tissue this timeAnatomy Check ListLocate each of the organs by using the descriptions and pictures.Liver--The largest structure of the body cavity.This brown colored organ is composed of threeparts, called lobes. The liver is not primarily anorgan of digestion; it does secrete a digestive juicecalled bile. Bile is needed for the digestion of fats.Heart - at the top of the liver, the heart is atriangular structure. The left and right atrium can befound at the top of the heart. A single ventriclelocated at the bottom of the heart.Lungs - Locate the lungs by looking underneath andbehind the heart and liver. They are two spongy organs.Gall bladder--Lift the lobes of the liver, there willbe a small green sac under the liver. This is the gallbladder, which stores bile.Stomach--Curving from underneath the liver is the stomach. The stomach is the first major site ofchemical digestion. Frogs swallow their meals whole. Follow the stomach to where it turns into thesmall intestine. You can also open the stomach to see what the frog’s last meal was.Small Intestine--Leading from the stomach, a small curly structure. Pull it out to see how long it is.Eventually it will widen to become the large intestine. Nutrients are absorbed in the small intestine.Large Intestine--As you follow the small intestine down, it will widen into the large intestine. Thelarge 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.)

Ms. KiriakopoulosSNC2DSpleen--Return to the folds of the mesentery, this dark red spherical object serves as a holding areafor blood, where harmful particles can be filtered out for the immune system.Esophagus--Return to the stomach and follow it upward, where it gets smaller is the beginning of theesophagus. The esophagus is the tube that leads from the frog’s mouth to the stomach. Open the frog’smouth and find the esophagus, poke your probe into it and see where it leads.Analyzing and Interpreting1. How is the mouth specialized in each of the three specimens?2. Explain how the structure of the intestines is related to their role in digestion.3. What is the function of the liver in digestion?4. What is the function of the gall bladder?5. Why do you think the gall bladder is located so close to the liver? Explain your answer.6. Trace the path of food through the digestive tract in the earth worm, frog and perch on aseparate piece of paper.7. Describe one problem that you encountered in performing the dissection and explain how yousolved the problem.8. How is the digestive system of the worm, the perch, and the frog each suited to its habitat?

Ms. KiriakopoulosSNC2DAnatomy of a Frog