The Digestive System of an Animal - Dissection Lesson 11 October 20th, 2010

An animal is able to process and absorb nutrients in the food using its digestive system. Digestive systems 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 the perch digestive system through dissection.

Question How does the digestive system of the perch, accomplish the process of digestion?

Materials & Equipment paper towels • preserved specimens of earthworm and perch • hand lens • scalpel or dissecting scissors • probe • dissecting tray • dissecting pins • forceps • perch • pen and/or pencil • paper

Procedure 1. Obtain a preserved specimen of a perch, dissection tools, and dissection pan. Rinse your specimen with water and pat dry.

2. Observe the external structure of the perch 2. Observe the external structure of the perch. Note the position and number of fins. Find the lateral line, and locate the gill cover and anal opening.

3. Examine the mouth of the perch.

Create a flap through the muscle wall Create a flap through the muscle wall. Make an incision from the bottom of the gill cover along the ventral side to the anal opening. Continue the incision up from the anal opening to the lateral line and then along that line to the head of the fish. Finish your flap by extending your incision back to the base of the gill cover.

Cut along the blue line... Only cut through scales, muscles, and skin Take special care not to cut too deep!

Lift the flap of muscle wall to look at the organs of the perch Lift the flap of muscle wall to look at the organs of the perch. If you have a female perch, the area may 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.

Gonads

Locate the liver (light brown), gall bladder (olive colour), esophagus, stomach, pyloric caeca, and intestines.

Anterior View 1. Gills 2. Heart 3. Liver 4. Pyloric caeca 5. Small intestine 6. Stomach 7. Swim bladder

Posterior View 1. Swim bladder 2. Gonad 3. Large intestine 4. Urinary bladder 5. Anus

Close-up: Body Cavity Ovary Muscle Swim Bladder Eggs Liver Stomach Gastric Cecae Small Intestine Spleen

Clean up your work area. Make sure to follow your teacher’s directions for safe disposal of materials. Wash your hands thoroughly.

Answer the questions and hand in Question 10 requires research