Biology-Mr.Willets
Lab-Platyhelminthes
Phylum Platyhelminthes (flatworms) contains a wide variety of organisms, both free-living and parasitic. The free-living flatworms are commonly called planaria. They have a primitive ladder-type nervous system with sense organs and a "brain". Their gut is incomplete (one opening) and extends from one end of the body to the other. Besides digesting food, it also helps circulate it. It is a gastrovascular cavity. Flatworms are acoelomic. They do not have a body cavity where the internal organs are located. You will examine both a living planaria and a stained slide of planaria showing its gut. Pg 403 in the book can help.
A. Live Planaria- Get a probe and specimen dish with a planaria. Use the stereoscopes to examine your specimen.
1. Movement-planaria has good muscular control as it moves along. It also has cilia on the ventral surface to help it glide. Some types of planaria can "ripple" their bodies and "swim".
2. Body Shape- This is the first phylum of animals to have bilateral symmetry. You can easily see the anterior end with its eyespots and sensory lobes (the bumps on the side). These lobes are sensitive to touch, vibrations and chemicals in the water. They are used to tell in which direction the current is flowing so that the planaria can swim upstream and avoid being swept away. They can also detect food.
The body is flat to make it easier for food and oxygen to diffuse to all the cells
3. Reaction to Light- The planaria does not remain in the middle of the dish where the light is brightest. It will move towards the edges.
4. Feeding- The mouth of planaria is located in the middle of the ventral surface. This makes it easier for food to get to both the front and rear of the animal. A muscular tube called the pharynx extends out through the mouth to get food. The outline of the pharynx can often be seen as a dark line in the middle of the animal. Planaria are scavengers. They eat whatever is lying around.
Place a small piece of liver in the dish. Observe the planaria as it feeds (if it feeds). Look for the pharynx to extend out from the middle of the ventral surface. While waiting for the planaria to feed, go on to other parts of this lab.
Draw the basic outline of planaria- Make the diagram large. Label: sensory lobes, eyespots, indicate which end is anterior.
B. Planaria Whole Mount- Get a prepared slide of planaria and examine it with both scopes.
This slide has been stained so that the entire gut is dark and can be seen. There are three branches to the gut- one in the front of the worm (the anterior branch) and two along the sides (the lateral branches) The pharynx is located where these three branches meet. The pharynx is not stained so you must decide where it would be. Use the large chart in the back of the room to help.
Make a diagram of the outline of planaria. Draw the gut. Label-anterior branch, lateral branches, pharynx.
Phylum Platyhelminthes contains two types of parasites- the flukes and the tapeworms. There are many varieties of each.
C. Sheep Liver Fluke- Fasciola hepatica
Examine the slide of the liver fluke -Fasciola hepatica. Use the stereoscope. You might also try scanning power. These live in the intestines or liver of sheep and other mammals. These worms have two suckers for attachment. One is located at the mouth at the anterior end and is called the oral sucker. The other is located a little further down on the ventral surface and is called the ventral sucker. The large chart in the back of the room can help you find them. The gut of the fluke is obvious. The dark structures located near the anterior end are gonads (they are not on the diagram on the chart).
Draw a diagram of the liver fluke. Label: oral sucker, ventral sucker, intestines, gonads.
D. Tapeworms- Get a slide of the tapeworm. The slide will be labelled- Moniezia expansa composite.(there is also one labelled Taenia ) Tapeworms live in the intestines of mammals including humans. Look at the slide with your eyes. The smallest part of the worm is the anterior end called the scolex. Find this part with your eyes before using the scopes. It has hooks and suckers for attachment. Examine this using either scope. (in some of these slides the hooks may not be visible) Consult the big chart for help. Pg 406 in the book is also useful. You will not see any sense organs since this is a parasite.
The sections of the tapeworm that are attached to the scolex are called proglottids. Their function is mostly reproductive. These have been separated from the scolex and put on the slide. Examine these under the scope. In the larger (older) ones, the eggs have been fertilized and fill the uterus (egg storage area). You can see the place on the side of the proglottid where the sperm can enter and the eggs can leave.
Make a diagram of a tapeworm scolex. Label hooks and suckers.
Biology - Mr. Willets
Questions- Flatworms
1) What phylum are flatworms in? ______________________________
2) What kind of nervous system do flatworms have? ___________________________ The fact that they have a nervous system is evidence that they have the ability to ______________
3) What kind of gut do flatworms have? _______________ It is called this because it only has one ______________ The other name for a flatworm's gut is ________________________________. This tells us that not only does it digest the food but also ___________________________________
4) Do flatworms have a body cavity? _________ What word describes this? ___________________
5) Planaria is the name for all ____________________________ flatworms
6) Planaria move using their ___________________ and their ______________
7) What evidence of cephalization can you see in planaria? ____________________________________
________________________________________________
8) What do the sensory lobes sense? ________________________________________________
9) Can a planaria see? ______ Explain ________________________________________________
10) Since there is no blood, food and oxygen get to the cells by ______________________ What feature of the flatworm body makes this happen more easily? _____________________________________
11) Where is the mouth located in planaria? _____________________________________
12) What is the name of the muscular feeding tube that sticks out of the mouth? ____________________
13) Because the mouth is in the_____________________of the animal, food can more easily get to the front and the rear.
14) What word describes how planaria gets food? ____________________ Does this type of feeding require speed? ________ What word would describe how planaria moves? _______________________
15) What are the two type of flatworm parasites? __________________ and ____________________
16) What do the liver flukes use to attach to the host? ___________________________
17) What feature of the liver fluke tells you it does not live in the intestines of the host but rather feeds on the liver? _________________________________________________
18) What is the front end of a tapeworm called? ________________ What does this have to help keep the tapeworm in the host? _____________________________________ Why would it not be correct to call this the "head" of the tapeworm? _______________________________________________
19) What are the sections that attached to the scolex of the tapeworm? _______________________
What is their function? _____________________________