mibexam12001

September 27, 2001 Name:__________________
Marine Invertebrate Biology
Exam #1 Key

There are 35 multiple choice questions on this exam (1.5 points each), three short answer and one essay question (30 points). Please check to make sure you have all 8 pages and remember to put you full name on the top of the first page and the scantron sheet.
Answer the multiple-choice questions on your scantron sheet by identifying the single most correct answer.

1. B
2. D
3. D
4. E
5. C
6. C
7. E
8. A
9. C
10. E
11. A
12. D
13. E
14. B
15. C
16. E
17. C
18. A
19. E
20. A
21. D
22. E
23. C
24. C
25. D
26. B
27. C
28. C
29. B
30. C
31. C
32. C
33. C
34. D
35. D

36. Completely label the following diagram of a sponge. Make sure to include direction of water flow and all cell types and sponge structures (12 points).

You should have correctly labeled the following for complete credit
Choanocytes
Pinacocytes
Porocytes
Archaeocytes
Pinacoderm
Ostia
Mesohyl
Spongocoel
Spicules
Water flowing from ostia through porocytes into spongocoel
Flagellum (no flagellated chambers)

37. Describe cephalization and bilateral symmetry in a cercaria larva (5 points).

Cephalization can clearly be seen in cercaria larva which have a distinctive head end with several specializations for finding and invading fish. Cercaria larva have an oral sucker, eye spots, digestive glands and chemosensors all on the head end which is critical for finding fish and invading their tissues. Bilateral symmetry is also seen in a cercaria larva in its tail region which has a distinctive right and left side and is used for swimming-in a similar motion to that of fish.

38. Draw and label a typical cell from what appears to have been the ancestral metazoan (3 points).

You needed to draw a choanoflagellate here and label the flagellum, microvilli, body of the cell and nucleus. It is thought that this one cell type probably formed a colony which may have been the very first multicellular animal.

39.) In the space provided (no credit for information outside of the box), describe why your mother may have been a flatworm (30 points).

Needed to cover four major topics in this essay: triploblastic germ layers, internal regulation, bilateral symmetry and cephalization. Under each of these topics I was looking for a basic understanding of what they are, specific examples to explain these terms and why they are particularly important in the phylum Platyhelminthes.
Important points that you might have emphasized for each included:
1. Triploblastic germ layers
Needed to mention the three germ layers: ectoderm (outside), mesoderm (middle) and endoderm (inside layer). This is the first animals where all three germ layers are present. The critical layer being mesoderm which allows for the development of organs and systems and large tissues which are impossible without a mesoderm. Although mesoderm can give rise to these wonderful structures, we don’t find large organs or systems in a flatworm because of limited diffusion distances. Thus, although flatworms have a mesoderm they are restricted to a very simple geometry (flat) in order to make sure all their cells are close to the environment.
2. Internal regulation
First time that we see a true system in any animal. This system is for osmoregulation and excretion and is important because it allows animals to move into new and often hostile environments. Without some type of internal regulation it would be impossible to regulate the internal cellular environment. This regulatory system is call the protonephridia and functions similar to advanced kidneys in that it uses selective reabsorption. Protonephridia work by using negative pressure created by the beating of cilia of flame cells. This draws in the internal fluids into the tubules of the protonephridia. The fluid then moves down the tubules towards the nephridopores which are the external openings of the system. At the fluid moves town the tubules material is selectively reabsorbed such that all of the good material is returned to the animal and any waste product or other material that is not recognized in eliminate. The protonephridial system is thought to be key to the success of the parasitic flatworms and probably led to advances organisms such as my mother.
3 & 4. Cephalization and bilateral symmetry
These two characteristics are first seen in the flatworms and are also found in essentially all animals that are more complex than flatworms. The ability to move in one direction and have a right and left side appears to by key to success of more advanced multicellular animals such as humans. These characteristics are easiest to see the life cycle of the liver fluke. In the cercaria larval stage cephalization can clearly be seen as they have a distinctive head end with several specializations for finding and invading fish. Cercaria larva have an oral sucker, eye spots, digestive glands and chemosensors all on the head end which is critical for finding fish and invading their tissues. Bilateral symmetry is also seen in a cercaria larva in its tail region which has a distinctive right and left side and is used for swimming-in a similar motion to that of fish. These characteristics can also be seen in the adult liver fluke which also has a distinctive head region with an oral sucker and bilateral symmetry which is clearly seen in the male and female openings on the right and left sides of this hermaphroditic animal.