FRESHWATER BIOLOGY (207) - Exam 1

Sept 19, 1995

1) Name a representative organism (common names OK) found in the

(a) littoral zone, (b) the pelagic zone, (c) the profundal benthic zone. 3 POINTS

2) In some areas during summer, great swarms of adult stages of aquatic insects (example, caddisflies) suddenly appear. (a) What is the purpose for such swarms?

(b) Why so many adults at once? 5 POINTS

3) FW organisms have made important physiological adaptations to maintain a proper water/salt balance in their internal tissues. What would happen to this balance if no effort was made to maintain this condition? 5 POINTS

4) Why are submerged aquatic plants generally restricted to the littoral zone of a lake?

5 POINTS

5) The larvae of holometabolous insects are often larger than the adult stage. What is one major reason for this? 5 POINTS

6) During a summer research project you measured and plotted the following data on the water temperature and the concentration of dissolved O2 at different depths in a shallow lake (also known as "vertical profiles"). You repeated the same measurements for a medium-sized stream/river of equal depth and with a high current flow rate. (a) Although you just lost your data book (bummer), you need to draw an approximation of these stream profiles (on the blank figure) for your boss in order to make a general comparison among the 2 systems. (b) If the data for the stream looks different than the lake, explain why. 10 POINTS

7) Besides their obvious, crucial role in reproduction, what other benefit do flying adults confer to aquatic insects? 5 POINTS

8) (a) Why are dragonfly larvae so important in determining the abundance of other small aquatic organisms? (b) What is the labium used for? 5 POINTS

9) Label the stream order for the illustrated stream/river system. 5 POINTS

10) (a) How are the highlighted (by arrows) body parts of these aquatic insects involved in gas exchange? Explain each one separately. (b) In the case of (#3), how is its bouyancy affected and does this increase or decrease (or both) the amount of energy the animal expends moving about? (c) Are these insects common in lentic or lotic environments? 12 POINTS

11) (a) In a stream system (for example, from the headwaters to the mouth of the Mississippi), what downstream trend is normally seen in the proportion of shredders versus collectors? (b) Why? 5 POINTS

12) List adaptations that the 2 illustrated stream organisms have to avoid being washed downstream. 5 POINTS

13) (a) Why do phantom midge larvae leave the profundal sediments at night and return the following morning? (b) What body part has adapted to aid this process?

(c) Why are they called "phantom" midges? 5 POINTS

14) Crayfish and amphipods are omnivores. (a) What does this mean and what advantages does this confer to these organisms? (b) Why are their population levels often abundant? 5 POINTS

15) (a) Which of the FW organisms shown is (1) planktonic, (2) benthic, (3) nektonic, and (4) neustonic? (b) What property of water helps the planktonic organism maintain its spatial position? (c) What property of water helps the neustonic organism maintain its position? (d) What 2 functions do the numerous leg hairs on the neustonic organism perform? 15 POINTS?

16) For a set volume of water, does a eutrophic lake contain more or less plant life than an oligotrophic lake and why? 5 POINTS