Final Exam, Spring 2003

Answers TO SOME QUESTIONS are in BOLD, BLUE font (NOTE: Answers for questions that ask for examples have a few of the possible answers that are acceptable - there may be other correct answers)

7. Discuss eutrophication in freshwater lakes as it relates to the N-cycle. Include a discussion of the ramifications to the Carbon cycle and to biodiversity of lakes.

Eutrophication is often the result of nitrogen inputs, so the N-cycle is altered as more nitrogen enters freshwater systems. This often comes about as humans alter the nitrogen inputs into agricultural systems. We've increased conversion of nitrogen gas into ammonium and nitrate ions, which are then put onto cropland, often in excess. This increased input often leaches into freshwater systems. Since nitrogen is often limiting in freshwater systems, this spurs the growth of algae, resulting in algal blooms, and sometimes in low dissolved oxygen conditions that cause fish kills. Carbon fixation is enhanced, and these systems may be a sink for atmospheric carbon (although it may get respired back into the atmosphere just as quickly by consumption of algae by zooplankton). The high inputs of limiting nutrients may allow some algae to do extremely well, outcompeting other species and reducing overall biodiversity in the system.

8. Consider the transport of carbon dioxide in blood of mammals. Address, in one sentence each, the following: 1) the forms in which carbon dioxide is transported, 2) the relationship between carbon dioxide in the blood and blood pH, and 3) how increased carbon dioxide in inhaled air affects breathing rate (9 points).

Carbon dioxide is dissolved as a gas and converted to bicarbonate in the blood. As more CO2 dissolves in the blood, more is converted to carbonic acid, which dissociates, reducing the blood pH. This sends a signal to the medulla to increase breathing rate. More CO2 in inhaled breath does the same thing.

9. Apply the concept of countercurrent exchange to one of the following two systems by: 1) identifying the specific matter or energy that is exchanged, 2) explaining how countercurrent exchange helps maintain homeostasis, and 3) listing the physiological system(s) involved (8 pts):

a. Nephron in a Mammalian kidney OR b. Arctic wolf legs

10. Ammonia is the least energetically expensive nitrogenous waste to produce. Why don’t all animals excrete ammonia (4 points)?

Ammonia is very toxic and requires a lot of water to dilute those toxic effects. So the cost in water requirements outweighs the cost of producing other more expensive compounds in water-limiting (terrestrial) environments.

11. Using Fick’s Law of Diffusion briefly state why mammals are relatively inefficient in gas exchange capacity, and then describe the adaptations they possess to help overcome those inefficiencies (6 points).

Because the have tidal breathing and dead air in the lungs, which decreases oxygen concentration in inhaled air - adaptations to overcome this inefficiency include large surface area of exchange, perfusion around alveoli, and a small distance for diffusion of gasses.

12. List one type of invertebrate with an open and one with a closed circulatory system. For one of the two, explain in one sentence one advantage to having that type of circulatory system (6 points).

See last review.

13. The respiratory, digestive, and circulatory systems are closely tied together. Provide three examples of how control and regulatory mechanisms of one system affect at least one of the other two systems during normal glucose metabolism or in a diabetic. Be specific (15 points).

See last review.

14. List one abiotic factor discussed in class and list two adaptations that plants have evolved to deal with extremes in that factor (6 points).

High salt or low water are abiotic factors to consider. Different plant species have adaptations that can help deal with either situation. For instance, mangroves have many adaptations that allow them to live in high salt environments, such as sequestration of salt in vacuoles and salt glands. They also can use excess salt to lower their osmotic potential, which allows them to draw up water from high saline waters. To deal with low water, plants may have long roots, they may have evolved a life cycle that's tied to the cycle or presence of precipitation (and have dormant life stages - seeds).

15. Choose either grass-dominated or tree-dominated biomes at different latitudes. Compare and contrast two specific biomes of the general type you chose, with regards to: 1) annual temperature and precipitation patterns, 2) plant and animal diversity, and 3) annual primary productivity (9 points).

The idea here is to compare more than one grass-dominated biome OR more than one tree-dominated biome. However, for students in Spring 2005, we did not go over this.

16. List two life history traits. Describe how each may evolve differently in different species, depending on particular environmental conditions (8 points).

17. Relate the concept of succession to either the study of soils formation or the cycling of nutrients in soil (6 points).

Soils form over long periods of time, and the formation of soil from bare rock is part of primary succession. As succession proceeds certain organisms dominate, and the ones that can exist on bare rock are very hardy things like lichens. Their presence adds organic matter to the inorganic material present, and the act of adhering to rocks may facilitate their breakdown. As organic matter builds up over time, larger plants can come in and their root systems begin to break down the rock even more. In later stages of succession many organisms contribute to soil formation in that manner and by dying and decaying. Cycling of nutrients goes along with succession also, and different organisms either contribute to nutrients in the soil or take it up from the soil. So depending on the type of organism, nutrients are building up or being depleted. During certain stages of rapid growth (early secondary succession, for instance), nutrients may be cycling through the ecosystem at a much faster rate than at other times, especially during primary succession, which occurs very slowly.

18. Explain one reason why food webs are more useful to study than trophic levels when examining energy flow in ecosystems, and one drawback to using a food web approach to study energy flow in ecosystems. Use no more than ONE sentence to answer each part (8 points).

19. Briefly describe, in one sentence each, two examples that illustrate the energetic or nutrient cycle connections between terrestrial and aquatic ecosystems (8 points).

20. Explain the importance of two of the following factors when considering metapopulations. Limit yourself to one sentence per factor (8 points).

c. Species dispersal ability

21. For each of the following graphs, answer the associated questions. There are four questions in this section, each worth 3 pts = 12 points.

a. Describe the relationship between the theoretical curve depicted in Figure 1 and real population dynamics?

b. What is the utility of studying a theoretical population growth curve such as the one in Figure 1?

c. What is, approximately, the carrying capacity for the population in Figure 2, and what is the biological meaning of carrying capacity?

d. If this represented a theoretical growth curve for a population of fish prior to humans harvesting them, what recommendation would you give to fishermen if they asked you to what population size they should harvest (i.e., what population size should they leave behind) to allow them to maintain a maximum sustainable yield?

22. Select one biogeochemical cycle and use a schematic drawing to illustrate part of that element’s major reservoirs, forms, and processes that move it from one reservoir to another or change it from one form to another. Use three processes to illustrate the cycle, include the biota, and indicate one way that humans are disrupting the cycle (10 points).

23. Lake Victoria, in Africa, is a large, deep, isolated lake that, until recently, contained hundreds of species of cichlid fishes found nowhere else (i.e., they’re endemic). They are threatened by the recent introduction of a top predator, the Nile perch. Many Lake Victoria cichlids have reduced population sizes or have become extinct since the Nile perch introduction. Use specific concepts from Biology 112, that you identify, to explain in OUTLINE form (DO NOT write an essay): 1) the high proportion of endemic species, 2) why the cichlids might be succumbing to the Nile Perch, and 3) what we need to know or do to preserve the remaining species (15 points).

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