Name: ____________________ Page 1 Ecology 1.018J/7.30 Quiz 1 October 2, 2008 Please put your name on every page!Space is provided for your answers; if you need more room, use the back of the *same* page. This exam is worth 100 points, with an additional 6 points of bonus problems. The number of points assigned to each question roughly corresponds to the amount of time you should spend answering it. Equations that may come in handy n = # e-transferred per mole of reductant ΔE0’ = E0’(oxidizing agent) - E0’(reducing agent) ΔG0’ = -nF(ΔE0’) F = Faraday constant (93.67 kJ V-1 mol-1) ΔG’ = ΔGo’ + RT ln ([C]c[D] d/[A] a[B]b) T = Temperature (K) R = gas constant (8.31 joules degree K- 1 mol-1) aA +bB  cC + dD Standard state reactants: 1M, 1atm, 25°C (298°K) *A table of standard reduction potentials may be found on the last page of the exam. 1. (11 Points) As you know, a group of organisms catalyze the oxidation of N compounds using either organic or inorganic carbon as their carbon source: NH4+ → NO2-→ NO3– (uses inorganic carbon) while others catalyze their reduction: NO3– → NO2-→ N2O → N2 (uses organic carbon) (i) (2 Points) What are each of these processes called? (ii) (4 Points) What is the “metabolic classification” of organisms that carry each of these processes out? List the carbon source and the chemical species being oxidized and reduced for each of the processes. (iii) (5 Points) How can each group of microbes “make a living” by doing essentially opposite things? That is, how does each process benefit the organism that catalyzes it? 2. Answer the following questions “True” or “False” (1 Point Each). ______ The limiting factor for productivity in an ecosystem is always the element that is in lowest concentration. ______ Net community production of an ecosystem can never be greater than net primary production. ______ N-limited lakes will often be very clear because nothing can grow in them since they are so nutrient poor. ______ Chlorophyll concentrations are maximal at the surface of the ocean where light intensity is greatest. ______ The amount of gross primary production in a forest is equal to the amount of carbon from CO2 fixed by photosynthesis of plants and bacteria in the forest.Name: ____________________ Page 2 3. (14 Points) D. J. Des Marais diagrammed the history of the Earth as a clock in units of billions of years ago (b.y.a.) (Science 289: 1703(2000)). A simplified version of this clock is reproduced below. The following questions refer to parts of the graph labeled with letters. (i) (1 Point) What appeared on Earth at “A”? (ii) (2 Points) What atmospheric event occurred at “B”? How did it affect life at that time? (iii) (2 Points) Describe the Earth’s atmosphere at the highlighted region “C”. What major gases were present? (iv) (3 Points) Describe the Earth’s atmosphere at “D”. What factors led to the differences between the Earth’s atmosphere between “C” and “D”? (v) (1 Point) Draw, based on this approximate scale, when on this “clock” humans appeared on Earth. (vi) (5 Points) Your friend, a geologist, wants your help investigating an ancient rock with curious banding and circular patterns. He has already demonstrated that the banding is not iron. What point on this graph represents the time the rock might be from? How would you test the origins of the patterning? What results would prove your hypothesis?Name: ____________________ Page 3 4. (11 Points) The graphs below describe the physical structure of two temperate lake ecosystems. I0=incident light intensity on the water surface. Temperature Log I0 1% I0 Depth Temperature Log I0 1% I0Depth A B (i) (1 Point) Label zc, the compensation depth. (ii) (2 Points) Based on this information, which lake would you expect to produce the most phytoplankton and why? (iii) (3 Points) Sketch on each of the graphs how you might expect the dissolved oxygen concentration to vary with depth. Why? (iv) (5 Points) Were these profiles measured in the summer or winter? Why? How would they differ if they had been measured six months earlier? (It may help you to diagram your response.)Name: ____________________ Page 4 5. (10 Points) In your readings, Morton wrote: “All over the world, by day and night, animals and bacteria and fungi and the plants themselves are using the oxygen which photosynthesis spits out into the atmosphere to turn organic material back into carbon dioxide and water. In so doing, they regenerate the energy the plants stored away. The two processes come close to canceling each other out. Today, though, things are out of balance. Today is a spring day...” (i) (2 Points) Complete this thought with three sentences or more of your own to explain what is “out of balance”. (ii) (2 Points) What are the animals, bacteria and fungi “using the oxygen” for? (iii) (2 Points) If the two processes Morton describes do “cancel each other out”, can NPP still be positive? Justify your answer. (iv) (2 Points) Over Earth’s history, have these processes always canceled each other out? Explain your answer. (v) (2 Points) Morton talks about “Eating the Sun.” Explain what he means by this.Name: ____________________ Page 5 6. (17 Points) Inspired by Priestley’s experiment involving a mouse, a plant, and a glass jar, you decide to build a self-sustaining closed system containing goldfish and aquatic plants. (i) (3 Points) What roles do the plants and fish play in your mini-ecosystem? How do they depend on one another? (ii) (6 Points) Before you seal off the system, you decide to do some tests to make sure your system will be balanced, i.e. the mix of fish and plants is adequate. You do this by temporarily placing the different components of your system into sealed containers and measuring the O2 concentration for three hours in the light and three hours in darkness. On the axes below, sketch 3 graphs of the change in O2 over time that you expect to see for the aquatic plants alone, the goldfish alone, and the aquatic plants and goldfish combined. Assume you are using sterile water. O2 concentration at time zero O2 Concentration(pg O2 L -1) Light Dark Time (hours) (iii) (6 Points) Explain the features of your graphs. (iv) (2 Points) You decide you are ready to assemble the final system, but you are very tired from all of your problem sets and accidentally fill the container with