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Show your work, including all of your calculations with proper units. If you only provide an answer value, you will only receive partial credit.  Of course, you should keep an electronic copy of your completed problem set. As mentioned in the syllabus, late homework will receive lower credit.

Question 1. Explain the timeline of oxygenic photosynthesis on Earth. Include information on when it arose in what different groups of organisms and how it affected Earth’s atmospheric composition. Provide a citation (Authors, year, title, publication) for your explanation. 15 points.

Question 2.  A) Make a drawing of the cross section of a leaf that shows how CO2 and water vapor diffuse into and out of the leaf.   B) Write equations that describe these diffusive fluxes as the product of a driving force and a conductance.  15 points.

Question 3.  A) Calculate the energy content of a mole of photons of wavelength 450nm and 650nm.  Show all of your calculations.

B) Imagine a leaf is receiving, say 1000 µmol m-2 s-1 of either 450nm or 650nm light.  Would you expect a higher rate of photosynthesis in one of these light types?   Explain.  (10)

Question 4.  Calculate the water use efficiency for leaves A, B, and C. (10)

Question 5. A corn field produces 10 metric tons of biomass per hectare over a 3 month (90 day) growing season. Sunlight energy incident on the corn field averages 250 Watts/m2 over a 12 hour day during the growing season.  The energy content of corn biomass is about 19 MJ/kg.  Calculate the energy efficiency (%) of corn production in this situation.  (20)

Question 6.  This problem requires you to calculate plant carbon balance based on the CO2 exchange rates of different plant tissues.  The point of this question is to help you appreciate that how plants allocate their resources to photosynthetic vs. non-photosynthetic tissues affects their growth rate.   30 points.

Plant A: average daytime (12 hr) leaf net CO2 uptake rate is 500 nmol CO2 g-1s-1; average nighttime leaf respiration rate is 50 nmol CO2 g-1s-1.  Average day and night (24 hr) respiration rate of roots and stems is 15 nmole g-1 s-1. Assume an initial total mass of 1 g, 80% of which is leaf and 20% is stem + root.

Plant B: All CO2 exchange rates of leaves, stems, and roots are the same as Plant A.  The difference is that this plant is 60% leaf and 40% stem + root.  Like Plant A, this plant is initially 1 gram total mass.

Calculate the size of Plant A and Plant B after 10 days of growth. To do this, you will need to calculate the new size of the plant at the end of each 24hr period. For simplicity, you can assume that each mole of CO2 gained or lost is equal to 12 grams of mass gain or loss.

I suggest you set up this problem in Excel to automate the calculations.  This will make it easier to repeat each day’s carbon balance and calculate the new size of the plant for the next day.

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