Module 1B: Photosynthesis and Ecosystems
Part 1: Modes of photosynthesis and the ecology of C3 and C4 grasses.
1) There are three general types of photosynthesis found in plants today. Below are simplified diagrams illustrating the major differences between these types structure and function.
a) What are the major differences between how C3 , C4 and CAM plants acquire CO2 and convert then it to sugars? (hint: think time and space)
b) Under what environmental conditions do you think each type of photosynthesis would be best adapted? Explain your answers. (hint: Think in terms of precipitation and temperature like you did with biomes and how plants exchange water and carbon dioxide)
c) What type of photosynthesis do you believe first appeared in the fossil record? Justify your answer by referring to the above figures.
2) Below is a map showing the simulated distribution of C4 grasses on the globe. (Adapted from Woodward et al. 2004) Using the same cities as for Module 1A fill in the predicted amount of C4 grasses in these regions and explain briefly why C4 is found in that abundance in the region.
City / Annual Temp. (°C) / Annual Precip. (cm) / Predicted C4 abundance (high/moderate/low)Briefly explain the abundance.
Chicago, IL / 9 / 89
Tuscon, AZ / 21 / 22
Tabora, Tanzania / 23 / 87
Toolik Lake, AK / -8 / 18
Beijing, China / 12 / 63
Valdivia, Chile / 13 / 240
Tromso, Norway / 2 / 101
Puntarenas, Costa Rica / 27 / 162
Chanthaburi, Thailand / 27 / 282
Fairbanks, AK / -2 / 27
Champaign, IL / 10 / 100
3) Below is a flow diagram showing the dynamic relationship between C4 -grass cover, fire, CO2 and the environment. (Blue: environment; Green: vegetation; Red: driver; Orange: effect). Pluses correspond to a “positive efffect” and minuses to a “negative effect”. For example tree growth has a negative effect on tree mortality. (Modified from Beerling and Osbourne, 2006)
a) Locate a “positive feedback loop” in the above diagram (a loop with an even number of positives and minuses). What do you think would happen to an ecosystem if this loop continued unchecked?
b) In your own words, explain how fire affects the amount of C4 grass cover.
c) In your own words, explain how CO2 affects the amount of C4 grass cover. (Bonus: How does CO2 affect the amount of fire?)
d) Below is a diagram showing the interactions between fire and mammals. (Grazers: eat grass; browsers: eat trees and shrubs) How does adding herbivory modify the effect of fire on C4 grass cover?
Part B) Photosynthesis and data visualization (take home)
Ecologists and paleoecologists, like most scientists, need a way to convert all those crazy numbers (Data) into a form that can be easily understood and shared. Scientists do not fear numbers any less. This can be easily done by creating figures and diagrams much like the flow diagrams or map in Part A. Below we’ve provided a table of simulated data derived from a grassland lake record representing the past 10,000 years (also provided in a spreadsheet). Doesn’t that look scary?! It needs to be repackaged if any sane scientist (or student) wants to produce hypotheses.
time / Charcoal pieces / Percent C4 Pollen / CO2 (ppmv) / time / Charcoal pieces / Percent C4 Pollen / CO2 (ppmv)0 / 444 / 63 / 310 / 5250 / 218 / 21 / 252
250 / 509 / 55 / 300 / 5500 / 955 / 97 / 249
500 / 483 / 59 / 295 / 5750 / 816 / 96 / 247
750 / 503 / 66 / 283 / 6000 / 921 / 99 / 244
1000 / 459 / 73 / 279 / 6250 / 930 / 96 / 242
1250 / 612 / 67 / 278 / 6500 / 860 / 96 / 220
1500 / 603 / 71 / 278 / 6750 / 966 / 98 / 236
1750 / 462 / 64 / 277 / 7000 / 279 / 80 / 234
2000 / 480 / 74 / 290 / 7250 / 304 / 43 / 231
2250 / 761 / 96 / 265 / 7500 / 369 / 38 / 229
2500 / 772 / 90 / 274 / 7750 / 297 / 54 / 226
2750 / 780 / 84 / 272 / 8000 / 413 / 53 / 230
3000 / 785 / 87 / 280 / 8250 / 440 / 53 / 221
3250 / 802 / 90 / 269 / 8500 / 405 / 42 / 219
3500 / 803 / 83 / 267 / 8750 / 330 / 27 / 220
3750 / 154 / 22 / 265 / 9000 / 336 / 54 / 200
4000 / 176 / 3 / 263 / 9250 / 631 / 25 / 212
4250 / 41 / 10 / 261 / 9500 / 312 / 48 / 210
4500 / 206 / 10 / 259 / 9750 / 674 / 80 / 208
4750 / 92 / 6 / 290 / 10000 / 302 / 25 / 206
5000 / 6 / 24 / 257
a) How do you think you should graph the above data? (e.g., histogram, scatterplot, pie chart etc.)
b) Thanks to the advent of the Internet there are no limits to what you can find. This includes a wonderful website ( that allows you to create your own graph paper! Using a graph paper of your own devising and artistic talent, create a graph using the table above which you think would best represent the data. Basic rules to follow: 1) the figure should be easy to understand at a glace; 2) everything should be labeled; 3) it should be visually striking; 4) be creative! (Do not worry about getting every data point. Be concerned only with the general trends.) For inspiration check out Information is Beautiful ( a blog devoted to visualizing data!
c) Using your favorite spreadsheet program (or preferably Tableau), construct the figure using the provided spreadsheet file. How does it compare to your own figure?
d) Construct a hypotheses on what is “controlling” the amount of C4 grass on the landscape. Is it CO2? Fire? Something else all together? What led to you concluding on this particular hypothesis? Given what you know from Part A. Could other environmental factors not shown here cause the patters in C4 you see? [J1]
[J1]Maybe include a sample hypothesis so they start thinking along the right path