Use the Following Information When Answering the Corresponding Questions)

Multiple Choice

Use the following information when answering the corresponding questions) .
Suzanne Simard and colleagues knew that the same mycorrhizal fungal species could colonize multiple types of trees. They w if the same fungal individual would colonize different trees, forming an underground network that potentially could transpor and nutrients from one tree to another S. Simard et al. 1997. Net transfer of carbon between mycorrhizal tree species in the fi Nature 388:579- 82) . Figure 29.2 illustrates the team's experimental setup. Pots containing seedlings of three different tree species were set up and grown under natural conditions for three years; two of the three species formed ectomycorrhizae Douglas fir, birch) and the other cedar) formed arbuscular mycorrhizae. For the experiment, the researchers placed airtight bags over the Douglas fir and birch seedlings; into each bag, they injected either carbon dioxide made from carbon- 13 or carbon- 14 ¹³CO₂ and ¹⁴CO₂, isotopes of carbon) . As the seedlings photosynthesized, the radioactive carbon dioxide was converted into radioactively labelled sugars that could be tracked and measured by the researchers.
Figure 29.2
-Referring to Simard et al. 1997) , which design element is the control in this experiment and why?

A) the cedar seedling, because it is not bagged
B) the cedar seedling, because it forms arbuscular mycorrhizae
C) the fact that all the seedlings are different species
D) the bags over the seedlings to contain the different types of carbon dioxide