#23 - Scientist: Some colonies of bacteria produce

[sxzhao]

I understand A is correct but having a hard time eliminating C. To me, both choices speak to the situation where phenazines are absent to provide support to the hypothesis.

Under choice A, wrinkle is formed to compensate for phenazines' absence. The fact that wrinkles increase contact with surroundings speaks to the same function of phenazines.

Under choice C, "being buried in nutrient-rich soil" compensates for phenazines' absence. The result that both groups grow with the same speed speaks to phenazines' function to help absorb nutrients needed.

Please help with my understanding here. Thanks!

[Adam Tyson]

I'm not seeing how answer C helps the argument at all, sxzhao. As we said in our initial explanation, the growth of the colony doesn't tell us much about what's happening in the center of the colony. Maybe it's growing because all the molecules at the edges have a generous supply of nutrients, and the ones at the center die off?

Another way to look at answer C is to say that when there are a lot of nutrients around, phenazines aren't essential to overall growth. But the argument isn't that phenazines are only needed when nutrients are scarce; it's just about what phenazines do. Answer C does nothing to support the hypothesis that they serve as nutrient pipelines.