[Campbell Biology P.716] The "WHAT IF?" question in Figure 31.22 asks about control treatmen... | Practice Question

The "WHAT IF?" question in Figure 31.22 asks about control treatments for the experiment. Based on standard experimental design principles, which two additional control treatments would be most helpful for a comprehensive interpretation of the results described?

  • A: (1) Cacao seedlings with endophytes but no pathogen (E+P-), to show the effect of endophytes alone; (2) Cacao seedlings with pathogen but no endophytes (E-P+), to show the effect of the pathogen alone.
  • B: (1) Cacao seedlings with endophytes but no pathogen (E+P-), to ensure endophytes themselves aren't harmful; (2) Cacao seedlings with neither endophytes nor pathogen (E-P-), to establish a baseline for healthy growth.
  • C: (1) Cacao seedlings with heat treatment, to see if heat stress affects endophyte colonization; (2) Cacao seedlings with drought, to test endophyte tolerance to water scarcity.
  • D: (1) Cacao seedlings inoculated with a different type of pathogen, to test pathogen specificity; (2) Cacao seedlings grown in different soil types, to see environmental influences.

Explanation

The existing experiment compares E-P+ pathogen present, no endophyte and E+P+ both present . To fully interpret the results, two crucial controls are needed: 1 E+P- endophyte present, no pathogen to confirm that the endophytes themselves are not harmful to the plant, verifying the 'symbiotic' nature. 2 E-P- neither endophyte nor pathogen to establish a baseline of healthy, uninfected plant growth, allowing for an absolute comparison of the pathogen's impact and the endophyte's protective effect against a truly healthy state.