A finding question with competing causes tests whether evidence supports one cause over another. Put the claim in a few words, including what changes, what it affects, and which cause it rejects. Then ask what result would separate the competing causes, because a result both causes predict can't tell them apart. If the claim says a response changes, track the effect across the change as well. A finding must support the whole claim, not only one part.
Hints
- Hint 1
Read the hypothesis as two questions: what should guide phosphorus allocation, and what competing cause do the researchers reject? Put both parts in a few words.
- Hint 2
Look at the trials in which carbon supply and water loss point in different directions. What would each proposed cause predict in those trials?
- Hint 3
The researchers reverse the treatments midway through each trial. Apply the hypothesis again after the reversal: which plant is supplying more carbon then?
Step-by-step
Separate the causes and track the switch
Step 1Put the claim in a few words
The fungus is supposed to change its phosphorus allocation according to which plant is currently supplying more carbon. What does that claim predict for a connected pair? The plant providing more carbon should get more phosphorus, so the favored plant depends on current carbon supply, not on which individual it is.
- Step 2
Separate the competing causes
Could water loss explain the same phosphorus advantage? The rival idea ties extra phosphorus to greater water loss, called transpiration, because the water flow could carry phosphorus into roots. When the same plant leads in carbon supply and transpiration, either cause could explain its phosphorus advantage. Let's use trials where the carbon supplier transpired less than its partner, because the two causes predict different winners there.
- Step 3
Test the findings against both parts
The researchers also reversed the light and humidity treatments between the two plants. Which findings pass both tests? Whenever it also transpired more leaves the two causes tied together, while faster-transpiring plant favors the water-loss rival when they conflict. The same individual continued means phosphorus no longer follows carbon supply after reversal. The phosphorus advantage must respond to the new carbon supplier.
- Step 4
Match the full hypothesis
In the finding with even in trials in which it transpired less, the plant supplying more carbon absorbs more tagged phosphorus despite lower water loss. It also reports that the phosphorus advantage switches whenever the carbon advantage switches. That shows allocation follows the current carbon supplier, both before and after the treatments change. Choice A.