Only some strains of the tobacco plant are naturally resistant to tobacco mosaic virus, never becoming diseased even when infected. ████ █████████ ███████ ████ ██████████████ ████████ ████ ███ ██████ ██████ ██ █████████ █████████ █████████ ████ ██ █████ ██████ █████████ █████████ ██ ████ ████████ ████████ ██ ███ ████████████ ███████ ██ █ ██████ ███████████ ██ ████████████ ███████ ██████ ████ ███████ ██ ███████ ██████ ██████ ███ ██ ██ ████ ████ ████████ ████ █████████ █████ ████ ██ █████ ██ ██████ ██████ █████ ██ ██████████ ████████ ███ █████ ██ ██████ █████████ ██ ███ ████████
The stimulus gives us the results of two experiments involving tobacco mosaic virus and salicylic acid.
First, some background: only some strains of tobacco plants are naturally resistant to tobacco mosaic virus. Resistant strains never get sick, even when infected with the virus.
Experiment 1: Researchers infected resistant strains with the virus. In those resistant plants, levels of naturally occurring salicylic acid increased fivefold. Nonresistant plants that were infected showed no such increase in salicylic acid.
So Experiment 1 tells us there's a correlation between resistance and salicylic acid production. When infected, resistant plants ramp up salicylic acid; nonresistant plants don't.
Experiment 2: Researchers took 50 nonresistant plants and exposed them to the virus. Half were injected with salicylic acid, and half were not. The 25 that received salicylic acid showed no signs of infection. The 25 that didn't receive it all got sick.
Experiment 2 tells us that when you give nonresistant plants salicylic acid, they behave like resistant plants. They don't get sick. This is evidence that salicylic acid can help the tobacco plants resist mosaic virus.
Since this is a Most Strongly Supported question, there's no argument to evaluate, and we don't need the correct answer to be something that must be true. We just need the answer that is best supported by the information in the stimulus. That's worth keeping in mind here, because although we can't prove that salicylic acid must be involved in helping the plants resist the virus, we do have strong evidence supporting that hypothesis. Resistant plants produce salicylic acid when infected, and nonresistant plants don't. And, when you inject nonresistant plants with it, they are less susceptible to the disease. This suggests salicylic acid may be a causal difference-maker in resistance to mosaic virus.
Which one of the following ███████████ ██ ████ ████████ █████████ ██ ███ ███████ ██ ███ ████████████
Tobacco plants that ████ ██████ ████████ ██ █████████ ████ ███████ ██████ █████ ███ ██ █████ ██ █████████ ████ ████ █████████ █████
The experiments never tested whether salicylic acid could cure plants that had already become diseased. In Experiment 2, the nonresistant plants were injected with salicylic acid and exposed to the virus, but we're told they
Producing salicylic acid ██ ██ █████ ████ ██ ███ █████████ ██ █████ ████ ███████ ██████ █████████ ██████ ███ ███████ ██████ ██ ███████ ██████ ██████
Both experiments support this. Experiment 1 showed that resistant plants produce elevated levels of salicylic acid when infected, while nonresistant plants do not. That's a correlation between natural resistance and salicylic acid production. Experiment 2 went further and showed that giving salicylic acid to nonresistant plants allowed them to resist the disease. Together, these results strongly support the idea that producing salicylic acid is at least part of how naturally resistant plants fight off tobacco mosaic virus.
Notice the careful language of this answer: "at least part of the mechanism." It doesn't claim salicylic acid is the entire explanation for resistance. That's an appropriately modest claim given the data, which makes it well supported.
Salicylic acid is ███ ████████ ██ ███████ ██ ███████ ██████ ████ ███ ███ █████████ ██ ███████ ██████ ██████
The stimulus tells us that when nonresistant plants were infected, there was no increase in naturally occurring salicylic acid levels. But that doesn't mean nonresistant plants produce no salicylic acid at all. They do have naturally occurring salicylic acid. It's just that their acid level didn't increase as much as acid level of the resistant strains.
It is possible ██ ████ ██ ██████████ ███████ █████ ███ ██████████ ██ ███████ ██████ █████ ██ █████████ ███ █████ ██ █████████ ████ ██ █████████
This suggests we could test whether an uninfected plant is resistant by measuring its salicylic acid levels. But the stimulus only told us about salicylic acid levels after infection. The fivefold increase in resistant plants occurred when they were
The production of █████████ ████ ██ ███████ ███████ ██ ███████ ██████ ███ ██ █████████ ███ ████ ███ ███████ ████ █████████ ██ ███████ ██████ ██████
This claims that we can increase salicylic acid production in certain strains and thereby make them resistant. But Experiment 2 didn't increase the plants' production of salicylic acid. The researchers injected salicylic acid into the plants from an external source. That's different from the plants producing it themselves. Nothing in the stimulus tells us whether it's possible to get nonresistant plants to produce more salicylic acid on their own.