If newly hatched tobacco hornworms in nature first feed on plants from

Question

If newly hatched tobacco hornworms in nature first feed on plants from the nightshade family, they will not eat leaves from any other plants thereafter. However, tobacco hornworms will feed on other sorts of plants if they feed on plants other than nightshades just after hatching. To explain this behavior, scientists hypothesize that when a hornworm's first meal is from a nightshade, its taste receptors become habituated to the chemical indioside D, which is found only in nightshades, and after this habituation nothing without indioside D tastes good.

Which one of the following, if true, adds the most support for the hypothesis?

A. Tobacco hornworms that first fed on nightshade leaves show no preference for any one variety of nightshade plant over any other.
B. If taste receptors are removed from tobacco hornworms that first fed on nightshade leaves, those hornworms will subsequently feed on other leaves.
C. Tobacco hornworm eggs are most commonly laid on nightshade plants.
D. Indioside D is not the only chemical that occurs only in nightshade plants.
E. The taste receptors of the tobacco hornworm have physiological reactions to several naturally occurring chemicals.

LamboWalker · Answer

Hornworms that first feed on nightshade do not eat anything else. It is concluded that this happens because the hornworm's tastebuds become habituated to some chemical present in the nightshade. We are required to strengthen the argument.

A. Tobacco hornworms that first fed on nightshade leaves show no preference for any one variety of nightshade plant over any other. 
Runner up. This is not exactly strengthening the argument, but can be left until a better option is found.

B. If taste receptors are removed from tobacco hornworms that first fed on nightshade leaves, those hornworms will subsequently feed on other leaves. 
Correct answer. The adaptation of taste receptors must then be the sole reason why those worms do not feed on anything else.

C. Tobacco hornworm eggs are most commonly laid on nightshade plants. 
This is weakening the argument if anything.

D. Indioside D is not the only chemical that occurs only in nightshade plants. 
Out of scope.

E. The taste receptors of the tobacco hornworm have physiological reactions to several naturally occurring chemicals. 
Again, out of scope of the argument.

Answer is  B .

unraveled · Answer

If newly hatched tobacco hornworms in nature first feed on plants from the nightshade family, they will not eat leaves from any other plants thereafter. However, tobacco hornworms will feed on other sorts of plants if they feed on plants other than nightshades just after hatching. To explain this behavior, scientists hypothesize that when a hornworm's first meal is from a nightshade, its taste receptors become habituated to the chemical indioside D, which is found only in nightshades, and after this habituation nothing without indioside D tastes good.

Which one of the following, if true, adds the most support for the hypothesis?

A. Tobacco hornworms that first fed on nightshade leaves  show no preference for any one variety of nightshade plant over any other . - WRONG. What about taste that differs from nightshade and other plants.
B.  If  taste receptors are removed from tobacco hornworms that first fed on nightshade leaves, those  hornworms will subsequently feed on other leaves . - CORRECT. This conditional gives a window where the conclusion may falter hence what passage said is right. Strengthens thus.
C. Tobacco hornworm  eggs are most commonly laid  on nightshade plants. - WRONG. Misses the taste aspect.
D. Indioside D is  not the only chemical that occurs only  in nightshade plants. - WRONG. Irrelevant. 
E. The taste receptors of the tobacco hornworm have physiological reactions to several naturally occurring chemicals. - WRONG. Would weaken somewhat.

Answer B.

agrasan · Answer

Hi  KarishmaB   MartyMurray

To explain this behavior, scientists hypothesize that when a hornworm's first meal is from a nightshade,  its taste receptors become habituated to the chemical indioside D , which is found only in nightshades, and after this habituation nothing without indioside D tastes good.

A. Tobacco hornworms that first fed on nightshade leaves show no preference for any one variety of nightshade plant over any other.

Can we eliminate (A) on the basis of reasoning that it is reiterating the fact    "its taste receptors become habituated to the chemical indioside D"   ?   Indioside D will be present in all varieties of nightshade plants so there should be no preference, thus, it is consistent with the premise.

guddo · Answer

If newly hatched tobacco hornworms in nature first feed on plants from the nightshade family, they will not eat leaves from any other plants thereafter. However, tobacco hornworms will feed on other sorts of plants if they feed on plants other than nightshades just after hatching. To explain this behavior, scientists hypothesize that when a hornworm's first meal is from a nightshade, its taste receptors become habituated to the chemical indioside D, which is found only in nightshades, and after this habituation nothing without indioside D tastes good. 
 
Which one of the following, if true, adds the most support for the hypothesis?

The hypothesis is a specific mechanism: first eating nightshade changes the hornworm’s taste receptors so that leaves without indioside D do not taste good. The best support should link the later eating behavior directly to the taste receptors, not to egg laying or general facts about nightshades.

A. Tobacco hornworms that first fed on nightshade leaves show no preference for any one variety of nightshade plant over any other.

This is consistent with “nightshades taste good,” but it does not specifically support the indioside D habituation mechanism.

B. If taste receptors are removed from tobacco hornworms that first fed on nightshade leaves, those hornworms will subsequently feed on other leaves.

This strongly supports the hypothesis. If removing taste receptors makes them eat other leaves, it shows the refusal is driven by taste reception, which is exactly what the habituation story predicts.  This is the strongest support.

C. Tobacco hornworm eggs are most commonly laid on nightshade plants.

This may explain why they often start on nightshades, but it does not explain why that first meal changes later taste and eating behavior.

D. Indioside D is not the only chemical that occurs only in nightshade plants.

This undercuts the “only indioside D matters” idea, because it suggests other nightshade only chemicals could be responsible instead. So it does not add support.

E. The taste receptors of the tobacco hornworm have physiological reactions to several naturally occurring chemicals.

This is too general. It does not connect the first nightshade meal to a lasting change in what tastes good. It does not support the key  habituation to indioside D  claim.

Answer: (B)

MartyMurray · Answer

While what you're said to an extent captures how we can eliminate (A), what you've said isn't completely accurate.

The idea of the argument is that the presence of indioside D becomes NECESSARY for something to taste good to a hornworm.

What you've said, " Indioside D will be present in all varieties of nightshade plants so there should be no preference," means that indioside D becomes SUFFICIENT for something to taste good to a hornworm. The facts presented by the passage do not support that inference.

So, we can say that, rather than reiterates something said by the passage, (A) actually adds new information indicating that different characteristics of different nightshade leaves do not affect hornworms' eating habits.

Accordingly, the reason we can eliminate (A) is not that it simply reiterates what the passage says but rather that the information it provides does nothing to indicate that habituation of taste receptors is the cause of the observed eating pattern.

After all, the fact that hornworms don't differentiate between different types of nightshade leaves doesn't indicate why they prefer nightshade leaves in general.

guddo · Answer

Yes, that’s a solid way to eliminate (A).

(A) is basically what you would already expect if the hypothesis is true: if indioside D is the key “good taste” chemical and it is present across nightshades, then all nightshade varieties should be acceptable, so no strong preference follows. That makes (A)  consistent  with the hypothesis, but it does not  test or strengthen  the causal mechanism, because even other explanations (like “they just imprint on the general nightshade taste”) could also produce no preference.

So (A) is not adding support; it is just  compatible  with the story.

If newly hatched tobacco hornworms in nature first feed on plants from

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