Question

Which of the following is MOST useful in determining whether two organisms are related?
A. Both are motile
B. Both ferment lactose.
C. Both are gram-positive.
D, Both are aerobic.

Answer 1

We have to choose the most specific choice.

Let's go through a process of elimination.

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A isn't the answer.

To be "motile" means "to be able to move."

Many organisms can move.
We humans can move.
So can birds.
So can bacteria.

Choice A is too general, you see?
Not specific enough.

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D isn't the answer either.

"Aerobic" means that the organism needs oxygen, in order to live.

Again, many organisms need oxygen to live.
That's why choice D is also too general.

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Now now, let's look at B and C.

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Choice B is talking about bacteria.
Because bacteria ferment lactose.

But there are two main groups of bacteria:
1. Gram positive
2. Gram negative

Bacteria from both groups can ferment lactose.

So choice B seems a little general.

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So now, we go with C.

Out of all the choices, C is the most specific.
It really narrows down the number of organisms that we could be talking about.

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Did you understand all of that, no problem?