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What does the bold "it" in the italicized line refer to, the bacterium or a desirable chemical?

Anyway the sentence containing it evades me. What does the sentence mean?

A bacterium is so small that its sensors alone can give it no indication of the direction that a good or bad chemical is coming from. To overcome this problem, the bacterium uses time to help it deal with space. The bacterium is not interested in how much of a chemical is present at any given moment, but rather in whether that concentration is increasing or decreasing. After all, if the bacterium swam in a straight line simply because the concentration of a desirable chemical was high, it might travel away from chemical nirvana, not toward it, depending on the direction it’s pointing. The bacterium will swim in a straight line as long as the chemicals it senses seem better now than those it sensed a moment ago. The bacterium solves this problem in an ingenious manner: as it senses its world, one mechanism registers what conditions are like right now, and another records how things were a few moments ago. If not, it’s preferable to change course.

Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness

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  • Can you clarify which line you are referring to by marking the sentence in bold font? I'm on a mobile viewport, not sure which is line 5.
    – mjjf
    Jan 2 at 5:50
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"It" is the bacterium.

The bacterium is in the presence of stuff it likes, and it wants to go in the direction where there is more of that stuff. It can't tell which direction that stuff is coming from. So, it (the bacterium) starts off by travelling in a random direction.

It might be that it is travelling in the right direction. If so, it would detect that the concentration of nice stuff is increasing. On the other hand, it may be travelling in the wrong direction. If that is so, it would detect that the concentration of nice stuff is decreasing. In which case it has to start travelling in the opposite direction.

So the sentence means something like:

"If:

--> the bacterium starts moving

because

--> it detects it is in the nice stuff and wants more of it

then

--> it is possible it is moving in the wrong direction (because it does not know what direction it is supposed to go).

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After all, if the bacterium swam in a straight line simply because the concentration of a desirable chemical was high, it might travel away from chemical nirvana, not toward it, depending on the direction it’s pointing.

In this case, "it's" refers to the bacterium that is swimming. I don't know what specific grammar rules are applicable, but the context shows that we are interested in the path a bacterium is swimming in relation to a "chemical nirvana". The fragment "it might travel away from chemical nirvana, not toward it, depending on the direction it’s pointing" tells us that the direction the bacterium is pointing may affect its path toward or away from this nirvana.

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There are three uses of "it" in the same sentence, and they don't all refer to the same thing. I think I can discern the intended meaning, but as the question has been asked we can deduce that there is some lack of clarity. I do not see this use of "it" as good style.

it might travel away from chemical nirvana, not toward it, depending on the direction it’s pointing

we see the three occurrences of "it":

it might travel ... not toward it ... direction it’s pointing

The first and third "it" refer to the bacterium and the second refers to the "chemical nirvana". Spelling it out

the bacterium might travel away from chemical nirvana, not toward the chemical nirvana, depending on the direction the bacterium is pointing.

Which is clear, but pedestrian. I would avoid the second "it" completely:

the bacterium might travel away from, not towards, the chemical nirvana depending on the direction it's pointing.

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