Passage - General Questions

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Passage Discussion

VIEWSTAMP Analysis:


This explanation is still in progress. Please post any questions below!

[tetsuya0129]

Hi Powerscore,

I have a problem with understanding a clause in Line 30 -32, quoted "...,whereas runs aways from it are shortened by an increased tendency of the bacteria to tumble and change direction."

My understanding regarding the entire second paragraph is the same as the above post, but the quote-unquote seems, to me, contradictory with the understanding!

Based on the clause, when the tumbling tendency increases, then bacteria will less likely to run away from the "good stuff", given "runs aways from it are shortened ".
I just can't figure out this clause! Any helps, please!?

Thanks!

[Frank Peter]

HI Tetsuya,

This is a fairly challenging passage, but the best way to aid in your understanding when you encounter technical material like this is to revisit other parts of the passage, since the additional material can often add valuable context.

The sentence starting around line 23 gives us better idea of what is going on here: "As the bacteria encounter increasing
concentrations of the attractant, their tendency to (25) tumble is suppressed, whereas tumbling increases whenever they move away from the attractant."

Now let's consider lines 30-32: "(30) whereas runs away from it are shortened by an increased tendency of the bacteria to tumble and change direction."

Recall that when the author talks about "runs" they are talking about "short smooth runs in relatively straight lines."

So in other words, what the author seems to be saying here is that the bacteria is less likely to move in a straight line away from the attractant; such movement is shortened by an increased tendency to tumble.

[Sydneymkim]

Hi,

How would you best outline each paragraph for this passage? I found it quite hard to simplify and feel like I was wasting time trying to write down important things from each paragraph. And even from my own outline, I was finding it hard to answer the questions. Could I please get someone to show me how they would outline it? Thank you so much in adv!

What I did was:

Paragraph 1 - Introduce B (shortened for Bacteria) and Researchers' question about how B's swim when attracted/repelled.

Paragraph 2 - one clue to the researcher's question is explained

Paragraph 3- two mechanisms are introduced to show how B detects change in concentration. The last sentence highlights evidence shows B comparing concentrations at different times (one of the mechanisms introduced)

[Rachael Wilkenfeld]

Hi Sydneymkim,

Let me give you my breakdown.

P1:Intro puzzle: question: How purposeful movement if random tumbles?

By this, I mean that the first paragraph structurally introduces a puzzle. We know bacteria engage in purposeful movement toward an attractant and away from a repellant. They do so by moving in straight runs and random tumbles. That drives the questions by scientists: How can there be purposeful movement if the bacteria sometimes randomly tumble?

P2: Movement in context: Obs of movement toward attractant. Closer=more straight, less tumble.

By this, I mean that the paragraph provides a deeper description of bacteria movement in the context of an attractant. In that case, as the bacteria move closer to the attractant, they suppress the random tumble in favor of longer, controlled runs.

P3: How control movement: 2 theories 1) simul front/back test 2) different time test. Exp shows change time (2).

By this, I mean that the paragraph serves to provide an explanation of how bacteria know to move toward an attractant and proposes two possible theories. The first theory is that the bacteria simultaneously test the front and back, and move in the direction where the attractant has a higher concentration. The second theory says that as bacteria move, they test the attractant level at slightly different times to compare when they detect more attractants and use that to determine which direction to move. The passage ends with experimental data suggesting that the bacteria engage in the second method of detecting attractants.

Ultimately, outlining/diagramming passages is a very personal project. I tend to focus on the structural piece much more than the details. In most passages, I also have a lot more on viewpoints than I do here because there are not a ton of viewpoints expressed in this passage. There are the two possible theories of detection by bacteria, and that's covered well in P3.

I'd also prephrase (though not in writing) the main point: I'd be looking for something like "although bacteria engage in both predictable straight runs and random tumbles, they are able to direct their movement toward an attractant seemingly by detecting the attractant level at different times and use that information to suppress tumbles as they move closer to the attractant they seek. " Though this passage does not have a main point question, it is always helpful to note the main point to focus on the purpose of the passage before jumping into the questions.

Hope that helps!