Q21

[tzyc]

I guess A represents how the bacteria change their movement depending on substances.
But I have a question about their behavior...
The passage says:
"Most types of bacteria swim very erratically;
short smooth runs in relatively straight lines are followed by brief tumbles, after which the bacteria shoot off in random directions"
This means they move straight and tumble alternatively correct? (straight, tumbling, straight...etc.)
The passage only says "attractant" and discusses how it behaves when there is attractant or leave from it. By the wording "attractant" I thought it is the thing bacteria like (so attract to it) but it actually includes harmful substance? (from Q17)
Also the sentence before the last sentence in the last paragraph... "If, on the other hand bacteria detect.....would not be uniform", why they cannot respond to the substance? Even if it's true that they detect the substance by front and back, or even it's suddenly or not I think they can still detect it either by front or back...can't they? (related Q20 maybe)

Thank you

[tommywallach]

Hey Tz,

I'm not totally sure what you want to know in general, so I'll just answer your specific questions and hope that helps!

1) Yes, they move straight and tumble alternately.

2) Attractant means the thing they like, not the harmful stuff.

3) I think this is saying that if the bacterium make it to the attractant (area where the attractant is high concentration EVERYWHERE), then this system would be bad, because there wouldn't be any difference front and back, so they might start tumbling away again, because they couldn't prove they were moving up the concentration gradient.

Hope that helped!

-t

[tzyc]

Hi, thank you for your answers.
I still have a question about 2)...
I wondered whether "attractant" includes harmful things because Q17 asks about it and I think the answer E for it shows the same behavior as when it reacts to "attractant".
(when it's moving away from "attractant" or harmful things, it increases tumbling)
If they are different, how can we infer the answer would be E?

Thank you