Although bacteria are unicellular and among the simplest autonomous

Hi everyone,
Got 5/6 correct in around 13 minutes.

----------------------------------------------------------------------------------------



P1

Paragraph one starts with a contrast: while unicellular bacteria (UB) are very small they have a sharp ability to sense the environment. They can be attracted by food and repelled by harmful substances.
Their movements consists on smooth runs and tumbles, the latter described as something random.
Their movements puzzle scientists who cannot explain how UB can reach food.

Brief summary: UB puzzle scientists because of their erratic movements

P2

Paragraph two attempts to explain the puzzling fact seen in P1. We can see that a bacteria when approaching an attractant increases its smooth runs (and decreases the tumblings) while when going away fro the attractant the tumbling increases (and the smooth runs decrease).

Brief summary: UB's behavior in presence of an attractant

P3

Paragraph three describes two methods that could be used by Ub to detect concentration of attractants. The first method is to perceive the concentration from the back and the from of the UB simultaneously. If it is perceived on the front side, for example, the UB will move with smooth runs in that direction.
On the other hand the second methods state that the UB could make measurements in different time frames. Then we are given that, if the first method is used and high concentrations of attractants are present both on the front and back side, the UB would not move.
Finally we are given that experiments suggest that the second method be used.

Brief summary: Two methods for detecting attractants concentrations are described and one is considered valid by experimental data

Main point

The main point is to investigate the behavior of UB when they move to attractants

----------------------------------------------------------------------------------------


1. It can be inferred from the passage that which one of the following experimental results would suggest that bacteria detect changes in the concentration of an attractant by measuring its concentration in front and back of the cell body simultaneously?

Pre-thinking

Inference question

Refer to the last paragraph.

"If, on the other hand, bacteria detect a chemical gradient by measuring it simultaneously at two distinct points, front and back, on the cell body, they would not respond to the jump in concentration because the concentration of the attractant in front and back of the cells, though high, would be uniform."


(A) When suddenly transferred from a medium in which the concentration of an attractant was uniformly low to one in which the concentration was uniformly high,the tendency of the bacteria to tumble and undergo random changes in direction increased.
As stated in pre-thinking the bacteria should not move

(B) When suddenly transferred from a medium in which the concentration of an attractant was uniformly low to one in which the concentration was uniformly high, the bacteria’s exhibited no change in the pattern of their motion.
In line with pre-thinking

(C) When suddenly transferred from a medium in which the concentration of an attractant was uniformly low to one in which the concentration was uniformly high, the bacteria’s movement was characterized by a complete absence of tumbling.
does the bacteria increases or decreases its smooth runs or does it stay put?

(D) When placed in a medium in which the concentration of an attractant was in some areas low and in others high, the bacteria exhibited an increasedtendency to tumble in those areas where the concentration of the attractant was high.
it should increases its smooth runs

(E) When suddenly transferred from a medium in which the concentration of an attractant was uniformly low to one that was completely free of attractants, the bacteria exhibited a tendency to suppress tumbling and move in longer, straighter lines.
Cannot be inferred

----------------------------------------------------------------------------------------


2. It can be inferred from the passage that a bacterium would increase the likelihood of its moving away from an area where the concentration of a harmful substance is high if it did which one of the following?

Pre-thinking

Inference question

From the second paragraph we know that as a UB goes away from an high concentration of an attractant its tumbling should increase. We can infer from this that when it moves away from a repellant it's tumbling decreases


(A) Increased the speed at which it swam immediately after undergoing the random changes in direction that result from tumbling.
Not in line with pre-thinking

(B) Detected the concentration gradient of an attractant toward which it could begin to swim.
Cannot be inferred

(C) Relied on the simultaneous measurement of the concentration of the substance in front and back of its body, rather than on the comparison of the concentration at different points in time.
Out of context. Mentioned in P3

(D) Exhibited a complete cessation of tumbling when it detected increases in the concentration of substance.
Opposite

(E) Exhibited an increased tendency to tumble as it encountered increasing concentrations of the substance, and suppressed tumbling as it detected decreases in the concentration of the substance.
In line with pre-thinking

----------------------------------------------------------------------------------------


3. It can be inferred from the passage that when describing bacteria as “swimming up a concentration gradient” (Highlighted), the author means that they were behaving as if they were swimming

Pre-thinking

Inference question

Toward an attractant


(A) Against a resistant medium that makes their swimming less efficient.
Not in line with pre-thinking

(B) Away from a substance to which they are normally attracted.
Not in line with pre-thinking

(C) Away from a substance that is normally harmful to them.
Not in line with pre-thinking

(D) From an area where the concentration of a repellent is weaker to an area where it is completely absent.
Not in line with pre-thinking

(E) From an area where the concentration of a substance is weaker to an area where it is stronger.
in line with pre-thinking


----------------------------------------------------------------------------------------


4. The passage indicates that the pattern that characterizes a bacterium’s motion changes in response to

Pre-thinking

Detail question

The concentration of an attractant or repellant


(A) The kinds of chemical attractants present in different concentration gradients.
Not in line with pre-thinking

(B) The mechanism that the bacterium adopts in determining the presence of an attractant.
Not in line with pre-thinking

(C) The bacterium’s detection of changes in the concentration of an attractant.
in line with pre-thinking

(D) The extent to which neighboring bacteria are engaged in tumbling.
Not in line with pre-thinking

(E) Changes in the intervals of time that occur between the bacterium’s measurement of the concentration of an attractant.
Not in line with pre-thinking


----------------------------------------------------------------------------------------


5. Which one of the following best describes the organization of the third paragraph of the passage?

Pre-thinking

Structure question

Two methods are introduced and described----> experimental data suggest that one be the best


(A) Two approaches to a problem are discussed, a test that would determine which is more efficient is described, and a conclusion is made, based on experimental evidence.
Not in line with pre-thinking

(B) Two hypotheses are described, a way of determining which of them is more likely to be true is discussed, and one said to be more accurate on the basis of experimental evidence.
in line with pre-thinking

(C) Two hypotheses are described, the flaws inherent in one of them are elaborated, and experimental evidence confirming the other is cited.
Not in line with pre-thinking

(D) An assertion that a species has adopted two different mechanisms to solve a particular problem is made,and evidence is then provided in support of that assertion.
Not in line with pre-thinking

(E)An assertion that one mechanism for solving a particular problem is more efficient than another is made, and evidence is then provided in support of that assertion.
Not in line with pre-thinking

----------------------------------------------------------------------------------------


6. The passage provides information in support of which one of the following assertions?

Pre-thinking

Inference question

Let's analyze the answer choices


(A) The seemingly erratic motion exhibited by a microorganism can in fact reflect a mechanism by which it is able to control its movement.
supported

(B) Biologists often overstate the complexity of simple organisms such as bacteria.
Not in line with pre-thinking

(C) A bacterium cannot normally retain a memory of a measurement of the concentration of an attractant.
Not in line with pre-thinking

(D) Bacteria now appear to have less control over their movement than biologists had previously hypothesized.
Not in line with pre-thinking

(E) Photosynthetic bacteria appear to have more control over their movement than do bacteria that are not photosynthetic.
Not in line with pre-thinking


----------------------------------------------------------------------------------------

It is a good day to be alive