Reading ComprehensionDifficulty: Hard

PT110 S1 P3 Q18 Explanation

Lamarck’s Theory

A free, expert breakdown of this official LSAT Reading Comprehension question.

TopicsInferenceScience

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Passage

In the eighteenth century the French naturalist Jean Baptiste de Lamarck believed that an animal’s use or disuse of an organ affected that organ’s development in the animal’s offspring. Lamarck claimed that the giraffe’s long neck, for example, resulted from its ancestors stretching to reach distant leaves. But because biologists could find characteristics never occurs. Yet new research has uncovered numerous examples of the phenomenon.

In bacteria, for instance, enzymes synthesize and break down rigid cell walls as necessary to accommodate the bacteria’s growth. But if an experimenter completely removes the cell wall from a bacterium, the process of wall synthesis and breakdown is disrupted, and the bacterium continues to grow—and multiply indefinitely—without walls. This inherited absence interactions among genes, without any attendant changes in the genes themselves.

A fundamentally different kind of environmentally induced heritable characteristic occurs when specific genes are added to or eliminated from an organism. For example, a certain virus introduces a gene into fruit flies that causes the flies to be vulnerable to carbon dioxide poisoning, and fruit flies infected with the virus will pass an ability that normally would have taken eons to develop through random mutation and natural selection.

The new evidence suggests that genes can be divided into two groups. Most are inherited “vertically,” from ancestors. Some however, seem to have been acquired “horizontally,” from viruses, plasmids, bacteria, or other environmental agents. The evidence even appears to show that genes can be transmitted horizontally between organisms that are considered to has long eluded biologists, and that may eventually prove Lamarck’s hypothesis to be correct.

What this question is testing

Inference

Your task

Find what must be true based on what the passage or stimulus states.

Common trap

Answers that are plausible or likely but not actually guaranteed by the text.

Winning move

Keep only the choice the statements fully support — eliminate anything that requires an extra assumption.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
18.

Which one of the following can be inferred from the passage about the absence of cell walls

Answer choices

  1. Unsupported: can be reversed3% picked this

    It can be reversed by introducing the

    Nothing in our Support Window talks about reversing the process and putting the wall back in. Since we're told that the change resulted from how the genes interact, not which genes are there, we don't have any support for thinking that adding or subtracting genes makes a difference here.

  2. Unsupported: introducing a gene5% picked this

    It can be brought about by a virally

    Nothing in our Support Window talks about adding in a new gene in order to cause a loss of cell wall. We were only told about a case of cell-wall loss as a result of a scientist yanking it out.

  3. Correct64% picked this

    It can be caused by the loss of a cell wall in

    Why this is right

    This is supported by the 2nd sentence in the 2nd paragraph. If an experimenter removes the cell wall from a bacterium, the process .. is disrupted and the bacterium continues to grow without walls. The absence of cell walls was caused by the experimenter removing one singular cell wall from one singular bacterium. From there, the bacterium keeps growing (i.e. reproducing), so it becomes a plural bacteria, and so this bacteria inherited its absence of cell walls from that researcher's removal of a single cell wall in a single bacterium.

    Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.

  4. Out of Scope: halted5% picked this

    It can be halted, but not reversed, by restoring cell walls to a

    The Support Window doesn't mention anything about a capacity to halt the absence of cell walls. What does that even mean? How can you halt an absence of cell walls? That would mean you again have cell walls?

  5. Unsupported: transmitted horizontally23% picked this

    It can be transmitted horizontally to

    The Support Window never discusses the capacity for "wall-lessness" to be transmitted from one bacteria to another. It's only saying that the original bacterium continues to reproduce in a wall-less fashion, but never that it transfers that trait to someone else. In fact, since we're told that wall-lessness is not a trait of the genes themselves (but the interaction between the genes) , it seems even less likely that it is a DNA-transmittable trait.

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