It was once assumed that all living things could be divided into two fundamental and exhaustive categories. Multicellular plants and...
GMAT Reading Comprehension : (RC) Questions
It was once assumed that all living things could be divided into two fundamental and exhaustive categories. Multicellular plants and animals, as well as many unicellular organisms, are eukaryotic—their large, complex cells have a well-formed nucleus and many organelles. On the other hand, the true bacteria are prokaryotic cell, which are simple and lack a nucleus. The distinction between eukaryotes and bacteria, initially defined in terms of subcellular structures visible with a microscope, was ultimately carried to the molecular level. Here prokaryotic and eukaryotic cells have many features in common. For instance, they translate genetic information into proteins according to the same type of genetic coding. But even where the molecular processes are the same, the details in the two forms are different and characteristic of the respective forms. For example, the amino acid sequences of various enzymes tend to be typically prokaryotic or eukaryotic. The differences between the groups and the similarities within each group made it seem certain to most biologists that the tree of life had only two stems. Moreover, arguments pointing out the extent of both structural and functional differences between eukaryotes and true bacteria convinced many biologists that the precursors of the eukaryotes must have diverged from the common ancestor before the bacteria arose.
Although much of this picture has been sustained by more recent research, it seems fundamentally wrong in one respect. Among the bacteria, there are organisms that are significantly different both from the cells of eukaryotes and from the true bacteria, and it now appears that there are three stems in the tree of life. New techniques for determining the molecular sequence of the RNA of organisms have produced evolutionary information about the degree to which organisms are related, the time since they diverged from a common ancestor, and the reconstruction of ancestral versions of genes. These techniques have strongly suggested that although the true bacteria indeed form a large coherent group, certain other bacteria, the archaebacteria, which are also prokaryotes and which resemble true bacteria, represent a distinct evolutionary branch that far antedates the common ancestor of all true bacteria.
The passage is primarily concerned with
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| It was once assumed that all living things could be divided into two fundamental and exhaustive categories. | What it says: Scientists used to think there were exactly two types of living things - no more, no less. What it does: Sets up the historical scientific view that will be challenged Source/Type: Statement of historical scientific consensus Connection to Previous Sentences: This is our starting point - no previous information to connect to Visualization: Think of a simple family tree with just 2 main branches splitting from one trunk Reading Strategy Insight: Note "It was once assumed" - this signals the author will likely challenge this old view What We Know So Far: Old scientific view = exactly 2 categories of life What We Don't Know Yet: What these 2 categories are, why this view might be wrong |
| Multicellular plants and animals, as well as many unicellular organisms, are eukaryotic—their large, complex cells have a well-formed nucleus and many organelles. | What it says: Category 1 = Eukaryotic (things like plants, animals, some single-celled organisms). These have big, complicated cells with a nucleus and lots of parts. What it does: Defines and describes the first of the two categories Source/Type: Factual scientific definition Connection to Previous Sentences: This directly builds on sentence 1 by identifying what the first of the "two categories" actually is Visualization: Eukaryotes = Complex cells like a factory with many departments (organelles) and a headquarters (nucleus) Reading Strategy Insight: Feel confident here - the author is simply filling in details about the framework already established |
Why It's Wrong:
- This completely reverses the actual direction of change described in the passage
- The passage shows movement FROM a dichotomous (2-category) TO a trichotomous (3-category) view, not the other way around
- The author states "it now appears that there are three stems in the tree of life," directly contradicting this choice
Why It's Right:
- Perfectly captures the passage's focus on explaining how scientific understanding evolved
- "Outlining the factors" matches how the author describes both old evidence (microscopic, molecular) and new evidence (RNA techniques)
- "Current hypothesis concerning the number of basic categories" directly addresses the central issue: 2 vs. 3 categories
- Reflects the passage's structure of explaining why scientists moved from 2-category to 3-category thinking
Why It's Wrong:
- The passage doesn't evaluate experiments or provide "proof" - it describes a progression of evidence and techniques
- The focus isn't specifically on prokaryotes being "more ancient than expected" but on discovering a third category
- "Proof" is too strong - the passage uses language like "strongly suggested" and "it now appears"
Why It's Wrong:
- This misidentifies the passage's primary purpose as summarizing differences rather than explaining the evolution of scientific understanding
- The passage doesn't systematically detail structural and functional differences between the groups
- The differences are mentioned as supporting evidence, not as the main focus
Why It's Wrong:
- The passage doesn't formulate new hypotheses about evolutionary mechanisms
- It describes discoveries about classification, not theories about how evolution works
- "Mechanisms of evolution" suggests processes like natural selection, which aren't discussed