Acacia trees are shrub-like, with some species having swollen thorns that serve as nests for three species of ants. A...
GMAT Reading Comprehension : (RC) Questions
Acacia trees are shrub-like, with some species having swollen thorns that serve as nests for three species of ants. A healthy tree can have hundreds of thorns, many containing one hundred ants each. Both the ants and the trees benefit. The ants get shelter and nectar from the base of the acacia leaves. And because the ants swarm to defend against birds or animals that interfere with the trees, the trees get protection from a major threat, browsing animals.
Researchers were puzzled to find that a grove of acacias fenced off from wild mammal herbivores looked sickly compared with their unfenced counterparts—the opposite of what might be expected, given that browsers had fed voraciously on the unfenced trees. The researchers had expected that without mammals to eat the fenced trees, the trees would shelter fewer and less aggressive ants—which turned out to be true—and that the trees would benefit from not having to use their resources to support the ants. But further investigation revealed that with reduced colonies, the ants became less well able to defend against a fourth species of ant. This ant species does not eat acacia nectar; it feeds away from the tree and does not defend it from attackers. Rather, it uses as its home the cavities created in the acacia trees by a wood-boring beetle.
According to the passage, which of the following is true?
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| Acacia trees are shrub-like, with some species having swollen thorns that serve as nests for three species of ants. | What it says: Acacia trees look like bushes and some have big thorns where ants live. What it does: Introduces the main players and sets up a relationship. Source/Type: Factual description Connection to Previous Sentences: This is our opening - establishes the basic setup. Visualization: Picture a bush-like tree with puffy thorns, each thorn housing multiple ants from 3 different ant species. Reading Strategy Insight: Simple introduction - we're learning about a tree-ant relationship. Expect this to develop further. What We Know So Far: Acacia trees + ants live together What We Don't Know Yet: How this relationship works, why it matters |
| A healthy tree can have hundreds of thorns, many containing one hundred ants each. | What it says: We're talking about a LOT of ants - potentially tens of thousands per tree. What it does: Provides scale/magnitude to help us visualize the relationship. Source/Type: Factual detail Connection to Previous Sentences: This builds on sentence 1 - we knew ants lived in thorns, now we know the impressive scale: 500 thorns × 100 ants = 50,000 ants per tree! Visualization: One healthy acacia = 500 thorns = 50,000 ants (like a small city of ants) Reading Strategy Insight: The author is helping us grasp the magnitude - this isn't just a few ants, it's a massive colony. |
| Both the ants and the trees benefit. | What it says: This relationship helps both sides - it's not one-sided. What it does: Gives us the key insight about the nature of this relationship. Source/Type: Author's conclusion/interpretation Connection to Previous Sentences: This explains WHY the relationship from sentences 1-2 exists - it's mutually beneficial, not parasitic. Visualization: Tree gets something + Ants get something = Win-win relationship Reading Strategy Insight: Key insight alert! We now know this massive ant-tree setup is cooperative. Expect the next sentences to explain HOW each side benefits. |
| The ants get shelter and nectar from the base of the acacia leaves. | What it says: The ants receive housing and food from the tree. What it does: Explains the first half of the mutual benefit - what ants get. Source/Type: Factual explanation Connection to Previous Sentences: This directly explains sentence 3 - we knew both benefit, now we're learning specifically how ants benefit. Visualization: Ants receive: Shelter (thorns as homes) + Food (nectar from leaf bases) Reading Strategy Insight: Feel confident here - the author is systematically explaining the mutual benefit. Expect the tree's benefit next. |
| And because the ants swarm to defend against birds or animals that interfere with the trees, the trees get protection from a major threat, browsing animals. | What it says: The ants act like bodyguards, protecting trees from animals that want to eat them. What it does: Completes the mutual benefit explanation - what trees get. Source/Type: Factual explanation Connection to Previous Sentences: This completes the picture from sentences 3-4 - we now understand both sides of the mutual benefit. Visualization: Tree provides: Shelter + Food → Ants provide: Defense against browsing animals Reading Strategy Insight: Complete picture achieved! We now fully understand this cooperative relationship. What We Know So Far: Complete mutualistic relationship between acacias and ants What We Don't Know Yet: Why the passage is telling us this - is there a twist coming? |
| Researchers were puzzled to find that a grove of acacias fenced off from wild mammal herbivores looked sickly compared with their unfenced counterparts—the opposite of what might be expected, given that browsers had fed voraciously on the unfenced trees. | What it says: Scientists found something weird: trees protected from plant-eating animals looked worse than trees that were being eaten. What it does: Introduces a puzzle/contradiction that challenges our understanding. Source/Type: Research finding Connection to Previous Sentences: This creates a puzzle - based on sentences 1-5, we'd expect protected trees to be healthier, but they're not! Visualization: Expected: Fenced trees (no browsers) = Healthy vs. Unfenced trees (eaten by browsers) = Unhealthy Reality: Fenced trees = Sickly vs. Unfenced trees = Healthier Reading Strategy Insight: Classic RC pattern - establish understanding, then present a puzzle. The rest will solve this mystery. |
| The researchers had expected that without mammals to eat the fenced trees, the trees would shelter fewer and less aggressive ants—which turned out to be true—and that the trees would benefit from not having to use their resources to support the ants. | What it says: Scientists thought: no browsers → fewer ants → trees save resources → healthier trees. The first part was right (fewer ants), but something went wrong. What it does: Explains the researchers' logical reasoning and notes where it went wrong. Source/Type: Research hypothesis and partial results Connection to Previous Sentences: This explains the thinking behind sentence 6 - shows the logical chain that led to wrong predictions. Visualization: Expected chain: No browsers → Fewer ants → Saved tree resources → Healthier trees Reality: No browsers → Fewer ants → ??? → Sickly trees Reading Strategy Insight: The reasoning made sense but missed something. We're getting closer to the solution. |
| But further investigation revealed that with reduced colonies, the ants became less well able to defend against a fourth species of ant. | What it says: Here's the missing piece: when there were fewer protective ants, they couldn't fight off a different, bad type of ant. What it does: Introduces the key factor that explains the puzzle. Source/Type: Research discovery Connection to Previous Sentences: This solves the mystery from sentences 6-7! The problem wasn't fewer ants per se, but that fewer ants couldn't defend against harmful ants. Visualization: Fenced trees: Fewer protective ants → Can't fight off harmful 4th ant species → Tree problems Reading Strategy Insight: Aha moment! The puzzle is being solved. Expect the final sentence to explain why this 4th ant species is bad. |
| This ant species does not eat acacia nectar; it feeds away from the tree and does not defend it from attackers. Rather, it uses as its home the cavities created in the acacia trees by a wood-boring beetle. | What it says: The 4th ant species is basically a freeloader - it doesn't help the tree at all, just lives in holes that beetles make in the tree. What it does: Completes the explanation by describing why the 4th ant species is harmful. Source/Type: Factual description Connection to Previous Sentences: This completes the puzzle solution - we now understand the full chain: fenced trees → fewer protective ants → invasion by harmful freeloading ants → sickly trees. Visualization: Complete picture: Unfenced trees: Many protective ants → Keep out freeloading ants → Healthy trees Fenced trees: Few protective ants → Freeloading ants move in → Sickly trees Reading Strategy Insight: Puzzle completely solved! The passage has come full circle - we started with cooperation, encountered a puzzle, and learned that disrupting the balance allows harmful parasites to take over. What We Now Understand: Complex ecosystem balance where removing one threat (browsers) can lead to invasion by a worse threat (parasitic ants) |
2. Passage Summary:
Author's Purpose:
To explain how removing one threat from an ecosystem can unexpectedly create bigger problems by disrupting natural balances.
Summary of Passage Structure:
In this passage, the author walks us through a surprising ecological discovery by first establishing expectations and then showing how research revealed those expectations to be wrong:
- First, the author describes a helpful relationship between acacia trees and ants, where trees provide food and shelter while ants provide protection from plant-eating animals.
- Next, the author presents a puzzling research finding that trees protected from browsers were actually sicker than trees that were being eaten.
- Then, the author explains what researchers expected to happen and notes that part of their prediction came true but the overall result was wrong.
- Finally, the author reveals the solution to the puzzle by showing how fewer protective ants allowed harmful parasitic ants to invade and damage the trees.
Main Point:
Protecting trees from their natural threats can backfire because it weakens the tree's natural defenders, allowing even more harmful invaders to take over and make the trees sicker than they would have been with the original threat.
3. Question Analysis:
This is a detail question asking us to identify which statement is true according to the passage. We need to find a choice that is directly supported by information explicitly stated in the passage, not inferred or assumed.
Connecting to Our Passage Analysis:
Our passage analysis revealed several key facts:
- Three species of ants live in acacia thorns and have a mutualistic relationship with the trees
- These three species get nectar from the base of acacia leaves and defend the trees
- A fourth species of ant was introduced that behaves very differently
- The fourth ant species creates problems for the trees rather than helping them
The passage analysis particularly highlighted the contrast between the helpful three species and the harmful fourth species, noting that the fourth species "does not eat acacia nectar; it feeds away from the tree and does not defend it from attackers."
Prethinking:
Based on our passage analysis, we're looking for a statement that can be directly verified from the text. The passage clearly distinguishes between the first three ant species (which are helpful and feed on acacia nectar) and the fourth ant species (which doesn't feed on acacia nectar and doesn't help the tree). This contrast suggests that any answer choice about ant feeding behaviors or the relationship between different ant species and the trees would be worth examining closely.
Why It's Wrong:
- The passage states that wood-boring beetles create cavities that the fourth ant species uses as homes
- These cavities are associated with the harmful fourth ant species that makes trees sickly
- The passage gives no indication that these beetle-created cavities benefit the trees
Common Student Mistakes:
- Assuming that because something is mentioned in the passage, it must be beneficial?
→ Focus on what the passage actually states about effects, not just what exists - Confusing the helpful thorns (ant nests) with the harmful cavities (beetle damage)?
→ Distinguish between natural tree features that help versus damage caused by insects
Why It's Wrong:
- The passage shows that browsing animals do feed voraciously on unfenced trees with ants
- The text explicitly states "browsers had fed voraciously on the unfenced trees"
- The ants defend against browsers, but this doesn't prevent all browsing
Common Student Mistakes:
- Thinking that "defense" means "complete prevention"?
→ Recognize that defense can reduce but not eliminate threats - Misreading the relationship between ant presence and browsing levels?
→ The passage shows browsers still feed on trees with ants, just less successfully
Why It's Right:
- The passage explicitly describes a fourth ant species that "does not eat acacia nectar"
- This directly contradicts the behavior of the first three ant species, which do feed on nectar
- The statement is precisely supported by the text without requiring any inference
Key Evidence: "This ant species does not eat acacia nectar; it feeds away from the tree and does not defend it from attackers."
Why It's Wrong:
- The passage mentions three ant species plus a fourth ant species, totaling four ant species
- The passage also mentions wood-boring beetles, making at least five insect species
- The choice incorrectly limits the number to three insects total
Common Student Mistakes:
- Forgetting about the fourth ant species mentioned later in the passage?
→ Track all species mentioned throughout the entire passage, not just the beginning - Not counting beetles as insects?
→ Remember that beetles are insects and should be included in insect counts
Why It's Wrong:
- The research findings show the opposite: fenced trees (protected from browsers) were sickly
- Unfenced trees that faced browsing pressure were healthier than protected trees
- This directly contradicts the idea that complete protection from browsing is best
Common Student Mistakes:
- Focusing only on the initial setup and ignoring the research findings?
→ Consider the entire passage, especially surprising research results - Assuming that protection from one threat is always beneficial?
→ Understand that ecosystems involve complex balances, and removing one element can have unexpected consequences