📐 SAT
📝 ACT
🎓 AP Exams
About Contact Blog Privacy Policy

ACT Reading: Natural Science (Drill 1)

Drill 1 · Reading · Natural Science

0 / 5
Next drill
Drill 2
→
More Act Reading Natural Science drills
Drill 1 — current you are here
Drill 2 5 questions → Drill 3 5 questions → Drill 4 5 questions →

About This Drill

ACT Reading: Natural Science (Drill 1) is a Reading practice drill covering Natural Science. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

Natural Science passages cover topics in biology, chemistry, physics, earth science, and related fields. As you read, follow the central scientific claim and the evidence used to support it. Pay attention to how researchers conducted their investigations and how findings relate to earlier theories. Questions may ask about main ideas, specific details, inferences, vocabulary in context, or the function of particular information.

Passage

NATURAL SCIENCE: This passage is adapted from the article "What Slime Molds Know" by Erin Calabrese (©2020, Science Today). Physarum polycephalum is not an animal, a plant, or a fungus. It is a slime mold, a single-celled organism capable of growing large enough to be visible to the naked eye and, under the right conditions, of solving problems that would challenge a moderately sophisticated computer algorithm. In a series of experiments that attracted wide attention in the scientific community, researchers at Hokkaido University placed oat flakes, a food source Physarum finds highly attractive, at positions corresponding to the locations of Tokyo and the surrounding cities on a scale map. They then introduced Physarum to the location representing Tokyo and observed what happened over the following days. The slime mold extended tentacle-like tubes in all directions, found the oat flakes, and then gradually eliminated the less efficient connections, reinforcing the routes that transported nutrients most effectively. After twenty-six hours, the network the organism had constructed closely resembled the actual rail network of the Tokyo metropolitan area, a system that had been designed by human engineers over more than a century. The slime mold has no brain, no nervous system, no centralized processing of any kind. It achieves this network optimization through a distributed biochemical process: tubes that carry high volumes of nutrients grow thicker and more stable, while underused tubes gradually contract and disappear. The result is a kind of bottom-up computation, a process that arrives at sophisticated solutions without anything resembling deliberate design. This finding has practical implications. Civil engineers and network designers have begun studying Physarum's optimization strategies as models for designing more efficient transportation and communication networks. The slime mold does not calculate; it responds. But the outcome of those responses can outperform human calculation in certain narrow domains. The deeper implication may be philosophical as much as practical. If a single-celled organism with no nervous system can produce solutions that rival human engineering, the question of what we mean by intelligence, and where it resides, becomes considerably more complicated.

Questions & Explanations

Question 1. The main purpose of the passage is to:

  • A) argue that slime molds are more intelligent than commonly understood.
  • B) describe how a brainless organism produces sophisticated network solutions and consider what this implies. ✓
  • C) explain why human engineers have failed to design efficient transportation systems without biological models.
  • D) compare the cognitive abilities of Physarum polycephalum to those of various animals.

Explanation: Choice B is correct. The passage describes Physarum's network-building behavior, explains the biochemical mechanism behind it, discusses its practical applications, and concludes with a philosophical implication about intelligence. Choice A attributes a value judgment ('more intelligent than commonly understood') that the passage presents more carefully. Choice C mischaracterizes the passage; it does not claim human engineers have failed. Choice D introduces a comparison to animals not made in the passage.

Question 2. According to the passage, in the Hokkaido University experiment, oat flakes were placed at positions that:

  • F) represented the locations of major cities around the Tokyo metropolitan area. ✓
  • G) were chosen at random to test whether the slime mold could find them.
  • H) formed a pattern that matched the existing Tokyo rail network.
  • J) were spaced equally apart in order to control for distance variables.

Explanation: Choice F is correct. The passage states that oat flakes were placed 'at positions corresponding to the locations of Tokyo and the surrounding cities on a scale map.' Choice G is incorrect: the positions were deliberately chosen to match city locations, not random. Choice H reverses the experiment's finding, the slime mold produced a network resembling the rail system; the oat flakes represented cities, not the rail lines. Choice J introduces equal spacing as a design feature not mentioned in the passage.

Question 3. The passage most strongly suggests that Physarum builds efficient networks through:

  • A) a centralized decision-making process directed by specialized cells.
  • B) random trial and error, with inefficient paths eventually being abandoned.
  • C) a distributed biochemical process in which high-use tubes thicken and low-use tubes contract. ✓
  • D) a genetic program that encodes the optimal network structure in advance.

Explanation: Choice C is correct. The passage explicitly describes the mechanism: 'tubes that carry high volumes of nutrients grow thicker and more stable, while underused tubes gradually contract and disappear.' This is a distributed biochemical process, not centralized or genetic. Choice A directly contradicts the passage, which states Physarum has 'no centralized processing of any kind.' Choice B suggests randomness; the passage describes a responsive, not random, process. Choice D introduces genetic pre-programming not mentioned in the passage.

Question 4. As it is used in the passage, the phrase 'bottom-up computation' most nearly means:

  • F) calculation performed by the lowest-ranked members of a research team.
  • G) a process that produces sophisticated results through local responses rather than central direction. ✓
  • H) mathematical modeling conducted at the cellular rather than the organismal level.
  • J) an approach to problem-solving that begins with the simplest possible case.

Explanation: Choice G is correct. In context, 'bottom-up computation' describes a process that 'arrives at sophisticated solutions without anything resembling deliberate design', the solution emerges from many local, decentralized responses rather than from any central intelligence directing the outcome. Choice F takes 'bottom' too literally as a hierarchy reference. Choice H is too technically specific in a way the passage does not support. Choice J describes a mathematical technique not applicable here.

Question 5. The final paragraph of the passage primarily functions to:

  • A) summarize the practical engineering applications described earlier in the passage.
  • B) introduce a philosophical question raised by the passage's scientific findings. ✓
  • C) challenge the claim that Physarum's network resembled the Tokyo rail system.
  • D) argue that human intelligence is less significant than previously believed.

Explanation: Choice B is correct. The final paragraph shifts from practical implications to a philosophical one: if a brainless organism can produce solutions that rival human engineering, 'the question of what we mean by intelligence, and where it resides, becomes considerably more complicated.' Choice A describes the function of the fourth paragraph, not the fifth. Choice C introduces a challenge to the experiment's finding not present in the passage. Choice D draws an overly strong conclusion the passage does not make.