TOEFL Reading Practice Online | Q&A 009

This is an original TOEFL-style academic reading passage with 9 comprehension questions, not reproduced from any official test. Try pacing yourself at roughly 1.5 minutes per question, and see the Reading practice set and more reading practice articles for additional timed practice.

Passage

Magnetic Sense: How Migratory Birds Find Their Way

[1] Every autumn, small songbirds such as the European robin leave their breeding grounds in northern Europe and travel more than two thousand kilometers to wintering sites around the Mediterranean and in North Africa. These birds usually migrate alone and at night, and young birds making the journey for the first time have no experienced adult to guide them. For more than half a century, researchers have asked how a bird weighing less than thirty grams can hold a consistent heading across such a distance. Part of the answer appears to lie in an ability that humans lack entirely: a sense of the Earth's magnetic field.

[2] Two separate mechanisms have been proposed to explain avian magnetoreception, and researchers still debate how much each one contributes. The first involves tiny particles of magnetite, a naturally magnetic mineral, that may be present in tissue near the upper beak or inner ear. These particles could, in principle, shift position in response to the surrounding magnetic field and trigger nerve signals that indicate direction or field strength, although some early findings that seemed to support this idea have since been challenged. The second mechanism is light-dependent and centers on a protein called cryptochrome, found in the retina. According to this model, magnetic fields alter the behavior of paired electrons produced when cryptochrome absorbs light, and the pattern of that alteration could allow a bird to perceive the field as a kind of overlay on its surroundings.

[3] Evidence for magnetic navigation comes largely from behavioral experiments rather than direct observation of the receptors themselves. In one widely used method, researchers place a bird in a funnel-shaped cage lined with paper; the bird's claw marks, concentrated on one side of the funnel, reveal its preferred direction of travel. When experimenters alter the magnetic field around such a cage using coils, birds shift their preferred heading accordingly, even when no other environmental cues have changed. Other experiments have shown that exposing birds to weak radio-frequency fields, far too weak to harm them, can disrupt their magnetic orientation. This supports the idea that the sense depends on delicate, easily disturbed biochemical processes of the kind the cryptochrome model proposes.

[4] Magnetic orientation is not the only tool available to a migrating bird, and it does not appear to work in isolation. Many species also orient using the position of the sun, the rotation pattern of the night sky, and, in some cases, familiar landmarks or odors. The magnetic sense seems especially valuable when other cues are unavailable, keeping a bird headed in the correct general direction when the sky is overcast or after it has been blown off course by wind. How the brain combines magnetic information with these other cues, and whether the magnetite-based or the light-based mechanism plays the larger role, remains an open question, and it is the focus of ongoing research in sensory biology.

Questions

1. What does the passage mainly discuss?

• (A) The distances traveled by different species of migratory songbirds
• (B) The dangers migratory birds face when magnetic navigation fails
• (C) A comparison between human and animal sense organs
• (D) Two proposed mechanisms behind birds' ability to sense Earth's magnetic field, and the evidence for this ability

2. The word "consistent" in paragraph 1 is closest in meaning to

• (A) steady
• (B) rapid
• (C) social
• (D) seasonal

3. Why does the author mention the European robin in paragraph 1?

• (A) To argue that all songbirds share the same navigation system
• (B) To contrast birds that migrate at night with those that migrate during the day
• (C) To introduce the puzzle of long-distance, unguided navigation that the passage goes on to explore
• (D) To describe the diet of migratory songbirds

4. According to paragraph 2, the cryptochrome model depends on which of the following?

• (A) Magnetite particles near the beak
• (B) Sound waves detected by the inner ear
• (C) Chemical signals from the bird's diet
• (D) Light absorbed by a protein in the retina

5. According to paragraph 3, what do researchers learn by placing a bird in a funnel-shaped cage lined with paper?

• (A) How quickly the bird can escape through the narrow end of the funnel
• (B) Which direction the bird prefers to travel, shown by its claw marks
• (C) How long the bird stays still after the magnetic field is removed
• (D) Whether the bird's vision has been impaired

6. The word "disrupt" in paragraph 3 is closest in meaning to

• (A) interfere with
• (B) improve
• (C) measure
• (D) duplicate

7. It can be inferred from paragraph 3 that the magnetic sense in birds

• (A) cannot be affected by any outside interference
• (B) is stronger in birds that migrate shorter distances
• (C) relies on biochemical processes that can be disturbed relatively easily
• (D) has been studied mainly by observing receptor cells directly

8. According to paragraph 4, migrating birds may use all of the following to orient themselves EXCEPT

• (A) the position of the sun
• (B) radio signals produced by other birds
• (C) the rotation pattern of the night sky
• (D) familiar landmarks or odors

9. The word "it" in the last sentence of paragraph 4 refers to

• (A) the brain
• (B) the question of how birds combine their cues and which mechanism matters more
• (C) sensory biology as a field
• (D) the magnetic sense itself

Answers and explanations

1. (D) Paragraph 2 describes the magnetite and cryptochrome mechanisms, paragraph 3 the experimental evidence, and paragraph 4 how the sense fits with other cues. Distances (A) are only background in paragraph 1.
2. (A) A "consistent" heading is a steady one that does not keep changing.
3. (C) The robin example sets up the central question: how a small bird, often traveling alone at night, keeps its direction over thousands of kilometers.
4. (D) Paragraph 2 says the cryptochrome mechanism is "light-dependent" and that cryptochrome is a protein "found in the retina." Magnetite (A) belongs to the other mechanism.
5. (B) Paragraph 3 explains that claw marks concentrated on one side of the funnel "reveal its preferred direction of travel."
6. (A) To "disrupt" something is to interfere with it or throw it into disorder.
7. (C) Radio-frequency fields too weak to harm the birds still disturb their orientation, which suggests a delicate biochemical process. Paragraph 3 also says evidence comes "largely from behavioral experiments rather than direct observation," which rules out (D).
8. (B) Radio-frequency fields appear only in paragraph 3, as something experimenters use to disrupt orientation. Paragraph 4 never says birds use radio signals from other birds.
9. (B) "It" refers to the open question named just before it: how the brain combines these cues and which mechanism plays the larger role.