Bioluminescence in the Deep Ocean: Reading Answers & Explanations
IELTS Reading practice test · 14 questionsAcademicmedium
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About this passage
The passage opens: “Far below the sunlit surface of the sea lies a vast region of permanent darkness. Sunlight is absorbed and scattered so quickly by seawater that almost none of it reaches beyond a few hundred metres, and past roughly one thousand metres the ocean is effectively black.”
- Passage length: about 799 words
- Questions: 14
- Question types: True / False / Not Given, Multiple Choice, Short Answer
“Bioluminescence in the Deep Ocean” is an original IELTS-style practice passage written by IELTS-Bank. It is not taken from an official IELTS or Cambridge test, so these answers only apply to our version.
Answer key at a glance
Bioluminescence in the Deep Ocean answers with explanations
Questions 1–6: True / False / Not Given
Do the following statements agree with the information given in the passage? Write TRUE if the statement agrees, FALSE if it contradicts, or NOT GIVEN if there is no information.
- 1
Sunlight fails to reach the ocean beyond a few hundred metres of depth.
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Answer: TRUE
Why: This sentence confirms the statement, so the answer is TRUE.
Evidence · Paragraph 1 “Sunlight is absorbed and scattered so quickly by seawater that almost none of it reaches beyond a few hundred metres, and past roughly one thousand metres the ocean is effectively black.”
- 2
Bioluminescence releases most of its energy as heat.
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Answer: FALSE
Why: This sentence directly contradicts the statement, so the answer is FALSE.
Evidence · Paragraph 2 “…energy is released in the form of light rather than heat. Because so little of the energy is lost as warmth, the glow is often described as cold light.”
- 3
Most bioluminescent light in the sea is blue or blue-green in colour.
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Answer: TRUE
Why: This sentence confirms the statement, so the answer is TRUE.
Evidence · Paragraph 3 “The overwhelming majority of marine bioluminescence is blue or blue-green.”
- 4
Dragonfishes are the only deep-sea animals capable of producing light.
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Answer: FALSE
Why: This sentence directly contradicts the statement, so the answer is FALSE.
Evidence · Paragraph 3 “A striking exception is a group of fishes sometimes called dragonfishes, which can produce and perceive red light.”
- 5
Anglerfishes are more common in the deep ocean than any other fish.
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Answer: NOT GIVEN
Why: The statement claims that anglerfishes are the most common fish in the deep ocean, but the passage never confirms or denies this, only mentioning anglerfishes in the context of their bioluminescent lures.
Closest related text · Paragraph 1 “In the deep ocean, living light is not a rare curiosity but one of the most common ways in which organisms communicate, hunt and survive.”
- 6
Remotely operated vehicles have improved scientists' ability to observe glowing animals in their natural habitat.
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Answer: TRUE
Why: This sentence confirms the statement, so the answer is TRUE.
Evidence · Paragraph 7 “The development of remotely operated vehicles and sensitive low-light cameras has transformed the field, allowing researchers to record living animals glowing in their natural surroundings.”
Question 7: Multiple Choice
Choose the correct letter, A, B, C or D.
- A. It requires the least energy to produce.
- B. It travels farther through seawater than other colours.
- C. It cannot be detected by predators.
- D. It generates more heat than other colours.
- 7
Why is blue light especially useful to deep-sea animals?
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Answer: B — It travels farther through seawater than other colours.
Why: This is the part of the passage that supports B — It travels farther through seawater than other colours..
Evidence · Paragraph 3 “…blue light travels farther through seawater than any other colour, so a blue signal can be seen across a greater distance in the open ocean.”
Question 8: Multiple Choice
Choose the correct letter, A, B, C or D.
- A. To attract prey towards the animal's mouth
- B. To signal to potential mates
- C. To hide the animal's silhouette from predators below
- D. To startle an attacker with a sudden flash
- 8
What is the purpose of counter-illumination?
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Answer: C — To hide the animal's silhouette from predators below
Why: This is the part of the passage that supports C — To hide the animal's silhouette from predators below.
Evidence · Paragraph 4 “By glowing gently downward, they erase the dark silhouette that a predator looking up from below would otherwise see against the faint light filtering from above.”
Question 9: Multiple Choice
Choose the correct letter, A, B, C or D.
- A. a special gland in the fin spine
- B. bioluminescent bacteria living in the lure
- C. reflected light from the surface
- D. chemicals stored in the fish's mouth
- 9
In many anglerfishes, the glow of the lure is actually produced by
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Answer: B — bioluminescent bacteria living in the lure
Why: This is the part of the passage that supports B — bioluminescent bacteria living in the lure.
Evidence · Paragraph 5 “…the glowing tip houses colonies of bioluminescent bacteria, which the fish shelters and feeds in exchange for their light.”
Question 10: Multiple Choice
Choose the correct letter, A, B, C or D.
- A. Because it helps the jellyfish hide from predators
- B. Because it warns other jellyfish of danger
- C. Because it advertises an attack to attract a larger animal
- D. Because it produces a loud sound as well as light
- 10
Why do scientists refer to a certain jellyfish's display as a 'burglar alarm'?
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Answer: C — Because it advertises an attack to attract a larger animal
Why: This is the part of the passage that supports C — Because it advertises an attack to attract a larger animal.
Evidence · Paragraph 6 “…rather than hiding the animal, the light advertises the attack in the hope of summoning something bigger and more dangerous to the scene.”
Questions 11–14: Short Answer
Answer the questions below. Choose NO MORE THAN THREE WORDS from the passage for each answer.
- 11
What is the name for the light-emitting molecule involved in the chemical reaction?(max 2 words)
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Answer: luciferin (also accepted: a luciferin)
Why: The answer “luciferin” is taken from this sentence — copy the word(s) exactly as they appear. It fits the 2-word limit.
Evidence · Paragraph 2 “…the reaction involves a light-emitting molecule, generally known as a luciferin”
- 12
What is the enzyme called that speeds up the light-producing reaction?(max 3 words)
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Answer: luciferase (also accepted: an enzyme called luciferase)
Why: The answer “luciferase” is taken from this sentence — copy the word(s) exactly as they appear. It fits the 3-word limit.
Evidence · Paragraph 2 “…an enzyme called luciferase that speeds the reaction along.”
- 13
Because so little energy is lost as warmth, what term is used to describe the glow?(max 2 words)
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Answer: cold light (also accepted: cold)
Why: The answer “cold light” is taken from this sentence — copy the word(s) exactly as they appear. It fits the 2-word limit.
Evidence · Paragraph 2 “…the glow is often described as cold light.”
- 14
What colour of light can dragonfishes both produce and perceive?(max 2 words)
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Answer: red (also accepted: red light)
Why: The answer “red” is taken from this sentence — copy the word(s) exactly as they appear. It fits the 2-word limit.
Evidence · Paragraph 3 “…a group of fishes sometimes called dragonfishes, which can produce and perceive red light.”
Estimated band score for this test
Your raw score out of 14 scaled to the 40-question IELTS Reading (Academic) conversion table. This is the same estimate the practice page shows after you submit. A single passage is a small sample, so treat it as a guide.
| Correct answers | Estimated band |
|---|---|
| 14 / 14 | 9.0 |
| 13 / 14 | 8.5 |
| 12 / 14 | 7.5 |
| 11 / 14 | 7.0 |
| 10 / 14 | 6.5 |
| 8–9 / 14 | 6.0 |
| 7 / 14 | 5.5 |
| 6 / 14 | 5.0 |
| 5 / 14 | 4.5 |
| 4 / 14 | 4.0 |
| 3 / 14 | 3.5 |
| 2 / 14 | 3.0 |
| 1 / 14 | 2.0 |
| 0 / 14 | 0.0 |
Full-test score? Use the IELTS band calculator.
Tips for the question types in this test
True / False / Not Given
- Read the statement first and underline the key idea, especially any qualifiers like "all", "only", "never", "always", "more than" or dates and numbers.
- Because the questions follow the order of the passage, scan for the paragraph that deals with the same topic rather than re-reading everything.
Common trap: Confusing "False" with "Not Given": choose False only when the passage actively contradicts the statement; if the passage is silent, it is Not Given.
Full True / False / Not Given strategyMultiple Choice
- Read the question stem carefully before the options so you know exactly what is being asked.
- Because multiple-choice questions follow passage order, locate the relevant section and read it in full — the answer usually depends on more than one sentence.
Common trap: Distractors that use exact words from the passage but distort the meaning.
Full Multiple Choice strategyShort Answer
- Read the instructions and note the exact word limit; going over it means zero marks even if the meaning is right.
- Turn each question into a set of keywords and predict what kind of answer it needs (a person, a date, a place, a noun).
Common trap: Exceeding the word limit (writing four words when only three are allowed).
Full Short Answer strategyPractise “Bioluminescence in the Deep Ocean” under exam conditions
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