第12章 Lesson 12: Living Lights
Very few organisms that live on land have the ability to glow in the dark, but it is a surprisingly common characteristic among deep-sea marine creatures. In fact, about 90 percent of animals that live 200 to 1,000 metres below the surface of the ocean are bioluminescent.
The word bioluminescence comes from the Greek word bios, which means living, and the Latin lumen, which means light. It refers to organisms that produce light as a result of a chemical reaction. Bioluminescence is a cool light. In a lightbulb, about 97 percent of the energy is used to create heat, and only 3 percent is used to create light. When bioluminescence is produced, very little energy is used to create heat. This is one reason that scientists are so interested in learning about bioluminescence and how it might be used to create more efficient, less wasteful light sources.
Ocean animals use bioluminescence in various ways. You might think that light would not be very effective as camouflage because it would draw attention to an animal instead of helping it hide. However, if you were an animal hunting a bobtail squid and you looked up at the squid's belly, its bioluminescence would allow it to blend with the stars of the night sky.
Other animals use bioluminescence to attract mates. This is the case with fireflies on land, who use light signals to attract others of the same species. It is also true of ocean species like the Bermuda fireworm.
One species of squid uses bioluminescence to confuse predators. If it feels threatened, it spews a cloud of bioluminescent chemicals. While the predator is surprised and confused, the squid has time to quickly escape.
Another possible use of bioluminescence is to lure prey. The cookie cutter shark is one animal that uses its light this way. Patterns of bioluminescence on the shark's underside may resemble small fish to predators like tuna or mackerel. When they come closer to investigate, the shark attacks. The anglerfish uses a similar method to catch prey. It extends a glowing lure from an appendage on its head. Other fish mistake the glowing lure for a meal and venture closer. When they do, the anglerfish moves quickly and snaps them up.
Because many bioluminescent animals live deep underwater, most people can't see them. However, tiny one-celled creatures called dinoflagellates live in the sea and produce much of the visible bioluminescence near the ocean's surface. In areas that have large numbers of dinoflagellates, the motion of waves, a boat, a porpoise, or even a hand can easily disturb them and cause them to glow. On a dark night, this eerie but beautiful sight can create quite a beautiful light show in the ocean!
I. Word List
organisms: living things
camouflage: the natural colouring of an animal which allows it to blend into its surroundings and make it very difficult to see
mates: animals of the same species, but opposite sex
investigate: to look closely at something
snap up: to take very quickly
II. Vocabulary skills—Find the correct words in the reading.
1. to hide or blend into your surroundings: c _ _ _ _ _ _ _ _ _
2. an animal that hunts other animals: p _ _ _ _ _ _ _
3. something that attracts: l _ _ _
4. a body part that extends out from the body: a _ _ _ _ _ _ _ _
5. odd or mysterious: e _ _ _ _
III. Reading skills—Answer the following questions.
1. What is a way that an animal can use bioluminescence to lure prey?
___________________________________________________________.
2. How does bioluminescence help camouflage the bobtail squid?
___________________________________________________________.
3. How is bioluminescence different from the light produced by a lightbulb?
___________________________________________________________.
4. What can cause dinoflagellates to glow?
___________________________________________________________.
5. Where do most creature that have bioluminescence live?
___________________________________________________________.
IV. Write T (true) or F (false) for each sentence.
___ 1. Most creatures that live on land can glow in the dark.
___ 2. Creatures that produce bioluminescence are very hot.
___ 3. The bobtail squid uses bioluminescence.
___ 4. The cookie cutter shark eats tuna and mackerel.
___ 5. Sometimes we can see bioluminescence on the ocean's surface.
___ 6. Some creatures use bioluminescence to make a pretty light show.