Read the passage.
coral reefs
a coral polyp is a tiny sea creature with a soft body. at its base, the polyp has a hard skeleton. a polyp attaches itself to a rock on the
bottom of the ocean. the polyp then divides, forming thousands of buds like the original polyp. their connected skeletons form a colony that
acts like a single living thing. over time, colonies combine to form a coral reef. a reef may grow for thousands of years. the world's largest reef,
the great barrier reef in australia, is more than 1,200 miles long.
coral reefs form in warm waters, often near shores with lots of waves. the waves bring oxygen and food to the reef. the water
must be fairly clear, because coral needs sunlight to live. corals work together with tiny sea plants called algae. the reef gives the algae a
home, and the algae create oxygen and food for the coral. many other plants and animals make their homes on the reef. for example, fish, sea
urchins, sponges, sharks, lobster, and octopus all live and hunt around coral reefs. even though coral reefs cover only about 1 percent of the
ocean floor, they support about 24 percent of all marine creatures.
coral reefs in many parts of the world are now at risk. pollution, harmful fishing practices, and other types of human activity can
damage the reefs. some research suggests that coral reefs could even disappear over the next 50 years. many groups are now working to
prevent further damage to coral reefs and preserve them for future generations.
how does the author develop the idea that coral reefs serve an important purpose?
o
1. by explaining that coral reefs are colonies of polyps that act as a single living thing
o
2. by describing how coral and algae work as partners in coral reefs and each other live
3. by explaining that many marine plants and animals depend on coral reefs for food and shelter
o 4. by describing how pollution and other harmful human activities put coral reefs at risk