IXL | Read about science and nature | 4th grade language arts

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Dunes at the Beach

Sand dunes are one of the most recognizable parts of certain sandy beaches. Dunes are important because they provide coastal lands with natural protection against wind, waves, and storm damage. Sand dunes also provide places for plants and animals to live. For example, seabirds like to nest in dune grasses. Sand dunes are also beautiful to look at for people who enjoy nature. But what exactly are sand dunes? And where do they come from?

Dunes are actually just piles of sand that are formed when wind and waves move sand onto the beach. First, strong waves pick up the sand and wash it up onto the beach. Once the sand has been dropped on the beach, it is moved and carried by the wind. Over time, wind blows the tiny grains of sand into large piles. A dune is made!

Weather can change the size and shape of coastal dunes, so beaches can change with the seasons. In the winter, bigger storms make stronger waves. These strong winter waves pick up and carry more sand, but they leave less of it on the beach. This causes the beach to get steeper and its dunes to become smaller. However, when summer comes, gentle waves leave more sand on the shore, and the beach takes on a shallower slope. More sand building up on the beach leads to bigger dunes.

Since the wind is usually blowing all day near the shoreline, the shape of the dune is constantly changing. Over time, dunes will grow, shrink, and move depending on the way the wind is blowing. If a strong wind blows grass onto a dune, then the grass may start growing there. The grass's roots and stems then help to trap the sand in the same spot, which makes the dune more stable against the wind.

What is the text about?

It is about the kinds of animals that live around sand dunes.

It is about how sand dunes are disappearing from beaches.

It is about which beaches in the U.S. have sand dunes.

It is about what sand dunes are and how they are formed.

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Read the text.

Tiny Cleaning Service

Throughout the world's coral reefs, there are small, hard-shelled sea animals called cleaner shrimp. These tiny animals are bright and colorful, allowing fish to easily spot them in the water. Cleaner shrimp have a mutualistic relationship with fish, meaning that the shrimp and the fish both get something by working together. The fish get cleaned by the shrimp, and the shrimp get meals from the fish that they clean.

The shrimp remove parasites from the fish. Parasites are tiny sea creatures that attach to fish and cause them harm. The parasites are too small for the fish to remove on their own, but the parasites are the right size to make a perfect meal for a little shrimp. The shrimp uses its tiny claws to pick the dangerous parasites off the fish, and then it eats the parasites.

If a fish has parasites and wants to be cleaned, it looks for a brightly-colored cleaner shrimp waiting on a rock. When the fish swims up to the rock, the cleaner shrimp does a strange dance. The shrimp rocks its body from side to side, and it waves its front legs in the air as if to say, "Fish Cleaning Service! Come right in!" This dance sends a signal to the fish that the shrimp is hungry and willing to clean the parasites off the fish. The fish then changes its color from light to dark. This color change provides a signal to the shrimp that the fish wants to be cleaned.

Cleaner shrimp do a thorough job of cleaning each fish. They will clean a fish from head to tail, and they will even climb into a fish's mouth to clean it. However, large fish could be dangerous for these tiny shrimp, so the shrimp have to be picky about which fish they choose to clean. They will only dance and wave to a fish that does not appear threatening. Also, they will wait until the fish darkens the color of its scales before starting the job. If a fish moves toward a shrimp but does not change color, the shrimp knows that instead of getting a meal, it is at risk of becoming one!

What is the text about?

It is about the kinds of fish that cleaner shrimp like to clean.

It is about the types of parasites cleaner shrimp eat off fish.

It is about how cleaner shrimp and fish help each other.

It is about how cleaner shrimp learn to dance for fish.

solution

The text says that cleaner shrimp and fish both get something by working

together.

It then discusses how cleaner shrimp get food from the fish while the fish get cleaned by the

shrimp.

So, the text is about how cleaner shrimp and fish help each other.

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