IXL | Read about animals | 7th grade language arts

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The Water Dog

In 2003, biologist Louis Zambrano was working at a lake near his home outside of Mexico City. His job was to find and count a type of amphibian called an axolotl (pronounced ACK-suh-LAH-tuhl). He found it to be boring, tedious work, mostly because he wasn't catching many of them. But then it occurred to Zambrano that he had uncovered a significant issue. This lake had once been teeming with axolotls, but now it barely had any. Where have they all gone? he wondered.

Axolotls are found only in a few freshwater lakes around Mexico City. In the past, sightings of these creatures had been fairly common—so much so that the species became a symbol of Mexican national pride. The Aztecs (a historic culture native to Mexico) gave these salamanders their name, which means water dog or water monster. According to Aztec mythology, a god by this name transformed into a salamander in order to escape from harm. In modern times, the Mexican painter Diego Rivera included the animal in at least one of his paintings. In 2021, Mexico's central bank updated its fifty-peso bill to include a prominent image of the axolotl. The fact that this nationally celebrated amphibian seemed to be disappearing from the wild began to alarm many different groups of people, and researchers like Zambrano worried that they might lose access to an animal whose unusual biology had long fascinated them.

To biologists who study amphibians, the axolotl is a salamander with truly astounding qualities. Most amphibians start out with gills. Then, as they mature, they develop lungs that allow them to survive on land. But the axolotl has characteristics of both a juvenile and an adult—feathery gills and lungs. Scientists aren't sure why it has developed this way, and the axolotl is the only known salamander to have done so.

In addition to being an object of fascination for biologists, the axolotl is also of interest to medical researchers. From a medical perspective, the most unusual thing about the axolotl is its regenerative ability. When most animals are wounded, they form scar tissue that eventually heals. The axolotl, though, doesn't form scar tissue. Instead, the cells around the missing part (be it a limb, a spine, or even parts of the brain) work together to actually regrow it. Because of this phenomenon, scientists estimate that axolotls are significantly more resistant to cancer than humans. Wouldn't it be amazing if this miraculous ability could be developed into treatments for human diseases and injuries? That's exactly what some scientists are trying to do, and with continued access to the axolotl, they might one day succeed.

After studying the mystery of the declining axolotl population, Zambrano and other scientists determined that water pollution was the likely culprit. Mexico City is one of the largest metropolitan areas in the world, and pollution in nearby lakes has increased as the city has grown. But there has been some immediate good news: conservationists have begun working with farmers to create pollution-filtering islands to help clean the city's lakes. After much research, scientists have concluded that these efforts have begun to make a difference, but they also stress that more needs to be done in order to revive the dwindling axolotl population. For Zambrano and his fellow researchers, saving this unique species of salamander is worth the effort.

What is the text mainly about?

It is about Louis Zambrano's attempts to replicate the axolotl's healing abilities in humans.

It is about how efforts to clean up Mexico's lakes have accidentally harmed the axolotl.

It is about the axolotl's biological features and the environmental dangers it faces.

It is about how Mexican biologists have come together to save the axolotl.

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Read the text.

Happy as a Quokka

Sometimes called the world's happiest animal, the quokka has a face that often appears to be smiling. With its plump cheeks and photogenic grin, the quokka has found fans all over the world. But there is more to this small Australian mammal than its adorable appearance; the quokka is a fascinating animal with many unusual biological and behavioral characteristics.

Once mistaken for large rats, quokkas are actually a type of marsupial. Like kangaroos, mother quokkas carry their young (called joeys) in a pouch until they are about six months old. When a joey reaches this age, it is about the size of a lime and ready to start observing the world. It starts by poking its head out of the pouch, and eventually it begins hopping around on its own. A fully grown quokka weighs between five and eleven pounds and is about the size of a small house cat.

Because of their small size, quokkas have developed specific survival instincts to avoid larger predators. One of their strategies is to seek out habitats that have recently been burned by a wildfire. This might seem like strange behavior, but there is actually a clever reason behind it. During a wildfire, most animals will flee for safety, leaving the area with few predators that could harm the quokkas. Additionally, the new growth that begins to develop after a fire is often high in nutrients.

Quokkas have adapted over time to survive in environments where nutrients are scarce. That's because quokkas have developed the ability to go for long periods of time without eating or drinking—sustaining themselves with fat stored in their tails. Some quokkas have been known to go without food for a month or more when they can't find the specific grasses and leaves they like to eat.

Despite their resilient nature, quokkas are still susceptible to illness. During the mid-twentieth century, researchers in Australia noticed that some quokkas in captivity showed symptoms of muscle paralysis. At the time, no one could figure out why quokkas were experiencing these symptoms, but eventually a connection was made between the animals' condition and a specific vitamin deficiency. Sure enough, when given more vitamin-rich foods like the ones they eat in the wild, the quokkas in captivity started to recover. Because of this discovery, scientists began to explore the idea that some muscle conditions in humans might also be related to vitamin deficiencies. This hypothesis turned out to be correct, and it has led to the development of important treatments.

Quokkas have contributed to human health in other ways, too. One study found that people can actually lower their anxiety by observing quokkas and other cute-looking animals. When test subjects spent thirty minutes looking at photos and videos of these animals, researchers found that it reduced their anxiety by an average of thirty-five percent. So, the next time you're feeling overwhelmed, a quokka "smile" might be just what the doctor ordered.

What is the text mainly about?

It is about how quokkas behave and what researchers have learned about them.

It is about how observing quokkas in the wild has health benefits for humans.

It is about how quokka illnesses can be treated with medicines designed for humans.

It is about quokkas' physical appearance and their clever hunting techniques.

solution

The text discusses the following ideas:

Quokkas are small, rat-like marsupials that look like they are always smiling.
They carry their young in a pouch like a kangaroo.
They avoid predators by seeking out areas inhospitable to other animals.
Quokkas are able to go without food or water for long lengths of time.

So, the text is mainly about how quokkas behave and what researchers have learned about them.

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