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4 . Chemists have spent the past century trying to make plastics that will break down in seawater. As it is, most plastics appear to take centuries to fully degrade in the ocean. But that may change. Scientists have just designed a new plastic that can break down in seawater within weeks, not decades or more.
Back in the 1930s, scientists created a now-popular plastic out of corn and potato starch (淀粉). It’s known as polylactide, or PLA. It’s a polymer (聚合物), which is a molecule made by linking many building blocks — called monomers — into a long string. Scientists had hoped PLA would quickly break down in the environment. And in some places, like compost pits (堆肥坑), it does. But not in seawater. Even after three years in ocean water, PLA remains largely unchanged.
Timo Rheinberger is a PhD student at the University of Twente in the Netherlands. His work on polymers has focused on boosting PLA’s breakdown. As part of that work, he became part of a team that just added some RNA-inspired breaking points to PLA. They put those breaking points in places where monomers in the PLA molecules are linked.
They weakened the links that joined up to 15 percent of a PLA’s monomers. Then, they soaked their samples in artificial seawater and measured how fast these tweaked versions of PLA broke down. The expected final product of PLA’s breakdown was a small molecule called lactic acid. So, they tested for that too.
As the team had hoped, seawater attacked the weakened links between monomers, splitting the polymer chain apart. The more breaking points the researchers added to the polymer, the faster the PLA broke down.
When they weakened 15 percent of PLA’s monomer links, the polymer broke down entirely within just two weeks. When they weakened only 3 percent of the links, the breakdown took about 2 years. This suggests the team can design how quickly PLA will break down in water by adjusting how many weakened links it has.
Mehlika Karamanlioglu teaches biomedical engineering at Istanbul Gelisim University. She, too, has studied environmental breakdown of PLA. “It’s a new approach,” she says of the Dutch technique. Theirs is also “a preliminary study,” Karamanlioglu says. So, more testing must follow. Scientists want to know how the strength of the new PLA compares to old PLA.
Rheinberger agrees. “You need a lot of material to start those studies,” he adds. And so far, his team has made only small amounts of the modified PLA.
Karamanlioglu notes the Dutch team also tested the breakdown of its PLA in artificial seawater. “I wonder if they checked [the water] for pollution,” she adds. If there were microbes (微生物), those microbes may have produced molecules called enzymes that sped up the PLA’s degradation.
1. What can we learn about PLA from the passage?| A．Lactic acid prevents the breakdown of PLA. |
| B．PLA breaks down faster in artificial seawater. |
| C．PLA’s breakdown relies on that of monomers. |
| D．Compost pits are the best places for PLA’s breakdown. |
| A．Systematic. | B．Comparative. | C．In-depth. | D．Early-stage. |
| A．Supportive. | B．Doubtful. | C．Optimistic. | D．Cautious. |
| A．Mehlika is confident about the application of the new PLA. |
| B．The cleanness of water also affects the breakdown of PLA. |
| C．The new PLA has better strength than the old PLA. |
| D．The new PLA have been produced in large amounts. |
5 . Horseshoe crabs are often called living fossils. These primitive arthropods have lived on earth for 360 million years, largely in the same form as they appear today. Despite their long history, the horseshoe crab’s existence is now threatened by human activities, including harvesting for medical research.
Any time a foreign object or substance enters the human body, there’s a risk of introducing infection. If you’ve had a vaccination, a surgery of any kind, or had a medical device implanted in your body, you owe your very survival to the horseshoe crab.
Horseshoe crabs have copper-rich blood that appears to be striking blue in color. Proteins in the horseshoe crab’s blood cells are released in response to even the smallest amount of bacterial endotoxin (内毒素), such as E. coli. The presence of bacteria causes horseshoe crab blood to clot or gel, part of its hypersensitive immune response system.
In the 1960s, two researchers, Frederick Bang and Jack Levin, developed a method of using these coagulation (凝固) factors to test for contamination (污染) of medical devices. By the 1970s, their Limulus amebocyte lysate (LAL) test was being used commercially to make sure everything from scalpels (手术刀) to artificial hips (髋关节) is safe for introduction in the human body.
While such testing is crucial to safe medical treatments, the practice takes a toll on horseshoe crab populations. Horseshoe crab blood is in high demand, and the medical testing industry catches as many as 500,000 horseshoe crabs each year to drain them of their blood. The crabs aren’t killed outright in the process; they’re caught, bled, and released. But biologists suspect the stress results in a percentage of the released horseshoe crabs dying once back in the water. Fortunately, management practices are in place now to protect the species.
In addition to their value in medical research, horseshoe crabs fill important ecological roles. Their smooth, wide shells provide the perfect substrate (基质) for many other marine organisms to live on. As it moves along the ocean’s bottom, a horseshoe crab may be carrying mussels, barnacles, tube worms, sea lettuce, sponges, and even oysters. Horseshoe crabs deposit their eggs by the thousands along sandy shorelines, and many migratory shorebirds, including red knots, rely on these eggs as a source of fuel during their long flights.
1. What feature of horseshoe crabs helps save lives?| A．They can improve their immune system. | B．Their blood is sensitive to bacteria. |
| C．They have copper-rich blood cells. | D．Their blood is striking blue. |
| A．Make use of. | B．Do harm to. | C．Run out of. | D．Contribute to. |
| A．By giving examples. | B．By making a comparison. |
| C．By quoting experts. | D．By offering a definition. |
| A．Science. | B．Travel. | C．Business. | D．Life. |
6 . Rhiannon Menn is the founder of Lasagna Love, a global nonprofit that connects neighbors through homemade meal delivery. In March 2020, her San Diego community shut down because of the pandemic. She and her husband own a design and build company, but their projects were put on hold. Rhiannon felt helpless and wondered what she could do to be useful. It didn’t take her long to decide.
“Cooking is my happy place,” she says. She ordered groceries online and got to work. She and her daughter, Cimorene, then three, made extra pans of lasagna, and Rhiannon posted in a local moms’ group on Facebook, offering to drop off a free home-cooked meal to anyone who wanted one. Some people requested a meal. Even more wanted to help Rhiannon feed those who were struggling.
Rhiannon created a spreadsheet for each volunteer, matching them with families who’d requested a meal. Word of what she was doing spread quickly on social media. “By summer, we had more than 100 volunteer chefs,” she says. Too many for one person to track. Someone offered to create an online portal (门户网站) to manage the volunteers and meal requests. This automated system freed Rhiannon to do what she really loves: cook and reach people in need.
For Rhiannon, lasagna is the best comfort food. But it’s about more than just food. “Our volunteers deliver a sense of hope with the meal,” she says. “We want people to know that a stranger cared enough about them to make them a meal. Kindness is contagious (传染性的), and it can transform communities.”
Lasagna Love currently has 25,000 volunteers—or Lasagna Chefs, as they’re called—across the United States, Canada and Australia, who have delivered more than 150,000 meals to families in their communities. “This movement has given me purpose in a way I didn’t have before,” Rhiannon says.
In her home, cooking is a family event. Cimorene, now five, has gotten good at layering the noodles. Rhiannon also has a three-year-old son and an 11-month-old baby boy. “I love that my kids are learning the importance of helping others,” she says.
Volunteer chefs log in to the portal and input how many meals they’d like to deliver that week. The system matches them with nearby families requesting a meal, and the volunteer texts the family to set up a delivery time. The meals are dropped off on doorsteps for contact-free delivery.
The organization is called Lasagna Love, but volunteers can deliver any home-cooked meal they’d like. Rhiannon’s recipe is her own take on lasagna, made healthier with grated zucchini and yellow squash. “I’ve shared my recipe, but volunteers are welcome to use their own recipes for any dishes they’d like to make,” she says.
1. Why did Rhiannon start Lasagna Love?| A．To help struggling neighbors. | B．To fight against the pandemic. |
| C．To help their design and build company. | D．To improve her neighbors’ cooking skills. |
| A．They are trained by experienced chefs. |
| B．They deliver their own meals to people in need. |
| C．They search for families in need by themselves. |
| D．They all follow Rhiannon’s recipe to make lasagna. |
| A．had no purpose in life before |
| B．is too busy to deliver meals now |
| C．likes posting her meals on social media |
| D．has set a good example for her children |
| A．Helpful and humorous. | B．Honest and successful. |
| C．Kind-hearted and generous. | D．Hardworking and ambitious. |
7 . Summertime, i.e. vacation season, is quickly approaching. And whether your ideal getaway is R&R on the beach, outdoor adventuring, or exploring a new city, it pays to plan.
I’d love to get away. How do I save for a vacation?
You’re not alone. One study says 71% of Americans are planning to take a trip for leisure in 2022. And they’re planning on spending 29% more than they did pre-pandemic in 2019. But you don’t have to go broke (身无分文) to get a break. Before you even start planning your travel, here’s how to make the trip you’ve been waiting for a reality.
● Make a sinking fund. These funds are where you set aside money with an intention to spend it on a big goal.
● Timing is everything. Research the cheapest places to go when the temperature rises, and plan accordingly. You’ll also get more bang for your buck by checking out destinations with a favorable exchange rate. For somewhere further east, your dollars will go far in Thailand or the Philippines.
● Book smart. Renting a home is often a better deal than booking a hotel. Not only will you save on the price tag, but you can cook instead of eating out for every meal.
How do I keep saving while I’m on vacation?
True story: travel doesn’t feel like real life, so it’s easier to splurge (挥霍). And if you’re visiting a popular tourist location, everything costs more. Here’s how to see the sights without losing sight of your budget.
● Set a daily spending limit and track what you buy to avoid overdoing it. Using cash or a prepaid debit card instead of a credit card can also help.
● Food is a money vampire. If you have access to a kitchen where you’re staying, make breakfast, pack lunch, and cook dinner when you can. If not, hit up a supermarket or farmer’s market for an easy, cheap breakfast. And when you do eat out, go for lunch or appetizers, where the menu items tend to be less expensive.
1. According to the passage, which of the following may help make your dream trip a reality?| A．Preparing enough fast food. | B．Borrowing money from friends. |
| C．Researching the cheapest places to go. | D．Carrying credit cards from different banks. |
| A．go out for meals | B．avoid using cash |
| C．set a daily spending limit | D．visit popular tourist locations |
| A．To help travellers save money. | B．To report some survey results. |
| C．To advertise some tourist attractions. | D．To compare different travel plans. |
