Indeed, it does. A Venus flytrap is a carnivorous plant that attracts, captures, and kills insects and digests and absorbs their nutrients. The leaves of the Venus flytrap, Which can open wide, have short, stiff hairs called trigger hairs. When anything touches these hairs enough to bend them, the two lobes of the leaves snap shut, trapping whatever is inside. The “trap” will shut in less than a second, capturing flies and other insects.
When the trap closes over its prey, finger-like projections called cilia keep larger insects inside. In a few minutes the trap shuts tightly and forms an air-tight seal in order to keep its digestive fluids inside. These fluids help the plant digest prey. At the end of the digestive process, which takes from 5 to 12 days, the trap reabsorbs the digestive fluid and reopens. The leftover parts of the insect blow away in the wind or are washed away by rain.
Frogs are able to make their croaking noises because they have simple vocal cords that have two slits in the bottom of the mouth. These slits open into what is called a vocal pouch. When air passes from the lungs through the vocal cords, a sound is produced. The inflating and deflating vocal pouch makes the sound louder or quieter.
That sound changes depending on the kind of frog there are as many different kinds of croaks as there are frogs! Frogs croak for the same reasons that many animals make noises: to track down and then select a mate, and to protect their territory from other male frogs.
There are many cities around the world that are “big,” meaning they have more than 10 million people living in them. Tokyo, Japan, ranks the largest, since it has 33.2 million people living in the city, according to 2005 estimates. The next biggest cities in order of size are São Paulo, Brazil (17.7 million), Seoul-Incheon, South Korea (17.5 million), Mexico City, Mexico (17.4 million), Osaka-Kobe-Kyoto, Japan (16.4 million), and New York City (about 8 million people).
Most of these cities are located in different places around the globe. In the United States, after New York, Los Angeles is the biggest city (with almost 4 million people), and then Chicago (with almost three million people). Populations of cities are constantly changing as people move in and out of them, according to the U.S. Census Bureau, a government organization that estimates how big or small cities are based on their populations, or the number of people living in them.
Like many inventions, the development of the modern zipper can be traced to a series of events. In 1893, Whitcomb Judson patented and marketed a “clasp locker,” a complicated hook-and-eye shoe fastener. Together with businessman Colonel Lewis Walker, Whitcomb launched the Universal Fastener Company to manufacture the new device. He did not use the word “zipper,” although many people often credit him as the zipper’s creator. Instead, it was Swedish-born Gideon Sundback, an electrical engineer who was hired to work for the Universal Fastener Company, Who gets the credit.
He was responsible for improving Judson’s fastener, and by December 1913, he had designed the modern zipper. Sundback increased the number of fastening elements from four per inch to ten or eleven, had two facing-rows of teeth that pulled into a single piece by a slider, and increased the opening for the teeth guided by the slider. Sundback also created a machine that was able to manufacture the zipper.
Because one meaning of the word “bald” that is not commonly used anymore refers to white markings. “Bald” used to refer to people with white hair. Due to excessive hunting, environmental pollution, and loss of habitat, the bald eagle population became dangerously low at one point, prompting the U.S. Congress to pass a law protecting it. Bald eagles were once listed by the U.S. Fish and Wildlife Service as an endangered species, meaning they were close to being extinct. Thanks to the laws protecting it, these birds have rebounded a bit. They are now listed as threatened, which means they are not as close to being extinct as they once were, but their numbers are still few (only about 50,000 in the United States), and it is illegal to hunt them.
Dams, which are structures that hold back water, have been built since ancient times. They are usually made of earth, rock, brick, or concrete—or a combination of these things. They are constructed to control the flow of water in a river, and they are built for a number of reasons. One reason is to prevent flooding. Heavy rains in high country may cause water levels in a river to rise. As the river flows downhill, it may overflow its banks, flooding communities located downstream. A dam can prevent this by stopping or slowing rushing water, allowing it to be released at a controlled rate. Dams are also frequently used to store water for general use and farming. When a river’s flow is restricted by a dam, water often spreads out behind the dam to form a lake or reservoir in the river valley. That water can then be used as needed, preventing water shortages and crop damage during long periods of dry weather.
A great number of dams today are used to make electricity. Such hydroelectric dams are built very tall, to create a great difference in the height of the water level behind and in front of it. High water behind a dam passes through gates in the dam wall that allow it to fall to the river far below. As the water falls, it flows past huge blades called turbines; the turbines run generators that make electricity. One of the world’s largest and most productive hydroelectric dams is the Hoover Dam, located on the Colorado River between Nevada and Arizona. Built in the 1930s, it is 726 feet (221 meters) high and 1,244 feet (379 meters) long. Its reservoir (Lake Mead)—the world’s largest— supplies water to several states, allowing huge regions of naturally dry terrain in southern California, Arizona, and Mexico to flourish. Many modern dams are used for all three purposes: flood control, water storage, and hydroelectric power.
Euclid’s Elements is a series of 13 geometry and mathematics books written by the Greek mathematician Euclid in Alexandria about 300 B.C.E. It is a collection of definitions, postulates (axioms), theorems, and mathematical proofs of the propositions. The 13 books cover Euclidean geometry and the ancient Greek version of elementary number theory. Along with the Greek mathematician Autolycus’s On the Moving Sphere, the Elements is one of the oldest Greek mathematical treatises to have survived, and is the world’s oldest continuously used math textbook.
Historians do not know a lot about Euclid’s life, but his work has proven important to the development of logic and modern science. Most of the theorems in the Elements were not discovered by Euclid himself, but were the work of earlier Greek mathematicians such as Pythagoras, Hippocrates of Chios, Theaetetus of Athens, and Eudoxus of Cnidos. However, Euclid is credited with arranging these theorems in a logical manner.
Dust mites are microscopic organisms that live in dust. These unwelcome visitors invade your nose and can irritate your mucous membranes, triggering nerve cells that signal the lungs to fill with air. When the air passages close and pressure builds up, your nose tingles and twitches, and you sneeze—forcing mucus (the slimy, moisturizing substance), dust, pollen, and mites out of your nose at speeds of up to 525 feet (160 meters) per second!
Sneezing is one of the body’s reflexes, an automatic way it rids itself of harmful substances like bacteria and germs. It also keeps the tubes that carry the air from your nose to your lungs healthy.
A fruit is the part of the plant that nourishes and protects new seeds as they grow. The plant’s ovaries develop into fruit once the eggs inside have been fertilized by pollen. Some plants produce juicy fruit, such as peaches, pears, apples, lemons, and oranges.
Others produce dry fruit, such as nuts and pea pods. If an animal doesn’t eat the fruit, or a human doesn’t pick it off, it falls to the ground and decays and fertilizes the soil where a new seed will grow.