A cobweb is an old, abandoned spider web that has collected dirt and dust. Sometimes the cobwebs you see in ceiling crevices and along floorboards are several draglines that spiders no longer use.
The common house spider—which feeds on many insects daily—often abandons webs that do not yield prey, and then constructs new ones until it finds a productive site. It’s best to sweep these old cobwebs away, and let your house spiders spin new webs, preferably outdoors!
Like barking, growling, and whining, howling is one of the few forms of verbal communication that dogs have. Its roots go back to dogs’ wolf ancestry, when wild wolves used howling to communicate over long distances. The howl swept through different pitches, which helped the sound carry over longer distances. Wolves use howling to let other pack members know their precise location if they happen to get separated.
Other members of the pack howl back in reply—an acknowledgement that the sent message has been received. Wolves also howl to discourage a rival pack from encroaching on their territory. Dogs today still display some of this behavior. If you leave your house or apartment, your dog may howl to try to reestablish contact with you. If the howling persists after you’ve left, it could be a sign of separation anxiety. And sometimes dogs howl to establish their territory.
The rays of light coming from the bottom of the pool pass from a denser medium (water) to a rarer medium (air) and are refracted (bend away from the normal).
When the rays return to the surface, they form an image of the bottom of the pool at a point, which is little above the real position.
The immune system protects the human body against germs, which are microorganisms that cause sickness and disease. There are four major types of germs— harmful bacteria (pathogens), viruses, fungi, and protozoa. This defense system begins with the skin, which stops germs from getting into your blood or tissues. If germs get into your body, for example through your nose or mouth, white blood cells called phagocytes and lymphocytes attack them. Phagocytes scout out and destroy invaders, and long-living lymphocytes remember the invaders and release chemicals called antibodies to make the body resistant, or immune, to them.
White blood cells live in the bloodstream, lymphatic system, and spleen. The lymphatic system (or lymph system, for short) is a far-reaching network that extends throughout your entire body. A clear liquid called lymph runs throughout the system, washing the body’s cells with nutrients and water and detecting and removing pathogens. Lymph is filtered through the lymph nodes, and then passes into the body’s bloodstream.
Cotton, which comes from flowering Gossypium plants, is a key vegetable fiber used for making clothes, and oil from its seeds can be used in cooking or for making soap. The cotton plant grows in 17 states that make up the U.S. “Cotton Belt”: California, Arizona, New Mexico, Texas, Oklahoma, Arkansas, Missouri, Mississippi, Alabama, Louisiana, Florida, Tennessee, North Carolina, South Carolina, Virginia, Georgia, and Kansas. In the United States, where cotton is no longer picked by hand, machines called pickers or strippers harvest the crops.
Cotton-picking machines have spindles that pick (twist) the seed cotton from the burrs that are attached to plants’ stems. Doffers— a series of circular rubber pads—then remove the seed cotton from the spindles and knock the seed cotton into a conveying system. Conventional cotton stripping machines use rollers equipped with alternating bats and brushes to knock the fluffy white bolls, which contain seeds and hairs, from the plants into a conveyor. After harvest, most of the cotton is pressed into large blocks for storage. These cotton bundles are then transported to the cotton gin, a machine that pulls out the seeds from the cotton bolls.
Absolutely. Being bitten by a plant-eating dinosaur such as Brachiosaurus, with its 52 chisel-like teeth, would certainly hurt! The bite of a Parasaurolophus, with its interlocking rows of teeth, might take off your fingers. In the Iguanodon, numerous sharp teeth were set in rows in the upper and lower jaws, and at steep angles to each other.
When the teeth were pressed together, the upper jaw was forced outward, creating a grinding motion between the teeth and its meal of crushed plant tissue.
The triangular shape of a tricycle, with its three wheels spread apart, is much more stable than a regular bicycle, which balances on two aligned wheels. (The “tri” [three] and “bi” [two] before “cycle” refers to the number of wheels each vehicle has.) Tricycles suit young children well; with larger heads and undeveloped muscles, little ones lack the coordination and balance needed to ride regular bikes. But as soon as they can learn to pedal, children can ride a tricycle, turning leg power into wheel power.
A tricycle is built for stability and not for speed: its pedals are attached to a sprocket in the center of its large front wheel, which moves around once for each completed pedal turn. So the larger the front wheel of a tricycle, the faster it will go—but it cannot be so large that young legs cannot reach the pedals! This design makes a tricycle unlike a regular bike, which has chain-driven sprockets that move its wheels a lot faster than its rider’s feet. Tricycles are also easier for little ones to steer and turn because they are pulled forward by the movement of their front wheels; regular bikes are powered by their rear wheels.
Butterflies and other insects fly from one plant to the next to feed on the sweet nectar— and sometimes the pollen—located in the interior of flowers. The sugar in nectar supplies insects with the energy they need, and pollen contains protein, fat, vitamins, and minerals. In the process of feeding, many insects transfer pollen—which sticks to their bodies—from one plant’s flower to another.
Pollen, which is a fine powdery grain from a flower’s male reproductive organ, must be transferred to the female reproductive organ of a flower for fertilization to take place and seeds to form.
Husbands and wives divorce when they can no longer live happily together. It is usually a sad thing, because when people marry they expect to be with their partner for the rest of their lives. But over the course of a marriage things happen, people can change, and the happiness that the couple was so sure of in the beginning sometimes disappears. When couples with children get divorced it is even more unfortunate because more people are affected. Many children feel bad when their parents divorce because their family will not be the same. After a divorce, they generally do not see one of their parents as much as they did before.
Still, just because the feelings between a mother and a father change doesn’t mean that their love for their children changes in any way. It’s important to remember that divorce is something that happens between a husband and wife—it has nothing to do with the kids. Many children feel that if they adjust their behavior somehow their parents will want to stay together, but divorces are not caused by anything children do.
According to the National Aeronautics and Space Administration (NASA), Which is in charge of space exploration and scientific discovery for the United States, the Hubble transmits about 120 gigabytes of science data every week. That’s equal to about 3,600 feet (1,097 meters) of books on a shelf. The growing collection of pictures and data is stored on magneto-optical disks. Among its many discoveries, Hubble has revealed the age of the universe to be about 13 to 14 billion years, which is a more accurate estimate than the Big Bang range of between 10 to 20 billion years.
Hubble also played a key role in the discovery of dark energy, a mysterious force that causes the expansion of the universe to accelerate. Hubble has shown scientists galaxies in “toddler” stages of growth, helping them understand how galaxies form. It found protoplanetary disks, clumps of gas and dust around young stars that likely function as birthing grounds for new planets. It discovered that gamma-ray bursts—strange, incredibly powerful explosions of energy—occur in far-distant galaxies when massive stars collapse.