Once seeds are fully developed, they need a good place to grow. If they just fell to the ground beneath their parent plant, they would struggle, competing against each other for sunlight, water, and minerals. Most seeds need to travel—by wind, water, or with the help of insects and other animals—to better places to germinate, or start to grow into new plants. Some seeds, like those from conifer and maple trees, have wings attached. Others, like those of dandelions, have parachutes made of tiny hairs. Both features allow the seeds to be carried great distances by the wind, and they sometimes land in spots that are good for germination. Water carries other seeds to good growing places; the hard, watertight shell of a coconut, for instance, allows it to travel many miles at sea before finding a beach where conditions are suitable for growth.
Seeds sometimes have to wait a long time before they find good places to grow, places where the sun, moisture, and temperature are right. Most seeds are designed for the wait, protected by a hard outer pod (except those of conifers). Some seeds wait years to germinate, and some just never do. But inside each seed pod is a baby plant, or embryo, and endosperm, a supply of starchy food that will be used for early growth if germination takes place. Then a tiny root will reach down into the soil, and a tiny green shoot will reach up, toward the light.
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.
Rain forests—thick forests of trees and other plants found in the lowland areas of the Tropics around the world—exist in parts of Australia, Indochina, India, the Malay Peninsula, the East Indies, in central and western Africa, and in Central and South America. Unlike forests in many other parts of the world, which have been affected by global climate changes like the Ice Age, tropical rain forests have been growing uninterrupted in some places for millions of years. During that time an unimaginable number of different types of plants and animals have evolved to use every food source and live in every spot there. Tropical rain forests have more plant and animal species than the rest of the world combined, and scientists continue to discover new species. Because tropical rain forests are located near the equator, their climate is warm.
The name “rain forest” comes from the fact that they receive a lot of rain—between 160 and 400 inches (4 and 10 meters)—throughout the year. Plants grow very quickly under such ideal conditions. In order to get the sunlight that they need for photosynthesis (the process by which they and other green plants make their own food), rain forest trees grow very tall, up to 130 feet (40 meters) high. Their tops form a huge canopy that shades most of the ground, protecting plants on the ground from excessive sunshine as well as wind. Rain forest trees have very shallow roots, for the soil in which they grow is poor, having long been depleted of nutrients by the needs of thick plant life over millions of years. But the abundant life all around contributes organic matter (the decomposed remains of plants and animals) to the surface of the soil, which is enough to nourish these grand, ancient forests.
Skin color—which ranges from light pink to dark brown—is determined by the amount and type of the pigment melanin there is in the skin. Melanin comes in two types: phaeomelanin (red to yellow) and eumelanin (dark brown to black).
Both amount and type are determined by four to six genes. One copy of each of those genes is inherited from your father and one from your mother. Each gene comes in several coding sequences, which results in a variety of skin colors around the world.
Antibiotics are medicines that help the human body fight bacteria, either by directly killing the offending germs or by weakening them so that the body’s own immune system can fight and kill them more easily.
The most widely known antibiotic is penicillin, which is made from mold. Penicillin kills bacteria by interfering with the formation of the cell walls or cell contents of the bacteria.
An earthquake is a great shaking of Earth’s surface. It is caused by the cracking and shifting of the plates of rock that make up the planet’s layered crust. As shifting plates suddenly slide past one another, vibrations in the form of waves are released. These shock waves travel through Earth, gradually weakening as they move farther from the spot (or spots) where the quake began, which is called the epicenter. Regions located near faults (places where cracks in Earth’s crust are known to exist), are particularly vulnerable to earthquakes.
Earthquakes vary in size and intensity. They may last a few seconds or continue for a few minutes. They may cause no damage, or they can result in widespread destruction and the deaths of thousands of people. Earthquake vibrations can be so violent that they collapse bridges and buildings, destroy highways, cause landslides, and lead to flooding if they occur in shallow water near a coast.
According to statistics from technology research companies such as Gartner Inc., in April 2002 the billionth personal computer (PC) was shipped. The second billion mark (some being ordered as replacements for older PCs) was reportedly reached in 2007. With personal computers becoming more popular around the world, research companies estimate that there will be more than two billion PCs in active use by 2015.
In the United States, more than half of the people who use a computer are also connected to the Internet.
Yes. Organic farmers also try to do more tasks using human power rather than gas-powered vehicles, thereby using less fuel and cutting down on pollution. Organic farms that raise livestock like dairy cows or chickens feed the animals with natural food, avoiding pollution-causing chemicals and growth hormones that make cows produce more milk and chickens produce more eggs.
Some organic farmers also allow their animals to roam in a large area (such animals are described as “free range”) rather than keeping them in small, climate-controlled pens for their entire lives.
On the outside, most electric cars look exactly like gas-powered cars. An electric car does not have a tailpipe or a gas tank, but the overall structure is basically the same. Instead of a huge engine, an electric car uses an electric motor to convert electric energy stored in batteries into mechanical energy.
Different combinations of generating mechanisms—solar panels, generative braking, internal combustion engines driving a generator, fuel cells— and storage mechanisms are used in electric vehicles.
Yes. Mars, the fourth planet from the Sun, is called the Red Planet. It looks red because the rocks on the surface contain rusted iron. It has an atmosphere with clouds, winds, and dust storms—its red dust floats in the atmosphere and gives the planet a red sky.
Mars, which has two moons, orbits the Sun every 687 days and rotates on its axis once every 24 hours and 37 minutes.