Polysaccharides are the most abundant carbohydrates. A polysaccharide molecule can contain thousands of glucose units. These highly complex carbohydrates include starches, cellulose, and glycogen. Starch is the usual form in which carbohydrates are stored as energy by plants.Plants can split starch into its simpler glucose units for use as energy when needed. Cellulose is known as a structural carbohydrate because of the fibers formed by its molecules.tarch is the usual form in which carbohydrates are stored as energy by plants. Plants can split starch into its simpler glucose units for use as energy when needed. Cellulose is known as a structural carbohydrate because of the fibers formed by its molecules.
When a meteoroid, comet, or asteroid enters Earth's atmosphere at a speed typically in excess of 20 km/s (72,000 km/h; 45,000 mph), aerodynamic heating of that object produces a streak of light, both from the glowing object and the trail of glowing particles that it leaves in its wake. This phenomenon is called a meteor or shooting star.
The asteroid known as 2012 DA14 will narrowly miss Earth this Friday, the closest asteroid flyby on record. But the planet has not always been so lucky. Earth's craters are enduring testaments to direct asteroid hits. And though millionsâin some cases billionsâof years of erosion have made it difficult to determine the exact size of the meteorites, there is a general scientific consensus around the world's largest craters, which mark the largest asteroid impacts. Here are the ten biggest known: