Read the passages and choose the best answer to each question. Answer all questions about a passage on the basis of what is stated or implied in that passage.

Time – 15 minutes

EFFECTS OF IONIZING RADIATION

  1. Everyone on Earth is continually exposed to small, relatively harmless amounts of ionizing radiation, known as background radiation, from natural sources such as soil and rock. However, other types of ionizing radiation—x–rays, ultraviolet radiation from the sun, and alpha, beta, and gamma radiation emitted by radioactive isotopes—have the potential to harm the human body. Ionizing radiation has enough energy to remove one or more electrons from the atoms it hits to form positively charged ions that can react with and damage living tissue. Most damage occurs in tissues with rapidly dividing cells, such as the bone marrow, where blood cells are made, and the digestive tract, whose lining must be constantly renewed.

2. Exposure to ionizing radiation can damage cells in two ways. The first is genetic damage, which alters genes and chromosomes. This can show up as a genetic defect in children or in later generations. The second type of damage is somatic, which causes victims direct harm in the form of burns, miscarriages, eye cataracts, some types of leukemia, or cancers of the bone, thyroid, breast, skin, and lung. Small doses of ionizing radiation over a long period of time cause less damage than the same total dosage given all at once. Exposure to a large dose of ionizing radiation over a short time can be fatal within a few minutes to a few months later.

THE COYOTE

1. All North American canids have a doglike appearance characterized by a graceful body, long muzzle, erect ears, slender legs, and bushy tail. Most are social animals that travel and hunt in groups or pairs. After years of persecution by humans, the populations of most North American canids, especially wolves and foxes, have decreased greatly. The coyote, however, has thrived alongside humans, increasing in both numbers and range.

2. Its common name comes from coyotl, the term used by Mexico’s Nahuatl Indians, and its scientific name, canis latrans, means “barking dog.” The coyote’s vocalizations are varied, but the most distinctive are given at dusk, dawn, or during the night and consist of a series of barks followed by a prolonged howl and ending with short, sharp yaps. This call keeps the band alert to the locations of its members. One voice usually prompts others to join in, resulting in the familiar chorus heard at night throughout the West.

3. The best runner among the canids, the coyote is able to leap fourteen feet and cruise normally at 25–30 miles per hour. It is a strong swimmer and does not hesitate to enter water after prey. In feeding, the coyote is an opportunist, eating rabbits, mice, ground squirrels, birds, snakes, insects, many kinds of fruit, and carrion—whatever is available. To catch larger prey, such as deer or antelope, the coyote may team up with one or two others, running in relays to tire prey or waiting in ambush while others chase prey toward it. Often a badger serves as involuntary supplier of smaller prey: while it digs for rodents at one end of their burrow, the coyote waits for any that may emerge from an escape hole at the other end.

4. Predators of the coyote once included the grizzly and black bears, the mountain lion, and the wolf, but their declining populations make them no longer a threat. Man is the major enemy, especially since coyote pelts have become increasingly valuable, yet the coyote population continues to grow, despite efforts at trapping, shooting, and poisoning the animals.


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