سؤال قراءة ستيب محلول — الإشارة والمرجعية (تدريب 4490)

(1) All animals must rest, but do they really sleep as we know it? The answer to this question seems obvious. If an animal regularly stops its activity and stays quiet and unmoving - if it looks as though it is sleeping - then why not simply assume that it is in fact sleeping? But how can observers be sure that an animal is sleeping? (2) They can watch the animal and notice whether its eyes are open or closed, whether it is active or lying quietly, and whether it responds to light or sound. These factors are important clues, but they often are not enough. Horses and cows, for example, rarely close their eyes whereas fish and snakes cannot close them. Yet this does not necessarily mean that they do not sleep. Have you ever seen a cat dozing with one eye partly open? Even humans have occasionally been observed sleeping with one eye or both eyes partially open. Animals don’t necessarily lie down to sleep either Elephant for example often sleep standing up with their tusks resting in the fork of a tree. Finally, while sleeping animals often seem unaware of changes in the sound and light and other stimuli around them, that does not really prove they are sleeping either. (3) Observation alone cannot fully answer the question of whether or not animals sleep. The answers come from scientists doing experiments in sleep laboratories using a machine called the electroencephalograph (EEG). The machine is connected to the animals measures their brain signals, breathing, heartbeat and muscle activity. The measurements are different when the animals appear to be sleeping than when they appear to be awake. Using the EEG, scientists have confirmed that all birds and mammals studied in laboratories do steep. (4) There is some evidence that reptiles, such as snakes and turtles, do not truly sleep, although they do have periods of rest each day, in which they are quiet and unmoving. They also have discovered that some animals like chimpanzees, cats and moles who live underground) are good sleepers while others like sheep, goats and donkeys are poor sleepers. Interestingly, the good sleepers are nearly all hunters with resting places that are safe from their enemies. Nearly all the poor sleepers are animals hunted by other animals; they must always be afraid.