Test 1 READING READING PASSAGE 1 below You should spend about 20 minutes on Questions 1-13, which are based on Reading Passage | Let's Go Bats A Bats have a problem how to find their way around in the dark. They hunt at night, and cannot use light to help them find prey and avoid obstacles. You might say that this is a problem of their own making, one that they could avoid simply by changing their habits and hunting by day But the daytime economy is already heavily exploited by other creatures such as birds. Given that there is a living to be made at night, and given that alternative daytime trades are thoroughly occupied. natural selection has favoured bats that make a go of the night-hunting trade. It is probable that the nocturnal trades go way back in the ancestry of all mammals. in the time when the dinosaurs dominated the daytime economy. our mammalian ancestors probably only managed to survive at all because they found ways of scraping a living at night Only after the mysterious mass extinction of the dinosaurs about 65 million years ago were our ancestors able to emerge into the daylight in any substantial numbers. B Bats have an engineering problem how to find their way and find their prey in the absence of light. Bats are not the only creatures to face this difficulty today. Obviously the night-flying insects that they prey on must find their way about somehow. Deep-sea fish and whales have little or no light by day or by night Fish and dolphins that live in extremely muddy water cannot see because, although there is light, it is obstructed and scattered by the dirt in the water. Plent of other modern animals make their living in conditions where seeing is difficult or impossible C Given the questions of how to manoeuvre in the dark what solutions might an engineer consider? The first one that might occur to him is to manufacture light, to use a lantern or a searchlight. Fireflies and some fish (usually with the help of bacteria) have the power to manufacture their own light, but the process seems to consume a large amount of energy Fireflies use their light for attracting mates This doesn't require a prohibitive amount of ene a male's tiny pinprick of light can be seen by a female from some distance on a dark night her eyes are exposed directly to the light source itself. However, using light to find one's ov way around requires vastly more energy, since the eyes have to detect the tiny fraction of light that bounces off each part of the scene. The light source must therefore be immens 18 www.TopSage.com