How Animals Work [antikvár]

How Animals Work Over a million different kinds or species of animals inhabit the Earth. They live on land and in the water and exhibit an amazing range of shapes and sizes, but they all have a number of things in common. They all move, feed, breathe, reproduce, grow and get rid of waste. These features are characteristic of all living things, but the animals' bodies are constructed to carry them out in many different ways. You will discover how various animals live, and how their bodies are made to do the jobs necessary to keep them fit and healthy. Polar bears can swim in the icy sea because they are protected by insulatingjur and layers of thick fat Muscles for Movement Animals can run, hop, crawl, fly or swim, and these movements are all brought about by muscles. Each end of a muscle is firmly fixed to a part of the body and, when the muscle contracts, it makes something move. Among the vertebrates (animals with backbones) — most of the muscles are attached to bones. Contraction of the muscles at the top of a wolf's leg, for example, pulls on the bones lower down in the leg and lifts the leg up. Other muscles swing it forward and put it down again — the faster this happens, the faster the wolf runs. All vertebrates are built on a similar plan, but the shape, arrangement and density of their bones vary. The skeleton of a bird's wing, for example, has the same basic structure as that of an ape's arm, but birds' bones, unlike mammals, are usually hollow. This makes them lighter, so flying is easier. Invertebrate animals do not have bony skeletons, they have The muscles in the neck, shoulders tough and sometimes very hard shells or cases (exoskeletons). and hindquarters of wolves are Insects and spiders have lots of joints, rather like suits of armour. very well developed. They give the The joints are moved when they are pulled by muscles fixed to wolf strength, stamina and speed. the insides of the armour.