Definicija i značenje
ETYM Latin, from anima breath, soul: cf. French animal. Related to Animate.
Or metazoan; Member of the kingdom Animalia, one of the major categories of living things, the science of which is zoology. Animals are all heterotrophs (they obtain their energy from organic substances produced by other organisms); they have eukaryotic cells (the genetic material is contained within a distinct nucleus) bounded by a thin cell membrane rather than the thick cell wall of plants. Most animals are capable of moving around for at least part of their life cycle.
In the past, it was common to include the single-celled protozoa with the animals, but these are now classified as protists, together with single-celled plants. Thus all animals are multicellular. The oldest land animals known date back 440 million years. Their remains were found 1990 in a sandstone deposit near Ludlow, Shropshire, UK, and included fragments of two centipedes a few centimeters long and a primitive spider measuring about l mm.
Feeding types.
Animals can be divided into three feeding types; herbivores eat plants and plant products, carnivores eat other animals, and omnivores eat both. As few animals can digest cellulose, herbivores have either symbiotic cellulose-digesting bacteria or protozoa in their guts, or grinding mechanisms, such as the large flattened teeth of elephants, to release the plant protoplasm from its cellulose-walled cells. Carnivores are adapted for hunting and eating flesh, with well-developed sense organs and fast reflexes, and weapons such as sharp fangs, claws, and stings. Omnivores eat whatever they can find, and often scavenge among the remains of carnivores prey; because of the diversity of their diet, they have more versatile teeth and guts than herbivores or carnivores. Many animals are adapted for a parasitic way of life, living on other animals or plants, and feeding solely by absorbing fluids from their hosts. Some animals absorb food directly into their body cells; others have a digestive system in which food is p.
Repared for absorption by body tissues.
Movement.
The mechanisms by which living organisms move vary from the flowing protoplasm of an ameba to the complex muscle-and-bone movements of a birds wing in flight. Wriggling, crawling, swimming, and the internal flow of fluids are often assisted by minute cellular organelles, cilia, that beat in a rhythmic pattern. Most animals have contractile tissue to assist with movement; the increased complexity of muscle systems in higher animals, coupled with a stiff skeleton, allows greater flexibility of movement.
Circulation.
In order to contract, muscles must have energy, which is obtained by breaking down sugars produced by the digestion of food, usually by combining them with oxygen (see respiration). In simple animals, the sugars and oxygen diffuse through the body to the contractile tissue; in higher animals they are carried by a blood circulatory system, which is pumped by the heart, to the muscles. In insects, the oxygen is carried through tiny branching air-filled tubes, called trachea.
Excretion. The circulatry system also carries waste products away from the cells. These are separated from the blood (in the kidneys of higher animals), and are excreted together with undigested food. The excretory systems of aquatic animals are also responsible for maintaining a correct fluid balance within the animals. This is particularly important in freshwater creatures, which tend to absorb water by osmosis.
Nervous system.
The movement and behavior of animals is controlled by the nervous system. Impulses pass from centers of controloften grouped to form a brainto the various muscles and glands. As animals become more advanced, their brains become more complex, and their nervous control more complete. Behavior varies from the simplest reflex action to the highly complex learned and intelligent behavior of the higher primates. In many animals special behavior patterns form an integral part of courtship.
Color and camouflage.
Most animals are colored in some way. Often the color is defensive, camouflaging the animal or disguising it as another that may taste bad or be venomous. Color can also act as a threat to enemies or competitors, and plays an important part in recognition during courtship. Some animals, such as chameleons, can alter their color to blend with the environment by changing the size of different colored patches in the skin.
A living organism characterized by voluntary movement; SYN. animate being, beast, brute, creature, fauna.
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