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| Control and Coordination in Animals |
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| Animals are different from plants because of their ability of locomotion. This ability probably developed as they have to search for food, unlike the plants that are autotrophic. Since they move from one place to another, the animals have to continuously encounter changes in their environment. In order to maintain a steady state within the body (homeostasis), all animals should be able to perceive these changes and adapt to them. |
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| With increasing complexity in their structure, the number and types of cells in the animal body increased. Thus it became necessary to have some coordinating mechanism. Two systems have been developed for better control and coordination of the various activities of the organisms. These systems are the nervous system and the endocrine system. |
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| Nerve Net of Hydra |
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| The nervous system is made up of units called the neurons which relay information by generating electric potential. The endocrine system, on the other hand, is made up of glands that secrete chemicals called the hormones. They are secreted into blood that carries them to the sites of action. |
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| Nervous System of an Insect |
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| Animals receive a variety of external information through specialised structures called sense organs (receptors). These are photoreceptors for light, phonoreceptors for sound, and olfacto receptors for smell. The receptors pass information to the brain by a type of nerve cells called sensory neurons. Another type of nerve cells, called motor neurons, transmit information from the brain to the effector organs. The effectors are mainly muscles and glands. The brain is a centre for the analysis of information, such as those related to hearing, vision, smell, taste, movement, flight and other muscular actions. |
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