The study of cellular Biology Topics is essential to understanding the workings of all living organisms.
What is meant by Control and Coordination?
All living organisms (plants and animals) respond and react to changes in the environment around them. The changes in the environment to which the organisms respond and react are called stimuli (singular of stimuli is stimulus). Living organisms show responses to stimuli such as light, heat, cold, sound, smell, taste, touch, pressure, pain, water, and force of gravity, etc. The response of organisms to a stimulus is usually in the form of some movement of their body part. For example, if a man touches a very hot utensil accidentally, he quickly pulls his hand away from the hot utensil. Here, heat is the stimulus and the man reacts by moving his hand away from the hot utensil. Similarly, when the sun is bright, we close our eyes. In this case, light is the stimulus and we react by closing our eyes.
(a) This father lion is responding to the bite he has received from his cub
(b) These are the leaves of the sensitive plant (Mimosa pudica) about to be touched with a pencil
(c) When touched with a pencil (or fingers), the sensitive plant responds by folding up its leaves
All living things (animals and plants) respond to stimuli acting on them.
When we are frightened by a dog, we run away as fast as we can. Here, fear (of the dog) is the stimulus and we react by running away. If we prick an earthworm with a needle, then the earthworm withdraws (moves back). In this case, pain (produced by pinprick) is the stimulus and the earthworm reacts by withdrawing. We know that a sunflower always faces the sun. Here, sunlight is the stimulus and the sunflower reacts by bending (or moving) toward the sun. We eat food when we are hungry (and need energy).
In this case, hunger is the stimulus and we react by eating food. From the above discussion, we conclude that the reaction to stimuli is a characteristic property of living organisms. Another word that is also used in place of ‘reaction’ is ‘response’. So, we can also say that the response to stimuli is a characteristic property of living organisms.
Both, plants and animals react (or respond) to various stimuli around them. But the method of reacting to stimuli is not similar in plants and animals. They react to stimuli in different ways. For example, plants bend towards light but animals do not bend towards light. The animal Amoeba reacts to the presence of food by moving toward the food particle. Similarly, Amoebae tend to aggregate (collect together) in moderately warm water which is their reaction to the stimulus called heat.
Amoeba and other protozoa react to mechanical obstacles by avoiding them. We find that the Amoeba (which is an animal) can react to different stimuli in different ways. Animals can react to stimuli in many different ways because they have a nervous system and an endocrine system involving hormones. The plants, however, react to stimuli in a very limited way. This is because plants do not have a nervous system like the animals have. The plants use only hormones for producing reactions to external stimuli.
From all the above examples we conclude that when a stimulus acts on our body, then we react (or respond) in a manner that is in the best interest of our body. The reaction (or response) that we give to the stimulus involves many organs of our body. It is, therefore, necessary that all the concerned organs should work with one another in a systematic manner so as to produce the required reaction. In other words, the various organs should cooperate with one another to provide a proper reaction to the stimulus. The working together of the various organs of an organism in a systematic manner so as to produce a proper response to the stimulus, is called coordination. We will now discuss the control and coordination of plants, animals, and human beings, one by one. Let us start with control and coordination in plants.