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Control and coordination:Plants and animals
All the living organisms 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 such as light, heat, cold, sound, smell, touch etc.
Coordination in plants
Coordination refers to ordered working of different but interrelated parts to perform one or more activities smoothly. Since the nervous system doesn’t exist in plants, they use a chemical system. Plants coordinate their behavior against environmental changes with the help of Hormones. Plants have various hormones that help them to coordinate growth and response to the environment. These are the chemical compounds which are released by stimulated cells. Hormones are diffused around the cell.
Different types of hormones present in plants are: 
- Auxins
- Gibberellins
- Cytokinins
- Abscisic acid
Auxin is synthesized at the tip of the stem and help in plant growth by elongating the cell.
Gibberellin is concerned with the growth of the stem, seed germination, and flowering. Cytokinins are present in the areas of cell division as in fruits and seeds. Also helps in opening of the stomata. Abscisic acid inhibits the growth of many parts and responsible for the closure of stomata.
The hormones in plants known as Phytohormones coordinate their behavior by affecting their growth. The growth movements in plants are either directional or nondirectional.
Directional Movements
Directional changes are called tropic movements. Tropic movements are the one which occurs in the direction of the stimulus. Positive phototropism is responding by bending towards the sunlight which can be seen in shoots. Negative geotropism is growing away from the ground which is also shown by shoots. Roots exhibit negative photo tropism by bending away from the light and show positive geotropism by growing towards the ground. Chemotropism is a movement of growth in plants in response to the chemical stimulus like the growth of pollen tubes towards ovules.
Non- Directional Movements
Non-directional movements are called nastic response and concerned to movements of plant parts. Nastic movements are independent of growth, and plant cells have to change their shape for this movement to occur. These changes take place in the opposite direction to the stimulus.
Control and coordination in animals
Nervous system and the hormonal system are two important aspects of control and coordination in animals.
The nervous system
Neurons form the basis of the functional as well as the structural unit of the nervous system. The main job of these neurons is to receive the external stimuli and then send it to the brain, so that the brain in turn can read those signals and direct them to the necessary parts of the body to take proper action. For example, when you touch something really hot, then the neurons will transmit this message to the brain that you are touching something really hot and the brain will then send a message back to the hands through the neurons, due to which you will immediately move your hand from there. This transfer of messages takes place through electrical impulses which move throughout the body through nerve fibres.
Take a look at the structure of a neuron. See the dendrites? These are nerve ending tips that are specialised for receiving the outside stimuli and is present in our sense organs. The moment these dendrites receive a stimuli a chemical reaction gets sparked off due to which electrical impulses are generated which in turn moves from the dendrite to the nucleus then to the axon and then finally to the nerve endings. There is a gap present in between two nerve cells which is known as synapse. From the nerve endings of one neurone, the synapse takes in the message and then transmits it to the consecutive neuron and thus through a chain action, these electrical impulses are carried from one part of the body to another to reach the brain.
The hormone system
All the actions of coordination and control cannot be performed by the nervous system alone. This is because the electrical impulses which are used by the nervous system for transmitting information cannot be accessed by all the cells, especially the ones which are not connected to the nerve tissue. And on top of that cells need some time to generate impulses and carry them from one place to another. This is why the endocrine gland of our body, secretes hormones which get mixed into our bloodstream and can reach all the target cells. Hormones perform the function of chemical messengers.
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