Control and Coordination

  • 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.
  • Both plants and animals respond to stimuli but in a different manner.


  • Control and Coordination in animals is done with the help of two main systems: 
    (i) Nervous system 
    (ii) Endocrine system 


  • Control and coordination are provided by nervous and muscular tissues.
  • Nervous tissue is made up of an organized network of nerve cells or neurons which is specialized for conducting information via electrical impulses from one part of the body to another.


  • These are specialized tips of some nerve cells that detect the information from the environment. 
  • These are located in our sense organs.
    (i) Ear: It acts as phonoreceptors (receiving sound). It helps in hearing and maintaining the balance of the body. 
    (ii) Eyes: It acts as photoreceptors (receiving light). It helps in seeing 
    (iii) Skin: It acts as a thermoreceptors (feels temperature). It helps in feeling heat or cold and touch. 
    (iv) Nose: It acts as olfactory receptors (sense of smell). It helps in the detection of the smell. 
    (v) Tongue: It acts as a Gustatory receptors (sense of test). It helps in the detection of taste. 


  • It is the structural and functional unit of the nervous system.

Functioning of Neuron

  • The information from receptors is acquired at the end of the dendritic tip of a nerve cell as a chemical reaction that creates an electrical impulse.
  • This impulse travels from the dendrite to the cell body and then at the end of the axon.
  • Chemicals are released at the end of the axon by the effect of electrical impulse.
  • These chemicals cross the gap (synapse) and start a similar electrical impulse in a dendrite of the next neuron.
  • The similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscle cells or gland.

Parts of Neuron

  • Dendrite: It acquires information.
  •  Cell body: The information acquired by it travels as an electrical impulse.
  • Axon: It is the longest fibre on the cell body called an axon. It transmits electrical impulses from the cell body to the dendrite of the next neuron. 


  • It is the gap between the nerve ending of one neuron and dendrite of the other neuron. Here, the electrical signal is converted into a chemical signal for onward transmission.


  • Reflex action is a quick, sudden and immediate response of the body to a stimulus. Example: Knee jerk, withdrawal of hand on touching hot object.
  • Stimulus: It is an observable or detectable change in the external or internal environment to which an organism reacts.
  • Reflex arc: The pathway through which nerve impulses pass during reflex action is called reflex arc.
  • Response: It is the final reaction after the reflex action. 


  • Voluntary: Controlled by fore brain. Example: talking, writing. 
  • Involuntary: Controlled by mid and hind brain. Example: heart beat, vomiting, respiration. 
  • Reflex action: Controlled by spinal cord. Example: withdrawal of hand on touching a hot object. 


  • In some situations such as touching a hot object, pinching etc. we need to act quickly, otherwise our body would be harmed. Here response is generated from the spinal cord instead of the brain. In this way, time for taking action is reduced which saves us from injury.


  • Human nervous system consists of two parts, Central nervous system (CNS) and Peripheral nervous system (PNS).
  • Central nervous system consists of Brain and Spinal Cord.
  • Peripheral nervous system consists of Cranial Nerves which arise from the brain and Spinal Nerves which arise from the Spinal cord.


  • Brain is the main coordinating centre of the body. It has three major parts:
    (i) Fore-brain (ii) Mid-brain (iii) Hind-brain

(i) Fore-brain

  • It is the most complex or specialised part of the brain. It consists of cerebrum.
  • Functions of the Fore-brain:
    (i) Thinking part of the brain.
    (ii) Control the voluntary actions.
    (iii)Store information (Memory).
    (iv) Receives sensory impulses from various parts of the body and integrate it.
    (v) Centre associated with hunger.

(ii) Mid-brain

  • Controls involuntary actions such as change in pupil size and reflex movements of head, neck and trunk.

(iii) Hind-brain

  • It has three parts:
    (i) Cerebellum : Controls posture and balance. Precision of voluntary actions. Example: picking pen. 
    (ii) Medulla : Controls involuntary actions. Example: blood pressure, salivation, vomiting. 
    (iii) Pons : Involuntary actions, regulation of respiration. 


  • Protection of the Brain: Brain is protected by a fluid filled balloon which acts as a shock absorber and is enclosed in the cranium (skull or brain box).
  • Protection of Spinal Cord: Spinal cord is enclosed in the vertebral column.


  • For taking place voluntary actions, the brain has to send messages to muscles.
  • The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.
  • The brain thus allows us to think and take actions based on that thinking. This is accomplished through a complex design, with different parts of the brain responsible for integrating different inputs and outputs.


  • Electric impulse will reach only to those cells that are connected by nervous tissue. 
  • After generation and transmission of an electrical impulse, the cell takes some time to reset its mechanism before transmitting another impulse. So cells cannot continually create and transmit impulse. 
  • Plants do not have any nervous system. 


  • It helps in overcoming the limitations of electric communication.


  • There are two types of movements in plants. 
    (i) Independent of growth 
    (ii) Dependent on growth 

(i)Independent of Growth

  • Independent growth has an immediate response to the stimulus.
  • Plants use electrical-chemical means to convey information from cell to cell.
  • For movement to happen, cells change their shape by changing the amount of water in them, resulting in swelling or shrinking of cells. Example: Drooping of leaves of ‘Touch-me-not’ plant on touching it.

(ii)Dependent on Growth

  • These movements are tropic movements i.e., directional movements in response to stimulus.
  • Tendrils: The part of the tendril away from the object grows more rapidly as compared to the part near the object. This causes circulating of tendril to circulate around the object.
  • Phototropism: Movement towards light.
  • Geotropism: Movement towards/away from gravity.
  • Chemotropism: Growth of the pollen tube towards ovule.
  • Hydrotropism : Movement towards water.


  • These are chemical compounds which help to coordinate growth, development and responses to the environment.
  • Main plant hormones are:
    • Auxin: These hormones are synthesized at shoot tip. It helps the cells to grow longer and involved in phototropism (response towards light).          • Gibberellin : It helps in the growth of the stem. 
    • Cytokinins: It promotes cell division. This is present in greater concentration in fruits and seeds 
    • Abscisic Acid: It inhibits growth. It also causes wilting of leaves and is also known as a stress hormone. 


  • Hormones are the chemical substances which coordinate the activities of living organisms and also their growth.
  • Endocrine glands : These glands secrete their product (hormone) into the blood and the main organ for releasing the hormones.


(i) Thyroxine: This hormone is secreted by Thyroid. The Thyroid is located in Neck/Throat region. It regulates the metabolism of carbohydrates, fats and proteins. 
(ii) Growth hormones: This is secreted by the Pituitary (master gland). This gland is located in Mid-brain. It regulates growth and development. 
(iii) Adrenaline: This hormone is secreted by Adrenal. The adrenal gland is located above both kidneys. It regulates blood pressure (increasing), heart beat, and carbohydrate metabolism (during emergencies). 
(iv) Insulin: This hormone is secreted by Pancreas. The pancreas is located below the stomach. It reduces and regulates blood sugar level. 
(v) Sex hormones:
(a) Testosterone in males:
This hormone is secreted by testis. The testis is located in genital area. Its changes associated with puberty (Sexual maturity).
(b) Estrogen in females: This hormone is secreted by Ovaries. The ovaries are located in the lower abdomen area. Its changes associated with puberty (Sexual maturity). 


Iodised salt is necessary because iodine is an essential part of the thyroxine hormone secreted by the thyroid gland. Thyroxine regulates metabolism of carbohydrates, fats and proteins. So, we must consume iodised salt which is necessary for proper working of the thyroid gland. It’s deficiency causes a disease called goiter (Swollen neck).


Diabetes is a disease in which blood sugar level increases.


The disease is caused due to the deficiency of insulin hormone secreted by the pancreas that is responsible for controlling blood sugar levels.


Injections of insulin hormone can help in the treatment of diabetes.


The excess or deficiency of hormones has a harmful effect on our body. Feedback mechanism makes sure that hormones should be secreted in precise quantities and at the right time. Example: Feedback mechanism to control the sugar level in blood is as follows:

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