The electrical impulse travelling through axon reaches the end of axon, from where the electrical impulse sets off a chemical reaction that releases some chemicals (neurotransmitters). These chemicals cross the gap or synapse and reach to dendrites of the next neuron and start a similar electrical impulse there.

Cerebellum, a part of hindbrain is responsible for maintaining posture and equilibrium of the body.

Smell of an agarbatti is sensed by olfactoreceptor present in the nose and the information is transmitted to olfactory lobe located in the fore-brain which interprets the information. In this way we detect the smell of incense stick.

• In most of the reflex actions brain is not involved and it is controlled by spinal cord. But in some reflex actions which are cerebral reflexes thinking process is involved. Such reflex actions involve brain.
• Example of cerebral reflexes are salivation at sight or smell of food, contraction of pupil of human eye in presence of bright light and peristalsis.

• Plant hormones are special chemical compounds released by different parts of the plant.
• They help to coordinate growth, development and responses to the environment.
• They are synthesised at places away from where they act and simply diffuse to the area of action.

Difference between the movement of leaves of the sensitive plant and movement of shoot towards light:

Auxin promotes growth of cell, gibberellins help in growth of stem, cytokinin promotes cell division.

The tendrils are sensitive to touch. When a part of tendril comes in contact with a support, the growth hormone auxin diffuses from the tip of tendril to the side of tendril that is not in contact with the support. This causes growth in the part of the tendril away from the support which further causes the tendril to coil around the support. Thus, the tendrils cling to the support.

Hydrotropism: Growth movements in response to the stimulus of moisture (water) are termed as hydrotropic movements (hydrotropism).

Experiment:

• To perform the experiment, take a plant (pea seedling) in a jar filled with sand.
• Place a porous pot filled with water in the wide jar.
• Roots of the plant will grow towards water and bend towards the water source showing positive hydrotropism.

Animal hormones are directly poured into the blood by the endocrine glands or ductless glands. Thus, a hormone reaches to the target organ / tissues / cells through blood. In target organ, hormone transmits the information to bring about the effect.

Importance of iodised salt:

• Iodine is necessary for the thyroid gland to make thyroxine hormone.
• Thyroxine regulates carbohydrate, protein and fat metabolism in the body to provide balanced and proper growth.
• Deficiency of iodine in our diet may lead to goitre, i.e., swollen neck and other metabolic disorders.
• Iodine is needed in very small quantity to synthesise thyroxine.
• Iodised common salt contains proper content of iodine.
• To avoid deficiency of iodine, iodised salt is recommended.

Adrenaline: Adrenaline is secreted by adrenal glands. It is secreted by medulla

of adrenaline and poured directly into blood.

Functions of adrenaline

• The target organ of adrenaline is heart. It increases rate of heart beat in order to supply more oxygen to our muscles.
• The blood supply to the digestive organ system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our muscles.
• Adrenaline hormone also causes increase in breathing rate. This happens because of the contraction of the muscles of the diaphragm and the ribs.

All these responses together make the body of the animal to be ready to deal with the situation.

• Insulin hormone regulates blood sugar levels. If this is not secreted in proper amounts, the sugar level in the blood rises. This causes many harmful effects.
• Deficiency of insulin secreted by pancreas also reduces uptake of glucose (sugar) by the body tissues. This causes harmful effects on the vital organs of the body.
• To treat harmful effects of increased level of blood sugar, the diabetic patients are provided insulin by injections of insulin.

(d) Cytokinin.

(b) synapse.

(d) all of the above.

Function of receptors:

• Receptors are the specialised cells located in our sense organs like the nose, the inner ear, the tongue, etc. They detect information from the environment. For example, gustatory receptors detect taste while olfactoreceptors detect smell.
• If receptors do not work properly, the information obtained from the environment will be delayed to reach the spinal cord or brain.
• In this situation, the response to the environmental stimulus is delayed causing harm to the body. For example, touching a hot object is an urgent and dangerous situation. If receptors are not working properly the response may be delayed and we may get burnt.

Function:

• Dendrites of a neuron collect information from the receptors and pass it to the cell body in the form of electrical impulse.
• From the cell body, impulse passes along the axon to its end.
• At end of the axon, the electrical impulse sets off chemical reaction to release certain chemicals (neurotransmitters).
• These chemicals cross the gap (synapse) between the endings of the axon and dendrites of the next neuron and start a similar electric impulse in the dendrites.
• Thus information received travels along the neurons of a nerve to the effector muscles or gland.

• When a plant placed in a dark room or in a box covered from three sides receives unilateral (light coming from one side, say window or a hole in a box), its apical tip detects light.
• In response to light auxin diffuses towards shady side of the plant, that is, on the opposite side of the direction of light.
• So, concentration of the auxin increases towards shady side of the shoot and here it stimulates the apical cells to grow longer than the apical cells situated towards light.
• So, more elongation of cells on shady portion causes bending of the stem towards light. This movement of the shoot is known as phototropism.

• Reflex actions will be disturbed because spinal cord is one of the components
• of reflex arc. So, the quick responses needed to safeguard the body will not take place. The delayed responses may cause harm to the body.
• For example, delayed response to touching a hot object may cause burn of the body part.
• Impulses from various body parts will not be communicated to brain.
• Messages from brain to body parts will not be communicated.

Different plant hormones help to coordinate growth, development and response to the environment in plants. They are synthesised at places away from where they act and simply diffuse to the specific area to produce effect. These plant hormones are called phytohormones.

• The process through which two or more organs interact and complement the function of each other is called coordination.
• In most of the multicellular organism’s body is very complex and to produce a response to a stimulus different organs must work together in a proper way.
• Thus, all organisms have some mechanism for control and coordination.
• For example, animals have nervous system and endocrine system for control and coordination.

Involuntary actions are controlled by either mid brain or hind brain whereas reflex actions are controlled by spinal cord.

The differences between the movement in sensitive plant and our legs are as follows.