Science Answer the following questions: [3 M]

Reflex action	Walking
It is a rapid, automatic response to a stimulus which is not under the voluntary control of the brain. It is a kind of involuntary action which involves the spinal cord. It is not based on our thinking.	It is a voluntary action which we undertake knowingly. The action of walking involves thinking by the brain. The central nervous system (brain, spinal cord) take part in the action of walking.

The plants do not have a nervous system but they can sense things in the presence of stimuli such as light, touch, water etc. and respond to them by the action of hormones. Thus, the plants coordinate their behavior against environmental behavior by using organic chemicals called hormones. This is called chemical coordination. The hormones in plants coordinate their behavior by affecting the growth of a part of the plant resulting in the movement of that plant part in response to a stimulus. The control and coordination in animals takes place by both nervous system and hormones.

The 3 regions of human brain are:

1. Forebrain.
2. Midbrain and
3. Hindbrain.

P is abscisic acid because it is antagonistic to growth and inhibits it.
Q is auxin because it causes bending of shoots towards the light.
R is gibberellins because it increases the cell division in a plant shoot and increases its length. S is cytokinin because it breaks the dormancy of buds and seeds.

Voluntary Action	Involuntary Action
Those action which need think and are performed by us knowingly are called voluntary action. Explanation: Writing, dancing.	Those actios which do not need thinking and are not performed by us knowingly are called involuntary action. Example: Digestion, respiration.

Digestion is an involuntary action as it does not involve the thinking process and is performed unknowingly by our digestive system.

Puberty and adolescence are the results of sex glands in human beings. In males, testes make male sex hormones called testosterone which is associated with male puberty, which the boys attain an age of 13 - 14 years. In females the oestrogen hormone is responsible for all the changes associated with female puberty which the girl attains at an age of 10 - 12 years.

When the agarbatti burns, it produces vapours having a characteristic pleasant smell which is detected by the olfactory receptors present inside our nose. The action of smell of agarbatti or receptors sets off chemical reactions which generate electrical impulses. The sensory neurons carry these electric al impulses to the sensory area of fore brain called cerebrum. This makes us detect the smell of burning agarbatti.

The unit which makes up the nervous system is called a neuron.

A neuron (or nerve cell).

The voluntary nervous system is a system which helps us to take voluntary actions which are under the conscious control of the brain.
Example: If a student is getting late for school and sees his watch. He starts walking fast. In this process, the eyes see the time and send the information to the brain through the sensory nerves. The brain analyses the information and sends the instructions to walk faster to the muscle of our legs through the motor nerves. The muscles of the legs act accordingly and make the student walk faster.

The growth of a plant part in response to a stimulus is called positive tropism and if the growth of a plant part is away from the stimulus, then it is called negative tropism. Example: The roots of a plant go towards earth in response to gravity is an example of positive geotropism whereas stem grows away from earth against gravity is an example of negative geotropism.

Tropisms:

1. These movements are always in the direction of the stimulus.
2. These movements are slow.
3. These movements are exhibited by all parts of a plant. For example, movement of shoot towards the light and not towards.

Nasties:

1. These movements are neither away nor towards the stimulus.
2. These movements are fast.
3. These movements are exhibited by the flat organs (like leaves and petals of flowers) of a plant. For example, the bending and dropping of leaves in ‘Touch-me-not’ plant.

The chemical coordination in animals takes place through the actions of chemicals called hormones which are release directly into the blood and are carried by the blood circulatory system to other parts of the body. Hormones travel all over the body but affect only particular organs at particular places which are called target organs. The organs control and coordinate several functions of animal body such as growth, development, metabolism, behavior and secondary sexual characteristics, etc.

It is an example of reflex action. The stimulus here is drawing pin lying on the floor. The pain is sensed by the receptors in the skin which triggers and impulse in a sensory neuron and transmits the message to the spinal cord. The impulse is passed onto a relay neuron, which in turn, passes it to the motor neuron. The motor neuron passes the impulse to a muscle in the feet. The muscle then contracts and pulls our feet away from the drawing pin.

The adrenaline hormone prepares our body to function at maximum efficiency during emergency situations like danger, anger etc. This adrenaline hormone increases our heartbeat, breathing rate, blood flow into muscles and causes liver to put more stored glucose into our blood. All these actions produce a lot of energy in our body and help us to cope up the emergency situations. Thus, when adrenaline is secreted in large amounts it prepares our body for action.

The pathway taken by the never impulses in our reflex action is called the reflex arc.

A reflex are (This is actually a spinal reflex are).

Thigmotropism	Thimonasty
The directional growth movement of a plant touch of an object is called thigmotropism. Example: Tendrils.	The non-directional movement of a plant part in responce to the touch of an object is called thigmonasty. Example: Mimosapudica.

Tendrils grow towards a stimulus hence it is a directional movement which shows that it is a case of thigmotropism whereas, the folding of leaves in mimosa plant does not depend on the direction of stimulus (touch) which shows that it is an example of thigmonasty.

The movement of a plant part towards light is called positive phototropism. Example? the stem of the growing bends towards light. The movement of a plant part away from light is called negative phototropism. Example? The roots of a plant move away from light.

The rapid, automatic response to a stimulus which is not under the voluntary action of the brain is called reflex action. Example: Moving our hand away on touching a hot plate.

Nervous System It is a system to coordinate the activities of bodies. It helps all other system of our body to work together. It receives information from the surroundings, processes it, interprets it and then responds accordingly. Endocrine System It is a group of endocrine glands which produces various hormones that helps in coordinating the activities of our body. The hormones produced by the endocrine glands act as messengers between the nervous system and the organs of our body.