Science [3 Mark Questions]

→ Iodine is essential for the synthesis of thyroxin hormone.
→ Thyroxin regulates carbohydrate, protein and fat metabolism in the body.
→ Thyroxin provide best balance for growth in the body.

The movement of a plant or other organism in response to light is called phototropism, either towards the source of light (positive phototropism) or away from it (negative phototropism).
This movement is caused due to more growth of cells towards the shaded side of the shoot as compared to the side of shoot towards light. More growth of cells is due to secretion of auxin towards the shaded side.
To demonstrate it we will place a potted plant in a box in which light comes from only one direction. In a few days we will observe that the shoot has moved towards the side from which light came in the box.

Hormones are complex organic compound which is released endocrine glands in a very small quantity to keep control over growth and development.Thyroid gland secrets thyroxin:
It plays vital roles in digestion, heart and muscle function, brain development and maintenance of bones Iodine is needed by the thyroid gland for the production thyroxin hormone. This hormone regulates fat, protein and carbohydrate metabolism in our body If this is in deficient quantity then the neck will swell up due to the enlargement of thyroid gland. This deficiency disease is known as goitre. Therefore the iodized salt is advised.

Gland	Hormones	Functions
Thyroid	Thyroxine	Regulates metabolism of carbohydrates, proteins and fats in the body.
Pituitary	Growth hormone	Regulates the growth and development of bones and muscles.
	Prolactin	Regulates the functioning of mammary glands in females.
	Vasopressin	Regulates the balance of water and electrolytes in the body.
	Oxytocin	Regulates the ejection of milk during lactation in females.
Pancreas	Glucagon	Helps to increase the sugar level in the body.
	Insulin	Helps to decrease the sugar level in the body.

1. Directional movements of the plant part towards or away from the stimulus.
2. When the tip of the tendril comes in contact with the support, more auxin is diffused from the tip towards the side of the tendril away from the support. As a result, that side grows faster and causes the tendril to bend around the support.

a - Receptor/ skin.
b - Sensory neuron.
c - Spinal cord.
d - Relay neuron.
e - Motor neuron.

• Reflex Arc.

A process in which green plants takes carbon dioxide and water and convert them into carbohydrates/ food in the presence of sunlight and chlorophyll.
Mechanism:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy.
3. Splitting of water molecules into hydrogen and oxygen.
4. Reduction of carbon dioxide to carbohydrate.

In plants, growth, development, and response to the environment are controlled and coordinated by a special class of chemical substances known as phytohormones. They are naturally occurring organic substances which are synthesized in minute quantities. These hormones are produced in one part of the plant body and are translocated to other parts. For example, a hormone produced in the roots is translocated to other parts where they are required.

1. Gibberellins
2. Cytokinins
3. Abscisic acid
4. Auxins

• The adrenaline hormone is secreted into the blood.
• The heart beats faster resulting in supply of more oxygen to the muscles.
• Blood is diverted to skeletal muscles.
• The breathing rate increases.
• The blood supply to digestive systems and skin is reduced.

• Electrical impulses have limited access to only those cells that are connected by nervous tissue/ neurons, whereas chemical signals can reach each and every cell of the body.
• Cells need time to reset in order to create repeated/ new electrical impulses whereas no such time is required for chemical communication.

Yes feedback mechanism is a very important aspect of hormonal co-ordination. The feedback mechanism of hormones is the mechanism through which the balance of hormone in the blood/ body is maintained. The increase or decrease in the concentration of that hormone can either stimulate the secretion of that particular hormone or inhibit the hormone secretion. This is called feedback.

	Nervous system mechanism		Hormonal system mechanism
1	The information is conveyed in the form of electric impulse.	1	The information is conveyed in the form of chemical messengers.
2	The axons and dendrites transmit the information through a coordinated effort.	2	The information is transmitted or transported through blood.
3	The flow of information is rapid and the response is quick.	3	The information travels slowly and the response is slow.
4	Its effects are short lived.	4	It has prolonged effects.

Auxins are a class of plant hormones(or plant growth regulators) with some morphogen-like characteristics. Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant's life cycle and are essential for plant body development.

Receptors are groups of specialised cells. They detect a change in the environment(stimulus) and stimulate electrical impulses in response. Sense organs contain groups of receptors that respond to specific stimuli.
Three types of receptors are:

1. Olfactory receptor: They detect the smell.
2. Gustavo receptor: They detect the taste.
3. Thermo receptor: they detect the temperature of the outer world.

Receptor through sensory motor passes the information to the spinal cord which then sends the information to the brain.

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.

	Auxins	Cytokinins
1.	Auxin is first introduced by F.W. Went.	Cytokinin is first isolated by Miller and Skoog.
2.	It is produced in the shoot apex and leaf primordia.	It is found in the endosperm and embryo of seeds, in fruits and roots.
3.	Auxins promote the growth of apical bud.	Cytokinins promote the growth of lateral buds.

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.

Cerebellum is located in hind-brain it is the largest structure of the hindbrain. The cerebellum receives information from the sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements. The cerebellum coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity.

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.

Take two small beakers and label them as A and B. Fill beaker A with water. Now make a cylindrical-shaped roll from a filter paper and keep it as a bridge between beaker A and beaker B, as shown in the figure. Attach few germinating seeds in the middle of the filter paper bridge. Now, cover the entire set-up with a transparent plastic container so that the moisture is retained.

Observation:
The roots of the germinating seeds will grow towards beaker A.

This experiment demonstrates the phenomenon of hydrotropism.

The growth movement in plants in response to light stimulus is known as phototropism. The shoots show positive phototropism and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source.
For Example: The flower head of sunflower is positively phototropic and hence it moves from east to west along with the sun.

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.

There are various organs in an organism. These organs must be carefully controlled and coordinated for the survival of an organisms. In the body of an organism various fluids are secreted from the glands of the endocrine system. These hormones are responsible for the overall growth and development of an organism. All others daily decision that includes voluntary and involuntary action are controlled by central nervous system(CNS).

The path taken by the nerve impulses in a reflex is called a reflex arc. In higher animals, most sensory neurons do not pass directly into the brain, but Sensory neurons passes signals from the receptors to the spinal cord from where they travel to brain and then brain sends them back via motor neuron to the effector part which helps in quick reflex. For example when we touch the hot pan by mistake we suddenly pull-off our hands. This response to the stimuli is known as reflex action.

Movement in sensitive plants	Movement in our legs
The movement in a sensitive plant is a response to stimulus(touch) which is a involuntary action.	Movement in our legs is a voluntary action.
No special tissue is there for the transfer of information	A complete system CNS and PNS is there for the information exchange.
Plant cells do not have specialised protein for movements.	Animal cells have specialised protein which help muscles to contract.

Reflex actions are sudden, involuntary reactions of the body in response to stimuli. They occur without the involvement of the conscious areas of the brain. Therefore, all reflex actions are unconscious actions. Somatic nervous system is responsible for reflex arcs. Reflex arc is the path of impulses in the reflex action.Reflex arcs are formed in the spinal cord and the information (input) reaches the brain. The brain is only aware of the signal and the response that has taken place. However, the brain has no role to play in the creation of the response.

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).

1. Phototropism: the growth response of a plant in response to light direction. Different parts of a plant exhibit different reactions to light. Stems exhibit positive phototropism while most roots exhibit negative phototropism.

2. Geotropism: the growth response of a plant in response to gravity. Roots exhibit positive geotropism while stems and leaves exhibit negative geotropism.

3. Chemotropism: the growth response of a plant to a particular chemical. Roots grow toward useful minerals in the soil but away from acids.

The adrenal glands are small glands located on top of each kidney. Theyproduce hormones that you can't live without, including sex hormones and cortisol. Cortisol helps you respond to stress and has many other important functions. With adrenal gland disorders, your glands make too much or not enough hormones.

The central nervous system (CNS) controls most functions of the body and mind. It consists of two parts: the brain and the spinal cord. spinal cord is centre for all the reflex actions. Brain the major centre of co-ordination in the body. The brain is the center of our thoughts, the interpreter of our external environment, and the origin of control over body movement.

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 Human brain has three parts- fore-brain, mid-brain, and hind-brain. Fore-brain Fore Brain It is the main thinking part of the brain and controls the voluntary actions. The forebrain processes sensory information that is collected from the various sense organs such as ears, eyes, nose, tongue, skin.

Adrenal gland is an endocrine gland which secretes adrenaline and helps us to face emergency situations. Some of its examples are dryness of mouth when fear or shivering of body when fear. This shows that the endocrine system coordinates our body activities.

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.

Hormones are the long range chemical messengers that are released into blood by endocrine gland in response to some signal. These hormones exert their effect on the target cells present distantly from their site of release. These hormones serve the function of chemical coordination in animals.
Hormones are released into the blood stream and can reach all cells but they affect only target cells. This is followed by generation of stimulus specific biochemical or physiological activity. In this way, hormones regulate functioning of different organs and tissues. Each hormone is under regulation of feedback mechanism which in turn ensures reliability of the system.