Science [2 Mark Questions]

In multicellular organisms, body organisation is complex. Different organs and tissues perform different specialised functions. Therefore, it is necessary that all the organs work together in a proper coordinating way, it needs a system of control and coordination.
In human beings, well-developed nervous and endocrine system were evolved for control and coordination.

The chemical coordination occurs in plants by means of plant hormones. They help to coordinate growth, development and responses to the environment. They are synthesised at places away from where they act and reach to the areas of action by simple diffusion.

In case of a spinal cord injury following signals will get disrupted :
(1) Reflex action, (2) Sensory impulses from different organs of body to brain through spinal cord will not be conducted and (3) Motor impulses from brain to different organs of body through spinal cord will not be transmitted.

The function of receptors: To receive / collect information about changes in the environment around us in form of stimuli. This information pass to central nervous system through sensory nerves in form of impulse.
If receptors do not work properly, external stimuli cannot be received and body will not respond towards it.

Insulin is a pancreatic hormone which helps in regulating blood sugar level. In the patients of diabetes, the blood sugar level rises due to deficiency of insulin. So, some patients of diabetes are treated by giving injections of insulin to maintain blood sugar level.

Adrenaline prepares our body in an emergency situation. When adrenaline is secreted into the blood body shows following responses :
The heart beats faster, breathing rate increases, blood pressure increases, skeletal muscles become more active, etc.
This is known as fight or flight response.

The use of lodised salt is advisable because iodine is essential for the synthesis of thyroxin hormone in thyroid gland. Deficiency of iodine causes goitre. Iodised salt fulfills the requirement of iodine of body and protects against goitre disease.

In animals, endocrine glands secretes chemical substances (Hormones) in precise quantities. They are directly released in blood and through blood circulation they reach to their target (Functional) site. Specific cells of body have specific molecules with which hormone molecules bind and transmit information.
Thus, chemical coordination take place in animals.

Growth hormone and thyroxin are related with growth in human.
(1) Growth hormone: It is secreted by the pituitary gland. Growth hormone regulates growth and development of the body.
(2) Thyroxin: It is secreted by thyroid gland. lodine is essential for the synthesis of thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body. This is necessary for balanced growth of body.

Properties of animal hormones are as follows:
(1) They are specific chemical compounds secreted from specific endocrine glands. (2) Hormones are chemical coordinators. (3) They show their action on specific target cells, tissues or organs. (4) They are transported through blood. (5) Their secretion is in extremely small quantities.
Hyper secretion or deficiency of hormone can lead to disorders.

Auxins are growth promoting plant hormones that induce cell elongation. When tendril comes in contact with a support, auxin stimulates faster growth on to a part of tendril away from the support. This causes the tendril to coil around the support.

The pea plant climb up other plants or fences with the help of tendrils. These tendrils are sensitive to touch.
When tendrils come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.
Growth of pea plant is directional and it respond slowly to stimuli.

Generally reflex action is shown by spinal cord and there is no active role of brain in it. However the information input also goes to the brain.
In some reflex actions such as mouth watering on seeing delicious food, heartbeats, breathing, movement of diaphragm, yawning, blinking of eyes, sneezing, etc. brain is involved.

Olfactory receptors in our nose are stimulated by the smell of agarbatti. This causes generation of impulse which is received at dendrite of sensory neuron. Such impulse is transmited to brain. In cerebrum message is interpreted and we detect the smell.

Synapse is the gap between nerve endings of axon of one neuron and dendrites of another neuron.
At the end of axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the synapse and start a similar electrical impulse in a dendrite of the next neuron.

Reflex action is an involuntary action controlled by spinal cord. Thinking is not involved in such action.
Walking is a voluntary action and is controlled by a cerebellum, a part of hind-brain. This action is shown as per wish of an individual.

A central nervous system is made-up of brain and spinal cord.
Brain is a delicate organ and it is an important organ for a variety of activity, therefore, it needs to be carefully protected. Brain is protected in a bony box called cranium. Inside the bony box, the brain is covered by meninges. Fluid between the meninges protects brain by shock absorption.
Spinal cord is protected in a hard skeletal structure called vertebral column or backbone.

In the arrangement of two consecutive neurons the axon fibre endings of one neuron and the dendrite endings of the next neuron having a microscopic gap is called synapse.

A chemical messenger, synthesised or secreted in extremely small quantities by endocrine glands and poured directly in blood is called hormone.

Different organs of the body jointly function systematically against the stimuli and react to express proper response against the stimuli is called coordination.

The changes, that take place in the external environment of living organisms (plants, animals, microorganisms, etc.) and induce definite types of reactions or responses, are called stimuli (singular - stimulus).

When the sugar level rises in blood, pancreas releases more insulin to regulate blood sugar level. As blood sugar level falls, insulin secretion is reduced by feedback mechanism.

(a) Pineal gland - Melatonin hormone
(b) Pituitary gland-Growth hormone
(c) Thyroid gland - Thyroxine
(d) Thymus gland - Thymocine

(a) Sensory neuron
(b) Relay neuron
(c) Motor neuron
(d) Effector = muscle in skin

Diagram (a) is correct, because roots show positive geotropism and stem shows negative geotropism.