Science [3 Mark Questions]

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• Functions of nervous tissue:
• It collects information from receptors of sense organs, sends it to brain via spinal cord.
• Brain processes (Analyses) information, makes decisions based on information and conveys decisions to effectors such as muscles or glands.
• Muscle tissue respond to nervous impulse:
• When a nerve impulse reaches the muscle, the muscle fibre moves.
• The movement at the cellular level begins.
• Muscle cells will move by changing their shape so that they shorten.
• Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to
• nervous electrical impulses.
• Thus, muscle tissue brings about movement.

• The hormone thyroxin is secreted from the thyroid gland.
• It is an iodized hormone (rich in iodine).
• Thyroxin is not formed when there is deficiency of iodine in the blood.
• As a result, the condition called hypothyrodism occurs in which the size of the thyroid gland gets gradually enlarged, this disease is called goitre.
• The iodized table salt provides proper amount of iodine for the formation of thyroxin in the thyroid gland.
• Hence, it is advisable to take iodized salt in daily food.

• It is necessary to maintain a definite blood sugar level in the human body.
• In the patients of diabetes the blood sugar level remains high due to the deficiency of insulin hormone from the pancreas.
• This higher blood sugar level causes several harmful effects.
• To prevent the diabetic patient from such harmful effects the blood sugar level is required to be maintained at
• certain definite level.
• Insulin is a hormone that reduces blood sugar level.
• Hence, the diabetic patient is given injections of insulin.

• All organisms show response to stimuli.
• However, the animals possess nervous system and sense organs, which are absent in plants.
• Animals use the nervous system as well as endocrine system for control and coordination of all their activities, while he plants possess only hormones to coordinate their activities.
• The hormones diffuse from cell to cell quite slowly in plants while most animals have blood for rapid transport of hormones.
• Because of all these reasons, the plants do not show immediate response.

• All living organisms experience the effects of changes in the atmosphere that surrounds them and tend to respond differently against them.
• The living organisms show a slow or rapid response to stimuli such as heat, cold, sound, touch, pressure, etc.
• Responses are expressed against these stimuli through hormones in plants and nervous system as well as hormones in animals.
• e.g. The plants bend in the direction of light.
• Man shows shivering effect in severe cold and perspiration in hot season.
• Thus, the response to stimuli is the characteristic of every living organisms.

• Hormones should be secreted in precise quantities as and when required.
• If body is not provided with adequate quantity of hormone then its functions suffer.
• For this, we need a mechanism through which this regulation is achieved.
• The timing and amount of hormone secretion are regulated by feedback mechanisms.
• e.g., if the sugar level in blood rises, it is detected by the cells of pancreas which respond by producing more insulin. Insulin helps in regulating blood sugar level.
• As the blood sugar level falls, insulin secretion is reduced.

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• As nerve impulses does not reach each and every cells of animal body, there is another means of communication between cells.
• Hormonal coordination achieved by special chemical compounds, called hormones.
• Hormones are known as chemical coordinators and diffused by those cells which have specific molecules on their surface.
• Hormonal coordination is slower but it can potentially reach all cells of the body.
• Hormonal coordination is effective in both plants and animals.
• Compared to electrical impulse it is steady and persistent.

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• Movement is a characteristic of living organisms.
• Various movements are connected with each other to perform specific functions.
• Each kind of a change in the environment induce an appropriate movement for the response.
• The movement depends on the event that triggers it.
• To recognise various events in the environment, there are controlled movements.

• 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 respond slowly to stimuli.

⇒ Functions of Neurons
(1) Neurons form an organised reticular structure which forms nervous tissue.
(2) Neurons carry sensations or instructions from receptors.
(3) From their sensations or instructions are carried as electric impulse.
(4) Further this impulse is converted into chemical signal so that it can be spread further.

Reflex action is such a situation in which, we do not think about but express an immediate response to changes in the environment for eg : We move our hands immediately after touching the hot pan.
→ In normal conditions any sensory impulse travel through the spinal cord to the brain which is protected in the skull. The brain thinks about it In response it sends impulse to the muscle. The arm can the be moved as the muscles contract. All these actions take a lot of time. Whereas, reflex action is very fast and it is carried out for protecting our body.
→ In the above example the sensation of heat is received by the nerves. Nerves directly innervate the muscles. So this action is completed very quickly Usually this type of structure is known as Reflex arc. Reflex arc is created in spinal cord, where the motor olfactory nerve and sensory nerve meet.

Animals have very little or none of the complex neuron network needed for thinking. So it is quite likely that reflex arcs have evolved as efficient ways of functioning in the absence of true thought processes. Even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.

Examples of reflex arc are :
(1) Due to sudden light on eyes, pupil contracts.
(2) Sudden reaction to extreme cold or extreme hot water.
(3) Movement of diaphragm
(4) Sudden closing of the eye when something comes near the eye.
(5) Coughing
(6) Moving the hand as soon as nail is hurted etc.

The nervous system present in the mid axis of the body is called CNS (Central Nervous System). The central nervous system consists of the brain and spinal cord.

→ Spinal cord is made up of nerves which supply information to think about. Brain is the main coordinating organ of the body CNS receive information from all parts of the body and integrate it.
→ The spinal cord carries the sensation as impulses to the brain. The brain sends its feedback sensation to the muscles.
→ There are 12 pairs of cranial nervous in the brain connecting head and upper body while 31 pairs of spinal nerves connecting the rest of the body constitutes the Peripheral Nervous System (PNS) which receives and coordinates instructions from all parts of the body.
→ In order to perform some voluntary actions like writing, talking, moving a chair, clapping etc brain has to send messages to the muscles. The PNS helps the brain to send these messages. Thus the brain allows us to think and further act based on our thinking.