Explain : Photoperiodism.

ANS:



Photoperiodism is the phenomenon in which the duration of light decides the flowering and germination in plants.

Plants are (i) Long-day plant and (ii) Short-day plant on the basis of the duration of light received by them.

Day neutral plants do not respond to photoperiodism.

Plants respond to photoperiodic stimulus by a specialised pigment present in them called phytochrome.

Write an explanatory note on HUMAN BRAIN.

ANS:


Human brain is the main coordinating center for all the activities of the human body.

It is protected by a bony box in the skull called cranium and three membranes called meninges.

There is a fluid called cerebrospinal fluid in the space between these membranes.

Cerebrospinal fluid acts as a cushion and protects the brain from mechanical shocks.

The brain is divided into three regions : (i) fore-brain (ii) mid-brain and (iii) hind-brain.

FORE-BRAIN consists of cerebrum and olfactory lobes.



Cerebrum is the most complex and specialised part of the brain.

It consists of two cerebral hemispheres.

It has sensory area to receive impulse from the sense organs and motor area to send impulse to muscles and effector organs.

Cerebrum has four regions having different centers of activity : (i) frontal lobe (ii) parietal lobe (iii) temporal lobe (iv) occipital lobe.



The frontal lobe possesses centres for voluntary muscular activities.

Parietal lobe possesses the centres for temperature control, smell and touch.

Temporal lobe possesses the centres for auditory and olfactory reception.

Occipital lobe possesses the centres for visual reception.



MID-BRAIN is a part of the brain stem and possesses the regions for visual reception, auditory reception and touch.

HIND-BRAIN consists of cerebellum, pons and medulla oblongata.



Cerebellum is situated on the posterior side of the fore-brain and it controls the rhythmic movement of muscles, body balance and posture.

Pons connects various parts of the central nervous system and cerebellum by the transverse bands of nerves.

Pons takes part in the regulation of respiration and helps in the movement of head as per audio-visual perception in coordination with medulla oblongata and spinal cord.

Medulla oblongata possesses the centres to regulate heartbeats, breathing, blood-pressure, sneezing, coughing, vomiting, swallowing, hiccups, etc.

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Write in brief about Spinal cord.

ANS:



Spinal cord is a cylindrical structure.

It is the posterior extension of of medulla oblongata.

The vertebral column and meninges protect the spinal cord.

There are 31 pairs of spinal nerves arising from the spinal cord.

These nerves connect various organs of the body to the brain.

They help in the conduction of impulses from brain to organs and from organs to brain.

They also perform reflex action.

Explain : Reflex action

ANS:





An unconscious and involuntary response of effectors to the stimulus is called reflex action.

Due to reflex action we suddenly withdraw our leg when we step on a very hot or pricking object.

Similarly, our response towards very hot or very cold water is sudden and involuntary.

The reflex action is performed by the spinal cord when the brain is busy or at rest.

In reflex action, a message from the receptors is relayed by sensory nerves to the spinal cord and the spinal cord sends response via motor nerve to the effector organ.

This entire pathway is called 'REFLEX ARC'.

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Write a note on Autonomous nervous system.
ANS:



The system which is responsible for the intervention in the activities of the organs located in the body cavity without the awareness of brain is called autonomous nervous system.

This system controls heart, blood vessels, glands, uterus and coelomic organs.

Autonomous nervous system is of two types : (i) sympathetic (ii) parasympathetic.

The involuntary actions of the body are controlled and regulated by the coordination of these two systems.

The effects of sympathetic and parasympathetic nervous systems are complimentory and contradictory.

For example : If the sympathetic system increases the heartbeats abnormally, the parasympathetic system decreases it and brings it back to normal.

Mention characteristics of hormones.

ANS:



They are specific chemical messengers.

Generally the origin and the target area of hormones are different.

They are directly poured into the blood (from the gland) and carried by blood circulation.

The effect of a hormone is either rapid or slow (i.e. it may increase or decrease the speed of some process). For example, acetylcholine increases the speed of the conduction of impulses whereas decreases (slows down) the effect of sex hormones.

Write a note on endocrine glands.

ANS:



Endocrine glands play an important role in coordination (in animals).

These are ductless glands and secrete hormones which are specific chemical messengers.

The main endocrine glands are hypothalamus, pituitary,, pineal, thyroid, parathyroid, pancreas, adrenal, testis and ovary.

Pituitary gland is called the master gland as it regulates the secretion of hormones by other endocrine glands.

The function of the pituitary gland is controlled by the secretion of hypothalamus.


Mention different endocrine glands, hormones secreted by them and the functions of these hormones

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Explain : Acid rain.

ANS:


Combustion of fuels and industrial smoke add pollutant gases like NO2, SO2, etc. in the atmosphere.
These gases dissolve in moisture present in air and form acids like nitric acid and sulphuric acid.
When these acids come back to earth through rain, it is called Acid Rain.
Acid rain harms various organisms, monuments and buildings.

Explain : Greenhouse effect.
ANS:


Gases like CO2 and methane have the property of absorbing heat.
These gases, when present in atmosphere, absorb the heat of the sun rays reflected by the earth.
This results in the warming of earth's atmosphere.
This is called Green-House Effect.
Due to Greenhouse effect, the ice on polar regions may melt increasing the sea level.

marvelous work . truly amazing.

can u pl post more diagrams ??

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