Why do birds migrate?


       In many parts of the world which experience extreme winter, food and water become scarce during winter. Besides the days also become very short. Most birds would starve if they remained in such places during winter. So they migrate to warmer and moister parts of the globe. Most of them breed during the period as they plenty of food around. With the onset of warmer weather in their original habitat, they return with their offspring.


MEANING OF HEAD SHAKE



When someone asks you if you want something, you will usually shake your head up and down if you mean ‘yes’  or from side to side if you mean 'no'. In most places, an up and down movement of the head signifies agreement, and side to side movement means disagreement. But did you know that in some places like Bulgaria, parts of Greece, Yugoslavia, Turkey, Iran, and Bengal, people shake their head from side to side to say ‘yes’ or to show agreement



 


Why does a lizard break its tail?

The breaking-off of the lizard’s tail is a defense mechanism which helps the lizard to run away unharmed from the attacker. There is a pre-set crack in the lizard’s backbone, from where the tail comes off. The broken part continues to turn and twist for a while thus detracting the attacker’s attention. The movement lasts till the energy stored in the tail muscles gets exhausted.

Why do we need to sleep?

Sleep is a normal activity of higher organisms. Every human being, on average, spends a third of his or her life sleeping. Babies and children spend more time sleeping than adults while old people sleep less. The sleep-wake cycle is controlled by an internal biological clock which usually coincides with the day-night cycle. We do not know yet what sleep does to our body except that we feel refreshed after a good night’s sleep. But what lack of sleep does to an individual is quite well known. Prolonged lack of sleep leads to irritability, lack of concentration and even hallucinations. Thus sleep certainly has a restorative                                                                     function which helps the body to face another active day.

Why do we feel breathless on high mountains?

  At high altitudes, the atmospheric pressure is much less than in the plains. As a result, the amount of oxygen per unit volume of air is lower and less oxygen reaches the lung per breath which is not sufficient to fulfill the body requirements. Thus, to get in more oxygen, our lungs have to make extra effort which causes breathlessness. Those who habitually live on the mountains, however, do not feel breathlessness because they have more hemoglobin in the blood to carry more oxygen.

Why do we yawn?


            Yawning occurs without any effort. It is a reflex action that forces oxygen into our lungs. The body’s oxygen supply is depleted after a long period of shallow breathing, which commonly occurs when we are tired, under stress, or have been sitting still for a long time. Yawning is believed to be induced by a high level of carbon dioxide in the blood. The wide opening of the mouth followed by a slow deep breath increases the oxygen level in the blood which helps relieve the tiredness.


Why do we perspire?



      Perspiration is a mechanism for keeping the body cool in a hot environment. This is important, because if body temperature rises above the average temperature of  by more than a few degrees, it could be life threatening. When the body temperature rises above the normal in hot surroundings, the sweat glands produce sweat which evaporates on the skin. This transfers the heat from blood vessels in the skin to the surrounding air. Sweating may also be triggered by pain, by intense emotions, fear or after eating very spicy food.                                    


Why does water cause our skin to wrinkle?

    The skin forms an elastic protective cover on our body. It consists of three layers; the upper layer of dead cells, the middle one of living cells and the lower most layers connected to muscles and fat. Normally the upper layer of dead cells acts as an effective water-proof barrier. But on prolonged immersion in water, the dry cells in the layer absorb water and swell. This causes the skin to form wrinkles which disappear when the skin dries out again.



                                    


Why does skin come in different colours?


 Skin colour is due to the dark pigment melanin which is produced by pigment cells in the lowest layer of the skin. There is the same number of pigment producing cells in the skin of all races but the amount of melanin produced varies. In dark-skinned people of tropical regions, there is more melanin because intensity of the ultraviolet radiation from the sun is stronger in the tropics. The extra melanin protects the skin from the harmful effects of ultraviolet radiation. In people living in the higher latitudes, the skin colour is lighter as they have less pigment. The lighter skin also helps in the production of vitamin D in the body under the low intensity of sunlight available. Other factors contributing to skin colour are the blood  in the blood vessels of the skin and the natural yellowish tinge of the skin tissue.


Why does sun bathing tan?

Tanning is a sort of natural protection mechanism provided by nature to the human skin. It involves an increase in the production of the pigment melanin which helps protect the skin against the dangerous effects of too much ultraviolet radiation from the sun.

The outermost layer of the skin contains cells called melanocytes that produce the pigment melanin. When the skin is exposed to the sun, the melanocytes get stimulated by the ultraviolet rays and produce more of melanin. This acts as a filter to block ultraviolet rays from penetrating the skin. The increased production of the brown-coloured melanin gives a darker colour to the skin, which appears as suntan.



 


Why do we have two eyes?


The two eyes working together enable us to perceive depth which is not possible to do with only one eye. Our two eyes view an object from approximately the same height but they see the object from slightly different horizontal angles. When processed by the brain these two slightly different images gives rise to perception of depth and make the object appear in three dimensions. This ability, called stereoscopic vision, also allows us to judge distances, to estimate how far an object is, which is essential to enable us to go about in our daily chores.




EYE CONTACT

Of all the ways we communicate with people, eye contact is the most powerful. Eye contact can be a loving gaze, a hostile stare, a nervous glance, or a refusal to look at a person Looking at a people and meeting their eyes are the first steps toward striking up friendships and making a good impression. But if you look at a person for too long, he or she may feel threatened.





            Failing to look at others causes suspicion as they wonder whether you are hiding something. Refusing to make eye contact also sends messages of arrogance, for it may convey that you do not consider the other person important.



            There are subtle, silent rules to eye contact and they vary from culture to culture. Most Asians prefer minimal eye contact whereas in America, the UK and most of Northern Europe moderate eye contact is preferred. The Hispanic cultures, along with cultures in the Middle East prefer very direct eye. So if you travel to another country, be sure to know what form of eye contact they are comfortable with, so that you don’t offend anyone!


Why do we get headache?

There are many reasons for headaches. It is, however, believed that we feel the ache when pain signals are sent to the brain by nerves in the face, neck and the back. They arise out of a common root called the cranial nerve. That is why any factor which causes stimulation of pain nerves in and around the face is felt as a headache. We get headaches when the muscles in our eyes get strained, like when we read very small print or read for very long hours, or if our eyes have some defect such as a squint. Headaches can also occur when the tiny bones in the inner ear which pick out the sound for us to hear get tired or if our neck muscles get strained. There is one form of headache called migraine which periodically occurs in some persons for no apparent reason. Migraine can be triggered by many factors such as eating ice creams or fatty foods, cold, dehydration or allergies to certain food items. Aching teeth and sores in the mouth can also induce a headache.

Why do we blink?


            Blinking helps to keep the eye lubricated and also to sweep away foreign particles. Lubrication helps maintain the transparency of the cornea – the transparent outer layer in front of the eyeball. Along the edge of each eyelid are tiny glands that release a watery fluid each time the eyelid closes. Each time one blinks, the tear glands also release some fluids. The fluids flush out the eye and also keep it moist. A sudden movement in front of the eye also makes one blink. This has protective value. It has been estimated that an average person blinks about 250 million times in a lifetime.


Why do men become bald?

Both, men and women may be affected equally by temporary hair loss due to stress, skin infection, disease, drug or radiation-induced side effects. Permanent baldness, seen mostly in men, is genetically governed. The gene for baldness is present on the X-chromosome. However, it does not express itself if a normal version is present on the partner chromosome. Since women have two X-chromosomes and men only one, a woman may carry a copy of the baldness gene on one X-chromosome with the other X-chromosome being normal. In such a case, the woman will not go bald. However, a copy of the baldness gene on the single X-chromosome of men predisposes them to the trait. It is unlikely (though not impossible) for a woman to carry copies of the baldness gene on both X-chromosomes. The tradition of keeping long hair allows women to cover patches of baldness better than men in whom the baldness shows.