Why do Bananas, unlike other fruits, grow upward?

The banana is actually a giant herb in the same biological family as lilies, orchids and palms. It is the largest plant on earth without a woody stem- a banana stalk is 93 percent water-and is consequently extremely fragile. Although it can reach a full height of fifteen to thirty feet in one year, even moderate winds can blow down a plant.

        The fruit stem or bunch originates at ground level. At this stage, the bunch consists of all the fruit enclose in leaf bracts. The individual fruit "fingers" (the technical name for a single banana) are pointed upwards. As the bunch or bud is pushing its way through the mass of tightly packed leaf sheaths known as the pseudo-stem, the fruit fingers remain pointed upward until they emerge at the top of the plant.

           The bananas exert tremendous pressure on the pseudo-stem. Before the fruits expand, the leaves enclosing them roll around themselves inside the trunk. After the fruit emerges from the leaves, the fingers point downward, but only because the bud surrounding them has changed direction.
            Once the entire bunch of bananas is mature, fully emerged from its sheath, and pointing downward, the individual leaf bracts enclosing the hands fall away, exposing the fruit. At this point, the individual flowers grow rapidly, filling out. Their increased weight bends the main bends the main stalk so that the individual fruits on the hand start to turn upward in about seven to ten days. This phenomenon is known as "negative geotropism".

What are those twitches and jerks that occasionally wake us just as we are falling asleep? 

It has probably happened to you. You are nestled snugly under the covers. You aren't quite asleep but you're not quite awake. Just as your brain waves start to slow, and as you fantasize about something, you are jolted awake by an unaccountable spasm, usually in a leg. This is called "hypnic jerk". It occurs when nerve fibres leading to the leg, in a bundle nearly as thick as a pencil, suddenly fire in a unison. Each tiny nerve in the bundle produces a harsh tightening of a tiny portion of muscle fibre that is linked to it down in the leg, and when they all fire together the leg twitches as a whole. 

        Sleep specialists haven't exactly pinned down what causes hypnic jerks or why they occur only at the onset of sleep. Although some theories exist, like the one which says that they are a natural part of body's transition from alertness to sleep.Another interesting hypothesis links hypnic jerks to evolution-that it evolved when humans used to slept in trees. That is why brain essentially misinterprets relaxation as a sign that a individual is falling from a tree and this cause muscles to react quickly.

What purpose Do Wisdom Teeth Serve?

Wisdom teeth are commonly regarded as being useless to modern man. But because nature rarely provides us with useless body parts, a little investigation yields a more satisfying answer. Primitive man ate meats so tough that they make beef jerky feel like mashed potatoes in comparison. The extra molars in the back of the mouth, now are known as wisdom teeth, undoubtedly aided in our ancestors mastication.

       As humans have evolved, their brains have gotten progressive larger and the face position has moved farther downward and inward. About the time that primitive man started walking in an upright position, other changes in the facial structure occurred. The protruding jawbones of early man gradually moved backward, making the jaw itself shorter and leaving no room for the wisdom teeth. Most people's jaws no longer have the capacity to accommodate these four, now superfluous teeth.

Why do horses sleep standing and How?

Horses have a unique system of interlocking ligaments and bones in their legs, which serves as a sling to suspend their body weight without strain while their muscles are completely relaxed. Thus, horses don't have to exert any energy consciously to remain standing-their legs are locked in the proper position during sleep.

        Most horses do most of their sleeping while standing, but patterns differ. Veterinary experts say that it is not unusual for horses to stand continuously for as long as a month, or more. Because horses are heavy but have relatively fragile bones, lying in one position for a long time can cause muscle cramps.

        While one can only speculate about why the horse's body evolved in this fashion, most experts believe that wild horses slept while standing for defensive purposes. In wild the horse's chief means of protection and escape from predators was its speed and they were much less vulnerable while standing and much less apt to be caught by surprise when lying down.

Why does present electricity runs on A.C rather than D.C?

Direct current flows only in one direction.Alternating current flows back and forth continuously. Thomas Edison was a proponent of direct current,which worked find in the early days of electric light, because the generators were very close to the lights that used electricity.

     But as demand for electric light increased, D.C. proved inadequate. Electric current loses the least energy when traveling at high voltages. It was then uneconomical to transform D.C in the high voltages necessary for long-distance transmissions. Direct current circuits would have required generating stations every three or four miles, unfeasible in the present scenario of sprawling cities.

http://www.diffen.com/difference/Alternating_Current_vs_Direct_Current

      In 1885, young man named George Westinghouse bought the U.S. patent for alternating current from inventor Nikola Tesla. Not only could A.C. transmit higher voltages more cheaply than D.C., the voltages could be raised or lowered by switching only one transformer. With its relative flexibility and lower cost, A.C quickly became a widely accepted standard.