Cell

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Cell The basic unit of plant and animal bodies; it comprises, at least, a nucleus or nuclear material and cytoplasm enclosed within a cell membrane. Many cells contain other specialized structures (organelles), such as mitochondria, chloroplasts, Golgi bodies, and flagella. Many simple organisms comprise a single cell, and may lack a membrane separating nuclear material from cytoplasm. Advanced organisms consist of a variety of co-operating cells, often specialized to perform particular functions and organized into tissues and organs. Plant cells are typically surrounded by an outer cell wall containing cellulose. Cell division may occur by splitting into two parts (fission), by mitosis, and (in the case of reproductive cells) by meiosis. All nucleated cells contain within their nuclei the entire inherited genetic information of that individual, but in specialized cells, such as a liver or brain cell, only a minute fraction of their genetic database is operational. >>

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When were the First Mechanical Clocks Made?

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The first mechanical clocks are believed to have been made in China in 1088 AD. Later in 1200s, they were first made in Europe. Such clocks made in Europe were driven by a weight on the end of a cord wound round a drum. As the drum rotated, it turned the hands of the clock. The earliest known clock was made in Spain in 1276 AD and the oldest mechanical clock that still works is in Salisbury cathedral in Britain. It was made in 1368. These clocks had devices called escapements to keep the hands turning at the correct rate, so that the clocks depicted the correct time.
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Why does Mistletoe Grow on Trees?

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M istletoe is a plant which grows on branches of higher trees. It is a partial parasite since it has green leaves containing chlorophyll and can make its own food by photosynthesis. It takes the water and minerals it needs from the sapwood of the host tree. It is found growing on trees like apple, hawthorn, willow, poplar and lime . The seeds of mistletoe are spread by birds and once the seed germinates on the host tree, it develops haustorium . The haustorium is a tough structure and ensures of a regular supply of water and nutrients from the sapwood of the host to the mistletoe. The plant then develops a clamp like structure on the tree to be placed firmly.
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Comet

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C omet A small Solar System body made of ice and dust. Comets are asteroidal in appearance at distances of many astronomical units from the Sun (when they consist of a bare , inactive nucleus), and are often spectacularly active when nearer to the Sun. The characteristic bright head (coma ) and streaming tails (both dust and ions) are created by solar heating, with emission of light from gas molecules and scattered light from the dust. The comet nucleus is a few km in size, irregularly shaped and very dark ; dust in the coma contains carbon and silica; there is evidence of polymerized organic molecules; the gases of the coma include water, carbon monoxide, carbon dioxide, ammonia, methane, and hydrocarbons. The source of comets is believed to be a spherical halo cloud about the Sun called the Oort Cloud. Observable comets are occasionally scattered into the inner Solar System by the gravitational fields of nearby stars and giant molecular clouds. Some ( eg Halley's comet) are...
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When was Radar Invented?

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Radar was invented during 1930s. Many countries worked on radar at this time, but the first successful radar was built by Britain in 1935. Radar works by sending out radio signals that bounce off distant objects. The radar set detects the signals that return and produces a picture indicating the position of the objects . British and American scientists worked together to invent methods of using short waves called microwaves.
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Who Made the First Telescope?

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Galileo Galilei (1564-1642) lived in Italy and is remembered as the first person to turn a telescope to the sky and make important astronomical observations. He built the first telescope in 1609 and then went on to make many. He observed that Moon was not smooth and perfect as it looks, but it was covered with mountains and craters. He also discovered that a pendulum could be used to measure time. He found this by watching a hanging lamp swinging in Pisa Cathedral. He realized that it took exactly the same time for each swing , whether the swings were large or small . He also observed bright satellites of Jupiter , sunspots and other things. The four largest moons of Jupiter are now known as the Galilean satellites. He made himself unpopular because he lived in a time when people believed that the Earth did not move and the Sun and Moon revolved around it. People believed what was written in the Bible. He was imprisoned and ended his life in a house arrest.
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