EXPLANATION TEXT

DNA - RNA

In recent years, scientific and technological developments have drastically changed human life on our planet, as well as our view both of our selves as individuals in society and of the universe as a whole. Perhaps one of the most profound developments of the 1970s was the discovery of recombinant DNA technology, which allows scientists to introduce genetic materials (or genes) from one organism into another.

In its simplest form, the technology requires the isolation of the piece of DNA, either directly from the DNA if the organism under study or artificially synthesized from an RNA template by using a viral enzyme called reverse transcriptase.

This piece of DNA is then legated to a fragment of bacterial DNA which has the capacity to replicate itself independently. Then recombinant molecule thus produced can be introduced into the common intestinal bacterium Escherichia coli, which can be grown in very large amounts in synthetic media. Under proper conditions, the foreign gene will not only replicate in the bacteria, but also express itself, through the process of transcription and translation, to give rise to large amounts of the specific protein coded by the foreign gene.

The technology has already been successfully applied to the production of several therapeutically important biomolecules, such as insulin, interferon, and growth hormones. Many other important applications are under detailed investigation in laboratories throughout the world.

Taken from TOEFL Cliffs.

How the spider make web

General Statement : A Spider web looks delicate but it is very strong. It can hold 4000 times a spider’s weight. But how does it form.Explanation : First the spider spins a thread of silk. The thread gets blown over to a branch by teh wind. Then she makes another two threads and makes a Y shape. Next she makes more threads and they look like spokes off a wheel. Then the spider goes in a spiral, out and back in, sits in the middle and waits for food.Closing : This is how a web is formed.

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How Day and Night Happen

The sun seems to rise in the morning, crosses the sky during the day and sets at night. However the sun does not actually move around the earth. Earth’s turning on its axis makes it look as if the sun is moves.

The earth makes a complete turn on its axis for 24 hours. It is called as rotation. It causes day and night. The earth also moves around the sun. It takes 365 days or a year. This process is called revolution. The revolution process causes the changes of the season

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How to Fly a Hot Air Balloon

A hot air balloon consists of a basket, four big gas tanks, a burner and the balloon or ‘envelope’.

First, the pilot puts four nylon poles into sockets on top of the basket. Then she puts the burner on top of the poles. Next, she connects the cables to the burner frame. The cables also go under the basket in order to hold everything together.

After this, she connects the hoses from the full gas tanks to the burner so that she can test it.

Next, two people hold the mouth of the balloon open while it is filled with cold air from the fan until it is quite fat and tight.

Now for the difficult bit. The pilot lies on the ground, half in the basket. She turns on the gas burner and points the flame into the ‘mouth’ of the balloon. This is so that the balloon slowly stands up.

When the pilot is ready to go, she heats up the air in the balloon a bit more. This results in the air in the balloon to be hot enough to get the balloon to rise off the ground

Recycling Glass Bottles

New glass bottles are made mainly of silica sand. The sand is melted in a furnace, at a very high temperature. Recycled glass bottles are made in a very similar way, but cost less and use up fewer natural resources.

What happens to the old glass bottles?

The process begins when people take their used bottles and jars to a bottle bank. Next, the bottles and jars are taken by lorry to the recycling plant. At the plant, bottle tops and lids are removed. After that, the glass is crushed into small pieces.

Where does the crushed glass go?

The crushed glass is then sent by lorry to a bottle factory. Here, it is mixed with a small amount of silica sand. It is then melted in a furnace, at a lower temperature than new glass.

How are the new recycled bottles made?

Finally, the hot liquid glass is drawn out of the furnace and fed into machinery that makes it into bottles.

Recycled glass is as pure and as strong as new glass. Glass can be recycled many times without losing its quality.

Making Organic Compost.

To grow beautiful flower or tasty vegetables, gardeners often put compost in their soil. Compost is produced by allowing vegetable matter to decompose naturally.

How do you start?

First, the compost’s ingredients have to be collected. Any raw vegetable or plant material is suitable, including leaves grass, vegetable peelings and fruit cores. To introduce helpful bacteria into the compost, some garden soil is also mixed in.

Where do you put it?

Next, the compost mixture is put into a special composting bin, or piled up in the corner of the garden. The compost is left alone for many months while nature does its work.

What turns it into compost?

Microbes, such as bacteria and fungi, soon begin to rot the vegetable material. As a side-effect, natural warmth is produced in the compost. This, in turn, helps to speed up the process. Eventually, natural decomposition transforms the waste vegetable material into soft brown compost.

What is the compost used for?

Finally, gardeners either dig the compost into the soil or spread it on the surface. Compost replaces nutrients in the soil, because it contains nitrogen and other important elements.

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