XII. Read the following passages and present their summary in Russian to your class-mates. Work in pairs.

Vitamin С Requirements in Man. Accumulated ex­perience and the experiments recorded show that, in adult humans, 10 mg. of dietary ascorbic acid is completely protective and curative over long periods. To allow a margin of safety a daily intake of 30 mg. is recommended. This is readily achieved by a normal Western diet — one orange, or half a grapefruit, or a generous helping of lightly-cooked cabbage. The recommended 30 mg. is of ingested vitamin, so that the aim of 70 mg. makes liberal allowance for maltreatment by the cook.

Vitamin В group. This group consists of series of water-soluble organic substances, which are found in all cells of all species, from the bacteria, protozoa, and yeasts up to the highest mammalian forms. Most of the members of the group are constituents of fundamental tissue enzy­me systems, involved in the oxidation of the foodstuffs, and are therefore indispensable for the normal functioning of all tissues. The best studied members of the group are thiamine, riboflavin, and nicotinic acid, generally found together in foodstuffs but not necessarily in the same pro­portions. Most of the vitamin В group can be synthesized by the intestinal bacteria.

Vitamin K. Vitamin K, one of the "youngest" vita­mins, discovered only some 30 years ago, is of great importance for the proper coagulation of blood. It is essen­tial for the formation of prothrombin, a protein substance necessary for clotting a blood vessel to stop a haemorrage.

In 1942, Academician Alexander Palladin, a prominent Russian biochemist, and his staff synthesized vikasol, a new preparation, which contains an analogue of vitamin K- During World War II, vikasol won a good repute for itself among army doctors. Injected intramuscularly or intravenously, it quickly stops various haemorrhages.

Now it is used as a preparation against inflamma­tions and as a means for increasing the resistance of organism to radioactive irradiation.

But vitamin K, as the scientists learned, is essential not only for blood clotting. It plays an active role in the so-called tissue breathing of the organism's cells, in the metabolism. It is as necessary for each living cell as air is vital for man.

TEXT 15.

Read and translate the following words:

to scatter, to evolve, to explode, to exist, diversity, tumultuous, nurturing, fossil record, to stabilize, to take shape, volume, to coalesce, to absorb, to photosynthesize, inhospitable, barren, diversification, iron-clad.

Way before trees appeared on Earth, animals and other land plants were scattered among the land mass. And way before land plants came the land animal. How did it happen, and where did they all come from?

They came from the oceans, where just a few billion earlier the first animal life evolved followed by plants. There was a time about 550 million years ago when life «exploded» on the planet. Animal life. Nearly all of the animal groups in existence to­day – as well as many that no longer exist – first appeared on Earth during this time. It was the Cambrian Period, and this time of tumultuous and co­lossal animal diversity is called the Cambrian Explosion.

Land plants evolved a little more quietly about 90 million years later, with trees evolving some 100 million years after the first land plants began to emerge from their oceanic origins. But neither animals nor plants could have evolved were it not for the protection and nurturing of the ocean.

According to the fossil record – about 3.5 billion years ago the first preserved life is found in the form of bacteria. They appeared in the oceans after the surface (crust) began to cool and stabilize, the land masses began to take shape, and clouds formed to produce massive volumes of rainwater that created the seas. The atmosphere was much different than today and surface was unprotected from the sun. This period is known as the Pre-Cambrian, the time that immediately followed the formative, molten and gaseous stage of Earth as it and the rest of the Solar system started to come together – or coalesce.

The first plants on the Earth were a form of blue-green algae which appeared and lived in the oceans about 3.4 billion years ago according to the fossil record, protected from the harmful high energy radiation of the sun. In the oceans, these plants were able to grow and photosynthesize as this high energy radiation was absorbed by water. Now to be perfectly clear about it, the first true algae (the kingdom protoctista) most likely made their first appearance about 2.4 billion years ago, but for sure by 1.8 billion years ago as the first acritarchs.

Although animals were the first life form on Earth, it was plants that paved the way for land animals to evolve. Plants did this by simultane­ously increasing the percentage of oxygen in the Earth’s atmosphere and decreasing the percentage of carbon dioxide, a powerful green house gas.

If you were to travel back about some 470 million years ago, Earth would seem lifeless, inhospitable and very barren. The first land plants made their appearance way before trees started driving their roots into the hard crust of the Earth’s surface, about 460 million years ago in the Ordovician period. Algae were the first land plants, moving from their aquatic origins to marshy and wet environments on land. It took consistent growth and diversification of land plants – including the eventual evolution of trees – to help break up the mostly iron-clad surface of the Earth.

Wordlist:

acritarch - акритарх; морской одноклеточный ископаемый организм ( неустановленной видовой принадлежности ) ;

Ordovician - ордовикский;

Cambrian - кембрийский.