Revision and development units 6 and 7

1. Look through the following text and find the answers to the given questions:

1. Who eats plants?

2. What is the form of carbon in the Earth's crust?

3. What energy is used by green plants and algae and what do they do with it?

4. What are the ways of forming carbon dioxide?

5. How are human activities now estimated?

6. Why is it hard now to estimate them?

It is known, that carbon, like water, cycles from the Earth into the atmosphere and back again. Green plants and algae use the sun's energy to convert carbon dioxide (and water) into carbohydrates. The plants are eaten by animals, including people and fish, who exhale carbon dioxide. It was discovered that carbon dioxide is also formed by decomposition of dead animals and animal wastes by microorganisms. The carbon dioxide passes into the atmosphere and is again used for photosynthesis. An equilibrium also exists between carbon dioxide in the atmosphere and dissolved carbon dioxide and H₂CO₃ in oceans and lakes. In addition it was estimated that much carbon is stored in the Earth's crust in the form of fossil fuels — coal, petroleum, and natural gas — and in the form of limestone and coral. Since the middle of the nineteenth century, it has been observed that the production of carbon dioxide by the combustion and the decomposition of limestones is increasing rapidly. In addition, it has been proved that destruction of tropical forests is reducing the quantity of carbon dioxide used up by photosynthesis. Human activities have now reached a scale where interference with the natural carbon cycle may well be significant. The longest continuous records of the concentration of CO₂ in the atmosphere unfortunately were made only in 1958, and therefore it's hard to be sure how harmful human activities have been since that time.

2. Read the text again and entitle it. Then divide the text into logical parts, give titles to all of them thus making a plan.

3. Write out all the sentences, expressing the main idea(s) of each logical part and translate them into Ukraininan.

4. Condense the sentences of the text where possible.

5. Write an abstract to the text in your own words using the plan and the sentences you've written out and condensed.

Remember: 1. An abstract is an introduction of a reader into the matter.

2. An abstract is much shorter than a summary.

3. Points in an abstract are more generalized than in a summary.

6. Revise the grammar and lexical material to Units 6 and 7 and translate the following text into Ukrainian without a dictionary:

THE ORIGIN OF COAL

Carbon compounds are very abundant in nature. All organic substances are carbon compounds, and dead animals or plant matter, once exposed to the air, decay very rapidly owing to the oxidation brought about by the agency of bacteria. The gaseous products of this process of decay escape in bacterial decomposition, and become trapped or fixed in rock. Coal and petroleum are supposed to be the result of this failure of nature's cleaning system.

When plant matter from the great prehistoric forests came submerged in swamps and bogs, the supply of air was limited, and complete oxidation was, therefore, impossible.

These beds of dead plant matter gradually became covered with deposits of sand and mud, so that the pressure above them became very great, the beds of plant tissue being pushed deeper into the hotter zones of the Earth's crust. As a result of this terrific compression, water is believed to have been pressed out of the plant remains and the chemical changes taking place resulted in the loss of hydrogen and hydrogen compounds such as methane (marsh gas).

The final result, after thousands of years, was coal: a material containing a high percentage of carbon. Different varieties of coal, dependent on the pressure involved, may be formed. The process of coal formation is generally believed as follows:

plant matter —> peat (29%C) —>lignite (43%C) ->bituminous coal (64%C) -> anthracite (87%C).

The percentages of carbon given above are average values from the analysis of a large number of coals, but the gradual increase in carbon content is clearly shown. If the pressure of the rock has been so great that all the hydrogen has been expelled, graphite is formed. Coal is not found, therefore, in the oldest rocks since the pressures involved would have expelled (видалили б) all hydrogen from the original plant tissue. The theory of the biological origin of coal may be represented by the following diagram:

atmospheric carbon dioxide —> photosynthesis —> sugar —> starch —> cellulose —>(plant tissue) —> wood —> coal.

Thus, the solar energy stored by plants during the process of photosynthesis millions of years ago is liberated as heat energy in the combustion of coal today.