Unit 8 Linear relationships (3) Cyclical process

Introduction

In the previous unit you learned how to write up a linear process, i.e. a process that consists of a series of stages and which has a beginning and an end. A natural process is more likely to be cyclical than linear. In a cyclical process there is no clear beginning or end, so that the cycle is continuously repeated. The diagram below should make the difference between the two types of process clear.

1. A linear process

Input		Step1 .--.		Step 2 , , , - > i- - U		etc		Output

2 . A cyclical process

stage

stage

stage

stage

A cyclical process is described in much the same way as a linear process except that it is not always clear where the cycle begins.

Task 1

This flow diagram illustrates the nitrogen cycle. Nitrogen is essential for human, animal and plant life, and over 90% of the Earth's supply exists as a gas in the atmosphere. The diagram shows how nitrogen is provided to living organisms and then returned to the atmosphere. Below the flow diagram is a list of sentences describing the stages in the cycle. The sentences are not in an acceptable sequence. Using the flow diagram as a guide, match the sentences with the stages in the flow diagram to produce a text in acceptable sequence.

Fixation by

lightning

Gaseous

Denitrification

1. Lightning contributes some nitrogen, in the form of nitrates, to the soil.

2. This gaseous nitrogen is returned to the atmosphere.

3. When animals eat the plants, the nitrogen they contain is synthesized into protein. *

4. When plants or animals die, proteins are decomposed by bacteria into amino acids which are in turn broken down into ammonium.

5. But at the source of most nitrogen is bacteria on plants, which 'fix' the nitrogen into ammonia.

6. The nitrates in the soil are absorbed by plant roots.

7. Some of the nitrates are degraded into nitrogen gas in the denitrification process.

8. The ammonium is broken down into nitrites.

9. The ammonium resulting from decomposition returns to the nitrite - nitrate - protein cycle.

10. The nitrites are converted into nitrates by soil bacteria.

About writing

When you write a text, it is usual to make the topic of the text very clear to your reader. This is done by stating the topic in a prominent position in the text, most frequently in the first sentence. A sentence which states the topic of a text, or of a paragraph or group of paragraphs, is called a topic sentence. (Sometimes this is known as the thesis sentence.)

Study the following text and diagram, then:

1. underline the topic sentence of paragraph 1;

2. complete the topic sentence of paragraph 2;

3. write a third paragraph beginning with this topic sentence:

'Bilharzia could be eradicated.'

1. Bilharzia is a disease found all over the world. It is spread by a small fluke, or flatworm (called schistosoma) which lives as a parasite in the water snail during one stage of its life-cycle, and in man during another stage. Three species cause human disease: one is found in parts of Africa, Spain and the Middle East, another in Africa and Central/South America and the last in the Far East. In these areas schistosoma eggs are present in slow-moving water.

W orms leave snail, pass into water.

Worms enter man.

Wo r m s ch a n g e f o r m and increase in number.

Wormschange and increase in number. Man develops

bilharzia.

Worms enter snail.

Worms leave body, pass into water.

The life-cycle of schistosoma, the parasite causing bilharzia

2. The life cycle of schistosoma

The first stage takes place in the water. When the eggs hatch, the embryoes enter the bodies of water snails. They develop into worms inside the snails. Eventually the worms return to the water, and penetrate the skin of any person who happens to be standing in the water. Once inside the human body they move through the blood vessels to the liver. They remain in the liver until they are adult, and then move to the bladder, where they lay their eggs, causing severe inflammation. Finally the eggs are excreted into the water, and the cycle begins all over again.

Two common types of topic sentence are:

1. the generalization: 'Bilharzia is a disease found all over the world.'

2. the preview:

'The life cycle of schistosoma can be divided into two stages.'

Task 3

Study the following sentences and state which of them would make good topic sentences, i.e. which of them could easily be developed to form a paragraph.

1. The planet Venus is 26,000,000 miles away from Earth.

2. Generalizations are very useful in writing.

3. Motor cars are a form of transportation.

4. Recent changes in Egypt have affected women's roles in at least two potentially important ways.

Though it is not always necessary to begin each paragraph with a topic sentence, it is useful to do so when you are not completely certain of your ability as a writer. The advantage of beginning a paragraph with a topic sentence is that it provides both the writer and the reader with a clear aim, i.e. in the case of a generalization, examples will be required, and in the case of a preview, details will be forthcoming. For example, if the writer produces this as a topic sentence:

There are several parasites which are a danger to human beings, then she or he is committed to producing further text about the topic of parasites of human beings. More than this, the reader will expect the writer to discuss specific parasites, and even more specifically, to discuss parasites which are a danger to human beings, including schistosoma. The specific information about what aspect(s) of the topic will be discussed in the text is known as the main idea. Often, the main idea is found in the topic sentence. In the sentence above, for example, 'parasites' is the topic and 'parasites which are a danger to human beings’ is the main idea.

Task 4

Read the following texts; for each text, write down the topic sentence and put a box around the main idea.

a)

We have only one clue as to how our Universe began. When starlight is passed through a spectroscope the bright spectral lines are displaced towards the red end of the spectrum. This red shift, due to the Doppler effect, tells us that the galaxies are rushing into Space away from our galaxy. One explanation for this is that all matter in the universe started as a single, super-dense mass which exploded. This explanation is known as the 'big bang' theory.

b)

There are two principal requirements for an explosive. First, it must remain stable unless it is struck or ignited, and then, once it is ignited, a chemical reaction must take place to cause heat and a large volume of gas to be produced in a very short time. In gunpowder, for example, the potassium nitrate, KNO₃, combines with the carbon in the charcoal to give carbon dioxide and some nitrogen gas.

c)

All rocks were originally formed during the period when the Earth was molten and then cooled down. A great deal of this igneous (fire-made) rock still exists in its original stage. However, hard though it is, igneous rock breaks up into grains of sand in the course, of millions of years of the action of wind and water, sun and ice. Some of this sand settled at the bottom of the sea and, over the ages, became pressed into hard rock forming strata of sedimentary rocks of varying thickness and composition, such as sandstone and limestone.

In addition to providing the writer and the reader with a clear indication of what the text should be about, the topic sentence also indicates what the text will not be about: for example, if the topic sentence is:

There are several parasites which are a danger to human beings.

you will not expect to find a discussion of, for example, nuclear energy in the text! Using your topic sentence as guide to the rest of your writing helps you follow the third principle of communication.

3 The relevance principle

Keep to your topic and your purpose for writing.

Task 5

Study the flow diagram and the text. Some of the sentences in the text should not be there: keep in mind the relevance principle, and discuss with a partner which sentences should be taken out.

Insects which transmit disease to man in their bites are called vectors, or carriers. Malaria is an example of a disease of this type. It is transmitted by a kind of mosquito called anopheles. Some diseases are transmitted by tiny water animals. The anopheles mosquito sucks blood from a person with malaria. Once in the stomach of the mosquito, the microbes multiply. House flies transmit microbes on their feet. The malaria microbes pass to the mosquito's mouth, and when the mosquito bites a person the malaria microbes pass into the person's blood. The parasites then enter the person's liver, in which they change and multiply. From there they pass into the blood cells, where they cause the malaria attack. The spread of insect-borne disease can be controlled.