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The topic sentence

Look at the first paragraph. Think about what the writer is doing in the first sentence.

Paragraph 1

Polychlorinated biphenyls (PCBs) comprise a group of 209 individual compounds which were produced commercially in large quantities up to the late 1970s (Muller, 1997). They were used in products as diverse as electrical equipment, lubricants, paints, plasticisers, carbonless copy paper and slide mounting for microscope slides. PCBs are among a broader group of organochloride chemicals, similar to the notorious DDT, which persist in the environment due to their ability to resist chemical and physical breakdown. They also accumulate up the food chain, with those organisms higher up the food chain typically demonstrating higher levels where contamination has occurred.

She is informing the reader what the paragraph will be about. The first sentence of a paragraph usually establishes the topic to be discussed in the lines which follow, and it is known as the topic sentence. A paragraph without a topic sentence may cause frustration for the reader who has to work hard to understand the purpose of the writing. The topic sentence is usually the first sentence in a paragraph but may sometimes be the second sentence – or the last.

Find the topic sentences in paragraphs 2, 3 and 4.

PCBs are fat soluble and accumulate in fat where they persist for many years after exposure has ceased. Negative health effects of exposure to these chemicals have been observed in both humans and other animals, and include carcinogenic, immunotoxic, reproductive and developmental effects.

Prior to the banning of the chemicals by the American Federal Government in the late 1970s, PCBs were discharged into waterways around the USA. As more health risks have been associated with PCBs, scientists have become increasingly concerned with the concentrations seen in fish, which have the potential to accumulate up the food chain to humans.

Modelling the concentrations and ages of sample fish will allow scientists to predict the effects PCBs will have in the future. The most accurate model for the degradation of PCBs is required to ensure the accuracy of any predictions, and is of the utmost importance when dealing with such potentially dangerous chemicals.

The topic sentences are the:

1,0,0

Correct! The first sentences of each paragraph are the topic sentences.

PCBs are fat soluble and accumulate in fat where they persist for many years after exposure has ceased.

Prior to the banning of the chemicals by the American Federal Government in the late 1970s, PCBs were discharged into waterways around the USA.

Modelling the concentrations and ages of sample fish will allow scientists to predict the effects PCBs will have in the future.

Incorrect.

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Incorrect.

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first sentences;second sentences;third sentences
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