Exercises in Science
..............Jack Kimball.............

Basic Points about Paragraphs


paragraph : a group of sentences connected to one idea

sentence : a group of words containing a subject and verb

topic sentence : the main sentence

general subject : broad idea

to relate : to connect; related : connected

energy : capacity for work

natural environment : the world of living things, especially outdoors

element : mass, matter or substance made of atoms and molecules

atom : smallest part of an element

molecule : a group of atoms

chemistry : the study of elements

cell (in biology): smallest structure of which all living things are made

solar cell : structure or device to make sunlight into electricity


Here are 3 points about paragraphs.

Point 1: An English paragraph is a group of related sentences on one subject. Sentences are related to each other so that the paragraph contains clear thoughts about one subject and only one subject. For example, if you are writing about solar power, all your sentences would relate to the sun as a source of energy.

Point 2: The most important or main idea is expressed in the topic sentence. In other words, the topic sentence contains the most significant or broadest concept, question or statement so that it unifies and covers all the other ideas in the paragraph. If your main idea is that solar energy is a good way to power cars, then your topic sentence might introduce the topic by asking a question: "Why do solar-powered cars make sense?" Or it might introduce the topic with a statement: "There are several reasons why solar-powered cars make sense." All the other sentences in the paragraph will support this main idea, explaining why solar-powered cars are beneficial.

Point 3: Most often the topic sentence will be at the beginning to introduce the main idea; or sometimes it can be at the end to summarize the main idea.

Topic sentence ..............................................................

Supporting sentences (facts, examples, comparisons, etc.) .......................................................................................



Supporting sentences.......................................................

Topic sentence.............................................

Less often, the topic sentence comes as the second sentence, and sometimes it can come in the middle of the paragraph with other sentences leading up to it.

Read the following.

(1) The chemical components, of acid rain are changing the natural environment. (2) Acid rain is the result of increased emissions of sulfur dioxide from burning coal and nitrogen oxide from car exhaust. (3) Although sulfur and nitrogen are sources of food for trees, grasses and other vegetation, when sulfur and nitrogen combine in the form of acid rain, these elements damage green leaf cells and impair the growth of plant life.

The general subject of this paragraph is acid rain. The topic sentence in this paragraph is the first sentence. It expresses the idea that the elements that make up acid rain hurt the environment. Sentences 2 and 3 directly support this idea. Based on the information in the first sentence, we expect the rest of the paragraph to discuss the chemistry of acid rain and the way it damages the environment. Therefore, the second sentence gives us information about the elements found in acid rain. The third sentence tells us how these elements affect plants.

Exercise 1
Read the following paragraphs. What is the general subject? Which is the topic sentence? Do all the other sentences relate to the topic?

Paragraph A

(1) Of the many types of energy, one major
category is kinetic energy or the energy of motion. (2) An example of energy in motion is when a bat hits a baseball. (3) The bat exerts a kinetic force that causes the ball to fly in the air. (4) Mechanical energy is a type of kinetic energy applied to objects. (5) Thermal energy is the energy of molecules in motion. (6) More and more students are doing research on energy these days.

What is the general subject? _____

Which number is the topic sentence? _____

Do all sentences relate to the topic? Yes _____ No _____ If no, which number(s)? ____

Paragraph B
(1) Medical scientists are finding a significant difference in how men and women develop heart problems. (2) Statistics show that women on average develop heart disease later in life than men. (3) One theory is that younger women who give birth to children develop wider coronary arteries, and this helps women to avoid heart attacks as they get older. (4) Most men do not believe this, however.

What is the subject? _____

Which number is the topic sentence? _____

Do all sentences relate to the topic? Yes _____ No _____ If no, which number(s)? ____

Read the following if you need some help with Exercise 1: In Paragraph A, above, the general subject is energy. Sentence 1 contains the main idea that kinetic energy is a major category of energy. The last sentence (number 6), which deals with students, does not directly relate to the topic. In Paragraph B the first sentence introduces the topic, the significant difference in the way men and women develop heart disease. Sentence 4, which discusses what men believe, is off the topic.

Exercise 2

The following paragraph about solar-powered cars is incomplete.
Read the paragraph and consider what might be a good topic sentence to unify all the ideas.

Solar-powered cars are very expensive because of the high development cost of solar batteries. In addition, the cells of the solar batteries can store only limited amounts of energy. So solar cars are not practical for driving on long trips. The biggest problem is the constant need to recharge the cells. This is especially difficult when one drives on cloudy days and at nighttime.

Choose one of the following as the topic sentence.

__(1) Solar-powered cars are expensive.

__(2) There are many advantages and disadvantages to solar energy.

__(3) The future practicality of solar cars depends on overcoming problems with solar batteries.

__(4) Solar batteries are the key to understanding how solar energy can be used to drive cars.

Exercise 3
Read the following paragraph about the solar system and think about a topic sentence that would connect all the ideas.

Mercury is the hottest planet in the solar system because it is nearest the sun. Mercury's surface is totally dry and it is so hot that there is no atmosphere. Venus is the second closest planet to the sun. The hot atmosphere of Venus is similar to that of Earth, but because Venus is so near the sun there are no bodies of water on its surface. Earth, the third closest planet to the sun, has a cooler atmosphere that sustains animals, plants and several bodies of water on its surface.

Choose one of the following as the topic sentence.

__ (1) The three planets closest to the sun are Mercury, Venus and Earth.

__ (2) Surface and atmospheric conditions vary widely among the three planets nearest the sun.

__ (3) The closer a planet is to the sun, the hotter it is.

__ (4) The surface and atmosphere of Earth are different from those of Mars and Venus.

Exercise 4
Read the following paragraphs and write your own topic sentence. Make sure that your sentence 1) covers the ideas in the paragraph and 2) relates only to the ideas in the paragraph.

Write a topic sentence that introduces the idea of birds and feathers.
(HINT: It could be a question.)

Feathers provide good insulation for birds. They can be hard or soft depending on weather conditions and water temperature. For example, some ducks have a thick layer of soft feathers called "down" that protects these birds from extremely cold air and icy water.

Write a topic sentence summarizing this paragraph about tropical rain forests.

Tropical rain forests are found in 70 different countries worldwide, including Brazil in South America, Indonesia in the South Pacific and Zaire in Africa. Plants that grow in these forests provide us with chocolate, fruit, coffee, rubber and wood. Recently, medical products have been developed from rain forest plants; these include medicines for high blood pressure and cancer.


Writing Exercise

Choose one of the following topic sentences and write a paragraph that develops the main idea.

The sky changes. (HINT: Describe the changes from night to day, or from sunshine to rain, or the difference between a winter sky and a summer sky.)

Solar-powered cars are a promising new technology.

A pond supports a community of living things.