Classifying is grouping objects or events based on common features. When classifying, you first make careful observations of the group of items to be classified. Select one feature that is shared by some items in the group but not others. Place the items that share this feature in a subgroup. Place the remaining items in a second subgroup. Ideally, the items in the second subgroup will have some feature in common with one another. After you decide on the first feature that separates the items into subgroups, examine the items for other features and form further subgroups until the items can no longer be distinguished enough to identify them as distinct.

How would you classify a collection of CDs? Classify the CDs based on observable features. You might classify CDs you like to dance to in one subgroup and CDs you like to listen to in another. The CDs you like to dance to could be subdivided into a rap subgroup and a rock subgroup. Note that for each feature selected, each CD fits only one subgroup. For example, you wouldn't place a CD into both rap and rock categories. Keep selecting features until all the CDs are classified.

Remember, when you classify, you are grouping objects or events for a purpose. The purpose could be general such as for ease of finding an item. The classification of books in a library is a general-purpose classification. The classification may have a special purpose. For example, plants may be classified as poisonous or harmless to humans.

Sequencing
A sequence is an arrangement of things or events in a particular order. A common sequence with which you may be familiar is the order of steps you must follow to make an omelette. Certain steps of preparation have to be followed in order for the omelette to taste good.

When you are asked to sequence things or events, you must identify what comes first. You then decide what should come second. Continue to choose things or events until they are all in order. Then, go back over the sequence to make sure each thing or event logically leads to the next.

Suppose you wanted to watch a movie that just came out on videotape. What sequence of events would you have to follow to watch the movie? You would first turn the television set to Channel 3 or 4. You would then turn the videotape player on and insert the tape. Once the tape has started playing, you would adjust the sound and picture. Then, when the movie is over, you would rewind the tape and return it to the store. What would happen if you did things out of sequence, such as adjusting the sound before putting in the tape?

Concept Mapping
If you were taking an automobile trip, you would probably take along a road map. The road map shows your location, your destination, and other places along the way. By examining the map, you can understand where you are in relation to other locations on the map.

A concept map is similar to a road map. But, a concept map shows the relationship among ideas (or concepts) rather than places. A concept map is a diagram that visually shows how concepts are related. Because the concept map shows the relationships among ideas, it can clarify the meaning of ideas and terms and help you to understand better what you are studying.

A Network Tree

Notice how some words in the concept map below called a network tree are circled. The circled words are science concepts. The lines in the map show related concepts, and the words written on the lines describe relationships between the concepts.

When you are asked to construct a network tree, state the topic and select the major concepts. Find related concepts and put them in order from general to specific. Branch the related concepts from the major concept, and describe the relationship on the lines. Continue to write the more specific concepts. Write the relationships between the concepts on the lines until all concepts are mapped. Examine the concept map for relationships that cross branches, and add them to the concept map.

An Events Chain

An events chain map is used to describe ideas in order. In science, an events chain map can be used to describe a sequence of events, the steps in a procedure, or the stages of a process.

When making an events chain map, you first must find the one event that starts the chain. This event is called the initiating event. You then find the next event in the chain and continue until you reach an outcome. Suppose your mother asked you to wash the dinner dishes. An events chain map might look like the one shown here. Notice that connecting words may not be necessary.

Cycle Concept Map

A cycle concept map is a special type of events chain map. In a cycle concept map, the series of events do not produce a final outcome. The last event in the chain relates back to the initiating event. Since there is no outcome and the last event relates back to the initiating event, the cycle repeats itself. Follow the stages shown in the cycle map of insect metamorphosis.

There is usually not one correct way to create a concept map. As you are constructing a map, you may discover other ways to construct the map that show the relationships among concepts better. If you do discover what you think is a better way to create a concept map, do not hesitate to change it.

Concept maps are useful in understanding the ideas you have read about. As you construct a map, you are organizing knowledge. Once concept maps are constructed, you can use them again to review and study and to test your knowledge. The construction of concept maps is a learning tool.

Making and Using Tables
Browse through your textbook, and you will notice many tables both in the text and in the labs. The tables in the text arrange information in such a way that it is easier for you to understand. Also, many labs in your text have tables to complete as you do the lab. Lab tables will help you organize the data you collect during the lab so that it can be interpreted more easily.

Most tables have a title telling you what is being presented. The table itself is divided into columns and rows. The column titles list items to be compared. The row headings list the specific characteristics being compared among those items. Within the grid of the table, the collected data are recorded. Look at the following table, and then study the questions that follow it.

What is the title of this table? The title is "Effect of Exercise on Heart Rate." What items are being compared? The heart rate for an individual and the class average are being compared at rest and for several durations after exercise.

What is the average heart rate of the class one minute after exercise? To find the answer, you must locate the column labeled "class average" and the row "1 minute after exercise." The data contained in the box where the column and row intersect are the answer. Whose heart rate was 110 after exercise? If you answered "the individual's," you have an understanding of how to use a table.

Making and Using Graphs
After scientists organize data in tables, they often manipulate and organize and then display the data in graphs. A graph is a diagram that shows a comparison between variables. Since graphs show a picture of collected data, they make interpretation and analysis of the data easier. The three basic types of graphs used in science are the line graph, bar graph, and pie graph.

A line graph is used to show the relationship between two variables. The variables being compared go on two axes of the graph. The independent variable always goes on the horizontal axis, called the x-axis. The independent variable such as temperature is the condition that is manipulated. The dependent variable always goes on the vertical axis, the y-axis. The dependent variable such as growth is any change that results from manipulating the independent variable.

Suppose a school started a peer-study program with a class of students to see how it affected their science grades.

You could make a graph of the grades of students in the program over a period of time. The grading period is the independent variable and should be placed on the x-axis of your graph. Instead of four grading periods, we could look at average grades for the week or month or year. In this way, we would be manipulating the independent variable. The average grade of the students in the program is the dependent variable and would go on the y-axis.

Plain or graph paper can be used to construct graphs. After drawing your axes, you would label each axis with a scale. The x-axis simply lists the grading periods. To make a scale of grades on the y-axis, you must look at the data values provided in the data table above. Since the lowest grade was 81 and the highest was 89, you know that you will have to start numbering at least at 81 and go through 89. You decide to start numbering at 80 and number by twos spaced at equal distances through 90.

You next must plot the data points. The first pair of data you want to plot is the first grading period and 81. Locate "First" on the x-axis and 81 on the y-axis. Where an imaginary vertical line from the x-axis and an imaginary horizontal line from the y-axis would meet, place the first data point. Place the other data points the same way. After all the points are plotted, connect them with a smooth line.

What if you wanted to compare the average grades of the class in the study group with the grades of another class? The data of the other class can be plotted on the same graph to make the comparison. You must include a key with two different lines, each indicating a different set of data.

Bar graphs are similar to line graphs, except they are used to show comparisons among data or to display data that does not continuously change. In a bar graph, thick bars rather than data points show the relationships among data.

To make a bar graph, set up the x-axis and y-axis as you did for the line graph. The data are plotted by drawing thick bars from the x-axis up to an imaginary point where the y-axis would intersect the bar if it were extended.

Look at the bar graph above comparing the wing vibration rates for different insects. The independent variable is the type of insect, and the dependent variable is the number of wing vibrations per second. The number of wing vibrations for different insects is being compared.

A pie graph uses a circle divided into sections to display data. Each section represents a part of the whole. When all the sections are placed together, they equal 100 percent of the whole.

Suppose you wanted to make a pie graph to show the number of seeds that germinate in a package. You would have to determine the total number of seeds and the number of seeds that germinate out of the total. You count the seeds and find that the package contains 143 seeds. Therefore, the whole pie will represent this amount.

You plant the seeds and determine that 129 seeds germinate. The group of seeds that germinated will make up one section of the pie graph, and the group of seeds that did not germinate will make up another section.

To find out how much of the pie each section should take, you must divide the number of seeds in each section by the total number of seeds. You then multiply your answer by 360, the number of degrees in a circle. Round your answer to the nearest whole number. The number of seeds that germinated would be determined as follows:

143	X 360 = 324.75 or 325°
129

• To plot these data on the pie graph, you need a compass and a protractor. Use the compass to draw a circle. Then, draw a straight line from the center to the edge of the circle. Place your protractor on this line, and use it to mark a point on the edge of the circle at 325°. Connect this point with a straight line to the center of the circle. This is the section for the group of seeds that germinated. The other section represents the group of seeds that did not germinate. Complete the graph by labeling the sections of your graph and giving the graph a title.