CBL Interfacing

Breathing: Germinating Peas vs. Earthworms

Processing The Data

Collecting Your Data From The CBL

Setting Up Your Data

Determining The Pressure Differences

Determining the Corrected Pressure Differences

Corrected Pressure Differences Per Gram of Earthworm

Setting Up Your Plot

Recording Your Plot

Analyzing the Results

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A. Collecting Your Data From The CBL

When the CBL reads done, the experiment is over, but the information must be transferred to the calculator and manipulated for analysis. To make the transfer perform the following steps:

Press ENTER.

A menu will appear. Choose GET CBL DATA.

MAKE SURE CBL SHOWS DONE will appear. Press ENTER.

TIME IN L1, DATA IN L2, L3 will appear. Press ENTER.

A menu will appear. Choose VIEW GRAPHS.

Press 2nd, OFF, ON, GRAPH.

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B. Setting Up Your Data

Now you need analyze your results and this will require several manipulations of your data.

In order to do that, your data must be put into the most meaningful form. There are three manipulations which must be done:

1. We are not interested in graphing the drop in pressure, but rather the change in pressure after each time interval. We will call these values pressure differences. Thus we will go to the list of data and subtract each pressure reading from the first pressure reading on the list.
2. We must subtract any pressure differences which are due to subtle environmental effects (the pressure differences recorded in the vial with glass beads) from the pressure differences in the respirometer with our biological sample. We will call these values the corrected pressure differences.
3. In order for our comparison between peas and earthworms to be meaningful, we must consider the mass of the sample we started with. We will determine the corrected pressure difference per gram by dividing the corrected pressure difference by the mass of the biological sample.

Once we have manipulated our data we will look at a graph of the corrected pressure difference per gram vs. time (measured in seconds).

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Determining The Pressure Differences

Before starting this section you need to adjust your calculator so that the numerical value of calculations is given with enough decimal places.

Press MODE and arrow down to float. Then arrow right to 6. Press ENTER.

Press STAT.

A menu will appear. Choose Edit.

Lists appear.

Record the first value in L2 and L3 on your data sheet.

L2 (pressure of earthworms) _________

L3 (glass beads) _________

Press GRAPH

Type: (the first value recorded in L2, which you recorded above)-2nd L2 STO 2nd L2 ENTER.

Type: (the first value recorded in L3, which you recorded above)-2nd L3 STO 2nd L3 ENTER.

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Determining the Corrected Pressure Differences

L2 now shows the pressure differences in the respirometer with earthworms. L3 shows the pressure differences in the respirometer with the glass beads.

But are some of those differences in the earthworm respirometer is due to environmental changes? We will use our control respirometer with glass beads to determine what the environmental pressure changes are. Those pressure changes will be subtracted from the pressure changes recorded in L2.

Type: 2nd L2- 2nd L3 STO 2nd L2 ENTER.

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Corrected Pressure Differences Per Gram of Earthworm

Finally, in order to compare the rate of respiration with other organisms, you need to determine the amount of respiration which occurred per gram. This mass was determined earlier and entered on your data sheet.

TYPE: 2nd L2 ÷ Mass of earthworms STO 2nd L2 ENTER.

This gives you the corrected pressure difference per gram of earthworm. Now you are ready to graph the data: L1 (time) vs. L2 (corrected pressure difference per gram of earthworm)

NOTE: EXPECT THESE VALUES TO BE VERY LOW.

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C. Setting Up Your Plot

Press 2nd, STAT PLOT.

A menu will appear. Choose Plot 1.

The screen shows Plot1. The following selections should be highlighted by moving the cursor to the appropriate item and pressing ENTER.

On

Type: line graph (2nd picture)

X lists:L1

Y list:L2

Mark: .

Press GRAPH, ZOOM, 9. The graph showing the rate of respiration per gram of earthworm should now appear.

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D. Recording Your Plot

The plot obtained in the experiment represents the change in pressure with respect to time. If available, use a TI-GRAPH LINK to print the graph; otherwise, sketch it in the space provided on your data sheet. In either case, label the axes.

Label each line on both of the graphs. To label some of the key points on the axes simply press TRACE. A flashing X is at the beginning of Plot 1. The x and y numerical values of that point are shown at the bottom of the screen. By arrowing to the right you can move the flashing X along plot 1 getting a few key points which will help you label your axes.

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E. Analyzing the Results

Finding the Slope of Your Plot

Press STAT, arrow right, and choose LinReg (ax+b)

In the next instruction DO TYPE THE COMMA (,).

Press 2nd L1, 2nd L2 ENTER. Several equations are shown. The slope is given as a=.

Record the slopes on your data sheet. Be sure to note if it is positive or negative.

Record the slope on your data sheet.

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