Biology Gas Pressure Sensor(Order Code BGP-DIN)

Many biology activities involve the production or consumption of a gas, resulting ina change in pressure. The Biology Gas Pressure Sensor can be used to monitor thesepressure changes. It can be connected to any of the Vernier interfaces (ULI, SerialBox Interface, MPLI, or Voltage Input Unit), as well as the Texas InstrumentsCalculator-Based Laboratory™ (CBL™) System. The following is a partial list ofactivities and experiments that can be performed using this probe:

• Monitor the production of O2 during photosynthesis of an aquatic plant in a closedsystem.

• Determine the rate of transpiration for a plant under different conditions.• Determine the rate of respiration in germinating pea or bean seeds.• Monitor the pressure of a confined air pocket as water moves in and out of a semi-

permeable membrane by osmosis.• Study the effect of temperature and concentration on the rate of decomposition of

H2O2.• Determine the effect of temperature on cold-blooded organisms by monitoring

their respiration.• Monitor the pressure exerted as yeast ferment sugars and produce carbon dioxide.• Study human respiratory patterns using the Respiration Monitor Belt.• Investigate the relationship between pressure and volume, Boyle’s law.• Study the effect of temperature on gas pressure, Gay-Lussac’s law.• Monitor barometric pressure associated with weather phenomena.• Measure vapor pressure of liquids.

Inventory of Items Included with the Biology Gas PressureSensorIncluded with your Biology Gas Pressure Sensor are accessories to allow you toconnect it to a reaction container, such as an Erlenmeyer flask. Check to be sure thateach of these items is included:• two ribbed, tapered valve connectors inserted into a rubber stopper.• one two-way valve• two Luer-lock connectors (white) connected to either end of a piece of plastic tubing.• one 20-mL syringe

How the Biology Gas Pressure Sensor WorksThe heart of this circuit is the SenSym SCX30ANC. It has a membrane which flexesas pressure changes. This sensor is arranged to measure absolute pressure. One sideof the membrane is a vacuum, while the other side is open to the atmosphere. Thesensor produces an output voltage which varies in a linear way with absolutepressure. It includes special circuitry to minimize errors caused by changes intemperature.

Pressure UnitsPressure can be measured in many different units. We quote values here inseveral of the units shown below. Some equivalent values for 1 atmosphereare:

1 atmosphere = 760 mm of Hg= 101.325 kPa= 29.92 in. of Hg (at 0°C)= 1.013 bar= 14.696 psi

We provide an amplifier circuit that conditions the signal from the SCX30ANCsensor. With this circuit, the output voltage from the Biology Gas Pressure Sensorwill be linear with respect to pressure, with 0.00 volts corresponding to 0.75 atm and3.0 volts corresponding to 1.54 atm. The output voltage increases 1 volt for each0.271 atm. This allows the sensor to be used over the range of 0.75 to 1.54 atm.

There is a plastic tube on the Biology Gas Pressure Sensor running from a port insidethe box to a three-way valve on the outside of the box. The two openings (or stems)on the three-way valve have a small threaded end called a luer lock. You may attachplastic or rubber tubing to one of the ports using the supplied adapter (alreadymounted on extra tubing). The adapter accepts tubing with an inside diameter of0.125 inches (3.2 mm), and commonly available 3/16-inch plastic tubing can beconnected to it. You can also attach the 20-mL plastic syringe included with theBiology Gas Pressure Sensor directly to this stem. The other port (pointing upward inthe figure below) of the three-way valve opens to the atmosphere and can serve as apressure release. As you set up your experiments, you can always return the pressureto atmospheric pressure by opening this side stem. When the blue control (or “off”)handle is aligned with one of the stems, it closes off this stem. Note: Since the sidestem also has a luer lock, it is possible to connect the syringe or the adapter withtubing in this side position.

Biology GasPressure Sensor

Biology GasPressure Sensor

System closed to the outside atmosphere Gas pressure sensor open to outside atmosphere

CalibrationWe feel that you should almost never have to perform a new calibration for thissensor. You can simply load the appropriate calibration file that was included in yourdata-collection program from Vernier. In older versions of the data-collectionprogram, there is no calibration file for this probe. If this is the case, and you feeluncomfortable performing a new calibration, call us and we will send you a free diskwhich contains the appropriate calibrations and experiment files. If you would like toperform your own calibrations, then follow the steps described here.

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The standard calibration procedure we use with all of our sensors is a 2-pointcalibration. All of the Vernier data-collection programs allow you to do a2-point calibration. For the first calibration point perform the following operation:

• Open the three-way valve on the sensor to the atmosphere so it equilibrates toatmospheric pressure. When the voltage reading displayed on the computer or CBLscreen stabilizes, enter the atmospheric pressure, as recorded with a barometer.

For the second calibration point, do one of the following:

• Connect the syringe to the Biology Gas Pressure Sensor and open the unused stemof the three-way valve by aligning the blue valve control with the stem that leadsinto the Biology Gas Pressure Sensor box. Move the plunger on the syringe so thatthe syringe volume is set at 10 mL. Close the unused stem leading to theatmosphere by aligning the blue valve control with it. Move the syringe plunger sothat the voltage reading displayed is 3.0 volts. Enter 1.54 atmospheres as the value.If you wish to calibrate in another unit, convert the 1.54 atmospheres using thevalue chart at the front of the booklet (e.g., for mm Hg, 1.54 atm X 760 mm Hg/atm= 1170.4 mm Hg.)

• Connect the extra piece of tubing that came with the sensor to the three-way valveof the Biology Gas Pressure Sensor. Place the end of the tube under water (seefigure below). The pressure reading will increase 9.679 X 10-4 atm for everycentimeter below the surface of the water. Note how far the air column in the tubeextends below the surface (in centimeters). Calculate the pressure you will need toenter, using the formula below:

Pressure = atmospheric pressure in atm + depth in cm X (9.679 X 10-4 atm/cm)

If you choose to use different pressure units, make the appropriate conversion.Enter your calculated value for the pressure to complete the calibration.

Sensor

Flexible Tubing

Ruler

Water

Specifications• Pressure range: 0.75 to 1.54 atm• Maximum pressure that the sensor can tolerate without permanent damage: 4 atm• Sensitivity: 0.271 atm/volt• Resolution using a 12-bit, 5-volt interface (ULI II, Serial Box): 0.000331 atm• Resolution using a 10-bit, 5-volt interface (CBL, original ULI): 0.001323 atm• Sensing element: SenSym SCX30ANC• Combined linearity and hysteresis: typical ±0.2% full scale• Response time: 100 microseconds

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NOTE: This product is to be used for educational purposes only. It is not appropriatefor industrial, medical, research, or commercial applications.

Suggested Experiments

Rate of Plant Transpiration

This experiment allows students to see how environmental factors such as heat, wind,temperature, and light affect the process of transpiration in plants. This is done byrecording the change in pressure inside a tube filled with water (see figure). As theplant takes in water, the pressure of an air pocket inside the tube drops. The rate ofpressure change is proportional to the rate of transpiration. To perform this activity,cut a leafy plant stem at its base and insert the stem into a 20-cm piece of plastictubing. Seal the stem in the tubing with petroleum jelly. Fill the tubing with waterand connect the open end to the Biology Gas Pressure Sensor. Secure the plant andtubing with a ring stand in an upright position with the Biology Gas Pressure Sensorelevated above the plant base. Connect the sensor to your interface box or CBL. Runthe data-collection program and load the appropriate calibration. Collect data for10 minutes with the plant under room conditions. Refill the water in the tube andrepeat the experiment with the plant exposed to a different condition. The resultinggraph shows a near linear drop in pressure as time progresses. When different factorssuch as wind are added, the graph of pressure change shows a larger negative slope.

Biology Gas Pressure Sensor

Confined Air

Water Filled Tube

Base of Plant

with fan blowing control

Rate of PhotosynthesisYou can use the Biology Gas Pressure Sensor to graph the pressure that occurs whenoxygen gas is produce by photosynthesis. To do this, place an aquatic plant, such aselodea, in a container filled mostly with water. Bubble your breath into the water tosaturate it with carbon dioxide. Seal the container with a single-hole stopper that willaccommodate a small section of glass tube. Connect the plastic tubing that comeswith the Biology Gas Pressure Sensor to the glass tube from the stopper. Connect theother end of the tubing to the sensor. When the container is sealed, it should be nearlyfull, with a small air space trapped at the water’s surface. Monitor the pressure in thecontainer for a 12 to 24 hour period of time. You can see in the graph below that thepressure rises as the plant photosynthesizes. When there is no light, the plant entersphotorespiration and the pressure drops as the oxygen is consumed by the plant.

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Biology GasPressure Sensor

water

air space

plant

Measuring Respiration of InsectsIn this activity the Biology Gas Pressure Sensor is used to measure the decrease in airpressure in a test tube as crickets consume oxygen for cellular respiration. Place acotton ball saturated with potassium hydroxide at the bottom of a 20 X 150-mm testtube. Insert a dry cotton ball to keep the crickets away from the caustic potassiumhydroxide. Place five adult crickets into the test tube. Seal the test tube with a one-hole stopper that has a glass tube inserted in the hole. Connect a small section ofplastic tubing between the glass tube and a Biology Gas Pressure Sensor. Monitor thepressure for a 10-minute period. Following the 10-minute period, open the air valveon the sensor to allow the tube to return to room pressure. Place the test tube in awater bath that is warmer or cooler than the room temperature. When the tube hasadjusted to the new temperature, close the three-way valve to the outside atmosphere.Monitor the pressure for another 10 minutes. Compare the data of the two collectionruns. Below is a sample graph of crickets at room temperature. To serve as a control,a second run was made without the crickets.

Gas Pressure Water Bath

Crickets

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Human Respiratory PatternsThe respiratory patterns of human subjects can be monitored and graphed using theBiology Gas Pressure Sensor connected to the Respiration Monitor Belt. TheRespiration Monitor Belt is sold separately by Vernier (RMB, $58). You can studyrespiratory patterns and examine how certain stimuli and conditions affect thosepatterns. Study the effect of carbon dioxide concentration on respiration rate byhaving students breathe into a sealed bag for a period of time. The graph belowdisplays the respiratory patterns of a 25-year old male using the Biology Gas PressureSensor and Respiration Monitor Belt.

The graph below displays the respiratory patterns of the subject holding his breath.Note the decreasing size of the waveforms once the subject releases his breath andbegins to take in more air.

Additional Biology ActivitiesOther activities that you can perform using the Biology Gas Pressure Sensor:

• Determine the rate of respiration in germinating pea or bean seeds.• Monitor the pressure of a confined air pocket as water moves in and out of a semi-

permeable membrane by osmosis.• Study the effect of temperature and concentration on the rate of decomposition of

H2O2.• Determine the effect of temperature on cold-blooded organisms by monitoring

their respiration.• Monitor the pressure exerted as yeast ferment sugars and produce carbon dioxide.

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Weather StudiesThe Biology Gas Pressure Sensor can be used as an accurate barometer for weatherstudies. The sensor is temperature compensated, so changes in room temperature willnot interfere with the data. It is especially interesting to watch pressure changes as astorm moves in. Note: For more precise barometric pressure measurements in therange of 0.80 to 1.05 atmospheres, Vernier also sells a Barometer (order code BAR-DIN, $56).

Boyle’s Law (Pressure vs. Volume)Boyle’s law is a classic physics and chemistry concept that can be easilydemonstrated using the Biology Gas Pressure Sensor. One easy way to do this is touse the plastic syringe included with the sensor. Connect the plastic syringe to one ofthe valve stems with a gentle 1/2 turn. Close the stem that leads into the Biology GasPressure Sensor box using the blue control handle and set the syringe to a volume of10 mL. Then close the open stem.

Pressure Sensor

The pressure inside the syringe is now equal to atmospheric pressure at a volume of10 mL. You are now set to collect pressure-volume data. Start your readings at 13mL and take readings in 1-mL increments until you reach 6 mL. At reading volumesbelow 6 mL or above 13 mL, you will go beyond the maximum and minimumpressure values that can be correctly measured with the Biology Gas Pressure Sensor.

Sample data collected with this sensor and the syringe are shown here:

Sample Boyle’s Law Graph

Note: To make pressure measurements in the range of 0 to 6.8 atm, Vernier also sellsa Pressure Sensor (order code PS-DIN, $66).

Gay-Lussac’s Law (Pressure vs. Absolute Temperature)Gay-Lussac’s law states that the pressure of a confined gas is directly proportional toits absolute temperature if the volume remains constant. The white, threaded adapterend of the long piece of plastic tubing can be connected to one of the valve stems

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with a full turn. The other end can be connected to the rubber stopper apparatus(included with your Biology Gas Pressure Sensor), which is in turn inserted into a125-mL Erlenmeyer flask. This provides a constant-volume gas sample.

This stopper can be inserted into an Erlenmeyer flask to provide a constant-volumegas sample. Pressure-temperature data can be collected using a temperature probe orthermometer along with the Biology Gas Pressure Sensor. Place the flask in waterbaths of different temperatures. Take data to see how pressure changes withtemperature. Remember that all temperatures should be measured using the Kelvintemperature scale. Using the same apparatus, pressure and temperature data may beextrapolated to determine a Celsius temperature value for absolute zero.

Studying Chemical Reactions by Monitoring Pressure

Many chemical reactions produce gases that can cause a pressure increase in a sealedcontainer. The pressure change can be used as a way of monitoring the rate ofreaction. As a very simple example, the graph here was made using the Biology GasPressure Sensor to monitor the reaction of Alka-Seltzer® and water. We made a holein the top of a plastic 35-mm film container. We then ran a tube from the BiologyGas Pressure Sensor through the hole and sealed it with silicone sealant. We thenplaced a piece of an Alka-Seltzer tablet and 10 mL of water in the container andsealed it. The graph shows the pressure increase as the reaction takes place. Note thesudden drop in pressure when the lid of the container pops off. You can study therate of reaction, change the temperature, etc.

Using the Biology Gas Pressure Sensorto Monitor the Rate of Reaction

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Using this Sensor with the Texas Instruments CBL SystemThis sensor can be used with the Calculator-Based Laboratory System from TexasInstruments. Here are some suggestions for using it with the CBL:• Connect the CBL unit to the TI graphing calculator using the link ports located on

each unit. Be sure to push both plugs in firmly.• Using a CBL-DIN adapter, connect the sensor to any of the analog input ports on

the top or left side of the CBL unit (CH1, CH2, or CH3). In most cases, CH1 isused. The CBL-DIN adapter is available from Vernier for $5.

• Run a program to monitor the signal from the sensor. We strongly recommendusing programs developed specifically for use with this sensor. Vernier hasprograms which support this sensor. One program we recommend for use with thissensor is CHEMBIO from the Vernier collection of programs.

The Vernier programs for the CBL are available on the Internet or they can beobtained in disk form. Once you have these programs, it is a simple matter toload them into a calculator using TI-GRAPH LINK™.• To obtain our programs through the World Wide Web, download the files

from our web site:www.vernier.com

• These programs can also be obtained on disk. The programs are a part of ourCBL Made Easy! Package, which includes Macintosh and IBM-compatibledisks and our CBL Made Easy! user's guide (order code CMEP, $12).

Other notes for using this sensor with the CBL System

1. The resolution of this probe when used with the CBL System is 0.0013 atm or1.005 mmHg.

2. If you write your own program for use with the Biology Gas Pressure Sensor,keep in mind the following:

• The voltage produced by this probe is linear with respect to the pressure itsenses. The slope and intercept for calibrating this sensor are:

For pressure readings in atmospheres:

Intercept (k0): 0.729 Slope (k1) : 0.271

For pressure readings in kilopascals:

Intercept (k0): 73.866 Slope (k1) : 27.459

For pressure readings in mm Hg:

Intercept (k0): 554.175 Slope (k1) : 205.825

For pressure readings in inches of Hg:

Intercept (k0): 21.875 Slope (k1) : 8.125

If you use these values in your program, you will get reasonably accuratepressure readings. Add or modify the command 4 line in your program so that itreads:

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For pressure readings in atm:{4,channel number,1,1,8.729,8.271}¸L6

For pressure readings in kilopascals:{4,channel number,1,1,73.866,27.459}¸L6

For pressure readings in mm Hg:{4,channel number,1,1,554.175,205.825}¸L6

For pressure readings in inches of Hg:{4,channel number,1,1,21.875,8.125}¸L6

• In place of "channel number", put a 1, 2, or 3 for channel the probe will beconnected to on the CBL.

• This probe should be used with the CBL set for the 0 to 5 volt range (operation1 in command 1).

• For more information on writing programs for TI graphing calculators and theCBL, see your calculator manual and the CBL System Guidebook.

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Vernier Software & Technology13979 S.W. Millikan WayBeaverton, OR 97005-2886

(503) 277-2299 • FAX (503) 277-2440info@vernier.com • www.vernier.com

Rev. 3/2/00