One of the rationales for this lesson is to have students active in the entire scientific process.  They need to be given a specific concept or problem to explore and, with teacher guidance, provided the opportunity to design their own investigation whenever possible.  Demonstrations of common procedures can quickly familiarize students with some necessary techniques, but students can only develop an understanding for the practical side of the scientific process and ownership of their own learning process when the entire lab, from design to conclusion, comes from them.  Cookbook style procedures may allow students to learn laboratory techniques, but they do not foster the evolution of critical thinking skills and appreciation for the rigor of the scientific method.  Lab is more than conducting cookbook procedures and answering questions about the results, and therefore, the primary student lab model presented here is a hands-on, minds-on inquiry one.
    Two teaching methods have been designed.  In the first one, the teacher can compile a list of students' responses to pre-lab question 12 and provide a list of possible hypotheses for class discussion and analysis.  He or she would demonstrate the basic protocol needed to perform any potential investigations, and then either the class or individual groups determine the feasibility of  the various proposed investigations and design and perform their own definitive labs with teacher guidance.  This approach could be used with all levels of biology classes.
    The other approach is simply to present the class with a lab assignment sheet and have them take full responsibility for all facets of their experiment including hypothesis formation, protocol design, etc.  The teacher makes the materials available, but students are expected to do their own preliminary research and are encouraged to go through the real trial and error process of scientific inquiry.  This approach would be appropriate for an AP level class or an independent research project.
     Regardless of  which approach a teacher takes, there are some practical concerns that must be addressed no matter what.  These are:

• germinated and sprouting seeds are fairly hardy organisms but it is important to keep them moist and hydrated to maintain their metabolic activity.  Sandwiching samples between paper towel that has been soaked and squeezed out is a good way to prevent dehydration, and plant samples should be kept damp this way whenever they are not being used.
• KOH can be highly caustic and care should be taken in its distribution.  A centralized location for students to use is recommended, and latex gloves should be made available for those particularly sensitive its effects.  Be sure students are aware that if they get any on themselves, they need to rinse the area immediately with ample running water.  All students should wear goggles.
• care should be used when adding or removing samples from respirometers to avoid contact and contamination with the KOH.  Using forceps is recommended.
• KOH reacts naturally with the CO₂ in the atmosphere; so it is important to use as fresh a solution of KOH as possible and to keep whatever container it is in as tightly sealed as possible.  Old KOH will be cloudy from the K₂CO₃ that has precipitated out and should not be used.
• Respirometers only work if they are tightly sealed; be sure students double-check all locations where gas might enter or exit to be sure it cannot.
• It is absolutely vital to control for the volume of the samples and keep the temperature constant.  The technique used here rests on the ideal gas law (PV=nRT); changes in the amount of oxygen (n) result in corresponding, testable changes in P and/or V.
• to control for volume, use water-displacement of the plant samples and match the measured volume(s) with comparable volumes of glass beads or some other inert, dense, non-absorbent substance.
• to control for temperature, respirometers need to be contained in water baths that were allowed to stabilize for at least 24 hours, and the respirometers should be permitted to equilibrate to the bath temperature for 10 minutes following insertion.
• for all methods of testing, the time frame for the model experimental system is 20 minutes following equilibration.
• while the lab protocol presented here has been written for use with CBL probes, not everyone has access to this technology.  The alternative is to use a water-displacement method such as the one described in the AP Biology Lab Manual (see diagram 1) or create a water-displacement apparatus by attaching the respirometers to a second 1-ml/0.01 ml graduated pipette with latex tubing.  Insert the second pipette into a 250-ml beaker containing water, and as the volume in the respirometer changes due to oxygen consumption, water is drawn up into the second pipette, permitting students to measure the rate of change.
• when using CBLs, it is possible to perform any potential experiment the teacher or the students design with only one probe.  If one has only one, be sure to test the control respirometer first and the the variable respirometer second, but if two biology gas sensor probes are available, then run the control in channel 1 and any variable in channel 2.
• whether one uses CBL probes or water-displacement methods, what is actually being measured is the rate of pressure or volume changes; hence, units are either mm Hg/sec or ml gas/sec.
• One will need to help students understand that changes in mm Hg or ml of gas correspond to units of oxygen being consumed, and a simple way to do this is to have students create an "artificial" unit that has a one-to-one correspondence with the pressure or volume unit (e.g. a change of 1 mm Hg of pressure or 1 ml of  volume would represent 1 unit of oxygen used).  It is possible, though, to use the ideal gas law to determine the actual mass of oxygen consumed, and this calculation might be appropriate for more advanced students to perform.
• in order to compare actual rates of respiration between different plant parts, it is important to incorporate the amount of actual tissue mass respiring.  Therefore, the final units of measurement should be units of oxygen/sec/mg of tissue.