CELL RESPIRATION QUESTION 1990:                  L. PETERSON/AP BIOLOGY

        The results below are measurements of cumulative oxygen consumption by 

        germinating and dry seeds. Gas volume measurements were corrected for

        changes in temperature and pressure.

                               Cumulative Oxygen Consumption (mL)

        Time (minutes) 0       10      20      30      40

220 C  Germinating Seeds       0.0    8.8     16.0    23.7    32.0

            Dry Seeds          0.0     0.2     0.1     0.0     0.1

100 C  Germinating Seeds       0.0     0.0     0.2     0.1     0.2

            Dry Seeds          0.0     0.0     0.2     0.1     0.2     

        a.  Using the graph paper provided, plot the results for the germinating seeds 

             at 220 C amd at 100 C.

        b.  Calculate the rate of oxygen consumption for the germinating seeds at 220 C,

             using the time interval between 10 and 20 minutes.

        c.  Account for the differences in oxygen consumption observed between:

               (1) germinating seeds at 220 C and at 100 C.;

               (2) germinating seeds and dry seeds.

        d.  Describe the essential features of an experimental apparatus that could be 

             used to measure oxygen consumption by a small organism. Explain why each 

             of these features is necessary.

  STANDARDS:   Parts a, b, and c together = 8 pts MAX

          one point for each of the following:

  a.  GRAPH(S)

  ___Correct orientation of x (independent) and Y (dependent) axes

  ___Scale and label axes

  ___Curves plotted (both lines drawn and identified as 100/220). 

         Histograms accepted if correctly drawn.

  ___Title of graph

  b.  RATE CALCULATION

  ___Setup (16 - 8.8)/(20 -10) or number 7.2 or 0.72    

  ___Rate Concept - units (volume/time)

          7.2 mL/10 min. or 0.72 mL/min.

  c.  EXPLANATIONS

  1.  TEMPERATURE VARIATION

  ___Seeds show no temperature regulation (at environmental temperature);

         do not increase O2 consumption to maintain preset temperature

  ___Temperature increase causes increased activity 

     (or increased respiration or metabolism)

  ___Extended explanation of respiratory enzyme reaction rate, rate increases (to limit) 

         with increased temperature (enzymes generally have Q10 about 2.)

  ___220 vs. 100 rates reversed in cold hardiness (genetically determined) seeds

  2. GERMINATING SEEDS VS. DRY SEEDS

  ___Dry seeds dormant and/or germinating seeds metabolically active

  ___Extended explanation of dormancy and/or metabolism

  ___Explanation of water based chemistry of respiratory enzyme reactions

  d.  EXPERIMENTAL APPARATUS  3 pts MAX

  ___ Method to separate O2 consumption vs. CO2 release

          Something (KOH, etc.) to remove CO2 (gas -> solid)

  ___Closed System

  ___Method to measure pressure/volume change = graduated tube/pipet, 

          containing bubble/water/Brodie

  ___Method to control temperature = water bath

  ___Method to control volume = glass beads or some other inert material vs. seeds

  ___Timing device

  ___Equal numbers of organisms in experimental and control

  Other techniques/methods for measuring O2 consumption

     one point for any of the following:

  __ Winkler titration to determine O2 concentration before and after

  __ Polarographic, oxygen electrode, Clark-type electrode

  __EPR measurement of O2 concentration changes, in gas flow-thru system

     one point for a detailed explanation for any one of the above techniques

     None of these require special techniques to distinguish volume of CO2 from volume of 

     O2; all are specific for O2. None of these depend on pressure changes. Other features of 

     procedure (constant temperature, appropriate controls, etc.) remain the same.