Exploring Plant Metabolism & Productivity
Part 2

Lab Summary

This practicing inquiry lab is a follow-up to Part 1.  In this lab students explore the extent to which there are energetic trade-offs between leaf morphology and metabolism (GPP & NPP). The lab uses a combination of more guided inquiry and student-directed methods.  Students are initially asked to share what they have learned in class and through pre-lab research and reading to continue to practice hypothesis generation and experimentation skills.  Although the question that students will be exploring is dictated by the lab, the hypotheses, procedures and data analysis and interpretation are more student-driven.


Conceptual Learning Objectives - Upon completion of this lab, students should be able to
  • determine/calculate  NPP, GPP and respiratory rate using the CO2 uptake method.
  • explain why the CO2 uptake method can be used to estimate energy uptake and usage by a plant.
  • explain why NPP reflects the energy available for growth and reproduction in plants.
  • explain why GPP is a measure of total energy harvested from photosynthesis.
  • develop and justify a biologically relevant hypotheses for why there may be variation (seasonal, developmental, environmental, physical) in NPP, GPP or respiration in plants.
  • use CO2 gas sensor and how measurements of plant CO2 uptake and release can be used to estimate GPP, NPP and respiratory rate in plants.

Scientific Skills - In the context of this lab students will practice and receive feedback on
  • understanding the conceptual relations between a biological process and a quantitative measure of that process.
  • developing a properly formatted and biologically-based experimental hypothesis and prediction.
  • identifying the dependent and independent variables in an experiment
  • designing an experiment with appropriate controls across treatments and trials
  • developing more sophisticated skills in using MS Excel for organizing, summarizing and analyzing data. 
  • choosing the appropriate graph to summarize data.
  • choosing the appropriate type of inferential statistical analysis to perform
  • using inferential statistics to analyze data and draw conclusions regarding an experimental hypothesis.
  • interpreting the r2 statistic and slope of a best fit linear equation.
  • drawing conclusions from their data analysis and place them in a biological context.
  • exploring the limitations in the design of the experiment and their influence on study conclusions.

Learning Theory & Pedagogy

The traditional approach to introductory biology labs has been to "cover" essential concepts and processes in class and then to immerse students in a highly guided hand-on lab experience which asks students to use these concepts to explain data.  Labs are often designed to confirm that a biological process is indeed occurring as we would predict.   These "confirmatory" labs require that students have been exposed to these abstract concepts and detailed processes prior to lab which are then often learned devoid any meaningful context to the learner.   However, in science it is observations that drive further exploration, not the reverse.  Moreover, in courses taught using more traditional lab experiences, there is pressure to cover concepts prior to lab.  This is often quite difficult, particularly in courses where class and lab are not taught by the same instructor, and where there is little flexibility in the lab schedule.  Therefore the purpose of this lab is not to teach students about the details of plant metabolism, rather it is to immerse them in a semi-guided exploration which yields observations that are intended to help students understand the broader connections between plant metabolic processes and morphological adaptations.  This lab is meant to precede a more detailed exploration of plant metabolic processes, and to provide a context for deeper exploration. This lab is also designed around the idea that students are likely to be more invested in a science experiment if they are allowed to make critical decisions about its' design and execution.  This elicits student ownership of the experiment, and generates intrinsic interest in the outcome.

Instructional Resources

  • An instructor guide which provide lab instructors with lab preparation instructions, suggested materials, learning theory and pedagogical suggestions.
  • A student PowerPoint tutorial which introduces them to fundamental aspects of plant metabolism, the energetic connections between photosynthesis and respiration in plants and how to use the CO2 uptake/release method to estimate GPP and NPP.
  • Lab manual appendix that teach students how to use the Vernier data loggers and gas sensors.
  • Lab manual appendix exploring experimental design, descriptive statistics, graphing and inferential statistics using MS Excel.

Required Materials
  • Vernier data loggers and CO2 gas sensor
  • Team computers with MS Excel
  • High intensity (>1600 lumen) florescent bulb lamps