Pea Structures and their Corresponding Rates of Cellular Respiration


Alisha Lowry, Emily Kliner, Chris Kim


CU Boulder, Fall 2006


In our lab investigation, we tested the different rates of respiration of different parts of germinating peas.  Plants are classified as photoautotrophs, using photosynthesis to produce their own food. Yet, plants must also undergo cellular respiration to convert the energy produced in photosynthesis, to usable energy in cellular respiration.  We tested the different parts of the peas including the seed coats, embryos, cotyledons, and the peas as whole in carbon dioxide production rates via cellular respiration. Accordingly, we hypothesized that if each individual part of the seed has a primary function, it will respire at corresponding rates to its function. 


To test this hypothesis we first placed whole germinating pea seeds in a gas chamber attached to a probe measuring CO2 production.  In the proceeding trials, we then removed the seed coats, cotyledons and embryos, and tested each seed structure individually in their CO2 production. We measured the mass of each tissue and recorded it on a data table to later calculate the rate of respiration through a corresponding calculation.  We ran four trials, each with the different structure of the peas. We hypothesized that the cotyledon will respire at the greatest rate because it stores the most glucose and nutrients by volume (products of cellular respiration), and therefore cellular respiration is required in this particular area more than others. 


Our results indicated that in fact embryos in germinating peas respire at the greatest rate.  The rate of CO2 was calculated by the parts per min/min./grams.  The embryo respired at a rate of 59.83ppm/min/g; where as the whole seeds respired at

6.89ppm/min/g; the cotyledons at 7.62ppm/min/g; the seed coats at 2.47ppm/min/g.  There is no statistical test required or necessary to show significance of which structure respired at the fastest rate. 


Our results are inconsistent with our predictions based on our hypothesis.  Based on the results, our hypothesis should be modified that embryos of germinating peas respire at the greatest rate.  Embryos are the basis of development in a plant, and require the most energy because they are constantly growing, and eventually grow into a pea plant.  We did not know enough background information about plant seed structure to know that embryos respires the fastest.  Rather, the experiment extended our knowledge and helped to explain why a seed structure respires at the rate it does, and how the function of the structures are directly related to their rate of respiration. 


While testing our experiment, there were little potential experimental problems that would cause our data to be unreliable.  However, factors such as temperature and testing the mass of each structure may have caused some alterations to the results.  For example, while peeling of each structure, such as the seed coat, some mass may have not been accounted for.  If some seed coats were significantly crumbled while peeling, the accurate mass of the structure may not have been used because it may have been lost as tiny and non-visible pieces.  Also, the temperature of each structure may have been different at the time it was tested, which may account for different rates of respiration.  However, the data collected is reliable because not only do embryos respire at the greatest rate, but almost 8 times faster than the other structures of the pea seeds. 


In further extended studies, perhaps germinating seeds of different plants, including flowers and other vegetables, respire at different rates as well.  In testing the structure of different seeds and their rates of respiration, we can compare and contrast the individual structure functions of different seeds to the functions of the structure in germinating peas. If embryos of other seeds also respire at the greatest rate, this would further support that the main function of embryos in all seeds is primarily for growth and development.