Today in class our main focus was on collecting the lab data. We used self-filling ampoules to test the amount of dissolved oxygen in our samples after 24 or 48 hours. One thing we discussed in class is that, although producers photosynthesize they also respire, thus removing some of the oxygen they produce. This makes the oxygen reading we got today inaccurate. In order to account for the oxygen removed during respiration I set up a bottle that was in the dark for 24 hours (dark = no photosynthesis, just respiration). The amount that was removed through respiration could then be added on to the change that we saw in the light. The formulas for these calculations are:
Net productivity = Light Bottle - Initial
Amount of Respiration = Initial - Dark Bottle
Gross Productivity = Light Bottle - Dark Bottle
Remember that Gross Production is the rate at which an ecosystem's producers capture and store a given amount of chemical energy as biomass in a given length of time. Some part of this energy is used by producers during cellular respiration. The amount that is remaining is called the Net Productivity.
You do not need to perform these calculations on your own data, but you must be able to apply them to data given to you on Monday's post-lab quiz.
Your Homework is to finish the lab write up according to the instructions I gave you today and to prepare for Monday's post-lab quiz.
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