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Calculating GPP and NPP

This lab explores how light affects photosynthesis by measuring dissolved oxygen in water with Elodea plants under light and dark conditions—demonstrating biochemical reactions and experimental design principles.

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    Mini Lab: Calculating GPP and NPP Name Open this Video and answer the questions while watching the video: https://youtu.be/voSQZcqgYNY 1. Where and what is the sample of water used in this lab? The sample water is from an algae covered fish tank. 2. What is the dissolved oxygen (DO) reading of the water sample? 7.4 mg/L 3. How many bottles are filled? 2 4. Why was the lid of the bottle put on under the water? All the air escapes forthe bottle to only be filled with water and the elodea plant 5. What plant is put in each bottle? The elodea plant 6. Describe the treatment to each bottle. (What was done differently to each bottle?) Why? One bottle was covered and in the dark while the other was in the light to measure the differences of its cellular respiration to demonstrate the effect light has on biochemical reactions, such as photosynthesis Pause the video and use what you've learned about experimental design t o answer these questions: 7. List 4 constants (the things that are the same for each bottle) in this lab: Same amount of water, same plant (Elodea) source, time measured, light source. 8. What is the independent variable? bottle covered or in the Iight __________________________________ 9. What is the dependent variable? (What will we measure?) Dissolved oxygen Play the video to get the results and answer these questions:

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    10. What is t h e DO level of the bottle that was in t h e light? 10.0 nng/L 11. What is the DO level of the bottle that was in the dark? 5.3 mg/L Fill in this chart: Initial Dissolved Oxygen (ppm) (both bottles) Final Dissolved Oxygen in Dark Battle (no photosynthesis, only respiration) Final Dissolved Oxygen in Light Bottle (both respiration and photosynthesis) 7.4 mg/L 5.3 mg/L 10.0 mg/L 12. Calculating Respiration Rate: Only respiration (and not photosynthesis) can occur in a dark bottle. Respiration rate is the decrease in DO overtime. To determine this for your sample, subtract the dark DO from the initial DO, then divide it by t h e time (usually i n days). This will give! . . an answer i n m g O/L/day. Use the formula below t o Respiration rate - i n i * i a L ) dar (mg. ) ] assist you. In a water solution, ppm = mg/L lime (days) R = (7.4-5.3)/(2) =1.05 O/L/day 13. Calculating Gross Primary Productivity: Gross Primary Productivity (GPP) is the total amount of carbon that was fixed by organisms over a period of time. To determine this for your sample, subtract the dark bottle DO from the light DO values, then divide it by the time (usually in days). This will give an answer in mg O/L/day. Use the formula below to assist you. , . (light or enriched D O (mg L ) - dark D O (mg Gross productivity = —- -------------------------—= ■ ------------------- ———— time (days) GPP = 10.0 mg/L-5.3/2 = 2.35 oyiVday 14. Calculating Net Primary Productivity: Net Primary Productivity (NPP) is the total amount of carbon that was fixed by organisms into living tissue minus that used for respiration over a period of time To determine this for your sample, subtract the respiration rate in mg O z /L/day from GPP in m g O/L/day. This will give an answer in mg oyL/day. Use the formula NPP = GPP - R NPP = 2.35O 2 /L/day-1.05O z /L/day =1.3 Q,/L/day 15. You can also use the formula below t o calculate the net primary productivity since the difference between the light bottle DO and the initial DO is essentially the same algebraic expression as GPP minus respiration rate.

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