Name: Crimson Waller AP Biology AP Lab 12- Dissolved oxygen & aquatic primary productivity (Lab bench) A.

Key concepts: 1. Dissolved oxygen Availability in ponds and lakes. Using the following diagram describe the effect that each of the factors has on availability of oxygen and explain why. a. Temperature: As the water becomes warmer, the ability of the water to hold oxygen decreases. b. Light & photosynthesis: If there is a bright light, aquatic plants can produce more oxygen. c. Decomposition and respiration: As the organic material dies, the microbial process begins to consume oxygen. d. Mixing & turbulence: waves, waterfalls, and rapids increase the oxygen concentration. e. Salinity: As water gets saltier, the ability to hold oxygen decreases. 2. Productivity: Define each of these terms in your own words. a. Primary Productivity: The rate that plants and photosynthetic organisms produce organic compounds. There are two types of primary productivity. Gross and net productivity. b. Gross productivity: Photosynthetic production of organic compounds in the entire eco system. c. Net productivity: Organic materials that are remaining after photosynthetic organisms in the eco system use these compounds for cellular respiration. 3. Why do we use dissolved oxygen as a measure of productivity? Does productivity include more than oxygen? We use dissolved oxygen as a measure of productivity because oxygen is one of the most easily measured products in both photosynthesis and respiration. Productivity is more than oxygen. You can measure productivity in three different ways. The amount of carbon dioxide used, rate of sugar formation and rate of oxygen production. 4. Using the diagrams below explain: a. How does putting a sample of pond water and algae/freshwater plants in the light enable us to measure gross productivity? Putting a sample of pond water and algae in the light will enable us to measure gross productivity because it lets us measure the oxygen after photosynthesis. b. How does putting a sample of pond water and algae/freshwater plants in the dark enable us to measure respiration? Putting a sample of pond water and algae/freshwater plants in the dark enables us to measure respiration because it lets us measure the amount of oxygen left after respiration. c. How does subtracting the two enable us to indirectly measure net productivity? Subtracting the two enables us to indirectly measure net productivity by subtracting the amount of respiration and photosynthesis.

5. What are the three ways that primary productivity can be measured? Highlight the way will be used in this lab? 1. The amount of carbon dioxide used 2. The rate of sugar formation 3. Rate of oxygen production B. LAB PART 1: EFFECT OF TEMPERATURE ON DISSOLVED OXYGEN 6. What is the relationship between water temperature and dissolved oxygen? As the water gets hotter/warmer, the ability to hold oxygen decreases. 7. Explain why this relationship exists. This relationship exists because oxygen is essential to any living thing and we must make sure that the water temperatures do not rise, or else all of the fish and organisms in the ocean may die. 8. So, now explain why the fish in the aquarium (on the LabBench Web site) above the radiator died? The fish in the aquarium above the radiator died because the radiator was radiating heat which was causing the water in the tank to get warmer and the ability to hold oxygen was decreasing in the water. C. A MODEL OF PRODUCTIVITY AS A FUNCTION OF DEPTH IN A LAKE 9. Why do we take an initial reading of dissolved oxygen? What purpose does this serve in the experiment? We take an initial reading of dissolved oxygen because we want to model a situation where the photosynthesis drops off sharply with the increasing depth in the aquatic environment. 10. Click on the closer look magnifying glass on the initial bottle. Why does the animation show oxygen being diffusing out of the freshwater plants? What does this signify? The animation is showing the oxygen being diffused out of the freshwater plants because the O2 is being used up in the respiration process, but it is being given off in the photosynthesis process. 11. Click on the closer look magnifying glass on the foil- covered bottle. Why does the animation show oxygen diffusing into the freshwater plants? What does this signify?

The animation is showing the O2 being used up in the respiration process, but no photosynthesis occurring. 12. Click on the closer look magnifying glass on the 100% bottle under the light. Why does the animation show oxygen diffusing both into and out of the freshwater plants? What does this signify? In this model, it is showing the O2 being used up in the respiration process and the O2 also being released in the photosynthesis process. This signifies that the light is going through the bottle and photosynthesis is occurring. D. ANALYSIS OF RESULTS 13. Measuring Respiration: Remember that plants (producers) perform both photosynthesis and respiration. To measure the amount of respiration that is happening in the bottle, we measure the amount of dissolved oxygen in the initial sample and then the amount of oxygen in the bottle kept in the dark. As shown in the illustration below, you then subtract the amount of dissolved oxygen in the dark bottle from the amount of dissolved oxygen in the initial bottle to calculate the amount of oxygen consumed in respiration. I have added some possible measurements to help. Explain why this calculation works. This calculation works because in the online lab It explained to us what the equation was and here it is shown that 6mg-1mg=5mg 14. Now, in your own words, explain why this calculation works. This calculation works because there was a 10 mg increase in dissolved oxygen from photosynthesis, but then 5mg were lost from respiration and the two added together show a 15mg gross productivity. 15. Measuring Net Productivity: Remember net productivity is the amount of sugars and dissolved oxygen produced by the plants in an ecosystem once you subtract out what the producers have consumed in respiration. So we actually already calculated that in the last example; I just called it net photosynthesis. Explain why this calculation works. This calculation works because 16mg subtracted by 6mg equals 10 mg of dissolved oxygen. 16. Print out the completed calculation table from Sample Problem page of the LabBench Web site, fill in your predictions on the graph as well, and attach it to this lab to show me that you have completed it.

17. Print out the Lab Quiz and attach it to this lab to show me that you completed it. http://www.phschool.com/science/biology_place/labbench/lab12/quiz.html?radio1=d&radi o2=c&radio3=a&radio4=c&x=64&y=8 SUMMARY QUESTIONS 18. Would you expect the dissolved oxygen levels in water sampled from a stream entering a lake to be higher or lower than the dissolved oxygen levels in water sampled from the lake itself? Explain. I would expect the dissolved oxygen levels in water samples from a stream entering a lake to be higher because the waves and rapids increase the oxygen concentration. 19. Would you expect the dissolved oxygen levels in water sampled from a lake at 7AM to be higher or lower than the dissolved oxygen levels in water sampled at 5PM? Explain. I would expect the dissolved oxygen levels in the water sampled from a lake at 7AM to be higher than the dissolved oxygen levels in water sampled at 5PM because there is more mixing and turbulance early in the morning. 20. One of the major sources of water pollution is the runoff from fertilizer used in agriculture and on suburban lawns as well as golf courses. In particular, the nitrogen and phosphorus nutrients in the fertilizer creates problems in the streams and ponds it flows into. They cause algal blooms and eutrophication in lakes. a. Why do nitrogen and phosphorus promote a lot of plant/algal growth? Nitrogen and phosphorus promote a lot of plant and algal growth because they are both nutrients that support algal and plant growth. b. What is meant by algal bloom? (Look it up!)

Algal growth is when a lot of algae grows all at once. It is caused by too much nutrients. c. What problems do algal blooms cause in ponds & lakes? Why isnt a lot more producers a good thing? (Look it up!) Algal blooms cause dead zones. The dead algae suck up all of the oxygen in the water and the fish stop functioning and begin to die. d. What is meant by eutrophication? (Look it up!) Eutrophication is when there are excess nutrients in a body of water and it causes dense growth of plant life and animals begin to die from the lack of oxygen in the water. 21. At what depthshallow or deepwill there be more primary productivity in a pond or a lake? Explain. When the water is more shallow there will be more primary productivity because that is where all of the plant and algae are in the ponds or lakes. 22. In an experiment, why do we use the mean of class data to make conclusions rather than individual student group data? We use the mean of class data because that will give us the average and if we took indivisual datas from everybody, there is a high possibility that there is an error somewhere in the students data. It is better to take an average.

23. AP exam FRQ (2008). Consumers in aquatic ecosystems depend on producers for nutrition. a. Explain the difference between gross and net primary productivity. Gross productivity is where Photosynthetic production of organic compounds in the entire eco system. Net primary productivity is when Organic materials that are remaining after photosynthetic organisms in the eco system use these compounds for cellular respiration. b. Describe a method to determine net and gross primary productivity in a freshwater pond over a 24-hour period. A method used to determine net and gross primary productivity in a freshwater pond is to first measure the initial amount of oxygen in the air. After that you check the oxygen level every 12 hours. For one of the 12 hour periods, you put it in the light and for the second part in the dark. To find the gross primary productivity subtract the initial from the amount of oxygen after photosynthesis.

c. In an experiment, net primary productivity was measured, in the early spring, for water samples taken from different depths of a freshwater pond in a temperate deciduous forest. Explain the data presented by the graph, including a description of the relative rates of metabolic processes occurring at different depths of the pond.As the net productity gets lower, the deeper the water gets. So the net productivity gets less the deeper the water gets. d. Describe how the relationship between net primary productivity and depth would be expected to differ if new data were collected in mid-summer from the same pond. Explain your prediction. The data would be different if we collected new data in the mid summer from the same pond because the temperature of the water would be warmer which would cause the ability to hold oxygen decreases and the sunlight would make more productivity in the producers.