A. Key Concepts
a. Temperature: As water becomes warmer, its ability to hold oxygen decreases.
b. Light & Photosynthesis: In bright light, aquatic plants are able to produce more oxygen.
c. Decomposition & Respiration: As organic material decays, microbial processes consume oxygen.
d. Mixing & Turbulence: Wave action, waterfalls, and rapids all aerate water and increase the oxygen concentration.
e. Salinity: As water becomes more salty, its ability to hold oxygen decreases.
2. Productivity: Define each of these terms in your own words.
a. Primary productivity: Is a term used to describe the rate at which plants and other photosynthetic organisms produce organic compounds in an ecosystem.
b. Gross productivity: the entire photosynthetic production of organic compounds in an ecosystem.
c. Net productivity: the organic materials that remain after photosynthetic organisms in the ecosystem have used some of these compounds for their cellular energy needs (cellular respiration).
3. Why do we use dissolved oxygen as a measure of productivity? Does productivity include more than
oxygen?
Since oxygen is one of the most easily measured products of both photosynthesis and respiration, a good way to gauge primary productivity in an aquatic ecosystem is to measure dissolved oxygen.
4. 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 algae/freshwater plants in the light enable us to measure gross productivity because we can measure 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 enable us to measure respiration because we can measure oxygen after respiration.
c. How does subtracting the two enable us to indirectly measure net productivity?
To enable us to indirectly measure net productivity by Subtracting respiration from photosynthesis enables us to measure the amount of oxygen left.
5. What are the three ways that primary productivity can be measured? Highlight the way will be
used in this lab?.
a. We can measure net productivity directly by measuring oxygen production in the light, when photosynthesis is occurring.
b. We can also measure respiration without photosynthesis by measuring O2 consumption in the dark, when photosynthesis does not occur.
c.Since net productivity = gross productivity – respiration, we can calculate gross productivity.
B. LAB PART 1: EFFECT OF TEMPERATURE ON DISSOLVED OXYGEN
6. What is the relationship between water temperature and dissolved oxygen?
The relationship between water and temperature and dissolved oxygen is when water becomes warmer, its ability to hold oxygen decreases.
7. Explain why this relationship exists.
The Oxygen in essential for cellular respiration in most organisms such as, aquatic environment, oxygen availability is influenced by a variety of chemical and physical factors.
8. So, now explain why the fish in the aquarium (on the Lab-bench Web site) above the radiator
died?
The fish in the aquarium above the radiator died because the aquarium's water temperature got warmer, losing its ability to hold oxygen, killing the fish.
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?
To find the amount of light available for photosynthesis drops off sharply with increasing depth in an 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?
When the oxygen is used up in respiration then the oxygen adds more off in photosynthesis.
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?
Oxygen is used up in respiration then their are no photosynthesis occurs.
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?
Oxygen is used up in respiration and when the oxygen is given off in photosynthesis.
a. Temperature: As water becomes warmer, its ability to hold oxygen decreases.
b. Light & Photosynthesis: In bright light, aquatic plants are able to produce more oxygen.
c. Decomposition & Respiration: As organic material decays, microbial processes consume oxygen.
d. Mixing & Turbulence: Wave action, waterfalls, and rapids all aerate water and increase the oxygen concentration.
e. Salinity: As water becomes more salty, its ability to hold oxygen decreases.
2. Productivity: Define each of these terms in your own words.
a. Primary productivity: Is a term used to describe the rate at which plants and other photosynthetic organisms produce organic compounds in an ecosystem.
b. Gross productivity: the entire photosynthetic production of organic compounds in an ecosystem.
c. Net productivity: the organic materials that remain after photosynthetic organisms in the ecosystem have used some of these compounds for their cellular energy needs (cellular respiration).
3. Why do we use dissolved oxygen as a measure of productivity? Does productivity include more than
oxygen?
Since oxygen is one of the most easily measured products of both photosynthesis and respiration, a good way to gauge primary productivity in an aquatic ecosystem is to measure dissolved oxygen.
4. 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 algae/freshwater plants in the light enable us to measure gross productivity because we can measure 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 enable us to measure respiration because we can measure oxygen after respiration.
c. How does subtracting the two enable us to indirectly measure net productivity?
To enable us to indirectly measure net productivity by Subtracting respiration from photosynthesis enables us to measure the amount of oxygen left.
5. What are the three ways that primary productivity can be measured? Highlight the way will be
used in this lab?.
a. We can measure net productivity directly by measuring oxygen production in the light, when photosynthesis is occurring.
b. We can also measure respiration without photosynthesis by measuring O2 consumption in the dark, when photosynthesis does not occur.
c.Since net productivity = gross productivity – respiration, we can calculate gross productivity.
B. LAB PART 1: EFFECT OF TEMPERATURE ON DISSOLVED OXYGEN
6. What is the relationship between water temperature and dissolved oxygen?
The relationship between water and temperature and dissolved oxygen is when water becomes warmer, its ability to hold oxygen decreases.
7. Explain why this relationship exists.
The Oxygen in essential for cellular respiration in most organisms such as, aquatic environment, oxygen availability is influenced by a variety of chemical and physical factors.
8. So, now explain why the fish in the aquarium (on the Lab-bench Web site) above the radiator
died?
The fish in the aquarium above the radiator died because the aquarium's water temperature got warmer, losing its ability to hold oxygen, killing the fish.
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?
To find the amount of light available for photosynthesis drops off sharply with increasing depth in an 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?
When the oxygen is used up in respiration then the oxygen adds more off in photosynthesis.
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?
Oxygen is used up in respiration then their are no photosynthesis occurs.
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?
Oxygen is used up in respiration and when the oxygen is given off in photosynthesis.
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.
The calculation works because of the 6 mg dissolved oxygen subtract for 1 mg dissolved oxygen equals 5 mg dissolved oxygen.
14. Measuring Gross Productivity: Remember gross productivity is the total amount of sugars
and oxygen produced by the plants in an ecosystem. I don’t like how this Web site shows you how to calculate gross productivity. The equation is correct, but it is a short cut, so it makes it more difficult to understand. So follow me with the illustrations and the possible measurements below.
and oxygen produced by the plants in an ecosystem. I don’t like how this Web site shows you how to calculate gross productivity. The equation is correct, but it is a short cut, so it makes it more difficult to understand. So follow me with the illustrations and the possible measurements below.
So the illustration shows us there was 10mg increase in dissolved oxygen in the jar as a result of
photosynthesis in the last 24 hours and there was 5mg decrease in dissolved oxygen in the jar
as a result of respiration in the last 24 hours. So the gross productivity (the full photosynthetic
production in this ecosystem) of the algae in the bottle is the 5mg dissolved oxygen lost to
respiration added back to the 10 mg dissolved oxygen accumulated in the bottle kept in the light.
So what the algae really produced in the bottle was a total of 15mg dissolved oxygen, it just lost
5mg to respiration. And remember, the oxygen is an indirect measurement of the sugars
produced in photosynthesis and lost in respiration.
photosynthesis in the last 24 hours and there was 5mg decrease in dissolved oxygen in the jar
as a result of respiration in the last 24 hours. So the gross productivity (the full photosynthetic
production in this ecosystem) of the algae in the bottle is the 5mg dissolved oxygen lost to
respiration added back to the 10 mg dissolved oxygen accumulated in the bottle kept in the light.
So what the algae really produced in the bottle was a total of 15mg dissolved oxygen, it just lost
5mg to respiration. And remember, the oxygen is an indirect measurement of the sugars
produced in photosynthesis and lost in respiration.
The 10 mg oxygen gained from photosynthesis and add it up to 5 mg oxygen lost to respiration so that equals to 15 mg oxygen as 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.
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.
The light oxygen has 16 mg dissolved oxygen and then subtracted to 6 mg dissolved oxygen so that equals to 10 mg dissolved oxygen by net productivity.
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.
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 expected that the level in water sampled from the stream to lake is going to be lower than the lake because most of the stream water is going to be warmer and if that mixed with the lake water then the temperature of the lake water is going to be warm as well.
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 expected that the oxygen levels in water sampled from a lake at 7 am would be higher than 5 pm because the temperature at in the morning would be colder and when it hits 5 pm the water becomes warmer causes of less oxygen.
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?
Both are considered limiting factors in vegetative growth. Both are two of the main components (potassium is the third) found in fertilizers.
b. What is meant by algal bloom? (Look it up!)
Is the visible appearance of millions of tiny plant-like organisms in the water. These tiny algae, or phytoplankton are present all year.
c. What problems do algal blooms cause in ponds & lakes? Why isn’t a lot more producers a good thing?
(Look it up!)
This creates problems for any underwater vegetation because the sunlight it needs to grow is being blocked out by all of the algae growing above it.
d. What is meant by eutrophication? (Look it up!)
Excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.
21. At what depth—shallow or deep—will there be more primary productivity in a pond or a lake? Explain.
All production happens at the meeting of two phases. Water and air, water and dirt, leaf and sunlight, etc. I don't know what is considered "primary" but it has to be near the surface.
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 to make the conclusion rather than individual student group data because to find average amount will help get more exact data for our conclusions.
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 amount of oxygen use for photosynthesis. Net productivity is amount of oxygen used in respiration and released in photosynthesis.
b. Describe a method to determine net and gross primary productivity in a freshwater pond over a 24-
hour period.
The amount of oxygen in an ecosystem.
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.
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 expected that the level in water sampled from the stream to lake is going to be lower than the lake because most of the stream water is going to be warmer and if that mixed with the lake water then the temperature of the lake water is going to be warm as well.
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 expected that the oxygen levels in water sampled from a lake at 7 am would be higher than 5 pm because the temperature at in the morning would be colder and when it hits 5 pm the water becomes warmer causes of less oxygen.
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?
Both are considered limiting factors in vegetative growth. Both are two of the main components (potassium is the third) found in fertilizers.
b. What is meant by algal bloom? (Look it up!)
Is the visible appearance of millions of tiny plant-like organisms in the water. These tiny algae, or phytoplankton are present all year.
c. What problems do algal blooms cause in ponds & lakes? Why isn’t a lot more producers a good thing?
(Look it up!)
This creates problems for any underwater vegetation because the sunlight it needs to grow is being blocked out by all of the algae growing above it.
d. What is meant by eutrophication? (Look it up!)
Excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.
21. At what depth—shallow or deep—will there be more primary productivity in a pond or a lake? Explain.
All production happens at the meeting of two phases. Water and air, water and dirt, leaf and sunlight, etc. I don't know what is considered "primary" but it has to be near the surface.
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 to make the conclusion rather than individual student group data because to find average amount will help get more exact data for our conclusions.
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 amount of oxygen use for photosynthesis. Net productivity is amount of oxygen used in respiration and released in photosynthesis.
b. Describe a method to determine net and gross primary productivity in a freshwater pond over a 24-
hour period.
The amount of oxygen in an ecosystem.
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.
The graph shows that the depth water increases the primary productivity decreases. When it is 30 meters deep the primary productivity starts to go down
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 relationship between net primary productivity and depth would be expected to differ if new data were collected in mid-summer from the same pond because then the net primary will increasing and causing the depth water will do the same thing.
metabolic processes occurring at different depths of the pond.
The graph shows that the depth water increases the primary productivity decreases. When it is 30 meters deep the primary productivity starts to go down
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 relationship between net primary productivity and depth would be expected to differ if new data were collected in mid-summer from the same pond because then the net primary will increasing and causing the depth water will do the same thing.