In this 40-minute extended task, students investigate the role of phytoplankton (microscopic, plant-like organisms that live near the ocean surface) in the Earth's carbon cycle. In addition, students analyze an authentic set of experimental data relating levels of iron and nutrients to the growth of phytoplankton, and use a resource library to research ocean locations where increased iron levels might affect phytoplankton growth.

Below are the questions, your answers, and the scoring criteria for each of the questions in this task. Use the navigation on the left to return to browsing the site or to take another task.

What is the primary source of carbon that is used by phytoplankton during photosynthesis?

A. Calcium carbonate shells of marine animals that have dissolved in salt water
B. Carbon chloride salt in water that has been carried by rivers to the ocean
C. Carbon dioxide from the atmosphere that has dissolved in ocean water
D. Hydrocarbon (sugar) molecules that are released into the water by phytoplankton

Your answer:  

Correct answer:  (C) Carbon dioxide from the atmosphere that has dissolved in ocean water.

Which form of carbon results from photosynthesis in phytoplankton?

A. Organic molecules such as sugars
B. Carbon dioxide in a gaseous form
C. Dissolved carbon dioxide in the form of carbonic acid
D. Non-organic carbon compounds such as calcium chloride

Your answer:

Correct answer: (A) Organic molecules such as sugars

“Upwelling” is the movement of water from the deep ocean toward the surface of the ocean.

Explain why “upwelling” is important for phytoplankton growth.

Your answer:

Sample Complete Student Response: 

Upwelling is important for phytoplankton because it brings nutrients that are stuck down on the oceans floor and provides important substances that help them develop.

Scoring Guide

Complete:
Student response provides a correct explanation that consists of two parts:

• Explains that upwelling brings nutrients (such as nitrates, phosphates, iron) from the ocean floor to the surface of the ocean.
• Explains that these nutrients are needed for phytoplankton to grow, develop, reproduce, live, survive.

Partial:
Student response addresses one part of a correct explanation.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Explain why phytoplankton growth occurs only near the surface of the ocean.

Your answer:

Sample Complete Student Response: It occurs only near the surface because the sun's rays cannot reach the depths of the ocean, and phytoplankton need sunlight to perform photosynthesis.

Scoring Guide

Complete:
Student response provides a correct explanation that consists of two parts:

• Explains that phytoplankton need sunlight for photosynthesis or provides a description linking chloroplasts (or chlorophyll) with sunlight.
• Explains that sunlight cannot penetrate deep into the ocean or states a comparison of sunlight between the ocean surface and the deep ocean.

Partial:
Student response addresses one part of a correct explanation.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Which graph best illustrates what you expect the experimental data to show? Click on the circle to the left of the graph that you selected.

A. Graph 1
B. Graph 2
C. Graph 3
D. Graph 4

Your answer:

Explain your answer.

Your answer:

Sample Complete Student Response:

Selection: (A)

Explanation: Iron is an essential nutrient for synthesis of chlorophyll in phytoplankton cells. If more iron is introduced to the cells then I think the density will increase.

Scoring Guide

Complete:
Student response selects (A) or (B) and provides a correct explanation that consists of three parts:

• Explains that iron is needed for the production of chlorophyll.
• Explains that phytoplankton contain chlorophyll.
• Explains that the more chlorophyll there is the greater the density of phytoplankton.

Essential:
Student response selects (A) or (B) and addresses two parts of a correct explanation.

OR

Student response selects (C) or (D) and provides a correct explanation that consists of the three parts that supports the selection of (A) or (B).

Partial:
Student response selects (A) or (B) and addresses one part of a correct explanation.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

What substance makes the contents of the bottles turn green?

Your answer:

Explain how this change in color is related to phytoplankton growth.

Your answer:

Describe how the bottle experiment data (graphs and table) support your explanation.

Your answer:

Sample Complete Student Response:

Substance: Chlorophyll

Explanation: The higher concentration of chlorophyll in the bottle implies that the phytoplankton, under the conditions of that bottle, produce chlorophyll more effectively, hence the greener water.

Description: The 5nmol water was the greenest, so at those conditions the phytoplankton were best at producing chlorophyll, whereas in the zero nmol bottle there was very little chlorophyll produced from lack of nutrients. The ten bottle, as I suggested earlier, tapered off in effectiveness of chlorophyll production.

Scoring Guide

Complete:
Student response provides a correct explanation that consists of three parts:

• States that the substance is chlorophyll.
• Explains that the change in color is due to an increase in phytoplankton population or an increase in chlorophyll concentration.
• Describes how the data from the table and/or graphs support the explanation.

Essential:
Student response provides an explanation that consists of two of the three components.

Partial:
Student response provides an explanation that consists of one of the three components.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

How do the data of the experiment for Location 1 compare with your earlier prediction of how phytoplankton density is related to increased amounts of iron added to samples of ocean water?

Use specific information from the data to support your answer.

Your answer:

Sample Complete Student Response: 

As the amount of iron increases in the ocean water, the more chlorophyll concentration will increase. Phytoplankton density increases as more iron is added to the ocean water. At 10 nmol Fe/kg, it had the most increase in Chlorophyll level as opposed the the others at 0, 1, and 5.

Scoring Guide

Complete:
Student response explains that the data for Location 1 agree with the prediction, (A) or (B), because the chlorophyll levels went up during the testing period, indicating that the phytoplankton were increasing in density. The response refers to specific data information in the graph and/or table.

OR

Student response explains that the data for Location 1 disagree or only partially agree with the prediction, (A), because the chlorophyll concentration decreases at the highest iron level at day 6. The response refers to specific data information in the graph and/or table.

OR

Student response explains that the data for Location 1 disagree or only partially agree with the prediction, (B), because there was no plateau. The response refers to specific data information in the graph and/or table.

OR

Student response explains that the data for Location 1 disagree with the prediction, (C) or (D), because the chlorophyll levels went up and did not remain at a steady state or went down. The response refers to specific data information in the graph and/or table.

Partial:
Student response explains that the data agreed with the prediction, (A) or (B), but the explanation is general without referring to specific data information in the graph and/or table.

OR

Student response explains that the data for Location 1 disagree or only partially agree with the prediction, (A) or (B), but the explanation is general without referring to specific data information in the graph and/or table.

OR

Student response explains that the data did not agree with the prediction, (C) or (D), but the explanation is general without referring to specific data information in the graph and/or table.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Which data did student select to view to answer Question 7?

Your action:

Scoring Guide

Complete:
Student selects data for Location 1 Chlorophyll to view and may or may not view other data.

Unsatisfactory/Incorrect:
Student selects data to view but not Location 1 Chlorophyll or does not select any data to view.

Consider the measurements of chlorophyll and nitrate levels for Location 3.

Which of the following conclusions is consistent with these measurements over the six-day period?

A. The concentration of chlorophyll increased and the concentration of nitrates decreased.
B. The concentration of chlorophyll decreased and the concentration of nitrates increased.
C. The concentrations of both chlorophyll and nitrates increased.
D. The concentrations of both chlorophyll and nitrates decreased.

Your answer:

Correct answer: (A) The concentration of chlorophyll increased and the concentration of nitrates decreased.

Which data did student select to view to answer Question 8?

Your action:

Scoring Guide

Complete:
Student selects data for Location 3 Chlorophyll and Location 3 Nitrates to view and may or may not view other data.

Partial:
Student selects data for Location 3 Chlorophyll but not for Location 3 Nitrates and may or may not view other data.

OR

Student selects data for Location 3 Nitrates but not for Location 3 Chlorophyll and may or may not view other data.

Unsatisfactory/Incorrect:
Student selects data to view but not Location 3 Chlorophyll and Location 3 Nitrates or does not select any data to view.

Consider the measurements of chlorophyll for Location 2.

Which statement about phytoplankton growth is consistent with these results?

A. The phytoplankton population increased significantly.
B. The phytoplankton population decreased significantly.
C. The phytoplankton population did not change significantly.
D. The phytoplankton population is not related to the chlorophyll concentration.

Your answer:

Correct answer: C

Which data did student select to view to answer Question 9?

Your action:

Scoring Guide

Complete:
Student selects data for Location 2 Chlorophyll to view and may or may not view other data.

Unsatisfactory/Incorrect:
Student selects data to view but not Location 2 Chlorophyll or does not select any data to view.

Consider the concentrations of nitrates and chlorophyll on Day 1 for Locations 1, 2, and 3.

How could the nitrate concentrations on Day 1 help explain the changes in chlorophyll concentrations and the effect of increasing iron levels over the six-day period at the three locations?

Your answer:

Sample Complete Student Response: 

To survive, chlorophyll needs nitrates for nourishment, and it makes sense that in Location 1, the experiment began with high levels of nitrates and then dwindled to a much lower level because they were being used. That occurs in Location 3 as well. In location 2, the nitrate level does not change significantly which makes sense because the chlorophyll level did not change significantly either.

Scoring Guide

Complete:
Student response provides a correct explanation that consists of three parts:

• Explains that nitrate concentrations on Day 1 in Location 1 are highest over the 6-day period. Location 1 shows substantial increases in chlorophyll levels so there are enough nitrates for phytoplankton growth.
• Explains that nitrate concentration is much lower in Location 2 than Locations 1 and 3. Chlorophyll levels at Location 2 remained the same over the 6-day period and may indicate that nitrates are limiting phytoplankton growth.
• Explains that nitrate concentrations on Day 1 in Location 3 are highest over the 6-day period. Location 3 shows substantial increases in chlorophyll levels so there are enough nitrates for phytoplankton growth.

Partial:
Student response addresses one or two parts of a correct explanation.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Which data did student select to view to answer Question 10?

Your action:

Scoring Guide

Complete:
Student selects data for all 6 data sets to view.

Partial:
Student selects data for all 3 Nitrate data sets but not all 3 Chlorophyll data sets.

OR

Student selects data for all 3 Chlorophyll data sets but not all 3 Nitrates data sets.

Unsatisfactory/Incorrect:
Student selects some data sets to view but not all Nitrates, all Chlorophyll, or both.

OR

Student does not select any data to view.

Scientists have hypothesized that adding iron to ocean water will increase phytoplankton growth. The data from which location best support this hypothesis?

A. Location 1
B. Location 2
C. Location 3

Your answer:

Explain your answer using specific information from the data.

Your answer:

Sample Complete Student Response: 

The data from Location 1 best supports this hypothesis because it demonstrates that as iron is added to ocean water, the phytoplankton grow causing the rise in chlorophyll concentration. As shown in the addition of 5 nmol Fe/kg, the level increased steadily from 0.52 micrograms chlorophyll/kg to 7.91 micrograms chlorophyll/kg and showed no sign of dropping.

Scoring Guide

Complete:
Student response indicates Location 1 or Location 3, and provides an explanation that refers to specific information from the data to support the scientists’ hypothesis that adding iron to ocean water will increase phytoplankton growth.

Partial:
Student response indicates Location 1 or Location 3 with a general, inadequate or incorrect explanation. For example, the data from Location 1 show that chlorophyll increased.

Unsatisfactory/Incorrect:
Student response indicates Location 2 with an inadequate or incorrect explanation.

Which data did student select to view to answer Question 11?

Your action:

Scoring Guide

Complete:
Student selects data for all 3 Chlorophyll data sets, but not all 3 Nitrate data sets.

Partial:
Student selects data for 2 of 3 Chlorophyll data sets, but not all 3 Nitrate data sets.

OR

Student selects data for 1 of 3 Chlorophyll data sets, but not all 3 Nitrate data sets.

Unsatisfactory/Incorrect:
Student selects some data sets to view but not all Nitrates, all Chlorophyll, or both.

OR

Student does not select any data to view.

Which location or locations (A, B, or C) shown on the map are High-Nutrient Low-Chlorophyll (HNLC) regions? (Check all that apply.)

A. Location A
B. Location B
C. Location C

Your answer(s):

Which resources were most helpful for determining the HNLC regions? (Check all that apply.)

Your answer(s):

Explain how you decided that the location or locations you selected are HNLC regions. You may use the notes you wrote in the “Notebook” during your research. Support your explanation with evidence from the resource library.

Your answer:

Sample Complete Student Response: Location C had the lowest chlorophyll levels as well as the highest phosphate and nitrate levels.

Part A: (C) Location C, Chlorophyll levels, Nitrate Levels, Phosphate Levels

Part B: Location C had the lowest chlorophyll levels as well as the highest phosphate levels.

Scoring Guide

This question was scored in two parts:

Part A: Indicates location(s) and information in Resource Library.

Part B: Explains the selections.

Part A

Complete:
Student response indicates Location A and/or Location C and selects the following three correct pieces of information from the resource library:

• Annual Average Surface Nitrate Concentration (Nitrate Levels)
• Annual Average Surface Phosphate Concentration (Phosphate Levels)
• Chlorophyll Levels in the Oceans (Chlorophyll Levels)
• There are no incorrect pieces of information selected

Essential:
Student response indicates Location A and/or Location C and selects two correct pieces of information from the resource library. There are no incorrect pieces of information selected.

Partial:
Student response indicates Location A and/or Location B and/or Location C and selects one correct piece of information from the resource library. There are no incorrect pieces of information selected.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Part B: Explanation

Complete:
Student response provides a correct explanation based on the selection of the location(s) and pieces of information from the resource library that consists of two parts:

• Indicates that selected location(s) has higher levels of nutrients (nitrates and phosphates) than those in the unselected location(s).
• Indicates that selected location(s) has lower chlorophyll levels than unselected location(s).

Partial:
Student response addresses one part of a correct explanation.

OR

Student response provides a general explanation about the location(s) selected and pieces of information from the resource library. Response does not include a comparison with the selected and unselected locations.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Composite Score:
Student response received one of four possible composite scores (Complete, Essential, Partial, Unsatisfactory/Incorrect) based on the student's combined performance on Parts A and B of the item. For example, a student response of Complete for Part A and Partial for Part B received a composite score of Essential.

Which location or locations (A, B, or C) shown on the map have the most carbon dioxide available? (Check all that apply.)

A) Location A

B) Location B

C) Location C

Your answer:

Which resources were most helpful for determining which location or locations have the most carbon dioxide available? (Check all that apply.)

Your answer:  

Explain how you decided that the location or locations you selected have the most carbon dioxide available? You may use the notes you wrote in the “Notebook” during your research. Support your explanation with evidence from the resource library.

Your answer:

Sample Complete Student Response: 

Colder water has higher CO2 levels available, location C is located near Antarctica so it is cold water.

Part A: Location C, Surface Temperature, Solubility/Temperature.

Part B: Colder water was higher CO2 levels available, location C is located near Antarctica so it is cold water.

Scoring Guide

The question was scored in two parts:

Part A: Indicates location(s) and information in Resource Library.

Part B: Explains the selections.

Part A

Complete:
Student response indicates Location B and Location C and selects the following two correct pieces of information from the resource library:

• Surface Ocean Water Temperature (Surface Temperatures)
• Solubility of CO2 in Water as a Function of Temperature (Solubility/Temperature)
• There are no incorrect pieces of information selected.

OR

Student response indicates Location B and selects the following three correct pieces of information from the resource library:

• Surface Ocean Water Temperature (Surface Temperatures)
• Solubility of CO2 in Water as a Function of Temperature (Solubility/Temperature)
• Surface Ocean Salinity (Surface Salinity)
• There are no incorrect pieces of information selected.

OR

Student response indicates Location C and selects the following two correct pieces of information from the resource library:

• Surface Ocean Water Temperature (Surface Temperatures)
• Solubility of CO2 in Water as a Function of Temperature (Solubility/Temperature)
• There are no incorrect pieces of information selected.

Essential:
Student response indicates Location B and Location C and selects one correct piece of information from the resource library. There are no incorrect pieces of information selected.

Student response indicates Location B and selects one or two correct pieces of information from the resource library. There are no incorrect pieces of information selected.

OR

Student response indicates Location C and selects one correct piece of information from the resource library. There are no incorrect pieces of information selected.

Partial:
Student response indicates all three locations (Locations A, B, and C), or Location A and Location B, or Location A and Location C. Response also selects at least one correct piece of information from the resource library. There are no incorrect pieces of information selected.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Part B

Complete:
Student response provides a correct explanation based on the selection of the location(s) and pieces of information from the resource library that consist of two parts:

• Indicates that selected location(s) has lower (cooler) water temperature than the unselected location(s).
• Indicates that solubility of carbon dioxide is higher at lower (cooler) temperature (or more carbon dioxide available at cooler temperature).

Partial:
Student response addresses one part of a correct explanation.

OR

Student response provides a general explanation about the location(s) selected and pieces of information chosen from the resource library. Response does not include a comparison with the selected and unselected locations.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Composite Score:
Student response received one of four possible composite scores (Complete, Essential, Partial, Unsatisfactory/Incorrect) based on the student's combined performance on Parts A and B of the item. For example, a student response of Complete for Part A and Partial for Part B received a composite score of Essential.

Which location (A, B, or C) shown on the map best meets the conditions needed to test the impact on phytoplankton growth of adding iron to the ocean? (Choose one location.)

A. Location A
B. Location B
C. Location C

Your answer:

Explain your choice.

Your answer:

Sample Complete Student Response: 

Location C has high nutrient levels, a high concentration of available carbon dioxide, and low levels of chlorophyll concentration. This would allow the results of adding iron to the water to have the greatest effect, and therefore create the best results.

Scoring Guide

Complete:
Student response selects Location C and provides a correct explanation that consists of three parts:

• Explains that location C has a high level of nutrients (nitrates and phosphates).
• Explains that location C has a low level of chlorophyll.
• Explains that location C has more carbon dioxide available for phytoplankton growth.

Partial:
Student response selects Location C and addresses one or two parts of a correct explanation.

OR

Student response selects Location A and explains that Location A has a high level of nutrients and/or a low level of chlorophyll.

OR

Student response selects Location B and explains that Location B has a high concentration of carbon dioxide.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

Scientists anticipate that adding iron to the ocean will have effects other than potentially increasing the growth of phytoplankton.

Describe one possible effect on the ocean ecosystem that should be investigated in order to understand more fully the impact of adding iron to ocean.

Your answer:

Sample Complete Student Response: 

The fish and other complex animals should be monitored to see how increased amounts of iron affect their bodily systems and to ensure that they will not be harmed by the increase.

Scoring Guide

Complete:
Student response describes a plausible effect on the ocean ecosystem and an investigation to understand more fully the impact of adding iron to the ocean.

Complete description consists of two parts:

• Describes a plausible effect on the ocean ecosystem.
• Describes a plausible investigation to study the effect stated in part (1).

For example:

• Decrease populations of other ocean organisms because iron may be toxic to these organisms.
• Measure/monitor population changes to ocean organisms.
• Increase populations of other ocean organisms because adding more iron results in more phytoplankton for animals who feed on phytoplankton.
• Measure/monitor population changes to phytoplankton and predators for phytoplankton.

Partial:
Student response addresses one part of a correct description.

OR

Student response provides a general description. For example: the iron may hurt other organisms.

Unsatisfactory/Incorrect:
Student response is inadequate or incorrect.

SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Science Assessment.