This lesson incorporates techniques and experimental designs used by researchers during the Southern Ocean Diatoms PolarTREC expedition and during post-expedition laboratory analysis. This guided inquiry lesson provides students the opportunity to explore photosynthesis and primary productivity using techniques to measure chlorophyll levels.
SWBAT: 1. Use models to predict chlorophyll levels in the global oceans 2. Identify variables that may influence the process photosynthesis in autotrophs 3. Develop a research question and design a controlled experiment to measure a variable’s effect on chlorophyll levels in plankton samples 4. Interpret chlorophyll data as a means of drawing conclusions on photosynthesis in plankton samples 5. Analyze data sets to report findings 6. Evaluate experimental designs
List or write brief paragraphs describing the steps needed to complete the lesson. Also, list or include a paragraph describing the content that must be covered prior to the start of the lesson.
Using models of chlorophyll concentrations in ocean regions, students will brainstorm possible reasons for chlorophyll levels in various locations. Teacher facilitated discussion leads to a list of possible variables to explore in individual or a classroom experiments. These incubation experiments use plankton samples or macro algae samples to test for the effect of a given variable on the chlorophyll levels. Students measure chlorophyll levels over the course of the incubation using a spectrophotometer. The chlorophyll levels will serve as a proxy for photosynthesis.
Prior to the lesson, students should have knowledge of the difference between autotrophs and heterotrophs. Food web ecology knowledge is not required, but this lesson could be used as a conclusion to a unit on food webs and nutrient sampling, or as an activity to introduce the idea. Knowledge of designing an experiment is necessary. If this lesson is used as the first inquiry activity of the year, or early in the year, scaffolding of the experimental design is suggested. This lesson can also be presented as a confirmation or structured inquiry activity by creating specific instructions related to the experimental design and/or providing table and graph templates for the activity.
Project chlorophyll map and ask students to record at least two observations about the map.
The guiding question is displayed in the classroom (and is also located on the student worksheet).
1. What factors influence the chlorophyll levels in phytoplankton samples?
2. Sentence prompt (if needed): How does ________________ affect the chlorophyll level in phytoplankton samples?
As students develop their investigations, teacher can prompt students with questions to help facilitate the process:
Chlorophyll extraction protocol
While the incubation experiments will be developed by the student groups, all groups should use the following protocol to measure chlorophyll levels to produce results.
Daily Check In
Before students leave the classroom, each student must complete an Exit Ticket to summarize the day’s events, ask for clarification on questions or issue related to the experiment and provide a plan for the next day. Exit tickets should be returned the following class period with comments/suggestions from the teacher.
To finish the investigations, students will submit a lab report to communicate findings and analyze results. As students begin to work on their report, the teacher can lead the group in a “speed-dating” activity. Students arrange their desks in long rows so that pairs of desks face each other. Students seated in one row will continue to move, while the students in the other row stay seated. As student move seats and sit across from their new “date”, they take turns describing their experiment and discussing their outcomes. Students should have approximately 5 “dates” and each date should be about 8-10 minutes long. This gives both students time to explain and ask questions. As the students continue to practice communicating their results, they refine their conclusions. Peers also help by asking for clarification and pointing out areas of improvement.
Students will submit a lab report (see rubric) as a completion of this investigation.
Southern Ocean Diatoms PolarTREC journals: https://www.polartrec.com/expeditions/southern-ocean-diatoms
A Spectrophotometer: A demo and practice experiment by BioNetwork
U.S. Global Change Research Program http://www.globalchange.gov/browse/indicators/indicator-ocean-chlorophyl...
NASA Earth Observatory Global Chlorophyll Map http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MY1DMM_CHLORA
Cara Pekarcik – North Quincy High School/PolarTREC (cpekarcik [at] comcast.net)
Alexa R. Sterling – PhD candidate; University of Rhode Island
LS2. B Cycles of Matter and Energy Transfer in Ecosystems (9-10): Photosynthesis captures energy in sunlight and stores it in chemical bonds of matter. Most organisms rely on cellular respiration to release energy in these bonds to power life processes. About 90% of available energy is lost from one trophic level to the next, resulting in fewer organisms at higher levels. At each link in an ecosystem, elements are combined in different ways and matter and energy are conserved. Photosynthesis, cellular respiration and decomposition are key components of the global carbon cycle.
HS-LS2-2. Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.
MS-LS1-6. Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.