Lesson 2 – Who’s who in the photosynthetic world from macro to microscale

Description: Students have an opportunity to use microscopes and then delve into what is unseen using scientifically accurate diagrams showing the special structures that the tiniest and most abundant Prochlorococcus use to support life.

Prerequisites and Considerations: Let your students’ background guide how much time you spend on the activities within this lesson. For instance, if your students already understand energy flow basics including photosynthesis and cellular respiration, certain parts of this lesson can be skipped. Other things to consider are their familiarity with cell structures and functions in eukaryotic plant cells. Since Prochlorococcus are prokaryotes, they are a fairly simple cell to use as an introduction to prokaryotes or as review, with thylakoid membranes containing photosystem and respiratory complexes.


See the NGSS listed as buttons in the left-hand menu and in the chart below. The buttons on the left are grouped to show the integrated three-dimensional nature of our lessons and modules. When applicable, if NGSS are addressed outside of bundles, they are listed separately. Connections to 21st Century Learning Skills and other published standards are also included in the chart below. In addition, for this lesson, here is a breakdown of:

What Students Learn
  • There are many different types of photosynthesizers.
  • Photosynthetic organisms, being able to capture light energy and transform it into chemical energy are recognizable by examining their internal structures and function.
  • Prochlorococcus is the world’s smallest and most numerous oxygenic photosynthesizer. What’s the scale, anatomy, organelle function, and life of Prochlorococcus at nano-scale?
  • Phytoplankton share common structures/metabolism with other photosynthesizers.
  • How Prochlorococcus was discovered and its role in oceanic / global productivity.
What Students Do
  • Card sort of 26 autotrophs and heterotrophs to stimulate student thinking on identification of photosynthesizing organisms.
  • Observe fresh or seawater phytoplankton with microscope.
  • Learn Prochlorococcus cell structure and functions. Relate scale of cell to light waves, virus, and eukaryotic chloroplast.
  • (optional) Review photosynthesis by working through a ‘webquest’ (1 x 50 min)
  • View video + teacher led discussion on Prochlorococcus place in oceanic / global productivity.
  • Add to student ongoing unit summary – What’s in ‘A Drop of Seawater’
Aligned Washington State Standards (Next Generation Science Standards)
Performance expectation(s): HS-LS2-3 Construct and revise an explanation based on evidence for the cycling of matter and flow of energy in aerobic […] conditions; HS-LS1-5 Organization for Matter and Energy Flow in Organisms—Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy; MS-LS2-5 Ecosystems Interactions, Energy, and Dynamics

The bundle of performance expectations above focuses on the following elements from the K-12 Science Education Framework:

Highlighted Science and Engineering Practice(s)

Highlighted Disciplinary Core Idea(s)

Highlighted Crosscutting Concept(s)

SEP-2: Developing and Using Models

SEP-6: Constructing Explanations

HS-LS2.B: Cycles of Matter and Energy Transfer in Ecosystems

HS-LS1.C: Organization for Matter and Entergy Flow in Organisms

MS-LS2.C: Ecosystem Dynamics, Functioning, and Resilience

CCC-3: Scale, Proportion and Quantity

CCC-4: Systems and System Models

CCC-5: Energy and Matter

CCC-6: Structure and Function

CCC-7: Stability and Change

Common Core: E2, E4, E5, E6* (*using microscope technology)

CTE – #’s 4, 12

21st Century Skills – #’s 1, 2 (Environmental literacy, Grade level dependent)



Who’s who in the photosynthetic world? How do we know who photosynthesizes? This lesson reviews what it takes to be a photosynthesizer, using light as an energy source while producing oxygen as a waste product.* Compare well known photosynthesizers and the invisible cells that can carry out all the functions of life from macro to microscale. Identify phytoplankton and discover Prochlorococcus. Through this students are introduced to phytoplankton, the basis of the oceanic food web. Students have an opportunity to use microscopes and then delve into what is unseen using scientifically accurate diagrams showing the special structures that the tiniest and most abundant Prochlorococcus use to support life. In Lesson 3 students will focus on an introduction to the technological tools that are used to observe and measure the photosynthesizers we cannot see.

(*Note: Standard high school study of photosynthesis is not supplanted by these lessons. This lesson is easily taught concurrently or after standard photosynthesis labs. *Optional Extension Labs are available as a review of photosynthesis with emphasis on oxygen production.)

Overview of Instructional Activities:

Lesson What students learn What students do
Part 1: Photosynthesizer or Not? (40 min) Small group activity Photosynthesizer or Not? Cards (or Photosynthesizer or Not? ppt.)
Photosynthesis or Not student worksheet)Photosynthesis webquest review with Webquest_review – Teacher key (+50 min)(optional) – Photosynthesis (4) Extension Labs (+50 min each)(optional) See instructions for virtual and hybrid options
– There are many different types of photosynthesizers.

– Chlorophyll is the common feature of all oxygenic photosynthesizers capturing light and producing sugars and releasing oxygen gas.

– Card sort of autotrophs and heterotrophs to Identify characteristics of the organisms who photosynthesize

-(optional) Review photosynthesis through a ‘webquest’

-(optional) Choose from four Photosynthesis Labs (see Extensions tab)

Part 2: Microscope Observations of Phytoplankton (30-60 min)—Go to Phytoplankton Spectrophotometer Lab Part 1A -Where do phytoplankton live? Observing microscopic photosynthesizers in their environment.

– Phytoplankton are basis of oceanic planktonic food web.

– Observe variety of phytoplankton using microscopes to see size and shapes of organisms in the wild
Part 3: Scale and anatomy (30 min) Pro Anatomy Slideshow with Pro Anatomy and scale_worksheet Prochlorococcus and other phytoplankton share common structures/metabolism with other cells/photosynthesizers.

– Chlorophyll and other pigments absorb light to split water, releasing oxygen and producing ATP.

Prochlorococcus scale, anatomy, organelle function, and life at nano-scale.

– Learn structures and functions found in Prochlorococcus cells. Compare to known structure of photosynthetic eukaryotic cells.

– Compare the scale of Prochlorococcus to viruses, light waves, eukaryotic chloroplast.

Part 4: Video clip(15 min) Video: Meet the obscure microbe that influences climate, ocean ecosystems, and perhaps even evolution. Article – may need teachers to lead. Amazing facts about Earth’s smallest oxygenic photosynthesizer, responsible for 20% of oceanic production and 10% of atmospheric oxygen production. – Learn from video short (3.5 min) and take notes summarizing Parts 1 – 3 to apply to Prochlorococcus.
Part 5: Assessment (20 min)
How will I know they know…– Formative assessment through worksheets and work listed above Or use PBL reflections ‘Know /Need to know’ and PBL summary table to add to ‘Drop of Seawater’ projects
– What do I know now?

– [PBL option] Making connections and seeing relationships in Drop of Seawater. What questions do I still need/want to ask?

– Draw a sketch from memory of Pro cell, virus, and extracellular vesicle; include how cell functions with captions about photosystem.

– [PBL option] Conduct reflection and ask new questions by adding to ‘Drop of Seawater’ art project.


Part 1: Photosynthesizer or Not? Card Sort (40 min)

Introduction: If students already have a working knowledge of photosynthesis, move directly to the Photosynthesizer or Not? Cards (Google Doc | Word Doc) sort activity. In groups of 2-4 students sort 26 cards to explore the characteristics of photosynthesizers. The activity both reviews photosynthesis and reveals that not all photosynthesizers are green and plant like. And, in fact, some are so small they are invisible. The Card sort activity includes the microorganisms that are used in subsequent lessons. (This also can be done as a class, using the quick Photosynthesizer or Not?ppt (Google Slides | PowerPoint). This can also be done online with students by having them drag and drop photos into categories using this Slide. They will need to work outside of the Presenter Mode function.)

Before Class:


Activity Sequence:

Step 1: Each group of 2-4 students works together to sort the Photosynthesizer or Not? Cards into 2 sets: “photosynthesizers” and “non-photosynthesizers.” As they organize the cards, have them write their thinking in the Photosynthesis or not? Worksheet.

Step 2: After groups finish sorting, have groups share ‘who’ they put in each group. Allow students to ask questions or challenge the placement of an organism. Keep visual notes on the overhead, to track and revisit their ideas later. Make sure to have them talk about a wide variety of the cards, including the Prochlorococcus (Pro).

Step 3: Next, ask and discuss the value and challenge to sorting organisms based on physical characteristics. (For example, coloration or size of an organism may make it difficult to decide if it is a photosynthesizer or not. Classifying based on physical or external characteristics ignores everything going on internally. To classify organisms based on a functional trait, an understanding of metabolism and/or DNA comes in.)

Step 4: Summarize the discussion and be sure to emphasize that chlorophyll is the common feature of all of the photosynthesizers (autotrophs) shown.

Final Step: Move on to Part 2


If students need more review use this (optional) Photosynthesis webquest review before or after the Photosynthesizer or Not? Card sorting activity, as a formative assessment. Use the Webquest Teacher key to review as a class, to build conceptual knowledge. For more photosynthesis review Labs see Extensions tab.*


Part 2: Microscopic Observation of Phytoplankton (30–60 min)


Purpose: Since the key idea for this unit is the Invisible Forest, and in particular Prochlorococcus (Pro) as the world’s most common form of phytoplankton; it would make sense to have students observe plankton for themselves, even though Pro is too small for student microscopes to resolve. The phytoplankton they do see will be tiny, so students can make the connection there are even smaller photosynthesizers in the water – and they make a huge contribution to global productivity.

Before class: Prepare microscopes and slides for groups of 3-4. Read part 1 of Teacher Lesson Plan / Background Phytoplankton Spectrophotometer Lab (Google Doc | Word Doc) Part 1A. *The best plankton are gathered in late summer/late spring (start of school year/end of school year) from local fresh or saltwater source or drawn from a saltwater tank cultured throughout the year.


A: Microscope observations of plankton (30–50 min)— Students prepare slides with a drop of water, (may be fresh or seawater plankton culture) observe plankton and make a sketch in lab notebook.

B: Show video Ted talk “The Secret Life of Plankton” (6 min) —This would be a great segue between plankton microscope observations and the introduction of Pro as world’s most numerous phytoplankton.


Part 3: Pro Anatomy Slide Show (30 min)


Introduction: Use this part of the lesson to explore Prochlorococcus (Pro) scale, anatomy, organelle function, and life at nano-scale. The Pro Anatomy Slideshow (Google Slide | PowerPoint) is an interactive illustration to learn about the internal workings of Prochlorococcus (phytoplankton). Use as an oral review of Pro cell functions, that shows off the unique structures of the smallest of photosynthesizers and their scale next to other plankton. The slideshow also has information about Pelagibacter a heterotroph in a somewhat symbiotic relationship with Pro.

Before Class: Download Pro Anatomy Slideshow (Google Slide | PowerPoint) (preview sequence and teacher notes); Print 1 per student on TWO pieces of Paper Pro Anatomy and scale_worksheet (Google Doc | Word Doc); Pull up on computer: video Meet the obscure microbe that influences climate, ocean ecosystems, and perhaps even evolution and link to Learn Genetics Size and Scale

Activity sequence:

Step 1: Hand out the Pro Anatomy and Scale Worksheet (Google Doc | Word Doc) (here it is in PDF for better formatting). Use teacher notes in Pro Anatomy Slideshow (Google Slide | PowerPoint) to present the cell structures and functions to students. Help apply their knowledge of photosynthesis in eukaryotes to understanding photosynthesis in prokaryotes, specifically Prochlorococcus (Pro).

Step 2: Students annotate Pro Anatomy and Scale Worksheet (in PDF) to tracing cell parts and function. Depending on your students, you may want to hand out pages 1 and 2 together or separate. This depends on how much scaffolding your student need. In either case, prompt your students to think of light waves interacting with chlorophyll in thylakoid membranes. [CCC Systems] [CCC Energy and Matter]. Compare the size and scale of Pro and its environment with wavelength of blue light it absorbs in photosynthesis (wavelength on worksheet is to scale).[CCC Systems] [CCC Energy and Matter].

Step 2b: For more on scale go to University of Utah Learn Genetics for sliding scale with powers of 10. Use Learn Genetics Size and Scale sliding bar to show relative sizes of cells and molecules. This Scale of the Universe YouTube video also does a terrific job showing providing perspective.

Step 3: Present video short (3.5 min) Meet the obscure microbe that influences climate, ocean ecosystems, and perhaps even evolution (to play click on image at start of Science Magazine article).

Step 4: Lead students through a discussion of Prochlorococcus place in oceanic/global productivity to bring content of Pro anatomy and ideas in slideshow together.

Step 5: Record current estimates of Pro, Pelagibacter, and virus load in their ‘Drop of Seawater’ diagram to loop their learning and reenforce scale.

Final step: Understand – Describe/Explain (keep it simple)

    • Ask students to do a rough sketch from memory of Pro cell, virus, and extracellular vesicle; and how cell functions. Write out general function of photosystem to add to the diagram. OR….
    • [PBL option] Revise and add any new information you’ve learned during this lesson to your ‘Drop of Seawater.’ Use the PBL summary table to help formulate ideas, before adding them to the diagram.


*Additional Photosynthesis Review: (Go to Extensions tab) choose among these optional extensions to give students practice in lab skills and build stronger conceptual knowledge of the process of photosynthesis:

  • Photosynthesis Extension Labs (4) —each of the four labs is adapted to focus on oxygen production. Each Lab contains materials and procedures, including technology applications with Vernier probes.
    • These experiments aim to provide context for the role chlorophyll plays in capturing and transforming light into usable energy, while producing oxygen as a waste product. Develops understanding of the role photosynthetic organisms play in providing oxygen for heterotrophs.
    • Photosynthesis Review webquest


How will I know they know?

  • Use the Photosynthesis Review Webquest as a formative assessment
  • Listening in during Photosynthesizer or Not? Card sort group-activity is a great formative assessment opportunity to see how much they recall of photosynthesis and their familiarity with phytoplankton
  • Review their Pro Anatomy and Scale Worksheet (in PDF) from the lesson to see they are making connections and comparisons accurately
  • Review student (PBL option) ‘Drop of Seawater’ summary table and revisions to ‘Drop of Seawater’ to see if new relationships are explained and shown, and any new information reflects content covered in this lesson.
  • (optional) Photosynthesis Extension labs have analysis questions that can be used to assess student understanding of photosynthesis. See the Extensions Tab for more information.


Part 1 – Photosynthesizers or Not?

Parts 2-5 – Phytoplankton: Microscopic Observations; Pro Anatomy & Scale


Additional Photosynthesis review options:


Science Friday article on Pro discovery – The Invisible Forest Under the Sea
Penny Chisholm’s TED talk on Prochlorococcus and discovery

Also, please see the Contributors Page (also listed in the left-hand menu) for a list of all of the teachers, scientists and students who have contributed to this module.