Floating Spinach: Investigating Photosynthesis

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Objective

SWBAT: 1) Understand that the main way solar energy is captured and stored on Earth is through the complex chemical process known as photosynthesis. 2) Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy. 3) Explain that the changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system.

Big Idea

Photosynthesis can be easily modeled and investigated through the use of spinach leaf disks, carbonated water, and light.

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment".

The lesson-planning document that I uploaded to this section is a comprehensive overview of how I approach lesson planning. This template includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these.

At the end of this particular lesson, students will be able to:

1. Understand that the main way that solar energy is captured and stored on Earth is through the complex chemical process known as photosynthesis. (PS3.D)

2. Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy. (HS-LS1-5)

3. Explain that the changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system. (HS-LS1-5, LS1-5)

I hope you get some value from my work! Please find the more intricate details of this lesson plan there.

Anticipatory Set ("Hook")

5 minutes

Teaching Challenge (Practice): How can I develop my students' ability to apply unifying ideas to make connections across science content? The answer, in part, is explained next.

"Parking Lot": “Enzymes are (+/-) affected by…"

At this point in the unit, students will have learned about enzymes, their structure and function, and what factors affect them. In my setting, I keep miscellaneous supplies for each of my eight teams in small plastic tubs that are kept at these team tables. Among these are colored pencils, rulers, whiteboard markers, and Post-It notes. Using one Post-It note each, students should reflect on what they learned about enzyme action from the Bromelin Lab completed earlier and jot down several things that they know will impair or improve an enzyme's function.

They should be able to recall some or all of these factors that affect the catalytic ability of enzymes:

  • temperature (extremely cold or hot)
  • salinity (extremely low or high levels)
  • pH (extremely low or high)

These Post-It notes can be affixed to a bulletin board or other surface in the classroom and should be a really quick collection of student thoughts. I have a designated bulletin board space for this purpose since I use this strategy frequently enough. I will then quickly read these aloud to emphasize the common answers and to rectify (if need be) any incorrect/incomplete responses.

In particular, students will be learning about the uber-important process of photosynthesis and, without properly functioning proteins (including enzymes), the entire reaction is a no-go! So, one topic relies on understanding the preceding one.

The takeaway here is that enzymes are the critical link between the inputs and outputs of any biologically-related chemical reaction. Really, any complex system relies on every component to properly function, and chloroplasts are no exception.

Instructional Input/Student Activities (Part 1)

10 minutes

Teaching Challenge (Practice): How can I support my students to compose, communicate and evaluate a clearly stated, evidence-based, compelling argument?

As a matter of self-assessment, students are directed to rate their understanding of the three goals explicitly included at the top of the student handout. I use the scale of "A"= I can do this, "B"= I am beginning to get this, and "C"= I cannot do this. You may wish to read them or have students read them aloud for greater effect.

Floating Disks: Predict-Observe-Explain #1 of 2 (P.O.E.)


There are a variety of strategies by which students can be guided in thinking about inquiry. There are full-fledged controlled experiments, a single "cookbook" style experiment, and quick teacher-led demonstrations, to name a few. Time is always a limiting factor, therefore I must pick and choose where and how I spend it. That being said, I like to use this version of the P.O.E. because it is quick, it gives a few boundary lines for students to follow but is sufficiently open-ended.

  • Predict: In this first step, students make a prediction about what they expect to happen in a given situation in the format of “If…then…because..." Here, the question is what will the spinach disks do in the video?
  • Observe: Students are directed to then make careful observations about the phenomenon (i.e. the behavior of the spinach leaf disks). I use four high-quality observations (quantitative and/or qualitative) as the "standard" bar and welcome even more than four!
  • Explain: Lastly, students are to make sense of what they observed using, among other descriptors, the role of enzymes that produce bubbles (they may or may not know that it is oxygen but it certainly stimulates their thinking)! If they cannot articulate it at this point, I help them out by walking them through "what we saw" and "what it means" including the bubbles (oxygen) and the buoyancy effect that is achieved as the bubbles accumulate on the leaf disk surface which effectively leads to the Disney/Pixar movie "Up"!

Instructional Input/Student Activities (Part 2)

10 minutes

Teaching Challenge (Practice): How do I support students to develop and use scientific models?

Photo-Synthesis”: A Systems Model

Direct Instruction: I share the basic inputs and outputs of photosynthesis via the Chloroplast PPT
with students. They, in turn, will then identify (on their own) which are inputs and which are outputs before moving on. This

At this point, I will explicitly identify the leaf disks (and ultimately the chloroplast) as the model and then explain the inputs, outputs, and throughputs of the chloroplast model, especially the role of enzymes that convert inputs to outputs.

Instructional Input/Student Activities (Part 3)

20 minutes

Teaching Challenge (Practice): How can I support my students to compose, communicate and evaluate a clearly stated, evidence-based, compelling argument?

Floating Disks Predict-Observe-Explain #2 of 2 (P.O.E.)

At this point, I will return to the same three-step format as in Part #1 and have students set up their own experiment.

Prior to lab, I will have prepared the leaves according to each treatment (exposing leaf disks for a total of 10 minutes per treatment). Then, I followed this protocol to flood the disks with carbonated water. In essence, the leaf disks need to be punched out of spinach leaves (4-5 per team). The air spaces inside need to be replaced with the carbonated solution. This typically takes some time to prep and with the experience level of my students coupled with the little time I have chosen to spend with this POE, the more heavy lifting I can do before class, the more streamlined things will go.

Students will investigate the difference between the effect of one factor

  • Treatment#1: 25°C versus 50°C
  • Treatment #2: 0% salt versus 10% salt
  • Treatment #3: pH 2 versus pH 7

Students will need to set up two beakers (containers) with carbonated water, 4-5 leaf disks per beaker (containers), and exposure to a light source at a distance of 20 cm (using the suggested heat sink method).

It should take about five minutes for the reaction to produce the desired effect.

In the linked video, it is plain to hear students making sense of the phenomenon in question. In particular, the female student articulated their team's hypothesis (that the lemon juice would interfere with the floating of the spinach leaves) and then several students described the evidence that supported their prediction (when comparing the lemon juice set up versus regular carbon dioxide solution).

Students should take an even closer look at the reaction as they complete the Observe-Explain sections.

Closure: What did we learn? Where do we go from here?

10 minutes

Teaching Challenge (Practice): How can I support my students to compose, communicate and evaluate a clearly stated, evidence-based, compelling argument?

As the lesson concludes, students will have learned that photosynthesis is a chemical reaction, catalyzed by enzymes and other proteins, and it occurs in the chloroplast. Using evidence from their POE (mini-experiment), students should then be able to connect the dots between the role of enzymes (comparing treated versus non-treated leaf disks) and whether oxygen bubbles (and buoyancy) is observed. Students will then make an argument whether enzymes are essential to the transformation of inputs into outputs according to prompt featured on slide #3 of the following Chloroplast Model PPT.

Finally, students will be directed to return to the goals for which they had previously self-assessed their understanding (A, B, C); this time they should use a different color or code to show learning and growth when compared to their initial self-assessment.