Lesson Plan on Photosynthesis

How do plants get energy?

Developed by Chantier 7 project team members

Activity #2: Light! Light! (Optional)

• Any submersed aquatic plant that is in good health and appears capable of photosynthetic activity (i.e., not dried or wilted). (e.g.,  Canadian waterweed (Elodea canadensis) or coontail (Ceratophyllum demersum)) – you can buy waterweed from any pet store where they sell fish/aquarium supplies
• Glass test tubes (20 × 150 mm)
• Racks to hold test tubes
• A light source (e.g., desk lamp)
• Large to medium sized drinking straws
• Thermometer

Activity #3: More Carbon Dioxide (Optional)

• Elodea, an aquatic plant available at many pet or gardening stores
• Bromothymol blue solution (acid-base indicator available for purchase online.  Yellow pH less than 6.0, blue pH above 7.6)
• Lights with clamp attachment
• Test tubes (one for each color and two additional as controls)
• Plastic wrap
• Aluminum foil

Worksheet: Please see appendices.

QEP POLs for secondary cycle 1 relevant to the concept of photosynthesis:

Elementary school:

Students explain the essential needs of living organisms (e.g. food, respiration) and describe metabolic activity (transformation of energy, growth, maintenance of systems and body temperature). They describe the function of photosynthesis, which they distinguish from respiration.

Secondary cycle 1:

​​Names the inputs and outputs involved in photosynthesis.
Names the inputs and outputs involved in respiration.

Children’s preconceptions relevant to the concept of photosynthesis:

• There is no difference between respiration and breathing.
• The main component of air is oxygen.
• There is no oxygen in exhaled air.
• Lighting a candle in a sealed jar with water proves that air is 21% oxygen (the water moves up the jar because the 21 % oxygen is consumed).
• All essential components for plants are absorbed from the soil via rots.
• Roots supply plants with energy.
• The sun keeps plants warm, and so they grow better.
• Plants breath. They inhale carbon dioxide, and they exhale oxygen.
• Plants get energy directly from the sun.

(Adapted from: https://scienceinquirer.wikispaces.com/file/view/RespirationCorr.pdf)

 

Assessment Items to explore or uncover students’ preconceptions around the concept of photosynthesis:

Question 1. Which of the following is TRUE about the sugar molecules in plants?
A. The sugar molecules come from the soil.
B. The sugar molecules are the result of a chemical reaction.
C. The sugar molecules are one of many sources of food for plants.
D. The sugar molecules are made from molecules of water and minerals.

(Retrieved from AAAS Item ME095005, http://assessment.aaas.org/items/ME095005#/0)

Question 2. Where does the food that a plant needs come from?
A. The food comes in from the soil through the plant’s roots.
B. The food comes in from the air through the plant’s leaves.
C. The plant makes its food from carbon dioxide and water.
D. The plant makes its food from minerals and water.

  (Retrieved from AAAS Item ME029006, http://assessment.aaas.org/items/ME029006#/0)

Questiom 3. What is TRUE about the inside of a plant cell?
A. The inside of a plant cell is completely solid.
B. The inside of a plant cell is completely filled with air.
C. The inside of a plant cell is completely filled with liquid water.
D. The inside of a plant cell contains liquid water and solid structures.

(Retrieved from AAAS Item CE065001, http://assessment.aaas.org/items/CE065001#/0)

 

Description of the Lesson:

The goal of this lesson is for students to (1) engage in experiments that enable students to gather evidence of inputs and outputs of photosynthesis, (2) understand the relationship between light and photosynthesis, and (3) understand the relationship between carbon dioxide and photosynthesis. This lesson plan includes the following steps:

Step 1: Introduction – Engage Students in Learning: In this step, teacher introduces the driving question of this lesson: “Plants need energy to stay alive and grow. How do you think plants get energy?”

Step 2: Background Knowledge Probes (BKPs): In this step, teacher use the assessments listed above to elicit students’ prior understanding and ideas of photosynthesis.

Step 3: Collecting and Making Sense of Data: In this step, teacher will conduct the Activity #1 – An Oxygen Factory. Teachers will then choose one of the option activities (i.e., Activity Option #2 – Light! Light! or Activity Option #3 – Role of Carbon Dioxide and Light) to provide students with more evidences for the upcoming discussion at the end of the lesson. While students are engaging in these activities, teacher can ask discussion questions to track students’ understanding of the concept. Students are also invited to record their observation on the worksheet given.

Step 4: Developing Evidence-Based Explanations: Following the activities, teacher engages in this step by inviting students to share their data with other groups and the whole class. Teacher may also post summary data on a class summary chart on the board.

Step 5: Evaluation: Teacher can assess students’ learning outcomes by choosing one of the post-assessment strategies: (1) Question and Answer/Exit Cards; (2) Create a multimedia poster; (3) Using the assessment questions listed above.

Details and procedures of each step are explained as follow:

 

Step 1 of The Lesson: Introduction – Engage Students in Learning

In Step 1, teacher will help students to connect the idea of food-web with photosynthesis. The goal of this step is to introduce the important role of photosynthesis plays in our ecosystem.

(1)  Introduction of the topic by saying: “Hello, we are going to learn about photosynthesis today. Before starting the lesson, does there anyone know where plants get their energy from?”

(2)  Teacher can prepare a feed-web (see Figure 1.) on transparency, doc cam, computer screen, or draw the figure on the board. Teacher can than ask the following questions to guide the discussion:

• All living things need energy to survive. How do us, human get energy?
• From this food-web figure (Figure 1), how do fox and rabbits gain their energy from?
• From this food-web figure (Figure 1), how do grass and trees gain their energy from? Do grass and trees ‘eat’ any other organisms?

Figure 1. Food-web
(Figure retrieved from MOSART Life Science Survey Test, Item form # 921, Q8)

 

(3)  Based on students’ response, teacher can re-voice students’ responses and write the responses on the board.

(4)  After students sharing their ideas about food-web, teacher can begin the class by introducing the driving question of this lesson: “Plants need energy to stay alive and grow. How do you think plants get energy?”

 

Step 2 of The Lesson: Background Knowledge Probes (BKPs) - Eliciting Student Thinking

The goal of this step is to elicit students’ prior understanding and ideas of the topic without evaluating their response or correcting their answers at this point.

(1)  Administer the instrument: To help teachers determine effective starting points for the students and to get to know students’ background knowledge, skills, attitudes, experience and motivation, before starting the lesson, you can administer the 3 assessment question provided above, in order to uncover students’ preconceptions around the concept of photosynthesis.

Teacher can use clickers to obtain students’ responses. If the school does not have clickers, teacher can ask the questions to the whole class and ask students to raise their hands for the answer. If there is no answer from students, teachers can also ask students to write their answer on a piece of paper and put them in a box. Teacher will then write some response on a board (or a chart paper) for discussion.

(2)  Pressing for explanations: After administering the test, teacher can share the data with students and ask students for the explanations. You may re-voice their explanations and write their response on a board. For example, teacher can ask: “We see that many of you choose option C as an answer. Does anybody want to share why they chose option C? What is your evidence for saying that?”

(3)  Introducing the term: Teacher can use the term “photosynthesis” to further probe students’ prior understanding. Teacher will then start the lesson by asking students what they think “photosynthesis” means and write down their responses on the board (or a chart paper).

 

Step 3 of the Lesson: Collecting and Making Sense of Data

The goal of this step is to help students to (1) develop their questions and/or predictions to learn more about the topic, and (2) test their predictions through hands-on inquiries, challenges, problems.

Teacher will first conduct the Activity #1 – An Oxygen Factory. Afterward, teachers can choose one of the option activities (i.e., Activity Option #2 – Light! Light! or Activity Option #3 – Role of Carbon Dioxide and Light) to provide students with more evidences for the upcoming discussion at the end of the lesson. These optional activities could help teacher to engage in ongoing, formative assessments to track students’ learning (e.g., walking around class to listen to their ideas, recording and displaying their ideas, observations, worksheets, student journals, students’ work products, etc.).

Details and procedures of each activity are explained as follow:

 

Activity #1: An Oxygen Factory

Part 1: Preparation: Teacher will have two different demo stations (i.e., Demo Station #1–Photosynthesis of an aquatic plant and Demo Station #2–Growth factors of a plant) prepared at least three days prior to the activity. Both teachers and students can create the demo stations.

Demo Station #1: Photosynthesis of an aquatic plant:

(1)  Place a submersed aquatic plant (e.g., Canadian waterweed (Elodea canadensis) or coontail (Ceratophyllum demersum) in a flask.
(2)  Fill a 500mL or 1L beaker with water.
(3)  Place the flask (with aquatic plants) into the beaker. Make sure that the aquatic plants are submerged in water.
(4)  Place a light source (e.g., desk lamp) near the beaker.

Demo Station #2: Growth factors of a plant:

(1)  Prepare 3 different pots of plants that are the same size (relevantly same size).
(2)  Prepare 3 terrariums (or 2 Liter soft drink bottles with the top cut off and saved for lid) with soil and 1 plant.
(3)  Terrarium 1: Add some oxygen gas, and seal the terrarium (or bottle lid). Label the terrarium.
Note: If you do not have access to oxygen gas, just seal the terrarium. Make sure the plant had been in a closed system at least for 3 days.
(4)  Terrarium 2: Add some carbon dioxide gas, and seal the terrarium (or lid for the bottle.) Label the terrarium.
Note: If you do not have access to carbon dioxide gas, place alkalizer in water, in an erlenmyer flask with a one-hole stopper, an elbow tube and glass tubing. Insert the tubing into the lid of the terrarium as the carbon dioxide is being produced).
(5)  Terrarium 3: The third terrarium is a control. Leave the plant in an unsealed terrarium.

 

Part 2: Observation: Students observe the plants at the two demo stations (i.e., Demo Station #1–Photosynthesis of an aquatic plant and Demo Station #2–Growth factors of a plant). Teacher can ask questions to elicit students’ ideas.

For example, for the Demo Station #1, teacher can ask the follow questions:

• What do you think is being produced in the flask?
• What is the evidence for this: Oxygen is being produced.
• The flask is foggy Inside. Why?”

For the Demo Station #2, teacher can ask the follow questions:

• What do you observe in the three terrariums?
• Where do you think the bubble comes from in the second terrarium?
• What gas do you think the bubbles are?
• What is happening in the third terrarium? Explain.
• What differences do you see between the first and second terrarium?”

Part 3: Recording observation: Teacher will ask students to observe the three different terrariums and write down their observation on their worksheet (Appendix A).
Note: The following Activity #2 and #3 are optional. These optional activities would allow teachers to help students collect more evidence/data for the final discussions at the end of the lesson.

 

Activity Option #2 – Light! Light!

The goal of this activity is to illustrate the causal relationship between light and photosynthesis (i.e., more light, more photosynthetic activity). Part 1: Preparation: (1)  Label 2 test tubes as either a treatment group or a control group. An hour or more before class, place a 5-cm segment of an aquatic plant into each treatment test tube. Note: Control test tubes are necessary to demonstrate that, with the combination of light and associated heat, bubbles may form at the surrogate’s surface, but few, if any, of those bubbles will be released from the surrogate and rise to the surface of the water. (2)  In separate test tubes, place an inert object similar in dimension to the plant segments (e.g., a 5-cm section of a drinking straw). The test tubes with these plant surrogates act as controls. If multiple plant species are available, add an additional test tube for each additional species and place 5-cm cuttings of those species into their own test tubes. Teachers should attempt to have all plant clippings be as similar as possible (i.e., taken from the same location on the stem of multiple plants). (3)  Fill all test tubes with the same amount of tap water, to within 2 cm of the top. Note: If multiple lamps and test tube racks are available, this experiment can be replicated by splitting the class into groups of three or four and carrying out the same measurements at each station.   Part 2: Activity: (1) Pass out the test tubes with plant segments to students. Students may work in a pair or groups. (2)  Lead a discussion to allow students to understand that the rate of bubble formation is a measure of the rate of photosynthesis. Teacher may ask: Where does the bubble come from? What do you think the bubbles are made of? Are they oxygen? Carbon dioxide? (3)  Place all tubes at a specified distance from a light source and allow 15 minutes for the plant to acclimate to the new environment. Make sure to plan for enough test tubes to carry out this experiment using multiple distances. (e.g., 15, 30, and 45 cm from the light source). (4)  After the test tubes containing plants or plant surrogates (e.g., straws) have been exposed to the light for at least 15 min, ask students to count the number of bubbles that emerge from the plant and float to the surface and measure the temperature in all tubes at the same time they count the number of bubbles. Note: Because the control tubes will collect bubbles, it is important for students to count only the number of bubbles that come from the plant or plant surrogate that rise to the surface. On the basis of the rate of bubble production observed, students should determine over what period of time (e.g., 15, 30, or 60 s) bubble production should be measured; the greater the bubble production, the less time necessary. Note: Increases in temperature can influence rates of photosynthesis and have been implicated in the spontaneous generation of bubbles from nonphotosynthetic materials. (5)  Ask students to construct a graph based on their data and write down their observation and explanation.

 

Activity Option #3 – Role of Carbon Dioxide and Light

(1)  Set up the lamps at least several feet apart and away from windows. (2)  Pour equal amounts of bromothymol blue into the test tubes or glasses (about 2/3 of the test tube or ½ cup in a small glass). Note: If you do not have enough solution, you may dilute it with a little water. Just be sure to use distilled water and dilute the entire supply only slightly. (3)  Cut equal-sized pieces of elodea for each test tube or glass (about 3 inches in length). Place a piece of elodea in each test tube or glass. Record the initial color of the bromothymol blue solution. Have students to label three test tubes (e.g., #1, 2, and 3). Talk about the role of bromothymol blue (pH indicator) by saying: “If the solution is blue, it is alkaline (basic). If the solution is yellow, it is acidic. If there is photosynthesis occurring, the indicator changes its colour from blue to yellow (Base–blue, neutral (pH range 6.0-7.6)–green, Acid–yellow). The reason for this colour change is that the carbon dioxide released during photosynthesis reacts with the water to form carbonic acid.” (4)  Have students to blow through a straw into the test tube #1; Cover the test tube (aluminum foil works well). Be sure to completely seal the vessel to keep gas from entering or leaving. Note: As they add Carbon dioxide into the tube, the bromothymol blue solution will change its colour to yellow (acidic). (5)  Have students to cover the test tube #2 completely with aluminum foil to block out any light. Test tube #3 is a control, so it should be left uncovered. (6)  Have students to write a hypothesis to explain which test-tube the solution will change colour, and to what colour. Teacher can ask: “Which test tube will have most photosynthetic activity? and Why?” (7)  Place the test tubes under the lamp. The plants should all be 12 inches (30 cm) away from their lamp. (8)  Let the test tubes sit for a one-hour to 24 hours. Record the final color of the solution for each test tube. (9)  Ask students to create a bar graph to illustrate their results. Ask students to compare their results with their hypothesis. Note: Teacher can have a class discussion to share their data.

 

Step 4 of the Lesson: Developing Evidence-Based Explanations

The goal of this step is to help students in changing their preconceptions through developing complex evidence-based explanations after their investigations in light of the data they gathered in the above activities. Teacher can ask students to share their data with other groups. Teacher may also post summary data on a class summary chart on the board.

(1)  Divide students into groups. (Groups of 2-3). Ask students to answer the questions on the worksheet (Appendix B). For example:

• Where does the water that appears on the side of the terrariums (Activity 1 – An Oxygen Factory) come from?
• Which conditions are necessary for bubbles to appear in the water (Activity 2 – Light! Light!)?
• Which gas in the atmosphere encourages plant growth?

Facilitate the discussion as teacher walk around the classroom.
Note: The important aspect here is that you allow students to make connection between evidence/data provided from the activities and their explanations for their answer.

(2)  Once students are finished with the worksheet, facilitate a class discussion. Teacher can lead a discussion about the similarities and differences in the group analysis.
Note: Teacher may go over the questions with students and have them present their answers and explanations. Or, teacher may ask students to present their data to the rest of class while teacher write down similarities and differences emerging from different groups’ data.

(3)  Go back to the driving question on the board: “Plants need energy to stay alive and grow. How do you think plants get energy?” Ask students if their view have changed and ask why. Again, encourage students to draw their explanations from the evidence/data from the activities. Teacher can use the following strategies:

Ø  Orienting students to each other’s thinking: For example, teacher can ask: Do you agree with what Student A said? and Why?
Ø  Pressing for explanation: For example, teacher can ask: Group A and B, both of you found results/data that are different than your previous predictions. Why do you think so?

Note: If time allows, you can show your students “photosynthesis song”: this video summarizes the process of photosynthesis, offering visual and musical sources: https://www.youtube.com/watch?v=C1_uez5WX1ohttps://www.youtube.com/watch?v=C1_uez5WX1o

 

Step 5 of the Lesson: Evaluation

Three strategies can be used to do a post-assessment; they are:

Option #1: Question and Answer/Exit Cards: Have students to fill out the worksheet page individually (see Appendix). After students fill out most part of the worksheet, ask them to discuss in a small group (3-4 students). Teacher can facilitate the group discussion while walking around the classroom by asking questions such as: “With regards to Input and its origin: Why do you think so? What evidence do you have from the activities we have done in class?” After going of worksheet page. 100 together, teacher may give the assessment items tested in the beginning and/or have them write exit cards (i.e., write a short reflection on what they learned and what they still unsure about).

Option #2: Create a multimedia poster: By creating a multimedia poster on what students have learned in lessons, they can draw various ways of representing ideas (e.g., write summaries of the facts, create visual arts, add sound). This will be done as a group project. As a group, students have another opportunity to discuss about their understandings on photosynthesis with their peers in informal ways. Specific steps are describe as follow:

(1)  In a group of 3-4, students will make a multi-media poster. The poster should represent their understanding of photosynthesis using multi-media of their choice (e.g., podcast, songs, YouTube, visual arts etc.). Students can draw from already existing sources (e.g., song from YouTube, pictures from encyclopedia).

(2)  Ask students to connect what they observe in their daily life to the concept of photosynthesis.

(3)  In their everyday life (e.g., home, school garden, or on the way to school), students can take a photo, make a collage, or draw a painting to connect the concept of photosynthesis to a moment in their daily life.

(4)  With the photo/collage/drawing, students are instructed to write a short essay or record a podcast that explains how their photo/collage/drawing (e.g., photos of flowers, collages of cows eating grass, cooking meals) relates to the concept of photosynthesis.

For example, a group of students may write: “The meals we eat are the products of photosynthesis. Vegetables grow because of photosynthesis. Meat is a product of animals eating producers or other consumers. Energy from photosynthesis is transferred to the consumer. Humans eat both vegetables and meat which are both products of photosynthesis.”

(5)  Teachers give specific guidelines and rubrics for students to follow. It is important for students to include the following key points in their short essays:

• The process of photosynthesis;
• Inputs and outputs of photosynthesis;
• Factors influencing the photosynthesis and the connection with their daily life experience.

(6)  After the completion of the multimedia posters, class can have a symposium, where students will have an opportunity to present their multimedia posters to other students in the classroom.

Option #3: Assessment question: administer the same question and to see if students’ responses had been change. Teacher can use the clickers to obtain students’ responses. If the school does not have clickers, teacher can ask the questions to the whole class and ask students to raise their hands for the answer. If there is no answer from students, teachers can also ask students to write their answer on a piece of paper and put them in a box. Teacher will then write some response on a board (or a chart paper) for discussion.
Note: You may re-voice their explanations and write their response on a board.

 

This lesson plan is inspired by the following sources:
Education.com: http://www.education.com/pdf/photosynthesis-of-elodea/
Eureka!: Science and Technology, Secondary Cycle One; Student Textbook B (Activity 8: An Oxygen Factory, pp. 36-37); Worksheet (U1 38, U1 39); Teaching Resource Guide, Volume 1 (p.53).
Ray, A. M., & Beardsley, P. M. (2008). Overcoming student misconceptions about photosynthesis: A model-and inquiry-based approach using aquatic plants. Science Activities: Classroom Projects and Curriculum Ideas, 45(1), 13–22.