Summary

In this lesson, students will build knowledge through reading an assigned passage, as well as analyze evidence produced from a teacher led demonstration to better understand the process of photosynthesis.

Grade Level

Elementary and Middle School

NGSS Alignment

This lesson plan will help prepare your students to meet the performance expectations in the following standards:

• 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.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Objectives

By the end of this lesson, students should be able to

• Explain the process of photosynthesis.
• Explain the importance of photosynthesis for both plants and animals.
• Understand the interdependence between plants and animals.

Chemistry Topics

This lesson supports students’ understanding of

• Chemical Reactions
• Photosynthesis

Time

Teacher Preparation: 20 minutes

Lesson: 120 minutes

Materials

For whole group instruction:

• Choice of potted plants (1 per group as a visual reference)
• Photosynthesis reading passage (1 copy per pair of students, created by author)

For Teacher Demonstration

• 4 test tubes with caps
  • Label 4 test tubes as A, B, C and D
• Distilled water (30 ml per test tube)
• Bromothymol Blue solution (1 ml per test tube added to distilled water)
• 1 Straw
• 1 eye dropper or pipette
• Elodea plant or other aquatic plant (two 4-6” pieces)
  • Can usually be purchased at a nursery or pet store
• Aluminum foil
  • enough to completely cover two test tubes
• Beaker

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Do not ingest Bromothymol Blue solution.
• Wear gloves when working with Bromothymol Blue solution.

Teacher Notes

• This lesson is designed for use with 4^th or 5^th grade students.
• Prior to this lesson the study of food chains and food webs should have occurred. The next concept of focus is how plants produce their own food through photosynthesis.
• Photosynthesis is a process by which plants make their food by taking in sunlight, water and carbon dioxide (CO₂). From this mixture glucose is produced as a food source for plants, and oxygen is released into the air. It is an important reaction for both plants and animals in relation to our survival through a food chain, and emphasizes the interdependence between plants and animals.
• This is a demonstration video of blowing carbon dioxide into a Bromothymol Blue Solution to observe a chemical reaction. This may be helpful for your background knowledge.
• This is a video of the demonstration using Elodea in Bromothymol Blue solution to show evidence that plants breathe out oxygen (this may be helpful for teacher background, or may be used if materials are not available to conduct the lab in the classroom).
• This video explains the process of photosynthesis. I may be helpful to show students, and/or for teacher background knowledge.
• The teacher demonstration uses the Elodea plant in a Bromothymol Blue solution that is rich in carbon dioxide. A color change of the solution will be observed over time as the plant “breathes in” the carbon dioxide present in the solution. This will cause a color change from a green/blue to yellow. This is evidence of the process of photosynthesis.

Lesson Plan Procedure

• Engage: Complete a review discussion about environments that will lead to the needs of a plant and how it meets those needs.
  • Review the various environments students should be familiar with such as wetland, forest, desert, marine, polar, grassland/prairie, and tundra.
  • Identify examples of the living and non-living found in all environments. For example: nonliving components of an environment: air, water, sunlight, rocks/soil; living components: plants and animals.
  • Identify the basic needs of animals and plants. Basic needs of animals: air, water, nutrients [food], a suitable place to live. Basic needs of plants: sunlight, water, nutrients, air, space to grow.
  • Bring the focus to how a plant’s needs are met. For example, “We understand how people and animals get their food and energy through a food chain, but how does a plant get its food?”
  • Conduct a student debate to informally assess student knowledge of photosynthesis by writing the statements shown below on the board. Divide the classroom into half where one side is the “agree” side and the other half is the “disagree” side.Students walk to one of the halves to show their answer. Once choices have been made let each side present their argument.
  • Agree or disagree statements:
    • Plants and animals breathe? (agree)
    • Animals breathe in oxygen and breathe out carbon dioxide (agree)
    • Plants breathe in oxygen and breathe out carbon dioxide (disagree).
    • Photosynthesis is the most important reaction on our planet.
• Explore: This portion of the lesson has two components, Activity 1 and 2.
• Activity 1: Build background knowledge and vocabulary
  • Divide students into 4 groups.
  • Using the provided photosynthesis reading passage, assign one paragraph (there are 4 total) to each group to read and become an expert on the information in order to present to the class (1 person in the group will summarize what they learned).Address any misconceptions that may arise in the retelling.

• Activity 2: Teacher Demonstration “Do plants breathe?”
• Note: if materials are not available for the demonstration, teacher may want to show a video of the demonstration as an alternative.
• Refer to the reading passage: Plants “breathe in” carbon dioxide . Explain that at the end of the demonstration the question “Do plants breathe?” should be answered.
• Procedure:

1. Label 4 test tubes as: A, B, C and D. Test tube B and D will be used as controls.
2. Fill each tube to the top with water.
3. Add a drop of bromothymol blue (BTB) solution to each test tube (water should turn to a bluish-green color).
4. Pour the water from test tubes A and B into a beaker. You will make this sample of water rich in carbon dioxide. Using a straw gently blow into the water until it turns yellow (the change in color is caused by the carbon dioxide that is exhaled).
5. Place a small piece of Elodea plant (4-6 inches) into test tube A.
6. Add half of the carbon dioxide rich water, from the beaker, back into test tube A.
7. Add the rest of the carbon dioxide rich water, from the beaker into test tube B.
8. Cap test tubes A and B to seal them.
9. Add elodea plant to test tube C and cap it. Then completely wrap test tube C with aluminum foil so no light can reach the solution.
10. Cap test tube D and wrap the test tube completely with aluminum foil so no light can reach the solution.
11. Place all test tubes near a sunny window for 24 hours. Ask student to make predictions of what changes may occur during the 24 hours. Compile and record these predictions for students to see (ex: on a white board or smart board).
12. After 24 hours remove the aluminum foil from test tubes C and D.
13. Have students draw and label the contents of each of the 4 test tubes on the student handout provided.
14. Students should record their observations of each test tube, before and after on the student handout provided.

• Explain: Write a CER (Claim, Evidence, Reasoning) statement
  • Teacher will guide students to write a claim: Referring back to the question “Do plants breathe?” Example: I claim that plants breathe in carbon dioxide, and release oxygen.
  • Support your claim with evidence from the investigation: The evidence shows the water in test tube A, containing the Elodea, changed from yellow, indicating a carbon dioxide rich solution, back to the greenish/blue color indicating a lack of carbon dioxide. The solution originally contained carbon dioxide because a person exhaled into it, causing the color to change to yellow. After the Elodea sat in the yellow solution it took in the carbon dioxide and released oxygen back into the solution causing the water to return to its original greenish/blue.
  • Reason the importance of Photosynthesis: Photosynthesis is important because we rely on it to change sunlight, water, and carbon dioxide into a chemical energy that our bodies can use for fuel obtained through the food chain.
• Elaborate: Extend student learning and understanding by connecting the lesson back to the food chain and how plants and animals are interdependent of each other.
  • Conclude: CO₂ is good for plants, but too much CO₂ is a problem for our planet. Build-up of CO₂ in our atmosphere leads to the Greenhouse Effect causing temperatures to rise.Sources of CO₂ are human activity such as burning fossil fuels (coal, oil, natural gas), land clearing, people and animals breathing out CO₂, and volcanic eruptions. Plants are extremely important to take in the CO₂ and maintain our atmosphere.

• Evaluate: Assess the level of understanding by assigning students to draw an image of photosynthesis and label it, then extend the image into a food chain model. For vocabulary development ensure that the students use the words photosynthesis, carbon dioxide, oxygen, water, sunlight, and include producers and consumers in the diagram.
• Example below: (note: all images are free usage, URL linked to each image)

• Finally, students will write about the process of photosynthesis. Depending on student ability you may provide a cloze passage with a vocabulary bank (see student handout).