Engage:
Have students create a word web about plants in their science notebooks. Encourage students to categorize information as they create the webs. A sample web is included in the attachments section. This web can be used as a pre-assessment of student knowledge about plants and photosynthesis, and students can add to the web as their understanding increases throughout the lesson.
Watch Mr. C’s Photosynthesis song. Have students add to their word webs following the video.
Explore:
Conduct two experiments to show the process of photosynthesis:
- Photosynthesis experiment from Wonderville.org: Put a water plant in a beaker or glass bowl of water. Place an inverted funnel over the plant and place in sunlight. Observe bubbles of oxygen that are released as photosynthesis occurs. Put a test the test tube over the funnel and mark the air level in the test tube. Have students hypothesize what will happen to this air level over time and explain the reasons for their predictions. Observe the oxygen level after 24 hours and discuss findings. Repeat procedure in the dark and compare the results.
- Experiment to show how lack of light affects leaves from Tomatosphere.org: Give each small group of students a potted plant, aluminum foil, scissors, and paperclips. Have students cut small shapes from the foil and clip them to the leaves of the plant. Place the plant in sunlight and water as needed. After one week, remove the foil and observe what happened to the leaves. Discuss what the change in color means in terms of photosynthesis.
In between observations, use this NOVA interactive website to explain what happens during photosynthesis. You may choose to project the interactive for whole-class discussion, or students may access it individually on computers during learning centers.
Explain:
Discuss results of experiments and watch photosynthesis videos:
Ask probing questions and have students add to the word webs in their notebooks.
- What do plants need for photosynthesis?
- Why can green plants photosynthesize but animals cannot?
- What happens to the carbohydrates and oxygen produced during photosynthesis?
Divide class into groups of four. Have two students in each group read “A Tree is Like a Hungry Kid” passage while the other two students read “A Plant Puzzle.” Instruct students to highlight or underline answers to questions as they find them in the passages. Following the reading, the group of four will share their findings. Each set of partners will summarize their passage for the partners who read a different passage.
Compare differences in terminology. One passage says sugar is produced during photosynthesis, while the other says glucose is produced. Explain to the students that glucose, sugar, and starch are forms of carbohydrates produced during photosynthesis. Watch Mr. C’s Photosynthesis song again. Pause the video when the chemical equation is displayed. Explain that carbohydrates are molecules composed of carbon, hydrogen, and oxygen, but they can vary slightly and have different names depending on the arrangement of the molecules. Students do not need to memorize the chemical equation, but they should understand that photosynthesis is a change where the inputs (water and carbon dioxide) are rearranged into different molecules (carbohydrates and oxygen) using energy from the sun.
Elaborate:
Give each group of four students a set of picture cards (included in Attachments section), a piece of chart paper, and markers. Have students arrange the picture and word cards on chart paper to show what happens during photosynthesis. Have students draw arrows and write explanations to explain the process. A sample card sort is included in the Attachments section.
