Study Photosynthesis with the Floating Leaf Disk Assay

Overview

Plants carry out photosynthesis to produce sugars that they need as an energy source to live and grow. During photosynthesis, oxygen—a gas that many living beings need to survive—is released. This makes photosynthesis one of the most important biological processes on Earth. In Part 1 of this lesson plan, students will utilize the floating leaf disk assay to demonstrate the production of oxygen gas during photosynthesis. They will then continue to design and conduct their own experiments in Part 2 of the lesson in order to investigate variables that affect the rate of photosynthesis in plants.

Remote learning adaptation: This lesson plan can be conducted remotely. The Engage section of the lesson can be skipped or done over a video call, then students can work independently during the Explore sections, using the Student Worksheet and the Leaf Disk Assay Video as a guide. Students will need to obtain their own materials such as a light source and a plastic syringe. For Part 2 of the lesson, students can adjust the independent variable they will investigate according to the materials available to them. The data analysis in the Reflect sections and the presentations of the results can be done over a video call, or by sharing a poster or slides on a class drive.

NGSS Alignment

• 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.

Materials

For each student group of 3:

• Green plant leaves, such as spinach or ivy
• Single hole puncher or sturdy straw
• Transparent cups, 5 or more (large enough to hold 300 mL)
• Baking soda (1/8 teaspoon)
• Tap water (room temperature)
• 1/4 or 1/8 teaspoon
• Measuring cup
• Liquid dish soap
• Plastic syringe, 10 mL or bigger (without the needle)
• Light source. Note: Any lamp with a CFL, halogen, incandescent, fluorescent, or LED bulb should work. The brighter the light, the better. With incandescent lightbulbs you have to be careful not to generate too much heat! You can also use direct sunlight outside. The type of light source will affect the rate at which photosynthesis happens. This is one variable that can be tested by students.
• Aluminum foil
• Permanent marker
• Paper towels
• Timer
• Lab notebook
• Pencil or pen
• Calculator
• Paper

For teacher:

• Bowl
• Aluminum foil

Extra materials for independent student investigations:

• To investigate the following:
  • Different light sources: LED, CFL, incandescent, halogen, sunlight
  • Different light intensities: Ruler or measuring tape
  • Different light colors: Colored cellophane sheets, tape
  • Water temperature: Thermometer, microwave, ice cubes
  • Different leaf colors: Yellow, red, and green leaves
  • Different plant types: Leaves from different plant species