High School Biology: Photosynthesis

SAT Level Biology:
Microscopic and Macroscopic Investigations of Photosynthesis

This lesson is for my SAT level high school biology class.  It’s something of a review – the students studied the photosynthetic reaction in their cell biology unit.  Here, the goal is both to review the most important aspects of the chemistry and to directly connect the very abstract-feeling photosynthetic equation with observable plant behavior. 

It is important to note that this class meets once per week for 2 hour periods.  The amount of homework I give for this lesson would be completely excessive for a class that meets daily, but is reasonable for students that have a full 7 days to complete the assignments.

Getting Started
• Do Now: How do plants gain weight? Write your answer in 100 words or less.
• Check homework: randomly call on students to answer questions assigned for homework.
• Discuss the Do Now. What explanations do people have for how plants gain weight? How could we hypothetically do experiments to determine if these ideas are correct?
• Randomly divide the class into groups of 2 students.

Photosynthesis from a Microscopic Perspective
• Write the basic photosynthesis equation (CO2 + H2O –> C6H12O6 +O2). This equation will be a review students, but it will have been several months since they studied this in the cell biology unit.
• Give students the handout Modeling Photosynthesis with Paper Atoms (by Kathleen M. Vandiver, copyright MIT) and the paper atoms. As a class, read through the instructions and answer any questions that arise.
• Carry out Modeling Photosynthesis with Paper Atoms activity.
• As a class, work together to create notes summarizing the information in this activity.

Photosynthesis from a Macroscopic Perspective
• Demonstrate how Elodea (an aquatic plant) will give off oxygen bubbles from the stem when it is in ideal conditions for photosynthesis. Ideal conditions include bright light and a good source of dissolved CO2 (provided by a pinch of baking soda added to the water). Explain that the rate of photosynthesis can be measured by counting the number of oxygen gas bubbles that escape from the stem or by capturing the oxygen in a test tube and measuring the gas level.
• Ask pairs to design a simple experiment investigating photosynthesis that can be carried out using the materials available. Remind students that it is important for all experiments to be controlled and in particular, explain the necessity of using a heat sink if light levels will be the independent variable. Experimental designs should include a question to be answered, a hypothesis, a materials list, a procedure, and a data chart.
• Have each group share their experimental design with the class and get constructive criticism to improve their experiment.
• Carry out experiments. Collect data. Write a brief conclusion.
• Share the experimental results and conclusions with the class.

Homework
• Rd. Ch. 24 of Biology by Miller and Levine Do questions #1 – 10 on page 629
• Bring in leaves or photos of leaves of 10 different plants.
• Work through: “Illuminating Photosynthesis” http://tinyurl.com/3bwl86w
• Refer to your textbook and your notes from when you studied photosynthesis during the cell biology unit. Write a brief explanation of the light-dependent reaction and the Calvin Cycle

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