In today's lesson students will use the data from two experiments to determine the importance of light to photosynthesis. In the first experiment, students will use colored filters to determine which color of visible light causes the highest photosynthetic activity. In the second experiment, students will use paper chromatography to separate the different colors of plant pigments. This is the first day of a two day lesson. Here is an overview of what students will learn today.
Use the following assessment probe and ask students to predict how the presence or absence of light will affect the growth of plants. This probe elicits student ideas about the role of photosynthesis in plant growth.
A biology class decided to test how light affected the growth of plants by using young bean plants. One set of plants was placed in a dark closet for a week. The other set of plants was placed on a shelf near a sunny window for a week. On the eighth day, the class measured the height of the plants.
This is what each lab group predicted might happen because of the experiment:
Group 1: "The plants in the dark closet will be the tallest."
Group 2: "The plants in the sunny window will be the tallest."
Group 3: "The plants will be about the same height."
Group 4: "The plants in the closet will stop growing and die."
With which lab group do you agree and why? Explain your reasoning. Draw a picture of the plant might look like in each situation.
Students should write their responses and pictures in their lab notebook.
based on Keeley, Page, Francis Eberle, and Joyce Tugel. 2007. Plants in the Dark and Light. Uncovering Student Ideas in Science: 25 More Formative Assessment Probes. NSTA press:Arlington, VA.
For this lab, each student group will need the following equipment:
Students will complete a modified lab based on Vernier photosynthesis lab in which students use a spectrometer to determine the effect of light on photosynthesis. After learning how to do the protocol, students will compare the rates of photosynthesis for an algal culture in different light conditions.
Making Sense of the Data
Once the data has been analyzed, students should consider the following questions:
based on: Redding, Kelly and David Mastermind. 2007. Photosynthesis. Biology with Vernier. Vernier Software and Technology: Beaverton, OR
Students will use paper chromatography to separate a mixture of algal pigments.
For this lab, each student group will need the following equipment
Determining the distance each pigment traveled.
Determining the Rf value of each pigment
After they complete their analysis, students should consider the following questions:
based on: Redding, Kelly and David Mastermind. 2007. Photosynthesis. Biology with Vernier. Vernier Software and Technology: Beaverton, OR.
Bring the class back together to discuss the results of the two labs. Using the information that they learned from both labs, student groups should design an experiment to test the effect of red, blue, and green light on the photosynthetic activity of algae. They should write a lab proposal and submit it for approval by the end of the period. (Note: I provide my students with an electronic copy of the protocol to save them time. They may email me their final draft.)
Student groups will conduct their experiment during the next class period.