AP Biology. Investigation 5: Photosynthesis. Investigation 5: Photosynthesis. Investigation 5: Photosynthesis

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1 AP Biology Learning Objectives To design and conduct an experiment to explore the Investigation 5: Photosynthesis effect of certain factors, including different environmental variables, on the rate of cellular photosynthesis. To connect and apply concepts, including the relationship between cell structure and function (chloroplasts); strategies for capture, storage, and use of free energy; diffusion of gases across cell membranes; and the physical laws pertaining to the properties and behaviors of gases. Pearson Education, Inc., publishing as Person Benjamin Cummings College Board, AP Biology Curriculum Framework AP Biology Investigative Labs: An Inquiry-Based Approach Copyright Rebecca Rehder Wingerden Background Photosynthesis fuels ecosystems and replenishes the Earth s atmosphere with oxygen. Like all enzymedriven reactions, the rate of photosynthesis can be measured by either the disappearance of substrate or the accumulation of product (or by-products). The general summary equation for photosynthesis is: 2 H2O + CO2 + light carbohydrate (CH2O) + O2 + H2O What could you measure to determine the rate of photosynthesis? In this investigation, you will use a system that measures the accumulation of oxygen Because the spongy mesophyll layer of leaves is normally infused with gases (O2 and CO2), leaves - or disks cut from leaves - normally float in water. What would you predict about the density of the leaf disk if the gases are drawn from the spongy mesophyll layer by using a vacuum and replaced with water?

2 Sample Data Sample Data Sample Data As photosynthesis proceeds, oxygen accumulates in the air spaces of the spongy mesophyll, and the leaf disk will once again become buoyant and rise in a column of water. Therefore, the rate of photosynthesis can be indirectly measured by the rate of rise of the leaf disks. Bozeman Biology: Photosynthesis Lab Walkthrough (7:00 min.) PreLab Complete the following before conducting this investigation: I. Read and be ready to complete the Procedure. II. Answer the following PreLab questions in Comp Book: 1. Summarize what you will be doing in this investigation. 2. What is the primary question you will be trying to answer in this investigation? Floating Leaf Disk Practice the floating leaf disk technique by measuring the rate of photosynthesis by testing a variable that you know affects photosynthesis (Steps 1-9). ET50 Table 1: Floating Disk Minutes Disks Disks The point at which 50% of the leaf disks are floating (the median) is the point of reference for this procedure. By extrapolating from the graph, the 50% floating point (ET50) is about 11.5 minutes. Using the 50% point provides a greater degree of reliability and repeatability for the procedure (data from Steucek, et al. 1985).

3 Leaf Disk Procedure Practice Prior to conducting this lab: - read Procedure steps 1-9 (p.s63-s67) and - create a table to record your findings. Data: - Table: recorded findings for both variables - Graph: disk floatings for both variables - Analysis: determine group ET50 for both variables Table 1: Floating Leaf Disk (Baseline) Minutes Disks Floats continue adding rows, as needed Baseline Standards: light 10cm from top of beaker 1 gram baking soda mixed in 100 ml of soap-water minimum of 10 leaf chads Graph 1: Floating Leaf Disks (Baseline) Disks Time (minutes) Key with CO2 (red) without CO2 (blue) Analysis: determine group ET50 for baseline data (put ET50 on graph) Designing and Conducting Your Investigation: Once you have mastered the floating disk technique, you will design an experiment to test a variable that might affect the rate of photosynthesis. You will then conduct your experiment and present your results to the class (whiteboard presentation). What factors affect the rate of photosynthesis in living plants? Your variable should have at least TWO levels. Bozeman Biology: AP Biology Lab 4: Plant Pigments and Photosynthesis (6:00 min.) Designing Your Investigation: Purpose: method that will be used, independent and dependent variable. Hypothesis: If (rational for the investigation), then (outcome that you would expect). Procedure: Steps discussing how you will modify the Floating Leaf Disk procedure: independent (levels), dependent, control and standardized variables. Data: table(s) to record findings Approval by Instructor

4 Sample Data Sample Data Sample Data Conduct Your Investigation: Conduct your experimental design and record data and any observation (Table 2). Calculations: determine ET50s for the variable you investigated determine the rate of photosynthesis* for the variable you investigated Graph your results to show the effect of the variable you tested on the rate of cellular respiration (aka: float rate) Graph 2: Leaf Disc Floats for (your variable) Graph 3: Rate of Photosynthesis for (your variable)* Photosynthesis Light Response Curve To correct this representation and make a graph that shows increasing rates of photosynthesis with a positive slope, the ET50 term can be modified by taking its inverse, or 1/ET50. This creates a more traditional direct relationship graph. The above goes in your Comp Book - Direct Relationship The problem with ET50 is that it goes down as the rate of photosynthesis goes up - it is an inverse relationship and creates the following type of graph (data from Steucek, et al. 1985). To correct for this representation of the data and present a graph that shows increasing rates of photosynthesis with a positive slope the ET50 term can be modified by taking the inverse of 1/ET50. This creates a graph like this (data from Steucek, et al. 1985). Whiteboard Presentation: Purpose: method that will be used, independent and dependent variable. Hypothesis: If (rational for the investigation), then (outcome that you would expect) because Procedure: Steps discussing how you modified the Floating Leaf Disk procedure. Discuss the different levels of the independent variable in your design. Analysis: - Graph 3-1/ET50 for variable tested (both of your levels) and baseline. Summary Statement: Describe how the IV influences the DV. (Claim - Evidence - Reasoning)

5 Conclusion Restate the purpose of this experiment (What method was used? Include the independent and dependent variables.) Restate your hypothesis for this experiment. Statement that answers the following question, Do the results of your experiment support or refute your hypothesis? This is your CLAIM. Then, list and explain, in detail, how the data that you collected led you to your statement. This is the EVIDENCE that supports your CLAIM. Include statistical test(s) to support your statement. Therefore, in conclusion remember your experimental purpose. Please type your conclusion. Comp Book and Conclusion will be DUE on the same day. Conclusion Photosynthesis Light Response Curve Comparing light response curves is a standard research technique in plant physiological ecology. When you compare the ET50 across treatments, you will discover that there is an inverse relationship between ET50 and the rate of photosynthesis. ET50 goes down as photosynthesis goes up. Inverse Relationship rate of