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Investigation 5: Photosynthesis
AP Biology
Pearson Education, Inc., publishing as Person Benjamin Cummings College Board, AP Biology Curriculum Framework 2012-2013
AP Biology Investigative Labs: An Inquiry-Based Approach
Copyright © Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
Learning Objectives • To design and conduct an experiment to explore the
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.
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
Background • Photosynthesis fuels ecosystems and replenishes the
Earth’s atmosphere with oxygen. Like all enzyme-driven 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
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
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?
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
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.) http://www.bozemanscience.com/photosynthesis-lab-walkthrough
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
Copyright © 2012 Rebecca Rehder Wingerden
PreLab
Complete the following before conducting this investigation:
I. Read Investigation 5: Photosynthesis 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?
Investigation 5: Photosynthesis
http://www.elbiology.com/labtools/Leafdisk.html
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).
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
Minutes Disks1 02 03 04 05 06 07 18 19 1
10 111 412 713 814 10
Table 1: Floating Disk
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).
Copyright © 2012 Rebecca Rehder Wingerden http://www.elbiology.com/labtools/Leafdisk.html
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ET50
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Investigation 5: Photosynthesis
http://www.elbiology.com/labtools/Leafdisk.html
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
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
Minutes Disks Floats
1234567891011121314
Table 1: Floating Leaf Disk (Baseline)
Analysis: determine group ET50 for baseline data (put ET50 on graph)
Copyright © 2012 Rebecca Rehder Wingerden http://www.elbiology.com/labtools/Leafdisk.htmlcontinue adding rows, as needed
Dis
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Graph 1: Floating Leaf Disks (Baseline)
Time (minutes)
Key • with CO2 (red) • without CO2 (blue)
Baseline Standards: • light 10cm from top of beaker • 1 gram baking soda mixed in
100 ml of soap-water • minimum of 10 leaf chads
Investigation 5: Photosynthesis
Bozeman Biology: AP Biology Lab 4: Plant Pigments and Photosynthesis (6:00 min.) http://www.bozemanscience.com/ap-bio-lab-4-plant-pigments-photosynthesis
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?
Copyright © 2012 Rebecca Rehder Wingerden
Your variable should have at least TWO levels.
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
Investigation 5: Photosynthesis
Copyright © 2012 Rebecca Rehder Wingerden
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)*
————The above goes in your Comp Book—————-
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis Investigation 5: Photosynthesis
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.
Direct RelationshipCopyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
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).
Sam
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Copyright © 2012 Rebecca Rehder Wingerden http://www.elbiology.com/labtools/Leafdisk.html
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)
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 5: Photosynthesis
Copyright © 2012 Rebecca Rehder WingerdenConclusion
• 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.
Conclusion
Please type your conclusion. Comp Book and Conclusion will be DUE on the same day.
Investigation 5: Photosynthesis
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 rate of photosynthesis goes up.
Inverse Relationship
Copyright © 2012 Rebecca Rehder Wingerden