ap biology - r. wingerden · investigation 5: photosynthesis ap biology pearson education, inc.,...

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


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


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



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?



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




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?


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).



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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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



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


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?


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



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—————-


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


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).

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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 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.


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


ap biology - r. wingerden · investigation 5: photosynthesis ap biology pearson education, inc.,...

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