QUESTION I-1999
I. The rate of photosynthesis may vary with changes that occur in environmental temperature, wavelength of light, and light intensity. Using a photosynthetic organism of your choice, choose only ONE of the three variables (temperature, wavelength of light, or light intensity) and for this variable
• design a scientific experiment to determine the effect of the variable on the rate of photosynthesis for the organism;
• explain how you would measure the rate of photosynthesis in your experiment;
• describe the results you would expect. Explain why you would expect these results.
_______________________________________________________________________________________________________
AP® BIOLOGY
1999 SCORING GUIDELINES
Question I
A. Experimental Design: The following experimental characteristics may earn I
point each. (Max 7 points)
• Score only the 1st independent variable (temperature, wavelength, intensity) manipulated, and the 1st factor used by the student to measure photosynthetic rate (02, C02, etc.).
• A 3 point maximum in Section A if the experiment will not work biologically. Examples: using an organism that is not photosynthetic, or using an apparatus that biologically will not measure photosynthesis as designed (i.e. potometer or respirometer). Not intended to mean a technical design flaw.
• State hypothesis (clear statement of a hypothesis, identifies it as a hypothesis, uses "If/then" statement
• Specify a control group for comparison
• Identify and hold constant at least one experimental factor that can affect photosynthetic rate
• Manipulate the independent variable (change the temperature, wavelength of light, intensity, of light)
• Describe what is being measured to determine rate (CO, or H,O consumption, 02 or carbohydrate production, growth, & flow measured with dye reduction, production of an intermediate product, etc.)
• Quantify the measurement of the variable (method & time frame of measurement)
• Rate calculation or definition
• Verify results through sample size (>1) or repetition
• Utilize statistical application of data (mean, t-test, ANOVA, etc.)
• Design an exemplary experiment
B. Describe expected experimental results (Max 2 points)
• Verbal or graphic description of expected experimental results (1 point)
• Verbal or graphic description of expected results across the entire range of biological activity (1 point)
• The graphs below represent 2-point graphs, but to earn any points, graphs must be accurately labeled
1999 SCORING GUIDELINES
• A 3 point maximum in Section A if the experiment will not work biologically. Examples: using an organism that is not photosynthetic, or using an apparatus that biologically will not measure photosynthesis as designed (i.e. potometer or respirometer). Not intended to mean a technical design flaw.
 |
C. Biological explanation of results (Max 3 points)
Temperature
• Enzyme kinetics or metabolic changes
• Enzyme denatures
• Photorespiration
• Stomata] closing w/high temp, limits CO, & lowers rate
• Excessive water loss, less reactant available for reaction
• Elaboration
Wavelength
• Absorption/reflection of light by chlorophyll
• Accessory pigments absorbing green light
• Relation between wavelength & energy
• Elaboration
Intensity
• More photons hit photosystems
• More e flow in the electron transport system/time
• Plateau caused by limiting factors
• Elaboration