10 January 2014 AP Biology/A2
· The Effect of Carbon Dioxide Concentration on the Rate of Photosynthesis
As an important process for all organisms, photosynthesis can be affected by both internal and external factors that impact autotrophic and heterotrophic organisms. The objective of this experiment was to determine how varying concentrations of carbon dioxide affect the rate of photosynthesis by using the floating disk method. It was hypothesized that an increase in concentration of carbon dioxide would increase the rate of photosynthesis. However, this hypothesis was proven incorrect when the ET 50s increased from 8 minutes to 11 minutes as concentration increased from 0.5% to 3.0%, indicating that it took longer for half of the leaf disks to rise and that the rate was slowing down. Therefore, it was concluded that varying carbon dioxide concentrations did affect the rate of photosynthesis and that an increase in concentration slowed down the rate of photosynthesis.
Photosynthesis is the process by which autotrophic organisms synthesize organic molecules like sugars from carbon dioxide, water, and inorganic salts. Pigments found within the chloroplasts of most photosynthetic organisms harvest light energy from the sun to excite electrons, which drive photosynthesis through both light reactions and the Calvin cycle. Using the amount of substrate consumed or the amount of products and by-products produced, one can measure the rate of photosynthesis of an organism. The purpose of this experiment was to observe the effect of varying carbon dioxide levels on the rate of photosynthesis by using the floating disk method described in the AP Biology Investigative Labs textbook. The floating disk method uses the oxygen by-product of photosynthesis to make sunken disks of leaves to float. Thus, the rate can be determined as the amount of time needed for all disks to float. We hypothesized that as the concentration of carbon dioxide increased, the rate of photosynthesis would also increase until the rate is “saturated” by reaching a maximum carbon dioxide level because carbon dioxide is a crucial substance for photosynthesis to occur; therefore, with more carbon dioxide present, photosynthesis would occur at a greater rate.
· Experimental Details
Preparation of Carbon Dioxide Solutions
1. Four plastic cups were obtained and each labeled with 0%, 0.5%, 1.0%, and 3.0% CO2.
2. Four solutions were created by measuring and placing 100 mL of distilled water in the 0% cup, 100 mL of distilled water and 0.5 grams of bicarbonate in the 0.5% cup, 100 mL of distilled water and 1.0 grams of bicarbonate in the 1.0% cup, and 100 mL of distilled water and 3.0 grams of bicarbonate in the 3.0% cup.
-All solutions were mixed thoroughly before starting the experiment.
Floating Disk Method
3. The method detailed on pages 65-67 of the AP Biology Investigative Labs textbook was used to sink 10 leaf disks in each solution.
-A hole puncher and spinach...