Inhibitors of Photosynthesis
in Aquatic Plants
By Marco DiVito
Central Catholic High School
PJAS 2015
Grade 9
Runoff
•
One of the largest and fastest growing threats to global
water resources.
•
Typical materials transported: fertilizers, petroleum,
pesticides, herbicides, and salts.
•
Runoff often leads to a disruption of aquatic ecosystems.
•
Rainwater collects and carries chemicals into lakes or
streams, possibly causing eutrophication or toxicity.
•
Eutrophication results in depletion of oxygen in the water,
killing off many other species.
Herbicide
•
Bentazon-benzothiadiazinone group
•
This group is designed to inhibit photosynthesis
•
Cause of selectivity not been discovered
•
Shown to be effective against cocklebur,
smartweed, and ragweed.
Chloroplasts
•
Photosynthesis occurs in chloroplasts, which are
double membrane bound organelles found in plant
cells
•
Thylakoid membrane suspended in the stroma
•
Photosystem 1 (PSI) and Photosystem 2 (PSII)reaction centers responsible for turning light energy
into chemical energy
Photosynthesis
•
Chloroplasts contain the
pigment molecule chlorophyll
•
Light excites chlorophyll
electrons
•
Energy transfer-redox reactions
drive synthesis of ATP and
NADPH
Photosynthesis
•
PSI releases NADPH directly
into the stroma
•
Electron flow results in H+
transfer through thylakoid
lumen
•
H+ pumping powers ATP
synthase
Elodea
•
Elodea Canadensis
•
Also known as American
waterweed
•
Commonly used in aquariums
•
Can function as a habitat,
shelter, or food source in
aquatic ecosystems
Purpose
•
The purpose of this experiment is to determine the
effects of a herbicide designed to inhibit
photosynthesis on a non-target aquatic plant
•
This and other plants could be exposed to the
herbicide via runoff from nearby fields
•
Photosynthesis will be quantified by the amount of
dissolved oxygen in sealed tubes at the beginning
and end of the trials
Hypothesis
•
Null: the herbicide bentazon will not significantly
inhibit dissolved oxygen production by elodea
•
Alternative: bentazon will reduce the dissolved
oxygen produced by the elodea
Materials
•
Basagran Herbicide (contains active ingredient bentazon)
•
20 150mm x 25mm test tubes with rubber stoppers
•
20 stalks of Elodea Canadensis
•
DO probe (Sper Scientific probe pen)
•
Micropipettes and pipette tips
•
Water
•
Test tube racks
•
Floodlights (75 watt)
•
Scissors
Stock Concentrations
0%
0.01%
0.1%
1%
Herbicide
(44%
bentazon)
0uL
11uL
114uL
1136uL
Water
50,000uL
49989uL
49886uL
48864uL
Total Volume
50,000uL
50,000uL
50,000uL
50,000uL
Procedure
1. Cut twenty 6 centimeter segments of Elodea Canadensis and inserted one into
each test tube
2. Made large quantities of stock solutions for bentazon.
3. Added 50mL of fluid to each test tube, with five tubes for each concentration.
4. Allow fluid in tubes to settle and reach a stable DO concentration
5. Measured the dissolved oxygen in each tube
6. Inserted one segment of elodea into each tube, then sealed the tubes with the
stoppers.
7. Set up floodlights facing tubes and waited 12 hours
8. Measured the dissolved oxygen in each tube
DO- Initial
Tube 1
Tube 2
Tube 3
Tube 4
Tube 5
20mg/L
P-value: 0.99
Dissolved Oxygen
15mg/L
10mg/L
5mg/L
0mg/L
0%
0.01%
0.1%
Concentrations of bentazon
1%
DO- Final Values (After 12 Hours)
Tube 1
Tube 2
Tube 3
Tube 4
Tube 5
20mg/L
P-value: 7.55E-07
Dissolved oxygen
15mg/L
10mg/L
5mg/L
0mg/L
0%
0.01%
0.1%
Concentrations of bentazon
1%
Analysis: Dunnett's Test (Final Values)
T-crit: 3.48
T-Value
Interpretation
0.01%
4.94
Significant
0.1%
6.74
Significant
1%
9.23
Significant
DO Changes
70%
59%
P-value= 1.56E-06
Percent Change
35%
0%
-10%
-32%
-35%
-69%
-70%
-105%
0%
0.01%
0.1%
Concentrations of Bentazon
1%
Analysis- Dunnett's Test (Changes)
T-crit: 3.48
Tests
T-value
Interpretation
0.01%
4.93
Significant
0.1%
6.26
Significant
1%
8.79
Significant
Key Questions
•
Does the herbicide bentazon inhibit
photosynthesis?
•
P-value<0.05- Yes
•
Do varying concentrations produce different
effects?
•
T-values of 4.93, 6.26, 8.79 all higher than alpha of
3.48- Yes-increasing concentrations have increased
effect
Conclusion
•
Null Hypothesis: bentazon will not inhibit dissolved
oxygen production
•
Reject null hypothesis for experiment
•
Accept alternate hypothesis
Limitations and Extensions
Limitations
•
Mixing could have affected DO
•
One herbicide used
•
Limited concentrations used
•
Window-variable light source
•
•
Possible temperature
fluctuation
Ingredients in water
Extensions
•
Different environmental conditions
(temperature, amount of light, natural
substances in water)
•
Different types of herbicides
(photosynthesis inhibiting and not)
•
Combinations of herbicides
•
Test synergistic effect of fertilizers
•
Different range of concentrations
•
Longer exposure times
•
Different model
•
Different ways to quantify photosynthesis
Works Cited
• "Cytochrome Complex in Electron Transport." Hyperphysics. N.p., n.d. Web. 27
Dec. 2014.
• "Elodea Canadensis (common Waterweed) and Elodea Nuttallii (Nuttall's
Waterweed)." Elodea Canadensis (common Waterweed) and Elodea Nuttallii
(Nuttall's Waterweed). Washington Department of Ecology, n.d. Web. 01 Jan.
2015.
• Gibson, Lance R. "Photosynthesis Inhibitors." Agronomy 317. Iowa State
University, 23 July 2004. Web. 20 Dec. 2014.
• "Herbicides - Weed Management (Penn State Extension)." Weed Management
(Penn State
Extension). Penn State University, n.d. Web. 23 Dec. 2014.
• "Native Freshwater Plants." - American Waterweed. Washington State
Department of Ecology, n.d. Web. 23 Dec. 2014.