Photosynthesis &Photosynthesis & Primary Production Primary Production
PhotosynthesisPhotosynthesis
• Solar energy powers the reaction
•Carbon dioxide and water used to make glucose
•Oxygen gas is released as a by-product
Fig. 4.5
6CO2 + 6H2O → C6H12O6 + 6O2
Solar energy
What is photosynthesis?
What are autotrophs?
inorganic materials
new organic compounds
PhotosynthesisPhotosynthesis
What absorbs light energy?
- Chloroplast contains the photosynthetic pigment chlorophyllchlorophyll
-Absorbs mainly red and violet- blue regions of visible light
Fig. 4.8b
Fig. 4.6
Chl a absorbance
Cellular RespirationCellular Respiration
- opposite of photosynthesis
-Releases energy in glucose, organisms store in ATP molecules until use
- Both autotrophs and heterotrophs respire
Fig. 4.5
6CO2 + 6H2O ← C6H12O6 + 6O2 Chemical energy
Primary Production (PPrimary Production (P°)°)
- What is primary production?
-Net gain in organic matter that results when autotrophs photosynthesize more than they respire, i.e., P >>> R
****Requires nutrients for organisms to grow, reproduce****
-This organic matter (new plant material) is available for heterotrophs
Primary Production Primary Production
‘‘primary’ production because primary’ production because photosynthesisphotosynthesis is the is the basisbasis of most marine biomass production of most marine biomass production
Primary productivityPrimary productivity is the is the raterate of primary of primary production, the rate at which plant material is production, the rate at which plant material is producedproduced
Compensation point
photoinhibition
Light intensity (I)
Ph
otos
ynth
esis
(P
)
+
0-
Pmax
Pg
Pn
Ic
respiration
Photosynthesis as a function ofPhotosynthesis as a function of Light Intensity Light Intensity
(P vs. I)(P vs. I)
Pg – Gross Primary Productivity
Pn – Net Primary Productivity
Pmax – maximal photosynthesis value
Ic – compensation light intensity
Compensation point
photoinhibition
Light intensity (I)
Ph
otos
ynth
esis
(P
)
+
0-
Pmax
Pg
Pn
Ic
Respiration R
Gross photosynthesisGross photosynthesis: Total photosynthesis before subtracting respiration: Total photosynthesis before subtracting respiration
Net photosynthesisNet photosynthesis: Gross photosynthesis minus respiration, i.e. Pg – R: Gross photosynthesis minus respiration, i.e. Pg – RIs available to support other trophic levelsIs available to support other trophic levels
Compensation pointCompensation point: Light intensity when photosynthesis equals respiration, i.e. : Light intensity when photosynthesis equals respiration, i.e. P = RP = R
Lower part of the photic zoneLower part of the photic zone
Ecological Zonation of the Marine EnvironmentEcological Zonation of the Marine Environment
Photic Zone
Fig. 10.20
Photic ZonePhotic Zone
Part of the pelagic that light penetrates (0 to 100-200m)
• Clarity of water:
•Seasons
•Location
Phytoplankton carry out photosynthesis
• Primary Production (Pº) is at maximum
• Responsible for up to 95% of all marine primary production
• start of the marine food chain
Marine Organisms Grouped by LifestyleMarine Organisms Grouped by Lifestyle
Fig. 10.19
2 easy ways to measure 2 easy ways to measure primary productionprimary production
Either measure Oxygen (endpoint of Either measure Oxygen (endpoint of the photosynthesis reaction)the photosynthesis reaction)
Or measure Chlorophyll a Or measure Chlorophyll a (approximates phytoplankton (approximates phytoplankton biomassbiomass
Today’s Lab:Today’s Lab:measuring measuring
photosynthesisphotosynthesis
Fig. 10.15
= Pn
= R
= Pg
Photosynthesis – Primary Production Photosynthesis – Primary Production ExperimentExperiment
Purpose:
To determine if more light produces more Net photosynthesis (Pn).
Hypothesis:
Net photosynthesis (Pn) in high light conditions will be greater than Net photosynthesis (Pn) in a low light environment.
MethodsMethods
Six groups of 2 people (some groups will have 3) Six groups of 2 people (some groups will have 3) Each group gets 2 BOD (Biological Oxygen Demand) Each group gets 2 BOD (Biological Oxygen Demand)
bottles. 1 will be the LIGHT bottle and the other the bottles. 1 will be the LIGHT bottle and the other the DARK bottle.DARK bottle.
Three groups will keep bottles under the high light and Three groups will keep bottles under the high light and three will put bottles in low light.three will put bottles in low light.
Measure and record t=26 hrs oxygen concentration in Measure and record t=26 hrs oxygen concentration in mg/L. Do NOT remove foil until you take the mg/L. Do NOT remove foil until you take the measurement. Use the same DO meter. (t=0 was measurement. Use the same DO meter. (t=0 was already done)already done)
Each group measure light levels in two environmentsEach group measure light levels in two environments
ResultsResults
Adjust initial and final oxygen concentrationsAdjust initial and final oxygen concentrations Light levelsLight levels
Record light levels in high light and low light Record light levels in high light and low light conditions for comparisonconditions for comparison
Errors?Errors? Record any animals.Record any animals. Record bubbles in light bottle.Record bubbles in light bottle.
ResultsResults
Adjust initial and final oxygen concentrationsAdjust initial and final oxygen concentrations Light levelsLight levels
Record light levels in high light and low light Record light levels in high light and low light conditions for comparisonconditions for comparison
Errors?Errors? Record any animals.Record any animals. Record bubbles in light bottle.Record bubbles in light bottle.
Results-photosynthesis experimentResults-photosynthesis experiment
CalculationsCalculationsGross photosynthesis Gross photosynthesis Pg = Pg = (Final O2-Initial O2) in Light Bottle(Final O2-Initial O2) in Light Bottle – ( – (Final O2-Initial O2) in dark bottleFinal O2-Initial O2) in dark bottle
Incubation periodIncubation period Incubation periodIncubation period
Net photosynthesis Net photosynthesis Pn= Pn= (Final O2-Initial O2) in light bottle(Final O2-Initial O2) in light bottle = Pg – R = Pg – R
Incubation periodIncubation period
RespirationRespirationR = (R = (Initial O2-Final O2) in dark bottleInitial O2-Final O2) in dark bottle
Incubation periodIncubation periodUnitsUnits
Oxygen concentration: mg LOxygen concentration: mg L-1-1
Incubation time: hrIncubation time: hrPg, Pn, R: mg oxygen LPg, Pn, R: mg oxygen L-1-1 hr hr-1-1
Nutrient experimentNutrient experiment Purpose: To evaluate if nutrient (nitrate)
concentration has an effect on phytoplankton Hypothesis: Increased nitrogen concentration yields
increased chlorophyll a production, and therefore, phytoplankton biomass
What was done ahead of time:What was done ahead of time: Phytoplankton culture was controlled for light and nutrients (Si and P), Phytoplankton culture was controlled for light and nutrients (Si and P),
and added NOand added NO33 in 3 different concentrations (0, 200, and 450 in 3 different concentrations (0, 200, and 450 M )M ) We will measure chlorophyll a (fluorescence as a proxy)We will measure chlorophyll a (fluorescence as a proxy)
MethodsMethods
Take bottle with phytoplankton,Take bottle with phytoplankton, Filter using vacuum-filtration apparatusFilter using vacuum-filtration apparatus
Place filter in tube, add methanol, agitate and crush Place filter in tube, add methanol, agitate and crush filter with metal spatulafilter with metal spatula
Put in freezer (-20Put in freezer (-20ooC) for 5 minutesC) for 5 minutes Centrifuge vial at top speed (5 minutes)Centrifuge vial at top speed (5 minutes) Transfer supernatant to cuvette (~ 2 ml)Transfer supernatant to cuvette (~ 2 ml) Put cuvette in fluorometer, read fluorescencePut cuvette in fluorometer, read fluorescence Convert to chlorophyll a (fluorometer does this)Convert to chlorophyll a (fluorometer does this)
Lab ReportLab Report
Write up experiments:Write up experiments: How light and nutrients affect phytoplankton production (of oxygen, of How light and nutrients affect phytoplankton production (of oxygen, of
cells/biomass)cells/biomass) Reports: double spaced, 4-5 pages, include tables and figures as neededReports: double spaced, 4-5 pages, include tables and figures as needed Figures, plot light versus average Pn (remember legend), plot nutrient Figures, plot light versus average Pn (remember legend), plot nutrient
concentration versus chlorophyll aconcentration versus chlorophyll a Remember the big picture/broader impact for discussion/introduction: Remember the big picture/broader impact for discussion/introduction:
how light and nutrients affect phytoplankton production in the ocean,how light and nutrients affect phytoplankton production in the ocean, what about nutrient limitation, light limitationwhat about nutrient limitation, light limitation changes in both over time, with nutrients in proximity to coastal zone (humans)changes in both over time, with nutrients in proximity to coastal zone (humans) Cloudy versus sunny daysCloudy versus sunny days