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