1.3 Light & Photosynthesis
Last updated
Last updated
Attenuation - reduction in intensity with distance in a medium
Input wave decreases in wavelength when traveling through any absorbent medium
at 1m only 45% of solar energy that hits the ocean remains, at 10m its only 16% and at 100m is 1% - Source
Light absorption - light is absorbed by colored objects or particles
detritus, chlorophyl, DOM and water will all absorb light as it passes
Scattering - when light encounters particles smaller than a wavelength
water & bacteria & suspended particles
Reflection & absorption go hand in hand - we see the colors that are reflected, not the ones that are absorbed (white=all, black=none)
Irradiance - the flux of radiant energy per unit area
PAR - the amount of light available for photosynthesis
400-700nm wavelength range
PAR changes seasonally and varies depending on latitude and time of day, with levels highest during summer at mid-day
Measuring PAR:
values range from 0 to 3,000 millimoles per square meter, at night PAR = 0
measured using a silicon photovoltaic detetor
PAR irradiance - radiant flux density, or the radiative energy recieved by unit surface area in unit time carried by photons on the PAR waveband
Kd - vertical attenuation coefficient for downwelling irradiance
determines the characteristics of the local light environment
Sources - Thomas' dissertation,
When PAR exceeds the capacity of the light-independent reactions (calvin cycle).
Electrons get transferred to oxygen but energy is not transferred photosynthetically
Excess energy can damage photosystems
Commonly exacerbated by environmental stressors like cold, nutrient limitation, etc.
Chloroplast - organelle within plant cells
Stroma - fluid
Thylakoid membrane - light reaction & calvin cycle
chloroplasts are very similar to cyanobacteria - believe that endosymbiosis led to full integration of chloroplasts
Chlorophyl - family of pigments that make plants green, absorb blue and red light, reflect green
chl a - all photosynthetic organisms have it, enables light energy to be transformed into chemical energy
chl b - algae and trees, increases light absorption and capacity of chl a
chl c2 - in some algae, allows chl a to absorb sunlight (reddish-brown in color)
chl d - in some cyanobacteria
chl f - absorbtion of red light very efficently
Photosystem 2 - oxidizes water and transfers electrons to photosystem 1
Photon enters photosystem 2 & is absorbed by light harvesting complex, moving it to P680
P680 absorbs red light at 680nm
electron is taken from water molecule (oxidized)
Photon excites the electron, moving it up in energy state
Electron transport chain moves electron from photosystem 2 to 1, making ATP
Photosystem 1 - generates NADPH, uses phosphorylation to generate ATP
photon enters photosystem 1, is absorbed by light harvesting complex, moving to P700
P700 absorbs light at 700nm
electron from photosystem 2 is excited, reacting to form NADP+
takes in two electron to make NADPH
NADPH & ATP produce a sugar complex, forming a glucose molecule
when photon excites electrons in PSI or PSII:
1 photochemistry of energy creation
2 emits heat
3 emits a photon with a longer wavelength (fluorescence)
in fully functional/healthy PSII, the fluorescence is predictable
increased fluorescence means that less of the photon energy is going into energy creation and more is being fluoresced
occurs in Stroma
Phase 1 - C is fixed by Rubisco
Rubisco - enzyme that fixes inorganic carbon to organic
if there is too much O2, rubisco will accidentally split O2, creating a toxic byproduct that plants have to deal with
Phase 2 - Reduction
Phase 3 - Regeneration
Radiometers - light meters, measure UV and visible light, describe shape of light field
Satellites - spectral radiometers measure light reflected from the surface layer of the ocean
Pulse amplitude modulated (PAM) -
Silicon photovoltaic detector - measures PAR
Created a computer model to simulate macromorphology based on light availability that matched the massive - platylike trend we see in nature.
Photoacclimation in shallow corals can also include increased concentrations in photoprotective pigments of the symbiont (xanthophyll, β-carotene) and host (fluorescent proteins), or greater dissipation of absorbed light-energy through non-photochemical quenching (Wall 2020)
