Definition for Photosynthesis

Photorespiration

Photosynthetic

The process whereby light energy is captured by plant, algal, or cyanobacterial cells and used to synthesize organic molecules from CO2 and H2O (or H2S).

---

PHOTOSYNTHESIS

BACKGROUND INFORMATION ON PHOTOSYNTHESIS

Energy Flow in Living Organisms:

       Primary producers ---> Herbiovores ---> Carnivores

   Primary Producers

Plants and certain types of bacteria and protists produce energy for the rest of living organisms on Earth Use energy fomr the sun - about 5% Aka "Autotrophs"

   Herbivores

Plant eaters; ability to digest plants Release energy stored in plants Aka "Primary Consumers"

   Carnivores

Eat Herbivores Aka "Secondary Consumers" So WHY does this RELATE to PHOTOSYNTHESIS?????

- Without photosynthesis plants could not grow - Herbivores and Carnivores (You and Me) would not be able to survive - We rely on plants in order to obtain their energy which we use to survive - Plants plan an important role in coverting CO2 into O2 so that humans can breath - Growing plants can provide multiple neds for humans (food, medicine, builing materials)

Photosynthetic Organisms They are largely self-sufficient Takes in: CO2, Water, Sunlight Produces: Sugars and Oxygen Types of Photosynthetic Organisms Prokaryotic Autotrophs: cyanobacteria unicellular grow rapidly in nutrient rich water Eukaryotic Autotrophs algea, photosynthetic protists, plants contain chlorophyll within chloroplasts LEAVES are the primary photosynthetic organs of a plant

WHERE PHOTOSYNTHESIS BEINGS !

CHLOROPHYLL light-absorbing pigment reflects the colour green there are 2 types: Chlorophyll a (blue-green) Chlorophyll b (yellow-green) composed of a porphyrin rings attached to a long hydrocarbon tail PORPHYRIN RING contains a magnesium aton at its centre surrounded by a hydrocarbon ring hydrocarbon ring has alternating double and single bongs electrons in these bonds absrob light energy and being the PHOTOSYNTHETIC process

PARTS OF A LEAF

Waxy Cuticle - protects from excessive absorption of sunlight and evaporation of water Epidemis Layer - allows light to pass through; located below the cuticle Chloroplasts - most abundant in the spongy and mesophyll layers Guard Cells - create openings called STOMATA that regulate the exhange of CO2 and O2 Vascular Bundles - transports water and minerals from roots to the leaf cells and carry carbohydrates from leaves to other parts of the plant

STOMATA allows for the exchange of CO2 to diffuse into air spaces within the leaf's mesophyll layers (where most cholorplasts are located) plants regulate the size of the openings under certain conditions to maximize CO2 intake and minimize water losee usually open in the day time and closed at night

CHOLOROPLASTS located within mesophyll and guard cell layers SITE OF PHOTOSYNTHESIS

Structure: Stroma - semiliquid material that is protein rich and located between the inner/outer membranes of the chloroplast - SITE OF THE CALVIN CYCLE

Thylakoids - located within the stroma; connected to membrane sites

Grana - a stack of thylakoids

Thylakoid Membrane - contains light-gathering pigment molecules (CHLOROPHYLL) and electron transport chains - SITE OF THE LIGHT REACTIONS

STOP! LETS TAKE RECAP WHAT WE HAVE LEARNED SO FAR

Photosynthesis takes place in oder for plants to grow Plants take in CO2, Water, and Sunlight to PRODUCE sugar and O2 Photosyntheis beings in the CHLOROPHYLL which is a light absorbing pigment Cholorphyll is found in CHOLORPLASTS of plants Chloroplasts are mainly found in the LEAF of a plant

PHOTOSYNTHETIC PIGMENTS


Photosynthetic Pigments

Chlorophyll a - transfers lgiht energy to carbon fixation reactions chlorophyll b - absorbs light energy that chlorophyll a does poorly, if at all Photosynthetically active radiation (PAR) - chlorophyll a + b combined with accessory pigments of wavelengths from 400nm to 700nm clusters of these pigments are referred to as PHOTOSYSTEMS (are embedded in the thylakoid membranes within the chloroplasts) absorb photons of specific wavelengths via light reactions, they transfer energy to form ATP and NADPH ATP and NADPH are synthesized in the stroma (located within the chloroplasts) PHOTOSYSTEMS

Structure:

   Antenna Complex:

web of chlorophyll molecules in the THYLAKOID MEMBRANE antenna pigment absorbs the photon and transfers energy to chlorophyll a molecule in the reaction centre chlorophyll a molecule absorbs energy and it is raised to high energy level redox reactions transfer excited electron to a PRIMARY ELECTRON ACCEPTOR, leaving chlorophyll in an oxidized state Reaction Centre: transmembrane protein complex containing chlorophyll a electrons absorb light energy and begin process of photosynthesis

TYPES OF PHOTOSYSTEMS

   PHOTOSYSTEM 2

called P680 best at absorbing photons with wavelength of 680nm

   PHOTOSYSTEM 1

called P700 best at absorbing photons with wavelength of 700nm Notes:

plants use photosystems 2 and 1 to produce ATP and NADPH referred to as NONCYCLIC ELECTRON FLOW

REDOX REACTIONS (OXIDATION-REDUCTION)

transfer of electrons from one atom to another reducing agent = oxidation (release of electrons) oxidizing agent = reduction (gain of electrons) "LEO says GER"

STAGES OF PHOTOSYNTHESIS

LIGHT REACTIONS:
    1. CAPTURING LIGHT ENERGY (PHOTON)
    2. CREATING ATP and NADPH from the LIGHT ENERGY

CARBON FIXATION (CALVIN CYCLE):

    3. PRODUCE GLUCOSE via CO2 with ATP and NADPH 

PART 1 & 2 Photon hits photosystem 2 and excites and electron of chlorophyll P680 which is captured by PRIMARY ELECTRON ACCEPTOR (pheophytin). Via REDOX reactions, the electron is transferred to PQ (plastoquinone) whihc is an electron carrier and then off the ETC (electron transport chain) ---- This occur 2x

Water splits into O2, H+ ions, and electrons via the Z protein. Two of the electrons replace the ones missed in chlorophyll P680. As a byproduct, O2 leaves the chloroplast. H+ ions remain in the THYLAKOID SPACE creating a PROTON GRADIENT

Electrons leaving Photosystem 2 go through a "Q cycle" and transports electrons through the b6-f cytochrome complex. Protons (H+ ions) are pumped in from STROMA into the THYLAKOID LUMEN creating a H+ gradient from chemoiosmosis. Four H+ ions for every two electons that pass through the transport chain. Electrons move through the PC (plastocyanin) andother parts of the ETC, replacing the two electrons that were lost by Photosystem 1 (just like what happened in Photosystem 2)

Electrons from Photosystem 1 pass through another ETC containing Fd (ferredoxin). They then move to the ENZYME NADPreductase that uses two electrons and H+ ions from the stroma to reduce NADP+ to NADPH

Protons (H+ ions) that accumulate in the thylakoid lumen contribute to an electrochemical gradient that drives the PHOSPHORYLATION of ADP to ATP. As protons move through the ATPase complex from the thylakoid lumen into the stroma, ATP is formed. Since light is required this process is called PHOTOPHOSPHORYLATION. ATP and NADPH then move into the CALVIN CYCLE

VIDEO LINK ON PARTS 1 and 2


http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic_Electron_Transport_and_ATP_Synthesis

PART 3

CALVIN CYCLE EQUATION:

   3 RuBP + 3CO2 + 9ATP + 6NADPH + 5H2O ---> 9ADP + 8Pi + 6NADP+ + G3P + 3RuBP

CARBON FIXATION REACTIONS

The initial molecule, ribulose 1,5-biphosphate (RuBP), reacts with CARBON DIOXIDE with the aid of RuBP carboxylas enzyme, the first stable molecules produced are 2 3-Carbon molecules called 3-phosphoglycerate (PGA)

There is a non-stable 6-carbon molecule that preceds PGA but it immediately breaks into 2 PGA molecules Once PGA is made ATP donates a phosphate group to PGA to form 1,3-biphosphoglycerate. It now had 2 phosphate groups, one each on the first and third carbons Now in the reduction and carbohydrate production stage, 1,3-biphosphate takes the H from an NADPH being reduced and releases its phosphate group to become 3-phosphoglyceraldehyde (3GP) 3GP can now be used to create carbohydrates for energy and regeneration of the original RuBP molecule