Date Chapter 8 Photosynthesis
Still gonna talk about ATP & Glucose
Still need to understand ph scale and Homeostasis H+ OH-
But now, adding light! Absorbed versus reflected
Their goals Use light energy to make chemical energy Use chemical energy to organic compound energy. Use organic compound energy to produce structure or energy the same way you do!
What s needed to pull this off? Energy Catalysts Raw materials to make sugar
Chloroplast 2 sets of major reactions now: Light Dependent Light Independent
Chlorophyll Light sensitive pigment, when excited by photons, release terminal hydro-carbon chain electrons that can do work. These electrons cycle back to the pigment to be used again and again! Chlorophyll a and Chlorophyll b are PRIMARY pigments **Notice placement of pigments
Accessory Pigments More pigments= more light energy to absorb Carotenoids Xanthophyll Anthocyanin
More pigments=more light absorbed= more power
Pigments are a catalyst!
Stoma Gas exchange occurs through the stomata, what gases and direction? Guard Cells are the doors, stoma are the openings
Everything we need? Energy-sun & ATP Catalysts-sun & enzymes Raw materials-co2 & H2O
More foundational items! Chloroplast, Chromoplast Chlorophyll, And accessory pigments Stomata Carriers Catalysts Visible light
Photosynthesis: An overview Redox reactions, fueled by pigments, enzymes and some visible light H2O is electron donor, CO2 is the electron acceptor So water =the oxidized item and CO2 = the reduced item (LEO GER) 2 main stages; light dependent and Calvin Cycle (aka Dark reactions)
Let s put it all together! Special pigments provide e- energy! Major Pigments: chlorophyll a and b (accessory pigments include xanthophyll, carotenoids and anthocyanin) Gas exchange: stomata Chloroplast (plastid): Double membrane like the mitochondria, house and control the reactions with their membranes & structure!
Draw and label the chloroplast Outer membrane Inner membrane Granum Thylakoid Stroma Stroma Lamellae
Light dependent reactions must occur first! Solar energy excites e- found on pigments housed in the thylakoid discs. (They respond to light much like photovoltaic panels!) Excited electrons are used to split water. There are 2 photo-systems used to make all end products of the Light dependent reactions those that are cyclic and those that are non-cyclic in electron energy.
PSII Happens first Details! Cyclic photosystems Occurs in the thylakoids Transfers electrons from excited pigments to catabolize H2O and use that catabolic energy to form ATP out of ADP. Electron eventually travels pigments in photosystem I. H2O+ADP +P ATP +H+H+O2 (catalysts are enzymes+light) O2 is given off as waste
PSI Happens second Non-Cyclic Occurs in the thylakoids Uses electrons from photosystem II Transfers electrons from catabolized water to assure we create NADPH, electron does not return to pigment, stays in product. H+H+NADP 2 NADPH (enzymes+light) Makes 2 NADPH
Name an enzyme.
NADPH??? What the what?? Their carrier is different! Why is this? How is this?
Photosystem II : Happens 1st e- split H2O (release of O2) e- s travel to Photosystem I down an electron transport chain as e- fall, ADP ---> ATP and water is catabolized Details of the light reactions! Photosystem I : Happens 2nd 2nd ETC transfers e- to NADP+ NADPH (capture H from the water, used in PII) These photosystems produce NADPH Products of the light reactions are: ATP, NADPH2 and O2
So what do we do with the light dependent products? There are 3 products of light reactions. Name them. What do we do with each one?
We want to make organic sugars! Glucose is the most commonly made monosaccharide! Remember the formula for glucose is: C6H12O6 So, we have H, we need O and C.where did we get each? And in what stage of photosynthesis and location?
Using the products of light dep reactions
3 stages
The Calvin cycle (Now that we have the products from light dependent reactions, what to do with them?) 3 steps to the Calvin Cycle: 1- Carbon fixation~ CO2 is attached to 2 C-RuBP ( rubisco an enzyme called ribulose biphosphate) keeps CO2 from exiting, produces PGAL. (3 C) 2- Reduction~ electrons from NADPH2 reduces PGAL into a 6 Carbon sugar (like glucose) by adding in more CO2 3- Regeneration~ Some of the 6 Carbon sugars that are made, are rearranged back into RuBP; ATP fuels all these reactions
Because PGAL is the first carbon structure made during the Calvin cycle, plants that do this are called C3 plants. (Most plants) PGAL is important as PGAL can be made easily into Glycerol, Pyruvic Acid, 6 Carbon sugars, starch, cellulose. One foundational molecule (PGAL) can be converted into 5 different compounds!
Summary 2 major reactions: 1) light dependent reactions ( photo ) in which NADP+ (electron acceptor) becomes NADPH and using Photophosphorylation ADP ATP 2) Calvin-Benson cycle ( synthesis ) in which using Carbon fixation we turn CO2 and products of light dependent reactions into organic sugars.
Alternative carbon fixation methods, Photorespiration: hot/dry days; stomata close; CO2 decrease, O2 increase in leaves; O2 added to RuBP; no sugars can be generated, the CO2 carrier is full of non-useful oxygen! Slows entire productivity down. Plants must waste ATP to remove O2 from RuBP before proceeding.
The burdens of a nasty But this (C3) photosynthetic pathway is water hungry. environment!
Solutions Two Solutions.. 1- C4 plants: PEP carboxylase (used instead of RuBP) fixes CO2 in to form a 4C molecule. PEP LOVES CO2 (Really reduced affinity for oxygen) Ex: Grasses, bamboo
2- CAM plants: open stomata during night, and store CO2 in the mitochondria until light reactions can run. Keep stomata (or lenticle) closed during day. Stored CO2 is called crassulacean acid. To free it up for use CAM plants run crassulacean acid metabolism breaking the acid back down into CO2 EX: cacti, pineapples, etc.
A review of photosynthesis