Photosynthesis Notes PDF

# Photosynthesis pt 1. - converting light energy into chemical energy - pulling in the bonds of glucose (building glucose) - used to build all organic molecules - done by plants, algae, cyanobacteria - **photoautotrophs** organisms that make their own food, y sugar, through photosynthesis - **end...

# Photosynthesis pt 1. - converting light energy into chemical energy - pulling in the bonds of glucose (building glucose) - used to build all organic molecules - done by plants, algae, cyanobacteria - **photoautotrophs** organisms that make their own food, y sugar, through photosynthesis - **endogonic rxn** - builds more complex molecules from simple molecules - input of energy (light) - opposite of cell resp, b/c it's building, not breaking down glucose $6CO_2 + 6H_2O + light -> C_6H_{12}O_6 + 6O_2$ ### Light & Waves + Electromagnetic Spectrum - plants absorb and redirect energy (light energy) - which travel in waves - waves measured by wavelength (λ) - visible light spectrum: 380-750 um - red has longest wavelength, violet has shortest ### Photosynthetic Pigments - **chlorophyll a** - main photosynthetic pigment - can differ in structure between plant to plant - **accessory pigments** - chlorophyll b (yellow green) - accessory pigments cannot convert any energy, they absorb it then pass any excess energy they absorbed to chl a. - helps plant absorb wider wavelengths of energy - accessory pigments can also move chlorophyll a, allowing for it to always have maximum light. - all leaves have accessory pigments, but you can't see the color b/c it's overpowered by green of chlorophyll - when leaves die, red, brown, orange pigments shown b/c chlorophyll a died - **green plants absorb red and violet light the most** - plants will die if put under only green light. - all the light will be reflected off and not absorbed. - plants have hormones that respond to particular wavelengths of light, causing them to grow towards that light. # Leaf Structure - in leaves, there is a lot of air space in mesophyll cells. - air space for the air taken in from the stoma. # Photosynthesis pt. 2 - guard cells around stoma to open and close stoma to not lose all $CO_2$ and $H_2O$ and reduce $O_2$ waste. - air is made up of ~21% $O_2$, less than 1% $CO_2$. - has veins (phloem and xylem tubes) ### Chloroplasts - **endosymbiotic theory** - cell ate a prokaryote - cell evolved to become own organism - still has DNA loop, 2 membranes, ribosomes # Photosynthesis Stages ### Light Reactions - light dependent reactions - **non-cyclic photophosphorylation** - most efficient + most common - occurs in thylakoid membrane - products: ATP, NADPH, $O_2$ (indirect waste)  - **Photosystem 1 (PSI)** - uses P700 (pigment: 700 nm) which is a type of chlorophyll a. - when light energy hits thylakoid in leaf, an electron jumps, and that energy is stored in bonds formed between H and NADP to make NADPH. - when e quantum leaps from PSI, it's missing an e and it gets replaced in PSII. - **Photosystem II (PSII)** - **oxidative photophosphorylation** - production of ATP - production of NADPH - 2 stages happen simultaneously: - ETC + ATP synthase (same as cell respiration) in thylakoid - brings $H^+$ in from stroma to interior of thylakoid - ETC connects both photosystems to light strikes and $e^-$ in thylakoid, etc. - quantum leaps and carried by ETC chain to replenish PSII (whose lacking e) - ATP is made from $e^-$ quantum leap - $e^-$ must be replaced at PSII, so $H_2O$ splits into $O_2$ and H - the e from H is given to PSII - $O_2$ is waste product excreted out of stoma - $H_2O$ is ultimate source of e  - **Cyclic Photophosphorylation** - way to make ATP - no glucose formation (glucose can only be made in Calvin cycle) # Photosynthesis pt. 3.  - mostly done by cyanobacteria (too small to store glucose) - large organisms (like trees) can't do cyclic b/c it wouldn't make enough ATP to power the entire tree - not very efficient, only short-lived - no good conversion of light to ATP - only product is ATP. - PSI occurs independently - PSII does not occur - guantum leaped e's replenish thylakoids back to PSI. - no need to split $H_2O$.  ### Calvin Cycle - **AKA C3 Pathway** - light independent reaction. - carbon fixing rxn - occurs in stoma - $CO_2$ enters through stoma - Standing reactant: $CO_2$ $Eq1: 6CO_2 + 6 RuBP -> 12 PGA$ $Eq 2: 12 PGA + 12 NADPH + 12 ATP -> 12 PGAL$ $Eq 3: 12 PGAL -> C_6H_{12}O_6 + 6 RuBP$ ### a. Eq 1 - $COz$ absorbed through stoma - binds with RuBP (5-C) by rubisco (rubisco/RuBP carboxylase) - an enzyme that binds $CO_2$ and RuBP together; active - one gas also fits in rubisco's active site. - since higher concentration of $O_2$ in air than $CO_2$, enzyme will let go of $CO_2$ to capture $O_2$ - rubisco does a bad job of capturing and keeping $CO_2$ (very inefficient) - $CO_2$ is first converted into 3-C compound PGA (same intermediate in male from glycolysis) ### b. Eq 2 - PGA made in Eq 1 is used as reactant, combined with products from light reactions (ATP and NADPH)  - product is PGAL, energy from ATP and NADPH used to form new bond ### c. Eq 3 - final products: glucose and RuBP - RuBP is regenerated to be starting reactant of Eq 1, making it a cycle/cyclic # Photosynthesis pt. 4.  ### C4 Photorespiration - when plants get confused whether they are performing cellular respiration or photosynthesis, is rubisco confused if it's supposed to pick up $CO_2$ or $O_2$ - **C4 plants**  - smart plants (ex: corn, sugarcane) - do C4 then C3 - C4 can make glucose, makes C3 pathway up to 9x more efficient - Cy has and enzyme PEP carboxylase - greater affinity to $CO_2$ - only binds to $CO_2$ - can capture $CO_2$ that rubisco drops - grabs + holds onto $CO_2$ - PEP used in glycolysis - $CO_2$ + PEP -> OAA in bundle sheath cells -> malic or aspartic acid (C-3) deeper in leaf - PEP converts $CO_2$ into OAA (used in Krebs) and moved deeper into leaf to get away from $O_2$ (into bundle sheath cells) - OAA converted to malic/aspartic acid (molecule not used in cell resp) and it's put even deeper into leaf (trying to get away from air from stoma) ### a. Kranz leaf anatomy - C4 plants have different leaf structure - the vein is surrounded by bundle sheath cells to store $CO_2$, further away from $O_2$ ### 2. CAM Plants - plants that close their stoma during the day so they don't dry out and lose water (ex: cactus and pineapples) - also do C3 pathway @ night - is less transpiration (water loss in plants) doing C4 and CAM is ideal in order to "power out" photosynthesis (most effective).  - we can genetically alter plants to do C4 and CAM to grow faster + more