bsc2010 chapter 10 photosynthesis

autotroph

“self feeders”, takes co2 → organic molecules and can sustain life w/o eating other organisms

heterotroph

“different feeders”, other organisms → organic molecules, depends on photoautotrophs for food and o2; they cannot exist without autotrophs

photoautotroph

uses energy from sun, takes h2o and co2 → organic molecules, includes plants, algae, some protists and prokaryotes

stroma

dense fluid inside chloroplasts that is outside of the thylakoids; similar to cytoplasm but for chloroplasts

thylakoid

connected sacs in the chloroplast, contains chlorophyll

granum

stacks of thylakoids are called

lumen

location of the ETC in photosynthesis

photosynthesis equation

6co2 + 6h2o + light energy (photons) → c6h12o6 + 6o2

mesophyll

interior tissue of the leaf containing 30-40 chloroplasts

stomata

pores on leaves that allows co2 to enter and o2 to exit

photo vs cell

photosynthesis

• endergonic

• reduces co2 → sugar

cellular respiration

• exergonic

• oxidizes sugar → co2

light rxn and calvin cycle

these are the two steps of photosynthesis, where h2o splits into h2 and o2 with the electrons being taken from them

light rxns

in the thylakoid membrane, this is step one of the photosynthesis process:

• split h2o

• reduce NADP+ to NADPH

• generate ATP from ADP via photophosphorylation

• release o2

calvin cycle

in the stroma, this is step two of the photosynthesis process

• ATP and NADPH → CO2 → G3P

• IN ORDER: carbon fixation, reeduction, regeneration of CO2 acceptor

chlorophyll

within thylakoid membranes, these reflect and transmit green light and are pigments within chloroplasts; photon absorbed by ________ → reflects green

visible light

wavelengths that produce colors we can see, being 380nm to 750nm

photons

also known as sunlight

chlorophyll a

the main photosynthetic pigment that contain colors violet, blue, and red

accessory pigments

alongside chlorophyll a, these are in place to broaden the spectrum of colors and absorb excessive light that would otherwise damage chlorophyll; chlorophyll b and carotenoids

carotenoids

these are a type of accessory pigment that transmits yellow, orange, or red light and is responsible for leaf color in fall

absorbs light

when a pigment _________, electrons move from a ground state to an excited state, giving off heat or fluorescence, allowing acceptance through an electron acceptor in a redox reaction, exciting nearby pigments, or dropping back down in energy levels

photosystem

consists of a reaction-center complex surrounded by light-harvesting complexes (aka pigment molecules) which funnel the energy from photons → reaction center

pheophytin

a primary electron acceptor in PSII, accepts an excited electron; being a pigment molecule structurally similar to chlorophyll

photosystem 2

in the thylakoid membrane, this is one of the photosystems that usually functions first, is best at absorbing wavelength 680nm and reaction-center chlorophyll a is p680

• photon hits pigment

• light energy passes amongst pigment molecules → excites p680

• excited electron from p680 → primary electron acceptor pheophytin

• H2O split by enzymes, electrons transferred from the H atoms to P680+, reduced to P680

• O2 byproduct

photosystem 1

in the thylakoid membrane, this is one of the photosystems that is best at absorbing wavelength 700nm and reaction center a is p700

• photon hits pigment

• P700 accepts replacement electrons from PSII via ETC

• electron passes → primary electron acceptor ferredoxin

pmf

energy released by the fall of electrons down the etc creates this across the thylakoid membrane, with the diffusion of H+ (protons) back across the membrane driving ATP synthesis

ferredoxin

primary electron acceptor of PSI

cytochrome complex

this structure provides a connection between PSII and PSI, allowing plastoquinone produced by both products to pass through to generate ATP

NADPH

product of PSI, made by enzyme NADP+ → transfer proton and two electrons from ferredoxin → forms ____________

ATP

product of PSII, made by the pmf

linear electron flow

the primary pathway involving both photosystems and produces ATP and NADPH using light energy

cyclic electron flow

using only PSI and produces ATP, but not NADPH; good for generating surplus ATP to satisfy the higher demands in the calvin cycle

mitochondria vs chloroplast

• intermembrane space → thylakoid lumen

• inner membrane → thylakoid membrane

• matrix → stroma

• ETC: inner membrane → thlakoid membrane

• PMF: intermediate space → thylakoid lumen

• ATP synthase: inner membrane → thylakoid membrane

• ATP location: mitochondrial matrix → stroma

rubisco

important CO2-fixing enzyme in the calvin cycle. most abundant enzyme on earth yet most demanding

• inefficent, catalyzes addition of CO2 to RUBP and addition of O2 to RUBP

• adds CO2 + RUBP → G3P

• one molecule is released for every five that continue around the cycle

photorespiration

rubisco adds O2 instead of CO2 in the calvin cycle

• O2 and organism fuel → release CO2, using extra ATP and producing no ATP or G3P

• carbon fixation favored over this process when CO2 high O2 low

• hot dry conditions are favored for this process

RUBP

in the calvin cycle, this is used to generate a 6 carbon molecule of G3P and is regenerated once five G3Ps are available, then recycled to regenerate the acceptor, requiring ATP in the process

c4 plants

plants that minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds by using enzyme PEP carboxylase

PEP carboxylase

this enzyme has a higher affinity for CO2 than rubisco and can fix CO2 even when CO2 concentrations are low

cam plants

plants able to open their stomata at night → take in CO2 → close during day → CO2 released from organic acids → use in calvin cycle

sun

even though PSII works before PSI does, the ____ is hitting them both at the same time and they work at the same time