self-feeders

produce organic molecules from CO2 and other inorganic raw materials

ultimate source of organic compunds for non-autotrophic organisms

producers

plants

use light as a source of energy to synthesize organic substances

obtain organic material by using compounds produced by other organisms

consumers

formed from remains of organisms that died in the distant past

represent sun's stored energy

contained in all green parts of a plant

sites of photosynthesis

two membranes

location of chloroplasts

tissue in interior of leaf

CO2 enters

oxygen exits

microscopic pores

third membrane system

sacs

segregate stroma from thylakoid space

can be stacked in columns--grana

green pigment

located inside thylakoid membranes

in presnece of light, green parts of the plant produce organic compounds and O2 from CO2 and water

6CO2 + 12H2O + light energy= C6H12O6 + 6O2 + 6H2O

direct product is a 3-carbon sugar, not glucose

six repetitions for glucose

water is split, electrons transferred with H+ from water to CO2, reducing it to a sugar

water is oxidized

endergonic

light reactions

Calvin cycle

steps that convert solar energy to chemical energy

water is split providing electrons and H+ and giving off O2

absorbed light by chlorophyll drives electron and H+ transfer to NADP+

reduce to NADPH

generates ATP through chemiosmosis

source of electrons

reducing power

incorporates CO2 from air into organic molecules already present in chloroplast--carbon fixation

reduces fixed carbon to carbohydrate (NADPH provides reducing power)

also requires ATP

makes sugar

occurs in stroma

Calvin cycles

light-independent reactions

light reactions: thylakoids

calvin cycle: stroma

absorb light at different wavelengths

participates directly  in the light reactions

blue green

accessory pigment

olive green

accessory pigments

hydrocarbons that absorb various shades of yellow and orange

photoprotection

when a molecule absorbs a photon

one electron is elevated to an orbital with more potential energy--excited state

only photons with energy eqaul to the difference between energies are absorbed

excited electron falls back to ground state

energy givenoff as heat and light

reaction-center complex

light-harvesting complexes

surrounded by light-harvesting complexes

-consist of various pigments bound to proteins

enable to harvest light over large surface area and larger portion of spectrum

holds pair of chlorophyll a

located in reaction-center complex

molecule capabel  of accepting electrons  and becoming reduced

special-molecular environment

use light to boost electron higher AND transfer to another molecule

first step of light reactions

PSI: P700

PSII: P680, functions in first light reaction

light drives synthesis of NADPH and ATP

1. photon stries a pigment molecule in PSII, boosting to excited state, as electron falls back down, next pigment is excited, contineus until it reaches P680 pair of chlorophyll a, excited pair

2. electron transferred to primary electron acceptor. becomes P680+

3. enzyme catalyzes splitting of water into two electron and two H+ and oxygen, electrons are supplied to P680+, H+ released into thylakoid lumen

4. photoexcited electrons pass to PSI by ETC (PQ and PC)

5. exergonic fall of electrons makes ATP, as electrons pass through cytochrome complex H+ are pumped  into lumen

6. light energy harvested by pigments in PS I, excited chlorophyll a P700, electron transfers to primary acceptor, creates electron hole P700+, accepts electron from electron chain

7. photoexcited electrons pass through redox reactions from PS I through ETC using Fd, no ATP

8. enzyme NADP+ reductase catalyzes transfer of electrons from Fd to NADP+, two electrons required to reduce to NADPH, also removes H+ from stroma

alternate path for photoexcited electrons

PSI but not PSII

electrons cycle back from Fd to cytochrome complex and continue to P700

no NADPH or release of O2

generates ATP

plants that have this capable of growing in low light

photoprotective

starting material regenerates

anabolic

carbon enters in form of CO2 and leaves as sugar

spends ATP and NADPH

glucose is not produced-G3P

requires three cycles

fixes three CO2

phases: carbon fixation, reduction, regeneration

incorporates CO2

catalyzed by rubisco

uses 6 ATP

produces  6-carbon intermediate that splits into two molecules

each molecule receives phosphate from ATP

NADPH gives a pair of molecules, reducing

loes phosphate becoming G3P

uses 6 NADPH

1 net G3P gained

first organic product of carbon fixation  is a three carbon compound

use photorespiration

occurs in C3 plants

hot, arid climates

stomate partially close--produce less sugar due to declining CO2 levels

rubisco binds to O2 instead--releases CO2

generates no ATP or sugar

decreases photosynthetic output

protective

preface Calvin Cycle with alternate mode of carbon fixation--four carbon compound

1. enzyme PEP carboxylase adds CO2 to PEP, four carbon product (occurs in mesophyll), higher affinity for CO2 than O2

2. mesophyll exports to bundle-sheath cells through plasmodesmata

3. four carbon compunds release CO2, made into organic material by calvin cycle, regenerates pyruvate which ATP converts to PEP  in mesothyll cells

open stomata at night

store CO2 in vacuoles--form of organic acids