Photosynthesis Flashcards
Autotrophs
sustain themselves by making organic molecules from inorganic raw materials obtained from the environment; (primary) producers
photoautotrophs
use energy from the light for this process
plants are ____autotrophs
photoautotrophs
some bacteria are ____autotrophs
chemoautotrophs
chemoautotrophs
use energy from the breakdown of inorganic compounds, like sulfur or ammonia
Heterotrophs
live on compounds produced by other organisms. Some eat plants and animals; Others consume the remains ofdead or decaying organisms (detritivores/decomposers)
Chloroplasts
organelles within the leaves of plants that are the major site of photosynthesis
Chlorophyll
green pigment located within chloroplasts
mesophyll
tissue in the interior of the leaf.
palisade mesophyll v spongy mesophyll
palisade mesophyll–closer packed, on top, spongy mesophyll have more spaces, covered by epithelial cells
stomata
plural of stoma
stoma
microscopic pores on the surface of the leaf–little holes on bottom of leaf allowing gases in and out not on top bc the sunlight’s heat could evaporate the water out–Carbon dioxide and oxygen enter leaf through.
cuticle
hydrophobic layer on top reduces water loss
Stroma
liquid within chloroplasts
Thylakoid membranes
home to light-dependent reactions and chlorophyll. on inside, hollow, separate stroma from thylakoid space (otherwise called thylakoid lumen) Thylakoid sacs stacked in columns called grana (sing. granum)
Equation photosynthesis
6CO2 + 6H2O (+light)–>C6H12O6 + 6O2
why does photosynthesis + respiration change to glucose and back?
change to glucose and back bc ATP is so unstable and plants can’t store it
reactants and products of light dependent reactions?
light reaction uses light and water, produces O2 as a waste, useful: ATP, NADPH (not listed as products bc intermediates)
other names for Calvin Cycle
CC/carbon fixation/light independent reaction/ dark reaction
Light reactions-
converts solar energy to chemical energyoccurs in thylakoids
steps photosynthesis
light reactions, Calvin cycle
photophosphorylation
uses light energy to add a phosphate group onto ADP, forming ATP
Light reactions-process
Chlorophyll absorbs lightElectrons and hydrogen are transferred to acceptor calledNADP+ (nicotinamide adenine dinucleotide phosphate)Water is split, giving off O2 as a waste product ATP is generated in photophosphorylation
Wavelength
distance between the crests of electromagnetic waves; longer wavelength=less energy; nm nanometers measures wavelength; wavelengths visible light power photosynthesis
carbon fixation–
taking carbon from an inorganic source and changing it into an organic compound
Calvin cycle
incorporates CO2 from air into organic molecules(carbon fixation) using electrons from NADPH and energy from ATP; occurs in the stroma
Why is Calvin cycle also called light-independent reactions, or dark reactions,
becausedoesn’t need light directlyonly happens in light
Visible light-
from 380 nm to 760 nmdetected as colors by human eye
Light behavior
Light can behave as waves (waves=radiation) or photonsphotons–particles of energy
photons
Shorter the wavelength, thegreater the energy of each photon
photon violet energy
double energy of photon of red
what powers photosynthesis?
Visible light powers photosynthesis, specificallyblue and red
Photosynthetic pigments-
the light receptors (Light can either bereflected or absorbed by matter)
Pigment
substance thatabsorbs visible light
Pigment details
Different pigments absorbdifferent wavelengthsWavelengths that are absorbed, disappear The color that is reflected is the color we see (black absorbs all, white reflects all)
o Spectrophotometer
device that can measure the ability of a pigment to absorb various wavelengths of light
Chlorophyll a
appears blue green–best absorbs violet and red; Can participate directly in light reactions
Chlorophyll b
appears yellow-green, best absorbs blue and orange; Can absorb light energy but must pass it to chlorophyll a
Carotenoids-
shades of yellow and orange; Some function in photosynthesis-best absorb blue, violet, green; others function in photoprotection
photoprotection
absorbs and scatters excessive light energy that would otherwise damage chlorophyll
why leaves change colors in fall
in fall, chlorophyll breaks down from cool tempphotosynthesis goes downcarotenoids are no longer hidden by chlorophyllthen gets too cold for carotenoids and turns brown
reaction center
where photosynthesis begins
What happens when photon absorbs light?
photon bounces from pigment to pigment (pigment in one antenna complex to another in another) until it reaches specific chlorophyll a molecule,located in the reaction center
Photosystem
an organization of chlorophyll and other proteins in the thylakoid of the chloroplast; Has light-gathering “antenna complex” made of a few hundred chlorophyll a, chlorophyll b and carotenoid molecules
What happens when chlorophyll absorbs photons of energy from light?
raises an electron in the pigment molecule from the ground state to an excited state (higher energy orbital). Compounds can only absorb photons corresponding to specific wavelengths. The wavelengths that are not absorbed will be reflected.
What happens once the electron is in the high energy state? Why?
it is very unstable, so either: The electron drops back down, giving off heat and sometimes light, or, the electron may be captured by an electron acceptor and used for later. any chlorophyll molecule can do this
What happens when light hits chlorophyll a molecule?
an electron isexcited and it is trapped by the primary electronacceptor before the electron can return to its ground state (functions as light-harvesting unit)
types of photosystems
Photosystem I (P700), and Photosystem II (P680)
Photosystem I (P700)
discovered before II–called P700 bc it best absorbs wavelengths of 700 nm (far red)
Photosystem II (P680)
best absorbs wavelengths at 680nm (plain red)
Noncyclic electron flow step one
PS II absorbs light and an electron is excited and it is captured by a primary electron acceptor
more common electron flow
noncyclic
What happens when an electron is excited and it is captured by a primary electron acceptor (Noncyclic electron)
In order to fill “hole” from lost electron in chlorophyll amolecule, an enzyme extracts electrons from water. H2O –> 2e- + 2H+ + 1/2O2– (photolysis)
photolysis
the breakdown of water in Noncyclic electron flow step two
What happens after photolysis?
Excited electron from electron acceptor passes to PS I through an electron transport chain
What happens when electron is passed to PS I?
noncyclic photophosphorylation. As electron “falls”, energy is captured by thylakoid membraneto produce ATP driven by light energy.
What happens AFTER electron is passed to PS I?
Electron reaches bottom of chain and fills a hole in P700
What happens AFTER electron fills hole in P700?
Electron acceptor in PS I passes excited electron down a second electron transport chain, transmitting them toa molecule called ferredoxin, which passes the electron to NADP+, forming NADPH
cyclic electron flow
PS I only. No release of oxygen or production of NADPH. light shines down on PS1, goes down e-t chain, and then Electrons cycle from ferredoxin back tothe first electron transport chain, which leads back to PSI.
cyclic photophosphorylation-
produces ATP using light energy but recycling the same electron (cyclic electron flow)
why is cyclic electron flow needed?
Needed because Calvin cycle needs more ATP than NADPH-so sometimes switches to cyclic in order to catch up with the production of ATP
chemiosmosis
Similar to chemiosmosis in mitochondria- uses an H+ conc gradient and ATP synthase to form ATP
differences between chemiosmosis in mitochondria and chloroplasts
High-energy electrons in mitochondria come fromsplitting of food, high-energy electrons in chloroplastscome from harvesting light energy; Mitochondria- proton gradient forms in the intermembrane space, chloroplast- in the thylakoid space
calvin cycle
Carbon enters in the form of CO2 and leaves in the form of glucose using ATP and NADPH
Why is G3P removed from the cycle?
to build a molecule of glucose (need 6 turns or 6CO2 molecules)
carbon fixation
6 CO2 attaches to 6 ribulose bisphosphate (RuBP) (5 Csugar) using enzyme rubisco. (Most abundant protein onearth).Splits into 12 3-phosphoglycerate.
Carbohydrate synthesis:
2 G3P are used tobuild on glucose
Net- Calvin cycle
uses 6CO2, 18 ATP, and 12 NADPH, producing G3P that can be made into glucose
50% of sugars made by photosynthesis are used for…
respiration
Green cells
only cells that perform photosynthesis;
what do nongreen cells do instead of photosynthesis
other molecules depend on organic molecules exported from leaves through veins
what do plants do with the extra sugar they make
store starch, stored in roots (transported as sucrose first)
phases CC
CO2 uptake phase, Carbon reduction phase, RuBP regen phase
CO2 uptake phase
6 RuBP –>+ 6CO2–>12 PGA
PGA
phosphoglycerate
Carbon reduction phase
12 ATP–>12 ADP, 12 NADPH –> 12NADP+ and 12Pi, 12PGA–>12G3P–> 2 + 10 G3P (2G3P go to glucose)
RuBP regeneration phase
10 G3P–>6RP()–>6RuBP, (6ATP–>6ADP,)
structure of chloroplast
double membrane; internal liquid called stroma; thylakoids;
