photosynthesis- lecture #12 Flashcards
what is the origin of all energy?
solar power
what are chloroplasts responsible for in photosynthesis?
capture of light energy
what organic materials are needed for cell activities?
carbohydrates, proteins, lipids, nucleic acid
where can carbon originate from?
carbon dioxide and organic sources
what is autotrophic nutrition? what uses this?
can fix their own carbon
carbon dioxide uses this
plants
what is heterophic nutrition? what uses heterotrophic nutrition?
can’t make carbon themselves, need carbon to be given to them
organic sources use heterophic nutrition
how do organic sources obtain carbon?
through decomposition (fungi, bacteria) or direct consumption
how do photoautotrophs work?
use light energy to synthesize organic compounds
what are photoautotrophs? examples
algae, protists, cyanobacteria
what is a redox reaction?
movement of electrons from water to carbon dioxide forming sugar
what happens to potential energy in a redox reaction? is it endergonic or exergonic?
potential energy of the electrons are increased along the way
endergonic reaction
what makes a redox reaction endergonic?
takes energy from the sun
what are 2 stages of photosynthesis?
light reactions
dark reactions (calvin cycle)
where did photosynthesis begin? what does photosynthetic bacteria consist of?
began in photosynthetic bacteria
highly folded plasma membrane
same structure as a chloroplast membrane
how can you re energize H2O
by using electrons
what are veins function in leaves?
veins export sugar to the roots and other non- photosynthetic structures
(responsible for transport)
why is it important for leaves to be flat?
to capture as much of the light energy from the sun as possible
why are chlorophyll pigments concentrated? what do they do?
provides characteristic green color and absorbs light energy
what drives photosynthetic reactions?
light absorption by chlorophyll
what is the photosynthesis equation
6CO2 +12H2O + light energy —> C6H12O6 + 6O2 + 6H2O
what is glucose assembled from?
2 three carbon intermediates
why is the inner membrane of chloroplasts not folded?
because we don’t put proteins in it
do chloroplasts have high or low SA
high SA because of the grana that are stacked inside
how does sunlight lift electrons? analogy
when you use a hammer and a bell at a fair, you put your energy into it and it increases potential energy
what does photosynthesis use as a reactant and also a product
water
where does O2 generated from photosynthesis come from?
water molecules
how many water molecules are needed to produce O2
need 2 H2O in order to produce O2
where do light reactions take place?
thylakoid membrane (the photo stage)
what is water split into? what does it release?
water is split into 2 protons and 2 electrons
releasing oxygen
what is the light absorbed by chlorophyll used to do?
used to power the transfer of electrons from water to NADP+
how is ATP produced in light reactions?
solar energy is converted into ATP
chemiosmosis produces ATP
what is the process of chemiosmosis in photosynthesis?
light energy is converted to chemical energy in the form of ATP to be used in dark reactions
what are dark reactions?
carbon fixation step
do light and dark reactions take place in daylight?
yes, but dark reactions do not require light
where do we store pigments?
thylakoid because it has good memory
what is an example of electromagnetic radiation?
sunlight
how does electromagnetic radiation travel?
in waves that have electrical and magnetic properites
what is wavelength?
the distance between crests
how is wavelength related to energy
inversely related to energy
shorter wavelength, higher energy
what are photons?
discrete particles of light, each has a fixed quantity of energy
what happens when light interacts with matter?
___,___,___
it can be reflected, absorbed or transmitted
what do pigments serve to absorb?
light energy
light must be absorbed if it can be used to perform work
what are the 3 pigments in chloroplasts?
chlorophyll a
chlorophyll b
carotenoids
what does chlorophyll a do?
participates directly in the light reactions
prevents waste
what does chlorophyll b do?
an accessory pigment
what are carotenoids?
group of accessory pigments
what is the least effective color?
green, because it is reflected
can’t be absorbed/ used to perform work
what do accessory pigments allow?
allow absorption of an increased number of wavelengths
what allows for increased absorption between pigments?
small structural differences
what type of light does chlorophyll a have?
chlorophyll a: blue green light
what type of light does chlorophyll b have?
chlorophyll b: olive green light
what type of light does carotenoids have? what does this light do?
carotenoids: yellow/orange light
serve as photo-protectants
absorb and dissipate energy
why are there 3 different types of pigments?
because you can’t do everything on your own
chlorophyll a gets everything from the other pigments
therefore, chlorophyll b and carotenoid are the people you hire to do stuff for you
what happens when pigments absorb light?
increased potential energy, excites electron to another orbital
how does an electron reach the excited state, what happens after the excited state?
photon is absorbed –> charges electron with light —> boosts the electron to an excited state –> electron drops back to the ground state quickly –> absorbs longer waves and releases
what is excess energy from electrons released as?
heat or light (fluorescence)
wasted light
what is a photosystem? what does it consist of?
reaction centre complex
a pair of chlorophyll a and light harvesting complexes
what does increased variety of pigment allow?
allows energy harvesting to occur over a greater SA and an increased spectrum of absorption
process of photon to center complex
photon strikes pigment
pigment reaches excited state
pigment transfers energy from pigment to pigment
gives energy (electron) to chlorophyll a
chlorophyll a gives electrons to reaction center
process of photon to center complex analogy
you strike the hammer on the plate
bell inside reaches the top (excited state)
as bell goes down theres a decrease in energy
the energy thats left would be given to chlorophyll a
chlorophyll a gives electrons to reaction center
chlorophyll a converts what type of energy to what type of energy?
converts light energy to chemical energy
(redox reaction)
what photosystems do thylakoids have
photosystem PSII and PSI
what wavelength does PSII and PSI have?
PSII: P680
PSI: P700
what comes first, PSI or PSII
PSII but has a shorter wavelength so remember it that way
what happens as the electron falls back down?
energy release stimulates excitation of a nearby electron
how long does the process of the electron continue for in photosystem II?
until the chlorophyll a pair of P680 is reached
what does P680 look like when its excited?
P680*
when P680 is excited H2O splits into what? what helps H2O do this?
H2O is split into 2H+, 2e- and O
assistance of an enzyme
what does photosynthesis use? (3)
H2O, CO2 and sunlight
what does photosynthesis create?
O2 organic compounds
where are photosynthetic pigments located?
thylakoid membrane
what are the products of light reactions?
NADPH, O2, ATP
what is the terminal electron acceptor in the light reactions of photosynthesis?
NADP+
Molecular oxygen (O2) produced in the light reactions originates where?
H2O
During the dark reactions of photosynthesis, electrons begin on_______and end up on ________
NADPH and CO2
the transfer of electrons from P680* to P700 is what type of reaction?
exergonic and coupled to the transfer of protons from the stroma into the thylakoid lumen
plants use sugars produced in the dark reactions to build what? ____,____,____
lipids, proteins and other important molecules in the cell
When H2O splits int 2H, 2e- and O, what are the electrons used for?
used to replace the donated pair from P680
what happens to H+ when H2O is split?
goes to the thylakoid lumen, creates a strong H+ gradient then goes through chemiosmosis (ATP synthase) to create ATP to be used in the calvin cycle
What happens to oxygen when water is split?
it gets released, in which we use to breath
what happens after electrons go from P680 to P680*? what happens next?
transferred via an electron transport chain (to get to photosystem I)
what does the electron transport chain consist of?
plastoquinone, cytochrome complex and plastocyanin
the fall of electrons going through photosynthesis is what type of reaction?
exergonic
what gets pumped through the electron transport chain into the lumen?
H+, to go to the ATP synthase to create ATP
the light harvesting complex transfers light where?
photosystem I
what happens in photosystem I?
the electrons of P700 are replaced with the electrons moving from PSII down the electron transport chain
photons also get absorbed
where does P700* pass electrons to?
moves down a second electron transport chain
what does the second electron transport chain use?
ferredoxin
what does the second electron transport chain do?
transfers electrons to NADP+ forming NADPH
is NADP+ an electron donor or acceptor?
acceptor
where does the NADPH get brought to?
calvin cycle (to be used later)
what is more energized, NADPH or H2O? why?
NADPH because more energy is released
why are light reactions called the z scheme?
in the form of a Z going through photosystem II, ETC and photosystem I
what does the cyclic electron flow consist of?
electrons move from ferredoxin to cytochrome complex to P700 in PSI (they get recycled)
is PSII ever used in cyclic electron flow?
never, only PSI
what is not released (2) and produced (1) in the cyclic electron flow?
no NADPH released
no O2 released
ATP is produced
why does the cyclin electron flow need to occur? (3)
to generate ATP
to recharge
to protect photosystem I and II against photoinhibition
what is the equation for dark reactions?
NADPH + ATP + CO2 –> glucose
what type of reaction is the calvin cycle? (catabolic or anabolic)
anabolic
creates order
non-spontaneous
what is the reducing power that the calvin cycle uses?
NADPH
what is G3P?
glyceraldehyde 3 phosphate (calvin cycle doesnt directly produce glucose, it produces G3P)
what are the 3 phases of the calvin cycle?
phase I: carbon fixation
phase II: reduction
phase III: ribulose bis-phosphate regeneration
what occurs during carbon fixation?
RuBP + CO2 are catalyzed by an enzyme called RUBISCO to form a 6 carbon intermediate
what does the 6 carbon intermediate do?
splits into 2 x 3-phosphoglycerate
(because the intermediate is very unstable
what is the first step of reduction?
3 phosphoglycerate accepts a phosphate form ATP forming 1,3 bis- phosphoglycerate (1,3 PGA)
what does 1,3 bisphosphoglycerate (1,3 PGA) do?
accepts 2 electrons from NADPH and releases one phosphate group
when 1,3 bisphosphoglycerate (1,3 PGA) accepts 2 electrons what does it form?
glyceraldehyde 3-phosphate (G3P)
(has more potential energy)
(also formed in glycolysis)
in the reduction phase for every 3 turns of the calvin cycle what is produced?
6 G3P
with the 3 cycles in reduction how many carbons have been consumed?
15 carbon from RUBISCO
in the III phase of the calvin cycle what is rearranged? what does this process require?
5x G3P are rearranged into 3x RuBP
(requires 3 ATP)
what does the net synthesis of one G3P require?
9 ATP and 6 NADPH
ATP and NADPH are products of the light reactions
on hot days what form is the stromata in?
stomata are closed
why are stomata closed on hot days?
prevents water loss
by preventing water loss what else simultaneously decreases?
CO2 intake and therefore increased O2 release from the light reactions
in respect to photorespiration what plants make G3P first?
C3 plants
in photorespiration, RUBISCO can bind to what?
O2 as well as CO2
what is the most abundant protein on earth?
RUBISCO
when RUBISCO binds to O2 or CO2 what compound is produced?
2 carbon
what is consumed and released during photorespiration?
O2 is consumed, peroxisomes and mitochondria rearrange the compound and CO2 is released
does photorespiration consume or produce ATP?
consumes
what do C4 plants produce?
4 carbon intermediate
what is the unique leaf anatomy in C4 plants?
bundle sheath is arranged around the veins of the leaf (between vein and mesophyll)
where does the C4 plant relocate CO2?
from mesophyll (oxygenated) to bundle sheath (no oxygen)
what is the process of CO2 being relocated to the bundle sheath an example of?
alternative to carbon fixation
what does the enzyme PEP carboxylase do in the alternative to carbon fixation?
combines PEP with CO2 forming a 4 carbon intermediate called oxaloacetate
what has a higher CO2 affinity, PEP carboxylase or Rubisco?
PEP carboxylase (because it does not have O2 affinity allowing for efficient CO2 fixation in hot, dry climates)
what does the mesophyll do with the 4 carbon intermediate product?
exports it to the bundle sheath cells via plasmodesmata
what happens to the 4 carbon intermediate in the bundle sheath cells?
it loses CO2 therefore is used as a substrate for Rubisco
the remaining 3 carbon molecule pyruvate is converted back to ___ at a cost of one ___ molecule
PEP at a cost of one ATP molecule
(the price required to increased the CO2 concentration in the bundle sheath cell)
the high CO2 concentration keeps Rubisco from binding to ___ which minimizes photorespiration
O2
in CAM plants photosynthesis adapts to what?
hot climates
(example is cacti)
in CAM plants is stomata open or closed?
open at night and closed during the day (helps to conserve water)
what do CAM plants prevent from entering?
CO2
once equilibrium of CO2 has been reached in CAM plants, where is the CO2 stored?
into organic acid
what does photosynthesis produce? (2)
chemical energy and carbon skeletons
what is chemical energy used to make?
all major organic molecules of plant cells
(50% is stored as fuel for cellular respiration)
leaves are autotrophic, what does that entail?
the remaining plant structures receive organic carbon structures via the veins (usually as sucrose)
organic carbon is delivered to other cells for what? (2)
cell respiration and anabolic reactions
glucose is stored as starch, what is starch to photosynthesis?
main ingredient of the plant cell wall
we use glucose
where is excess sugar stored in plants?
roots, seeds and fruits
sap transport is bidirectional, what does that mean?
sap goes up into the leaf through the roots
sap goes down the leaf simultaneously
how many metric tons of carbohydrates do plants produce per year?
160 billion metric tons
