C1.3 Photosynthesis Flashcards
photosynthesis
energy of sunlight used to produce glucose from carbon dioxide and water. oxygen as waste product
glucose formed in photosynthesis can be stored as
temporarily stored as starch
photosynthesis in relation to the atmosphere
maintains its composition.
only natural process that releases oxygen into the atmosphere
why is it improtant that oxygen from plants is converted into ozone in the atomsphere
to protect life from UV light that reachs earth from the sun and cause mutations in nucleic acids
photolysis
light energy used to split water
what is light
a form of electromagnetic radiation produced by the sun
what is the result of photolysis
releases oxygen and allows hydrogen atoms to be retained on hydrogen acceptor molecules
ATP is also generated from ADP and P, using energy from light
what is the hydrogen atoms and ATP from photolysis used for
the hydrogen is carried to a series of reactions that result in the formation of glucose
what else carries out photosynthesis instead of plants
algae and cyanobacteria contain photosynthetic pigments, producing glucose and oxygen
cyanobacteria
the first organisms on earth to produce oxygen, 2.8 billion years ago
have accessory pigments called phycobilin and transfers energy from this to chlorophyll a
red and green algaie
developed 1.5 bn years ago
red has same pigments as cyanobacteria, deriving color from phycoerythrin
green algae have chloroplasts contained chlorophyll a and b which is why theyre green
purpose of chromatography in photosynthesis
ideal technique for separating biologically active molecules
what are chromatograms run on
adsorbent paper, powdered solid or on a thin film of dried solid
absorption spectrum of pigments are obtained by
measuring their absorption of colours. results are then plotted as a graph showing the amount of light absorbed over the wavelength range
what causes absorption of energy of blue and red light in chlorophyll
the chemical structure of the chlorophyll molecule
how is light energy transformed to chemical energy
absorption of light excites electrons. accessory pigment transfer excited electrons to chlorophyll a which leads to a series of reactions ultimately forming glucose
action spectrum
action spectrum of chlorophyll is the wavelength of light that are used in photosynthesis
limiting factor for photosynthesis
an environmental factor that when in short supply, affects rate of photosynthesis
effect of carbon dioxide concetnration on photosynthesis
shows positive correlation, suggesting it is the limiting factor.
at much higher concetration it reaches a plateau meaning another factor is limiting
effect of light intensity concentration on photosynthesis
positive correlation, showing its limiting factor
reaches plateau, suggesting other factor is limiting
effect of temperature on photosynthesis
at low temperature there is correlation
at high temperature, rate of photosynthesis abruptly drops and falls. there is clear optimum temperature for photosynthesis
due to enzymes controlling photosynthesis
what is FACE
free air carbon dioxide enrichment experiments
investigate effects of carbon dioxide enrichment on trees
used to try to predict the effects of increasing global warming
the two stages of photosynthesis are
light dependent reactions and light independent reactions
light dependent reactions
photolysis
hydrogen removed and retained by NADP/hydrogen acceptor
ATP generated from ADP and P, using light energy
oxygen given off as waste product
photophosphorylation
ATP being generated from ADP and Pw
where do light dependent reactions occur
in the grana of chloroplast
light independent reactions
glucose synthesized using carbon dioxide
products of light dependent reactions are used in glucose production
requires a continous supply of products from light dependent but does not directly involeve light energy
where do light independent reactions occur
in the stroma of the chloroplasts
photosystems and where are they located
arrays of pigment molecules that can generate and emit excited electrons.
located in thylakoid membranes of grana and occur in cyanobacteria and chloroplasts
what does each photosystem contain
several hundred chlorophyll molecules
accessory pigments and proteins/light harvesting complements
all harvest light energy of different wavelengths and funnel energy to single chlorophyll molecule of the photosystem, known as reaction core. chlorophyll is then photoactivated
what are the two types of photosystems present in the thylakoid membrane of the grana
photosystem 1 activates with wavelength 700 nm, called P700
photosystem 2 activates with wavelength 680 nm, called P680
what happens when light energy reaches a reaction centre
ground state electrons in the reaction centre are raised to an excited state by the energy recieved
means high energy electrons are releases and these electrons bring about the biochemical changes of the light dependent reaction
spaces vacated by high energy electrons are continously refilled by ground state electrons
LHC proteins
consist of enzymes which catalyse formation of ATP and catalyse conversion of hydrogencarrier to reduced carrier
also consist of electron carrier molecules
what do the different types of pigments enable
enables light energy to excite electrons in a controlled way and direct these electrons along electron transport chains
purpose of different pigments
allows plants to harvest light from a range of different wavelengths, increasing flow of electrons to the reaction centre
where do the photosystems electrons come from
PS 1 electrons come from PS 2
PS 2 electrons come from splitting water molecules
generation of oxygen by the photolysis of water in photosystems
excited electrons from photosystem 2 are accepted and passed along a chain of electron carriers
as a result of energy transfers, excitation levels of the electrons fall back to ground state and they fill vacancies in reaction centre of ps 1
vacancies are then filled in ps 2 by electrons from the water systems
2 is a ctalyst that splits the water molecule, triggering release of hydrogen and oxygen atoms, and ground state electrons
from the split water molcule, oxygen is cretes and hydrogen ions used in reduction of NADP
ATP production by chemiosmosis in thylakoids
in grana, synthesis of ATP is coupled to electron transport via movement of protons by chemiosmosis
hydrogen ions trapped within the thylakoid space activates rotary mechanism of ATP synthase moving down gradient
ATP is synthesized
as excited electrons pass from PS 2 along electron transport chain, some of energy causes pumping of hydrogen ions/protons from matrix into thylakoid.
Protons accumulate, causing pH to drop which results in proton gradient, sustaining synthesis of ATP.
protons pass down gradeient though ATP synthase resulting in ATP
Reduction of NADP by Photosystem 1
excited electron from photosystem 1 are passed two at a time to NADP, reduced to form NADPH + H
electrons released by ps 1 are transferred back to 1 instead of moving into the NADP. This movement of electrons result in formation of ATP molecules
electrons cycle repeatedly through ps 1 and the first portion of the electron transport chain but do not pass through 2, NADPH is not formed and water is not requred
The ADP and NADP diffuse back into the grana for resuse in light dependent reactions
sequence of reactions, repeated again and again, the light dependent reaction are formed
non cyclic photphosphorylation
in the reduction of NADP by photosystem 1, pathway from 2 to 1 is linear, with electrons being accepted by NADP
cyclic photophosphorylation
because electrons move in a cyclin manner, production of ATP is known as
what is the calvin cycle
the light independent reactions
carbon fixation by rubisco
carbon dioxide is combined with an acceptor molecule in the presence of a special enzyme rubisco in the stroma
high concentrations of it are requird because it works slowly and not effective at low carbon dioxide concentration
ribulose biphosphate is a 5 carbon sugar and carbon dioxide is added to it in a process known as fixation.
after theyve combined it splits into 2 molecules of glycerate 3 phosphate
synthesis of triose phosphate
glycerate 3 phosphate is immediately reduced to triose phosphate using NADH and ATP
reduced NAD supplies the hydrogen to reduce glycerate 3 phosphate and ATP supplies the necessary energy
is the reduction step
regeneration of Ribulose Biphosphate
triose phosphate is metabolised to produce the molecule that first reacts with carbon dioxide. regeneration of acceptor step
5 molecules of triose phosphate are converted to three molecules of RuBP allowing calvin cycle to continue
remaining triose phosphate can be used to synthesize other products including glucose. each run of the cycle generates two molecules of triose phosphate, three turns are needed to produce 6 molecuels.
this allows 5 to be converted to RuBP and one to be used in the formation of other molecules
synthesis of carbon compounds
metabolism of the green plant is sustained by the products of photosynthesis
synthesis of carbohydrates, amino acids and other carbon compounds uses the products of the calvin cycle and mineral nutrients
product synthesis steps
interdependence of the light dependent and independent reactions
light dependent reactions provide the NADPH and ATP, which in turn provides the electrons and energy needed to produce carbohydrates in the light independent reactions
what happens to photosynthesis reactions if there is no light
lack of light stops light dependent reactions and thus, NADPH and ATP are not produced which stops the light dependent reactions
what does carbon dioxide act as in photosynthesis
a terminal electron acceptor at the end of reactions and a proton acceptor at the beginning of reactions
what happens with the removal of hydrogen carbonate in photosynthesis?
slows electron transfer through the electron acceptors in ps 2 since it is bound to proteins, which are needed for the activity of the electron transport chain
what happens with the removal of carbon dioxide in photosynthesis?
depletion of carbon dioxide not only causes cessation of carbon dioxide fixation but also a strong decrease in the activity of ps 2
