Module 5.6 Flashcards
Photosynthesis
what is the relationship between respiration and photosynthesis
the products of one are the raw materials for the other
respiration removes oxygen and adds carbon dioxide photosynthesis removes carbon dioxide and adds oxygen
components of a chloroplast
outer membrane
inner membrane
lamellae
grana
thylakoid
stroma
DNA
what is the envelope
the outer and inner membrane with the intermembrane space
the outer membrane is highly permeable
What is the stroma
fluid filled matrix
contains the enzymes needed to catalyse the reactions of the light-independent stage of photosynthesis
also has starch grains, oil droplets, small ribosomes and DNA
What are the grana
stacks of thylakoid membranes
where the light-dependent stage of photosynthesis occurs
make big surface area for distribution of photosystems, electron carrier and ATP synthase
What is a thylakoid
less permeable and folded into a flattened discs that form stacks
thylakoid membrane is less permeable
creates compartment of thylakoid space
holds photosystems
what are the lamellae
the thylakoids within one granum may be connected to thylakoids within another granum by the lamellae
what is a photosynthetic pigment
absorbs light of a particular wavelength for light harvesting in photosynthesis
where are photosynthetic pigments located
primary pigment reaction centre contains chlorophyll 700 or 680
accessory pigments are around the funnel of the photosystem
what is photolysis
the splitting of water molecules using light energy
creating 1/2 o2 and 2 protons
what happens when light strikes PSII - non cyclic
the photons energy is channelled to the primary pigment reaction centre
the light energy excites a pair of electrons in the chlorophyll molecule
what happens to the electrons after they are excited from PSII - non cyclic
the energised electrons escape from the chlorophyll molecule and are captured by an electron carrier
the electrons are replaced by electrons derived from photolysis
how do electron carriers work
they contain an Fe 2+ ion which can accept and donate the electrons becoming reduced and re-oxidised to pass the electron to the next carrier in the chain
what are electron carriers
proteins with iron at its centre embedded in the thylakoid membrane
how is the electron carrier used - non cyclic
as electrons are passed along the chain of carriers some energy associated with the electrons is released
this energy is used to pump protos across the thylakoid membrane into the thylakoid space creating a proton gradient
what happens at PSI - non cyclic
the electrons from the electron carrier chain are captured by another molecule of chlorophyll in PSI replacing those lost from excitation from light energy
what does ferredoxin do - non cyclic
accepts the electrons from PSI and passes them to NADP in the stroma
what does the proton gradient do - non cyclic
the protons diffuse down their concentration gradient through channels in the thylakoid membrane associated with ATP synthase
the flow of protons causes ADP and inorganic phosphate to join forming ATO
What does NADP reductase do - non-cyclic
catalyses the reaction to form reduced NADP from NADP accepting protons and electrons in the stroma
products of the light dependent stage - non cycluc
ATP and reduced NADP
what happens in cyclic phosphorylation
light strikes PSI
a pair of electrons in the chlorophyl molecule become excited
they escape and pass to an electron carriers system then pass back to PSI
products of cyclic phosphorylation
the passage of electrons along the electron carriers generates a small amount of ATP but not photolysis of water occurs so no protons or oxygen are produced and no reduced NADP is generates
what does RuBisCO do in the calvin cycle
catalyses the reaction between carbon dioxide and ribulose bisphosphate (RuBP) which is a five carbon compound
what does the reaction of carbon dioxide and RuBP form
an unstable intermediate six carbon compound that immediately breaks down into two molecules of GP
what is carbon fixation
when the carbon from the carbon dioxide in the air is added to organic molecules to be used as biological building blocks and fuel for respiration
occurs when carbon dioxide is combined with RuBP to form GP
what happens to GP in the calvin cycle
hydrogens from the reduced NADP made in the light independent stage reduce GP to TP
energy from ATP is also used at the stage
how much ATP is used to convert GP to TP
2 ATP molecules for every molecule of carbon dioxide fixed
What happens to TP in the calvin cycle
10 in every 12 molecules are used to regenerate RuBP which uses energy from ATP
10 TP molecules make 6 RuBP molecules
the remaining 2 TP molecules are the product
uses of TP
the starting material for the synthesis of carbohydrates lipids and amino acids
regeneration of RuBP
why does the calvin cycle only run during daylight
requires ATP and reduced NADP from the light dependent reaction which can only occur in daylight
the pumping of protons into the thylakoid space in the light dependent reaction raises the pH to around 8 which is optimum for RuBisCO
RuBisCO is activated by the presence of extra ATP in the stroma
what are the limiting factors for photosynthesis
light intensity
carbon dioxide concentration
temperature
water availability
how does light intensity effect the rate of photosynthesis
when carbon dioxide and temperature are at constant favourable levels light is the limiting factor so when light intensity is low rate of photosynthesis is low
as light intensity increases so will rate of photosynthesis util a certain point when a different factor is limiting the process
why is light intensity a limiting factor
light provides the energy for the light dependent reaction which produces the products for the light independent reaction
light also causes stomata to open so gaseous exchange and transpiration can occur
effect of low light intensity on the calvin cycle
GP cannot be reduced to TP
TP levels fall and GP accumulate
if TP levels fall RuBP cannot be regenerated
RuBP levels fall
effect of carbon dioxide concentration on rate of photosynthesis
levels in the atmosphere and aquatic habitats ate usually high enough that it is not usually a limiting factor
but if levels are low rate of photosynthesis will be low as the calvin cycle cannot run
effect of low carbon dioxide concentration on the calvin cycle
RuBP cannot accept it so accumulate
GP cannot be made
if GP levels fall TP cannot be made
effect of water stress on the rate of photosynthesis
stomata close reducing gaseous exchange
rate of photosynthesis greatly reduces
effect of low temperature on the rate of photosynthesis
calvin cycle uses enzyme controlled reactions to low temperatures reduce enzyme activity
effect of temperatures of 30 on rate of photosynthesis
oxygen competes for RuBisCOs active site reducing the amount of GP and then TP
RuBP initially builds up but then cannot be regenerates
what happens to the rate of photosynthesis at temperatures of 40 or above
enzyme may denature reducing concentrations of GP then TP then RuBP
