8.3 Photosynthesis Flashcards
What is part of photosynthesis called that uses light directly?
light dependent
What is part of photosynthesis called that does not use light directly?
light independent
What are light independent reactions dependent on?
can work in dark but only shortly, need substances produced by light dependent reactions
what does the inner membrane of a chloroplast enclose?
third system of interconnected membranes called thyla koid membranes
What are thylakoid membranes?
third system of interconnected membranes enclosed by inner membrane of chloroplast
What is within thylakoid?
compartment called thylakoid space
What are the products of light dependent reactions
light energy converted into chemical energy in form of ATP and reduced NADP
What do ATP and NADP serve as for light independent reactions?
energy sources
What is a stroma
compartment which inner membrane of the chloroplast encloses; protein rich with enzymes to use for calvin cycle (light independent reactions)
What is the calvin cycle?
anabolic pathway for light independent reactions that require endergonic reactions so that ATP is hydrolised and reduced NADP is oxidized
What are photosystems?
chlorohyll and accessory pigments grouped together in large light harvesting arrays (contain chlorophyll)
Where are photosystems located?
in thylakoids, an arranment of membranes inside chloroplast
What do photosystems I and II have?
light harvesting arrays (with chlorophyll), reaction centres and many chlorophyll molecules that absorb light energy
What happens when chlorophylls in the reaction centre absorb energy?
when energy is absorbed from photon of light an electron within molecule gets excited. which makes chlorophyll photoactivated
How can a chlorophyll get photoactivated?
chlorophyll absorbs energy from photon of light, electron gets excited
What is a special property of chlorophylls in the reaction centre?
can donate excited electrons to electron acceptor
What is the electron acceptor of photosystem II called?
plastoquinon
What does plastoquinon do?
collects to excited electrons from photosystem II, then moved to another position in the membrane
Describe a property of plastoquinone
Hydrophobic; has no fixed position but remains within mmbrane
what does the absorption of two photons of light cause?
produces one reduced plastoquinone, where chlorophyll at reaction centre lost 2 electrons to plastoquinone
Can photosystem II repeat the process of producing a new plastoquinone?
Yes it can repeat the process and produce a second reduced plastoquinone
What does photo phosphorylation produce?
ATP using energy from light
Who carries out phosphorylation?
thylakoids
What does a thylakoid membrane include?
photosystem II; chain of electron carriers; photosystem I; ATP synthase
How are electrons carried from reaction centre of photosystem II to chain of electron carriers?
reduced plaetoquinone is needed
What happens once plastoquinone transfers its electrons?
electrons are passed from carrier to carrier in chain
What happens when electrons pass through the electron carrier chain?
energy is released from excited electrons from photosystem II which provides protein pumps to pump H+ across thylakoid membrane the lumen of the thylakoid; concentration gradient developed;
How is a concentration gradient created across the thylakoid membrane?
excited electrons from photosystem II is passed along electron carrier chain (cytochrome complex) which releases energy that actively transports H+ across membrane into lumen; photolysis also increases H+ concentration
How is ATP generated in thylakoids?
High concentration of H+ in thylakoid space is reduced by passing them through the enzyme ATP synthase; energy is released through the passive transport of H+ (down concentration gradient) synthesizes ATP from ADP +Pi
What is the process called when H+ passes through ATP synthase from high concentration to low, to convert ADP to ATP
chemiosis
What is the production of ATP in chlorophylls calld?
photophosphorylation
What occurs when electrons reach end of carrier chain?
passed to plastocynanin to be passed to photosystem I
How does photoactivation work in photosystem I?
chlorophyll molecules within photsystem I absorb light energy to pass it the two chlorophyll in the reaction centre which re-excites the electrons (raise to higher level)
Why does a second photoactivation need to happen at photosystem I?
much of the energy has been lost from electrons (move down in energy level) and needs re charge
What happens to electrons after photosystem I?
passed to ferredoxin which becomes reduced ferredoxin to reduce NADP, to form NADP.
What is plastocynanin?
a water-soluble electron acceptor in the fluid inside the thylakoids
What happens when NADP runs out in a chloroplast?
electrons return to the electron transport chain that links the photosystems, rather than being passad to NADP
What is ferredoxin?
protein in fluid outside the thylakoid
What is cycling photosphorylaiton?
flow of electrons along chain to allow more ATP production
Where does carbon fixation occur in plants and algae?
light independent reactions, in the stroma
How does photosystem 1 replace its loss electrons?
with electrons emitted by phosphosystem II and passed along electron carriers
Which photosystem can absorb more light to produce more excited electrons?
Photosystem I
Where does calvin cycle occur in the chloroplast?
stroma
Does CO2 react with a 2 carbon compound (calvin cycle)?
No. reacts with 5 carbon compound known as RuBP
What is produced from Co2 and RuBP?
two molecules of glycerate 3-phosphate
What does the stroma contain large amounts for for the calvin cycle?
rubisco (maximizes carbon fixation)
What is the ratio of hydrogen and oxygen in sugars?
2:1
Whats needs to be added to glycerate 3-phosphate to become a carbohydrate?
Hydrogen because RuBP when converted to glycerate 3-phosphate has reduced amount of oxygen
What is needed to add hydrogen to glycerate 3-phosphate?
ATP and reduced NADP (NADPH) produced from light dependent reactions; ATP provides energy for reaction; NADPH provides hydrogen atoms
What is the first carbohydrate of light independent reactions?
triose phosphate
What happens if triose phosphates are combined?
can form hexose phosphate; hexose can condense to starch
Why cannot all triose phosphate produced be converted to starch or hexose phosphate?
supplies of RuBP would run out; triose phosphate must be regenerated to RuBP
What is important rule for calvin cyle to continue indefinitely?
as much RuBP must be produced as consumed
What occurs in the last phase of the calvin cycle?
series of enzyme catalyzed reactions convert triose phosphate into RuBP
How many molecules of RuBP would be produced with 5 molecules of triose phosphate?
3 molecules of RuBp
For every six molecules of triose phosphate formed in light independent, how many must be converted to RuBP?
five
What structual features do all chloroplasts share?
double membrane forming outer chloroplast envelope; extensive system of internal membrane called thylakoid; small fluid filled spaces inside the thylakoids; colourless fluid called stroma (contains enzymes); stacks of thylakoid called grana
If a chloroplast has been photosynthesizing rapidly, what could be seen in chloroplast?
starch grains or lipid droplet
function of granum
a stack of thylakoids for absorption of photons of light
function of thylakoid space
with a very small volume steep concentration gradient builds up after relatively few absorbed photons
function of stroma
containing all the enzymes of calvin cycle; lots of rubisco; naked DNA and 70S ribosomes (synthesis for protein possible)
function of chloroplast envelope
creates a compartment in which enzymes and other components photosynthesis is concentrated
function of starch grain
storage of carbohydrate produced by photosynthesis until it is exported from chloroplast
function of thylakoid membrane
provide large surface area for light absorbing photosystems; site for electron flow; generation of proton gradient and chemiosmosis
Draw Diagram of chloroplast
thylakoid membrane; thylakoid; thylakoid space; grana; stroma; 70S ribosome and naked DNA; starch grain; lipid droplets; chloroplast envelopes (inner/outer)
How does photolysis occur at photosystem II?
After electrons have been transferred to the plastoquinone (becomes reduced), the chlorophyll becomes strong oxidizing agent (wants to get reduced); polerizes water and splits it; into H+ and O2
