Photosynthesis Flashcards
Process of light dependent reaction
-chlorophyll molecule absorbs light energy and a pair of e- is raised up energy level (excited) . e- leave chlorophyll - chlorophyll is ionised (photoionisation)
-excited e- passed from e- carrier to e- carrier in a series of redox reactions. series of e- carriers is located in the thylakoid membrane. each e- carrier is a lower energy level than previous one so e- loose energy
-the energy is used to pump H+ into the thylakoid space
-H+ move from high conc inside thylakoid to a lower conc in the stroma, through atp synthase.
Atp synthase comines ADP+Pi to form ATP
-H+ pass through ATP synthase and are taken up (along with e- bu NADP to form NADPH)
-Photolysis - splitting water with light provide e- to replace those lost from chlorophyll during photoionisation
How ATP is made during LDR
-chlorophyll molecule absorbs light energy and a pair of e- is raised up energy levels so e- leave chlorophyll
-exited e- passed from e- carrier to e- carrier in a series of redox reactions
-series of e- carriers are located in thylakoid membrane
-each e- carrier is a lower energy level than previous one so e- lose energy
-energy is used to pump h+ into thylakoid space
-h+ move from high conc inside thylakoid to a lower conc in the stroma through ATP synthase
-ATP synthase combines ADP+pi to from ATP
role of photolysis in LDR
-splitting water with light
-so provides e- to replace those lost from chlorophyll molecule during photoionisation
-h+ pass through atp synthase and are taken up (along with e-) by NADP to from NADPH
How chloroplasts adapted to carry out LDR
-thylakoid membrane has large SA > chlorophyll, e- carriers and enzymes to attach
-proteins in grana > hold chlorophyll in precise place for max absorption of light
-ATP synthase in thylakoid membrane > atp production
What does the LDR produce?
-reduced NADP (NADPH)
-ATP
-Oxygen (by-product)
What are the products of the LDR needed for?
LIR
What are the electrons produced in photolysis used for?
passed along chain of electron carrier proteins
What are the H+ ions produced in photolysis used for?
-picked up by NADP to make NADPH
-pumped to create electrochemical gradient and diffuse through ATP synthase (allowing ATP to be formed)
What causes chlorophyll to become ionised?
absorbs light energy, which raises energy level of electrons (excited state), causes them to leave chlorophyll
What happens to the electrons after they leave chlorophyll?
they are passed along an electron carrier chain in thylakoid membrane
What do the electrons passing through the chain do?
release/lose energy
What is the energy released by electrons passing through the electron carrier chain used for?
to pump H+ ions into the lumen of the thylakoid
What is created as H+ ions are pumped into the lumen of the thylakoid?
an electrochemical gradient
What are the 3 main steps of the LDR?
photoionisation
chemiosmosis
photolysis
How are electrons passed along the electron carrier proteins?
series of redox reactions
What are the electrons used for after being passed along the electron transfer chain?
accepted alongside H+ to form NADPH
What is the energy lost from the electrons used for?
pumping H+ ions against their electrochemical gradient
What happens in photoionisation?
-light absorbed by chlorophyll
-raises electrons an energy level SO they are lost from the chlorophyl
Why do plants benefit from having different coloured pigments?
absorb different/more wavelengths of light for the LDR
Why might not all light be used in photosynthesis?
some could be reflected
some light is incorrect wavelength
ATP produced by chemosmosis
-h+ pumped from stroma using hydrogen pump in the thylakoid membrane
-do this via the energy from e- released when water is split (photolysis) which also produces H+
-creates and maintains conc gradient of H+ across thylakoid membrane with high conc inside thylakoid space and low conc in stroma
-protons only cross thyalkoid membrane via ATP synthase
-as protons pass through ATP synthase they cause changes to structure of enzyme which then catalyses combination of ADP+Pi = ATP
How co2 arrives in stroma of chloroplast
diffuse from atmosphere through stroma, spongy mesophyll and into palisade cell
rubisco function
enzyme that catalyses reaction between RuBP and CO2
Role of atp produced my LIR
convert GPP to TP to regenerate RuBP
Fate of triose phosphate produced during calvin cycle
combined to form organic molecules including glucose. most is used to regenerate RuBP
Explain how CO2 absorbed by plants is incorporated into organic molecule
-co2 enters stroma by diffusion and reacts with 5c ribulose biphosphate (RuBP) to form 2x molecules of 3C glycerate-3-phosphate (GP)
-reaction catalysed by rubisco
Roles of ATP and NADH in LIR
-atp =hydrolyse to convert glycerate-3-phosphate (GP) into triose phosphate (TP) and TP back into RuBP
-NADH = convert GP into triose phosphate
Describe events in calvin cycle
-CO2 and RuBP from 2x glycerate-3-phosphate in presence of rubisco
-GP converted to triose phosphate with ATP and NADH
-Some triose phosphate forms useful organic molecules eg glucose
-majority of triose phosphate recycled to RuBP and ATP
What is used in the Calvin cycle?
-NADPH
-ATP
-CO2
What is required in order to form triose phosphate molecules?
ATP and a H from reduced NADP
Give 2 examples of what the glucose can be used to make?
glycerol used to make lipids
combine with nitrates to form amino acids
stored as starch
used in cell walls as cellulose
How many times does the Calvin cycle need to happen before a hexose sugar (e.g glucose can be made)?
6
Why is ATP needed for the second time in the Calvin cycle?
to regenerate the RuBP by joining a TP molecule to the molecule that donated it’s carbon atom for use in making organic molecules
How many Carbon atoms leave the 2 x TP molecules to be used in organic molecules?
1
What is GP reduced to form?
triose phosphate
What is the role of the reduced NADP in the Calvin cycle?
donates H to reduce molecule GP
Why won’t the LIR occur if the LDR doesn’t occur?
-no ATP
-no NADPH
-needed for LIR (converting GP to TP)
Why will the rate of LIR decrease if rate of RuBisCo decreases?
-no CO2 reacts with RuBP
-so no GP
Where is RuBisCo found in a cell?
stroma of chloroplasts
LIR
1) Co2 enters stroma via diffusion and reacts with RuBP (5C)
- catalysed by rubisco
2) FoRMS 2x GP (3C)
3) NADPH from LDR used to reduce GPinto TP using energy from ATP
$)NADP is reformed and goes back to LDR to be reduced again by accepting more H+
5) some TP converted to useful organic substances eg glucose, strach, cellulose, nucleotides ect
6) most TP used to regenerate RuBP using ATP from LDR
