Photosynthesis Flashcards
Why is energy needed in?
Active transport
Anabolic reactions (building of polymers)
Movement of cilil, flagella, muscles
What is the general structure of chloroplast?
Starch grain –> energy storage
Ribosomes –> protein synthesis
Thylakoid –> site of light-dependent stage
Granum –> stacks of thylakoid membrane –> connected by intergranal lamella
Stroma –> site of light-independent stage
What is the main pigment used in photosynthesis?
Chlorophyll a
–> absorbs mainly red + blue light
Reflects green light.
Located in reaction centre
What other pigments are used?
chlorophyll b
xanthophylls
carotenoids
–>absorb different wavelengths of light
-> embedded on membrane of chloroplast
Different wavelengths = different shades on plant
form a light harvesting system
role = absorb/harvest light energy + transfer energy efficiently to reaction centre.
What are the adaptations of chloroplast in light-dependent reaction?
Contain both DNA + ribosomes
Arranged in way to maximise light absorption
Thylakoid membrane = Large SA area
Thylakoid membrane contains ATP synthase
Summarise photophosphorylation:
Light-dependent reaction = thylakoid membrane
ATP produced by ATP synthase
To catalyse production of ATP —> energy provided to ATP synthase by diffusion of protons down proton gradient –> chemiosmosis
Protons move from thylakoid to stroma
How is a proton gradient maintained?
Active transport of H+ from stroma into thylakoid space.
Ensures steep concentration of H+ in thylakoid space compared to stroma
What is photoionisation?
Chlorophyll absorbs light:
–> energy transferred to electrons in PSII
~~> electron = excited state
Electron gain energy -> leave chlorophyll
Chlorophyll = positively charged .: oxidised
What happens after photoionisation?
Electrons move down collection of protein complexes
–> electron transfer chain in series of redox reactions
Lose energy as they go down until reaching PSI
—> releases energy
E- + NADP + H+ = NADPH
What happens in photolysis?
Light energy spilts water into:
E-
H+
O2 –> diffuses out of stomata
Electrons produced replace ones lost from chlorophyll during photoionisation.
Protons –> maintain high conc of H+ in thylakoid membrane
What is cyclic phosphorylation?
Light energy hits PSI
–> Different wave lengths absorbed
1 electron = excited
electron carried back to electron transport chain
Releases energy –> AT of H+
Returns back to PSI
*no photolysis
*no NADPH formed
What is the light - independent reaction?
Takes place in stroma
Uses carbon dioxide as raw material.
Calvin cycle
What is the 1st stage of Light-independent reaction?
Ribulose bisphosphate (5 C) + CO2
= 2 Glycerate 3-phosphate
(3 C)
Fixed CO2 (removed from environment + fixed in molecule)
Catalysed by Rubisco (lowers Ea)
What is the 2nd stage of light-independent reaction?
Glycerate 3-phosphate —> Triose phosphate (3 C)
GP reduced
Hydrogen needed from NADPH
ATP —> ADP + pi
~~> provides energy for reaction
NADP, ADP, pi = back to thylakoid membrane
How does triose phosphate form organic substances?
80% of TP converted back into Ribulose bisphosphate. –> continuous cycle using ATP
20% –>
produces glucose (used in respiration)
produces amino acids –> proteins
produces lipids
combine with 3 fatty acids = triglyceride
