B11. Photosynthesis (A2) Flashcards
Which organelle in the leaf does photosynthesis occur within?
Chloroplasts
How are leaves adapted for photosynthesis?
Large surface area to absorb sunlight; Arrangement of leaves to minimise overlapping, shadowing; Thin, most light absorbed in first few micrometers, short diffusion pathway for gases; Transparent cuticle and epidermis, let light through photosynthetic mesophyll cells underneath; Long, narrow upper mesophyll cells packed with chloroplast that absorb sunlight; Stomata open and close in response to light intensity; Air spaces in lower mesophyll, allow for rapid diffusion in gas phase of CO2 & O2;
What is the overall equation of photosynthesis?
6CO2 + 6H2O =light=> C6H12O6 + 6O2
Describe the structure of chloroplasts.
Double membrane envelope,outer/inner membrane; Thylakoid; Granum / Grana (100 disc like structures); Intergranal lamellae; Stroma, starch grains, 70s ribosomes, loop of DNA
What are the stages of photosynthesis?
Capturing light energy; Light dependant reaction, occurs in thylakoid membranes; Light independent reaction, occurs in stroma
What is oxidation and reduction?
Oxidation is loss of electrons; Reduction is gain of electrons
What is photoionisation?
Photosystem absorbs light energy; Exciting a pair of electrons, raising them to the next energy level; Excited electrons leaves photosystem; Photosystem is ionised as a result
What are photosystems?
Funnel like structures found in the thylakoid membrane; Collection of photosynthetic pigments that absorb light
Describe the differences between photosystem I and photosystem II.
Photosystem II absorbs light in 680 nm wavelength, P680, located at the start of the electron transport chain, photolysis occurs here; Photosystem I absorbs light in 700 nm wavelength, P700, located in middle of electron transport chain
What is photolysis?
Light energy used to break down H2O; H2O => (2H+) + (2e-) + (1/2 O2)
What is photophosphorylation?
Production of ATP via light dependant reaction
Explain what occurs in non-cyclic photophosphorylation.
Light absorbed by PSII, P680; Photoionisation; 2e- taken by electron acceptor proteins, passed to electron carrier proteins, down electron transport chain; Chemiosmosis; Photoactivation of PS1, P700, results in release of 2e- reducing NADP+, NADPH; Photolysis replenishes 2e- from PSII, P680
Explain what happens occurs in cyclic photophosphorylation.
Light absorbed by PSI, P700; Photoionisation; 2e- taken by electron acceptor proteins, passed to electron carrier proteins,down electron transport chain; Chemiosmosis; De-energised e- return to PS, restoring electron supply; NADP+ not reduced, H2O not needed to replenish electron supply
What are the differences between cyclic and non-cyclic photophosphorylation?
Cyclic: PSI; P700 active reaction centre; e- revert to PSI; ATP produced; H2O non required; NADPH not synthesised; O2 not evolved; predominant in bacteria
Non-cyclic: PSII & PSI; P680 active reaction centre; e- from PSI are accepted by NADP+; NADPH & ATP produced; O2 evolved; Predominant in green plants
Where does photolysis occur in non-cyclic photophosphorylation?
PSII, P680; Contains oxygen-evolving complex, catalyses photolysis
H2O => (2H+) + (2e-) + (1/2 O2)
Explain what occurs in chemiosmosis.
Energy released from alternative redox of ETC is used to actively transport H+ ions from stroma into thylakoid lumen through proton pump; H+ gradient between stroma and thylakoid lumen created; H+ ions diffuse via facilitated diffusion through chemiosmotic channel; Activating ATP synthase, catalysing the reaction between ADP + Pi = ATP
Why do electrons release energy as they move down the electron transport chain?
Electron carriers are alternatively reduced, as they gain e-, and oxidised, as they lose e-, gradually releasing energy
What do photosystems consist of?
Primary pigments, chlorophyll; Accessory pigments, carotenoids; PSII, chlorophyll B; PSI, chlorophyll A
Why do photosystems have different pigments?
Efficiently absorb light over a larger range of wavelengths
What is chromatography and how does it work?
Experimental technique used to separate mixtures; Different compounds travel through material at different speeds, causing separation
What is the equation for calculating Rf values?
Distance traveled by pigment / Distance traveled by solvent
Describe the method used for chromatography of a leaf.
Draw line in pencil 1 cm above bottom of filter paper; Cut section of healthy leaf and place in mortar; Add 20 drops of acetone, grind leaf to release pigments; Extract pigments using capillary; Spot on pencil line; Suspend paper in solvent; Mixture dissolved in solvent (Mobile phase); Dissolved material passes through static material (Stationary phase)
What are the limitations of paper chromatography of a leaf?
Not as specific as other chromatographic techniques; Doesn’t give data on amount of each pigment present or wavelengths they absorb
Describe the light-independent reaction.
Occurs in stroma; Ribulose bisphosphate carboxylase catalyses the fixation of carbon dioxide to ribulose bisphosphate; Unstable 6 carbon molecule formed; Dissociates into 2 molecules of gylcerate3phosphate; GP reduced to 2 molecules of Triose phosphate using NADPH & ATP; Triose phosphate regenerated into Ribulose bisphosphate using ATP; 1 additional carbon left over
What factors are needed for photosynthesis?
Presence of photosynthetic pigments; CO2; H2O; Light energy; Suitable temperature
What are the main limiting factors for photosynthesis?
Light intensity, light dependant stage, more ATP and NADPH for calvin cycle; CO2, raw material, calvin cycle, carbon fixation; Temperature, enzyme optimum temperature
