lecture 8

Question 1

photosynthetic pigments

Answer 1

• light receptors
• pigments absorb visible light
• wavelengths not absorbed reflected/transmitted
• chlorophyll a (main photosynthetic pigment)
• chlorophyll b and carotenoids (accessory pigments; protect from excess light and broaden spectrum)

Question 2

Action spectrum

Answer 2

• shows that violet-bue and red light work best for photosynthesis

Question 3

pigment

Answer 3

• absrobed photo raises electron to excited state
• falls back down releasing energy

Question 4

photostems

Answer 4

• PS 2: functions first
• PS 1: functions second in chain
• solar-powered transfer of electrom from chlorophyll molecule to primary electron acceptro
• two possibel routes
  – linear electron flow (primary pathway involving both PS producing ATP and NADPH using light energy)
  – cyclic electron flow (less common, involved PS 1 producing ATP, no NADPH or O2)

Question 5

linear electron flow (12 steps)

Answer 5

• photon hits pigment, energy exhcanged among pigment molecules until reach special chlorophyll (P680)
• excited electron transferred from P680 to primary electron acceptor
• water split, electrons replace lost by P680
• split water form oxygen (diffusing out) and H+ ions (lowering PH in thylakoid space)
• each electron captured by primary electron acceptor of PS 2 falling down transport chain to PS 1
• movement of electrons through cyovhrome complex pumps H+ ions into thylakoid space
• diffusion of H+ across membrane (into stroma) allows ATP synthesis
• PS 1, transferred light energy excites chlorophyll (P700) losing an electron to electron acceptor
• electron replaced by electron passed from PS 2
• each electron passed from PS 1 to protein ferredoxin (Fd)
• electrons used by enzyme (NADP+ reductase) to reduce NADP+ to NADPH
• chemical energy in NADPH available for rxns n calvin cycle

Question 6

cyclic electron flow

Answer 6

• same steps as in 8-10
• Fd gives electron back to cytochrom complex (not NADP+ reductase)
• generates H+ gradient driving ATP synthesis (no NADPH or O2)

Question 7

light rxns

Answer 7

• generate ATP and increase potential energy f electrons by moving then from water to NADPH
• AT_ and NADPH produced on side facing stroma (calvin cycle taking place)
• cyclic electron flow only makes ATP