Biology 1002B Lecture Notes - Lecture 8: Light-Independent Reactions, Photosystem Ii, Reduction Potential

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Biology Lecture 8 (Feb. 1, 2016)
TOPIC: Photosynthesis
Distinction between autotrophs (photoautotrophs) and heterotrophs.
- Heterotroph: an organism that cannot fix carbon and uses organic carbon for growth
(doesn’t produce own food – C-H bonds)
- Autotroph: is an organism that produces complex organic compounds (such as
carbohydrates, fats, and proteins) from simple substances present in its surroundings,
generally using energy from light (photosynthesis) or inorganic chemical reactions
(chemosynthesis)
Two phases of photosynthesis
- Two phases: Light reactions and Calvin cycle
o Light reactions capture light energy by pigment molecules to synthesize NADPH
and ATP
H2O provides electrons to reduce NADP+ to NADPH; releases O2
o Calvin cycle uses electrons and protons from NADPH to convert CO2 into
carbohydrate
Referred to as carbon fixation; reduction reaction
Structure and function of a photosystem - what do the different parts do?
- Lie on the thylakoid membrane; comprised of antenna complex and reaction centre
o Antenna complex absorbs photons of light as they come in; energy bounces
around until it reaches reaction centre
o Reaction centre has a small number of proteins attached to chlorophyll a molecule
and an electron-accepting molecule called primary electron acceptor
- Photosystem uses energy from photons to oxidize reaction centre chlorophyll; electron
transfers to primary electron acceptor and moves down ETC
Definition of photosynthesis, light reactions, Calvin cycle, redox potential, chloroplast, thylakoid
membrane, lumen, P680, P700 (+ and * for each), chemiosmosis,
- Photosynthesis: process used by plants and other organisms to convert light energy,
normally form the sun, into chemical energy
o The conversion of CO2 into an organic form (glucose, more free energy because
there are lots of C-H bonds)
o This is because carbon and hydrogen are not very electronegative, so it is easy to
break these bonds and use the electrons to do work
o C-H BONDS ARE A GOOD SOURCE OF ELECTRONS
o In CO2, oxygen is very electronegative so it is harder to steal electrons from them
o This means that photosynthesis is an endergonic process (there is an increase in
free energy, products have more free energy than reactants)
Since it’s endergonic, the process is also anabolic
- Oxidation: loss of electrons; molecule is called a reducing agent
- Reduction: gain of electrons; molecule is called an oxidizing agent
- Oxidation-Reduction Reaction: involve the transfer of electrons between species,
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Document Summary

Heterotroph: an organism that cannot fix carbon and uses organic carbon for growth (doesn"t produce own food c-h bonds) Autotroph: is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis) Two phases: light reactions and calvin cycle: light reactions capture light energy by pigment molecules to synthesize nadph and atp. H2o provides electrons to reduce nadp+ to nadph; releases o2: calvin cycle uses electrons and protons from nadph to convert co2 into carbohydrate. Referred to as carbon fixation; reduction reaction. Photosystem uses energy from photons to oxidize reaction centre chlorophyll; electron transfers to primary electron acceptor and moves down etc. Definition of photosynthesis, light reactions, calvin cycle, redox potential, chloroplast, thylakoid membrane, lumen, p680, p700 (+ and * for each), chemiosmosis, Since it"s endergonic, the process is also anabolic.

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