Lecture 14 : Photosynthesis Flashcards
photosynthesis
process that converts light energy into chemical energy
Autotroph
sustain themselves without eating anything derived from other organisms
Heterotrophs
- obtain their organic material from other organisms
in what organisms does photosynthesis occur?
plants, algae, certain other protists, and some prokaryotes`
What are the components of the chloroplast?
Outer membrane, intermemebrane, innermembrane space, stroma, thylakoid, granum, and thylakoid lumen.
Where are chloroplasts mainly found?
in the cells of the mesophyll (the interior tissue of the leaf)
stomata
Small openings on the underside of a leaf through which oxygen and carbon dioxide can move
Photosynthesis equation
6CO2 + 6H2O + light energy ——> C6H12O6 + 6O2
What are the two stages of photosynthesis?
light reactions and calvin cycle
Where do the light-dependent reactions take place?
thylakoid
what are the main events of the light reactions?
H2O is split and O2 is released, NADP+ is reduced, ATP is made from ADP through photophosphorylation
Where does the Calvin cycle take place?
stroma
what does the Calvin cycle do?
makes sugar from CO2, using ATP and NADPH provided by light reactions
absorption spectrum
graph plotting a pigment’s light absorption versus wavelength
3 types of pigment
chlorophyll a, cholorphyll b, carotenoids
primary electron acceptor
in chloroplasts, an acceptor of electrons lost from chlorophyll a; found in the thylakoid membrane
what is the first step of the light reactions?
Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor
steps of the light reactions?
- photon hits pigment and excites reaction center
- excited electron from PSII (turned to PSII+) is transferred to primary electrons acceptor
- H2O is split and electrons from the hydrogen atoms reduce PSII+ back to PSII and in the process release O2 and H+ into the thylakoid space
- electrons “fall down” from PSII to PSI
- Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane
- transferred light energy excites P700, which loses an electron to an electron acceptor (now P700+ but then accepts an electron passed down from PS II via the electron transport chain)
- Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I
- The electrons are then transferred to NADP+ and reduce it to NADPH in the stroma
Chlorophyll molecules are not isolated, rather they are organized with other small molecules into a complex
photosystem
a photosystem has what two complexes
reaction-center complex and light-harvesting complexes
reaction-center complex
holds chlorophyll a and primary e- acceptor
primary e- acceptor
molecule capable of accepting e- and becoming reduced
light harvesting complex
antennae for the reaction center complex
Photophosphorylation
Diffusion of H+ (protons) across the membrane from thylakoid space to stroma (chemiosmosis); drives ATP synthesis
basic purpose of light reactions
generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH
Steps of the Calvin cycle
- 3 molecules of CO2 enter and combine with RuBP (rubisco used for carbon fixation) —> 6 molecules of a 3 carbon sugar
- 6 ATP creates 6 ADP
- 6 NADPH –> 6 NADP+ and 6P
- Reduction (Phase 2)
Output: 3C-1P
- Phase 3: Regeneration - 3 ATP –> 3ADP + 2P
- 1 G3P as output, 5 left are used to regenerate the 3 original molecules of RuBP
very broad summary of calvin cycle
Carbon enters the cycle as CO2 and leaves in the form of sugar (CH2O)
