Energy Transfers In and Between Organisms Flashcards
What two reactions can photosynthesis be separated into?
- light dependant reactions
- light independent reactions
what features are in a thylakoid membrane
- phospholipid bilayer
- electron transport chain (proteins)
- PS1
- PS2
- ATP synthase
Non-cyclic phosphorylation
first stage of the light dependant reaction
photolysis of water
photon of light enters the thylakoid disc where it uses energy to split (lyse) water molecule into hydrogen ions, electrons, and oxygen gas
second stage of the light dependant reaction
photoionization of PS2
- PS2 is a complex of photosynthetic pigments i.e. chlorophyll A & B, carotene. each respond to a different wavelength of light
- energy from a photon of light is transferred to an electron, that becomes energised.
- this leaves the photosystem (ionising it) and join the electron transport chain.
- electrons are replaced by the photolysis of water
third stage of the light dependant reaction
energised electron
energy from energized electron pumps H+ across the membranes into the thylakoid through the proton pumps, of the electron transport chain. once all of the energy is used, the electron joins PS1
fourth stage of the light dependant reaction
electron is struck by another photon of light, it becomes energized again and leaves PS1 and enters the stroma
fifth stage of the light dependant reaction
chemiosmosis
increase in H+ inside thylakoid disc gives an electrochemical gradient. H+ move into the stroma down their electrochemical gradient, by facilitated diffusion through ATP synthase. this provides the energy for phosphorylation of ADP into ATP
sixth stage of the light dependant reaction
Reduction of NADP
NADP is a coenzyme. it collects the energised electrons from PS1 and the excess H+ from chemiosmosis. it becomes reduced
what is a coenzyme
it is not an enzyme.
it carriers molecules e.g. H+ and e- from one reaction to another, without changing them
process of cyclic phosphorylation
only involves PS1, e- become energized through photons of light they leave PS1 and join the electron transport chain, using the energy to pump H+ into the thylakoid. the e- returns to PS1. H+ moves with others in chemiosmosis providing energy for the phosphorylation of ADP to ATP
light-independent reaction/Calvin cycle
Calvin Cycle takes place in the stroma of the chloroplast and uses the products of the LDR (ATP & reduced NADP) to form glucose. The reactions can be divided into three main stages: carbon fixation, reduction, and regeneration.
Carbon fixation
CO2 is ‘fixed’ by adding it to a 5 C-molecule called ribulose bisphosphate (RuBP), forming a 6-carbon molecule. This reaction is catalysed by an enzyme called Rubisco.
The unstable molecule breaks down to form two 3-carbon compounds called glycerate-3-phosphate (GP).
Reduction
- isomerization reaction converts GP into a 3-carbon compound called triose phosphate. ATP (LDR) is hydrolyzed into ADP.
- reaction requires electrons from the electron carrier to reduce NADP (LDR). Reduced NADP transfers electrons to GP, reducing it to GALP.
- TP is converted into organic molecules, e.g. glucose, some regenerate RuBP. For every 6 molecules of GALP, 1 produces organic molecules whereas 5 will be used for RuBP regeneration.
Regeneration
- GALP is converted back into RuBP - this process requires energy which is generated by ATP hydrolysis.
- cycle is completed and another round of carbon fixation takes place.
what is a limiting factor
a limiting factor is that which prevents the rate of reaction increasing
