8.3 : Photosynthesis Flashcards
what is photoactivation?
when electrons at ground state are excited until they reach their reactive state
what is a photosystem?
the process by which chlorophyll absorbs light energy, and uses the energy to raise an electron in chlorophyll to a higher energy state.
what does the inner membrane of the double membrane around chloroplast fold into?
the inner membrane folds extensively to form a system of branching membranes = thylakoids, these are arranged into flat, compact piles = grana –> between grana, are loosely arranged tubular membranes = stroma
what occurs in the grana?
this is where the light-dependent reaction takes place –> chlorophyll inside the grana absorbs light energy, which is absorbed in the thylakoid membrane in the grana.
what occurs in the light-dependent reaction? where is it located?
- photolysis takes place = use of light energy to split water
- hydrogen is removed and retained by NADP
- photophosphorylation = the process of utilising light energy from photosynthesis to convert ADP to ATP (oxidation of ADP+Pi)
- oxygen is given off as a waste product
- location : grana
what occurs in the light-independent reaction? where is it located?
-build up of larger molecules using carbon dioxide.
-products of the light-dependent reaction are used (NADPH2, ATP) in the build up process.
-requires a continuous supply of NADPH2 + ATP (which are the products of the light dependent reaction)
-location : stroma.
(calvin cycle)
what is the driving force in photophorphorylation?
light (needed to make ATP)
what is chemiosmosis?
Oxidising ADP+Pi to ATP by an enzyme catalysed reaction, by protons going down the concentration gradient, into the proton pool.
how does light energy excite electrons?
light energy is absorbed & reached reaction centre –> ground-state electrons in chlorophyll go through photoactivation, where they are raised to ‘excited state’ by the light energy being received and absorbed –> the result is that the high - energy electrons are released and bring about biochemical changes of the light-dependent reactions.
(spaces left empty by excited electrons = constantly refilled by ground-state lectrons)
explain how the elections get excited in the light dependent reactions, explaining all the steps.
1) excited electrons in PSII (photosystem) are picked up & passed along a chain of electron carrier proteins.
2) as they pass, energy that is lost causes a proton pump where H+ (protons) are transferred from the stroma to the thylakoid space (low to high), where the protons accumulate –> causing an elecrochemical gradient to be created in the thylakoid membrane, and the pH drops (chemiosomosis)
3) as a result of these energy transfers, electrons get transferred back to ground state, and fill the vacancies (empty spaces) in the reaction centre of PSI.
4) vacancies in PSII are empty & filled up by ground-state electrons from H2O molecules.
what type of pathway is the pathway of electrons?
linear pathway –> phosphorilation reaction = non-cyclic phosphorilation.
how is the structure of chloroplast related to its function?
-double membrane bounding the chloroplast : contains grana and stroma & is permeable to CO2, O2, ATP and other products of photosynthesis.
-photosystems with chlorophyll pigments arranged in thylakoid membrane of grana : provide huge surface area for maximum light absorption
-thylakoid spaces within grana : restricted regions for accumulation of protons and establishment of the gradient.
-fluid stroma with loosely arranged thylakoid
membranes : site of all the enzymes of fixation, reduction and regeneration of acceptor steps of light-independent reactions, and many enzymes of the product synthesis steps.
