Photosynthesis Flashcards
Define photosystems
Systems of photosynthetic pigments within a chloroplasts
Describe the structure of a photosystem
-Funnel shaped
-Reaction centre in middle, antenna complex surrounding it where pigments are
-Primary pigments and accessory pigments
-In thykaloid membrane
Name the types and subtypes of chlorophyll, and their locations
-Chlorophyll a (P680)- photosystem 2 (PII)
-Chlorophyll a (P700)- photosystem 1 (PI)
-Chlorophyll b- PII
Why do accessory pigments exist?
To absorb wavelengths of light that primary pigments can’t.
Define Photophosphorylation
The synthesis of ATP from ADP in the presence of light
Name the two stages of photosynthesis
-Light dependent stage
-Light independent stage (Calvin cycle)
LIC: describe non cyclic photophosphorylation
-Light absorbed by photons, excite electrons from PII and PI
-e- carried by electron carriers (NADP) down electron transport chain
-e- loose energy, energy used to pump H+ ions into thykaloid space
-e-reduces NADP to NADPH by NADP reductase enzyme
-H+ returns to stroma via ATP synthase, proton motive force catalyses ADP to ATP
-Photolysis occurs, water split into O, H+ and e-. e- replaces moving e from PII and PI
Define photoylsis
The splitting of water molecules into oxygen, protons and electrons in the presence of light
What are the products of non cyclic photophosphorylation?
-NADPH
-Oxygen
-ATP
Describe cyclic photophosphorylation
-Photons absorbed by pigments in PI, excites electrons
-e- taken by NADP, down electron transport chain
-H+ pumped into thykaloid space then return to stroma via ATP synthase, ATP made
-e- returns to PI
What’s the difference between cyclic and non cyclic photophosphorylation?
- Cyclic- no reduction of NADP, no photolysis, no oxygen production, less ATP generated than non cyclic
Where does the LDS take place?
On the thykaloid membane
Where does the LIS take place?
The stroma (cytoplasm of chloroplast)
Can the LIS/ calvin cycle happen in the dark and why?
No. Would eventually run out of ATP and NADPH, which is generated in the LDS, which needs light
Describe the LIS/Calvin cycle
-Carbon fixation- (5c) RuBP (Ribulose biphosphate) binds with CO2 to make a 6c intermediary, which splits into 2 GP (3c)
-Reduction of GP- H+ from 2NADPH and energy from 2ATP used to reduce GP to TP. Produces TP, 2NADP and 2ADP
-Regeneration of RuBP -5/6 of TP phosphorylated by ATP (turns into ADP) to make RuBP
-Remaining 1/6 of TP used o make other organic compounds e.g glucose
What is needed to make one molecule of glucose in the LIS/Calvin cycle?
-6 turns of calvin cycle
-6RuBP, 12GP, 12TP.
-10TP used to regenerate RuBP, 2TP used to make glucose
Note: TP can also be used to synthesis amino acids, fatty acids and glycerol
What is the compensation point?
The point in time where the rate of photosynthesis and respiration are exactly equal
What is a heterotroph?
Organisms that can’t produce their own energy and must rely on other organisms for it (Organisms that do not photosynthesise)
What is a photoautotroph?
Organisms that produce their own energy through photosynthesis.
(Note: Auto- automatic- done without effort)
