Photosynthesis Flashcards
what is oxygenic photosynthesis?
A redox process that involved light and gas exchange. It converts carbon dioxide and wter into carbohydrates and oxygen. It is endergonic.
what is different about non-oxygenic photosynthesis?
during non-oxygenic photosynthesis other molecules donate the required ions and electrons to carry out photosynthesis
what are the steps in photosynthesis?
Takes place in the mesophyll cells
organised into the light dependent and independent reactions (calvin cycle)
describe the light dependent reaction
occurs in the thylakoid membrane
there are photosystems embedded into the thylakoid membrane
light energy is absorbed by pigments in the light harvesting complex, this released energy due to its excited state and this energy is absorbed by another pigment molecule. This is then passed to cholorophyll in the reaction centre. Light is converted to chemical energy in the reaction centre. Chlorophylll gives up electrons to an acceptor and is oxidised into an ion. This acceptor is part of a series of acceptors, the final one being NADP+ which is reduced to NADPH.
what is chlorophyll and what does it do
Chlorophyll is a pigment that absorbs red and blue light and reflects green. It is a major pigment attached to the photosystems in the thylakoid membrane
what are photosystems?
Embedded protein complexes that allow for the capture and transport of electrons in the thylakoid membrane
what are the main electron acceptors in photosynthesis?
The main electron acceptor is NADPH and Fd
what happens in photosystem 2?
In photosystem 2 (the first photosystem)
- it absorbs photons and passes this through the light harvesting complex
- It generates energy to chlorophyll in the p680 reaction centre
- It releases the electron from the chlorophyll to a primary electron acceptor molecule, through a photoact
- then passes it though a chain of acceptors
- Then it gets passed to photosystem 1
simulateously:
- Water is getting split into H+ and O2, releasing 2 electrons that replace the missing electrons in P680
- the H+ ions enter the thylakoid space/lumen and the oxygen bonds to create O2, which is released into the atmosphere
what happens in photosystem 1?
- also has a p700 reaction centre and a light harvesting complex
- p700 absorbs light and relays e- from the ETC to Fd (ferredoxin)
- electrons are accepted by ferredoxin-NADP+reductase
- NADPH is formed (it is reduced as per the name)
what happens in electron transport?
Electrons are passed from PSII to PS1 through ETC and electron acceptors
- its first passed through plastoquinone
- then cytochrome complex
- protein plastocyanin
- once plastocyanin is reduced (accepted the e-), it transfers the e- to P700
what is photophosphorylation?
Once we have NADPH we can use ATP synthase to make ATP through photophosphorylation
using light to phosphorylise
e.g. using light and its energy that is harnessed through the photosystems in order to create NADPH to make ATP from ADP + Pi
what is chemiosmosis/chemiosmotic mechanisms?
chemiosmotic mechanisms- the physical/chemical machinery used for photophosphorylation
describe the dark reactions?
carbon fixation = light independent reaction = dark reactions
explain the key points of the calvin cycle
fixation
- 3 carbon dioxide molecules are fixed into 6 molecules of 3-PGA (3-phosphoglycerate)
reduction
- energy in 6 ATP and 6 NADPH is used to reduce 3PGA into 6 molecules of GA3P (glyceraldehyde-3-phosphate)
- 1 GA3P forms 1/2 glucose molecule
regeneration of RuBP
- 5 GA3P molecules use 3 ATP to form 3 molecules of RuBP
- RuBP is the carbon dioxide acceptor (ribulose biphosphate)
Rubisco catalyses the reaction between carbon dioxide and RuBp
therefore 2 cycles produce 1 glucose*****
what is RuBP and RuBisCo?
RuBp is Ribulose biphosphate
RuBisCo ribulose 5-biphosphate carboxylase/oxygenase
