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Photosynthesis : Light dependent

OCR A2 Biology
by

Tre Briercliffe

on 24 June 2013

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Transcript of Photosynthesis : Light dependent

Role of water
photosystem 2 contains an enzyme that can split water into H ions, electrons and oxygen in the present of light
+
Photolysis
2H O 4H + 4e + O
2
2
+
-
2H 0
2
4e
4H
O

-
2
+
Reduced NADP
NADP
H
+
ATP Synthase
Oxygen used in respiration or diffuses out of stomata
light
to be used in light independent stage
Cyclic Phosphorylation
light strikes photosystem I (P700)

light
Excited electrons then pass to an electron acceptor
before traveling back to the chlorophyll molecule from which they were lost
ATP
ADP + P
Some ATP is made in this process
ATP may be used in light independent stage
May be used in guard cells
Guard cells only have photosystem I to bring in potassium ions, lowering water potential and causing water to follow by osmosis - swelling guard cells and causing them to close
Light
Light is absorbed by photosystem II and passed to chlorophyll a P680
2 electrons are emitted
2e
-
Electron acceptor
2e
Non Cyclic Phosphorylation
These excited electrons are at a higher energy level
The electron acceptor passes them along a chain of electron carriers to photosystem I
ADP + P
ADP + P
ATP
ATP
electron carrier chain
energy released from electrons is used to make ATP
-
Light
Light is absorbed by photosystem I and passed to chlorophyll a P700
It emits two electrons
2e
-
2e
-
Which rise to a higher energy level
... and are picked up by a second electron acceptor
electron acceptor
Both photosystems have now lost electrons
What does this mean in terms of their charge?
PSII accepts the electrons from photolysis
PS I accepts electrons from PSII
Positive (and unstable!)
replaces lost electron in non cyclic phosphorylation
2H 0
2
4e
4H
O

-
2
+
Hydrogen ions from photolysis go to combine with electrons in second electron acceptor....
2e
-
2NADP
Reduced NADP
2H
+
NADP Reductase
Z scheme
energy levels
Exam Question:
Last lesson Revision:
match the questions with the answers -all relating to content covered so far - this is the end shape
The light dependent reaction takes place in the Thylakoid membrane..........
What are the products of photosynthesis and what are they used for?
Product
Where and what used for
Take 5
1.
5.
4.
3.
2.
Exam Questions...
Some ATP is made - how?
Chemiosmosis
light
e
-
H
+
-
e
+
H

+
light hits PSII
electron released - higher energy level
electron acceptor - energy from electrons causes H+ to be pumped across membrane
Proton moved to inside of thylakoid membrane
+
H

+
H

+
H

concentration gradient/Proton gradient
ATP Synthase
+
H

ATP
ADP + P
flow of ions through enzyme provides energy to add P
Full transcript