Photosynthesis Flashcards
Where do all the reactions in photosynthesis take place?
chloroplast
What are the products of the light dependent reaction?
O2
ATP
NADPH
What are the products of the light independent reactions?
Glucose
ADP + Pi
NADP (oxidised)
What can glucose be used for?
- respiratory substrate
- stored as starch
- converted (e.g. to beta glucose to form cellulose)
What is the endosymbiotic theory of the chloroplast?
- That the chloroplast used to be its own free-living bateria until being taken in by a cell and having its photosynthetic ability harnessed for the cells use.
- evidence for this = double membrane, DNA, 70s ribosomes
What is the fluid within the chloroplast called?
stroma
What is a stack of thylakoids called?
granum
What are the ‘branches’ between granum called?
intergranal lammelae
Where do the light dependent reactions take place?
thylakoids
Where do the light independent reactions take place?
stroma
What are some of the structural adaptations of the chloroplast?
- high surface area of thylakoids + densely packed w/ photosystems
- stroma surrounds thylakoids - short diffusion distance
What is a photosystem?
The protein within the membrane that carries out the absorption of light
- has multiple different photosynthetic pigments
- increases area over which photons can be harvested
What is the difference between the reaction centre pigment and the accessory pigments?
the reaction centre pigment is always chlorophyll A, accessory pigments may not be chlorA (e.g. ChlorB, xanthophyll, carotene, phaeophythn)
what is the purpose of accessory pigments?
to catch a greater range of wavelengths of light
What is the purpose of Thin Layer Chromatography? (TLC)
To measure the Rf values of different pigments
What is the purpose of the Stationary Phase (silica gel) in TLC?
acts as a constraint on the components in the mixture to make them move slower than the mobile phase
What is non-cyclic photophosphorylation (NCPP)
photophosphorylation that involves both photosystems 2 and 1, as well as 2 electron acceptors + 2 ETC’s
What is the first step in NCPP?
light hits PSII and this causes excitement of 2 electrons, which get accepted by an electron carrier after leaving PSII
What is the second step in NCPP?
- electrons are passed down an ETC from the electron carrier, which releases energy to allow ADP + Pi to form ATP
- light also hits PSI, which causes 2 electrons to leave it to be accepted by an electron carrier. However, they are soon replaced by the 2 electrons which originally left PSII
What is the third step in NCPP?
like step 1, electrons are passed down another electron transport chain, except this time they are receieved by NADP, the final electron acceptor, which is reduced to form NADPH.
What is Cyclic Photophosphorylation?
photophosphorylation that only involves PSI, as well as only 1 ETC and 1 electron acceptor.
What are the steps of CPP?
- Electrons from PSI passed to electron acceptor
- Electrons go down ETC, photophosphorylating ADP to form ATP
- Electrons passed back to electron deficient PSI
- cycle continues as long as light is present
What is photolysis?
the splitting of water molecules via light energy
- occurs in thylakoid lumen
What is H2O split into?
2H+
2e-
1/2 O2
compare cyclic and non-cyclic photophosphorylation
NCPP - uses PSII and PSI, has ATP and NADPH as products
- involves photolysis
- fate of electrons is to go into NADP reductase to form NADPH
CPP - uses PSI, has ATP as product
- doesn’t involve photolysis
- fate of electrons is to continue in cycle going from PSI, electron acceptor, to ETC, back to PSI
What are the steps of the Calvin Cycle?
- 6CO2 + 6RuBP -> 6C intermediate (catalysed by RuBisCO)
- 6C molecule breaks down into 12 G3P molecules (3C)
- 12 G3P -> 12 TP
- turns 12 ATP -> 12 ADP
- turns 12 NADPH -> 12 NADP - 2 TP (out of 12) moves from Calvin cycle to form glucose etc. the rest stays within the cycle
- 10 TP converted to 6 RuBP
- 6ATP -> 6ADP
What is photorespiration?
When RuBisCO adds O2 into the calvin cycle instead of CO2
- BAD for the plant
What happens to Calvin Cycle in low CO2 environment?
Calvin Cycle stops - RuBP builds up, GP + TP levels decrease massively
What happens to Calvin cycle in no light environment?
Calvin Cycle stops - GP levels build up, RuBP + TP levels decrease massively
(no light = no NADPH input, therefore cycle stops as GP is made)
What is a limiting factor?
Any factor that can slow the rate of reaction when in inadequate supply
What are the limting factors for photosynthesis?
- CO2
- light
- temperature
- NOT water - lack of water would kill plant before having an effect on the rate of photosynthesis
How do you measure rate of photosynthesis?
using photosynthetometer, measure the length that the bubble has travelled and then the width of the capillary tube
using V=πr2h
Volume = amount of oxygen evolved
use timer - e.g. amount of oxygen evolved in 1 min etc
what is the rate of respiration in plants?
constant = PLANTS ALWAYS RESPIRING
What is the light compensation point?
When rate of photosynthesis and rate of oxygen production are equal (no net carbohydrate production)
