Photosynthesis Flashcards
What is photosynthesis?
The process by which the energy of sunlight (photon) is converted into the energy of glucose
Where are chloroplasts in plant cell?
All green parts of the plant (including stems and leaves)
What type of membrane does the choloplast have?
Double membrane (both are phospholipid bilayer)
Within the interior space of the membranes is a semi liquid material called
Stroma
The stroma contains____
What are they needed for?
Enzymes
Needed to catalyze photosynthesis
Thylakoids:
Disks within the stroma (bound by the membrane)
Grana:
Stacks/columns of thylakoids
Lamellae
Unstacked thylakoids that connect adjacent grana
Numbers of visible light spectrum
400nm to 700nm used by photosynthetic organisms
Pigments
Photosynthetic compounds that can absorb the energy from a certain wavelength
Two pigments
Chlorophyll (a and b)
Carotenoids
Chlorophyll a
Most important because it forms the reaction for light dependent stage
Absorbs: red and violet
Reflects: blue, yellow, green
What is an accessory pigment?
They absorb wavelengths not used by chlorophyll to maximize absorption of the suns energy (secondary function provides protection)
Chlorophyll b
Absorbs less red and blue than a
Reflects green and yellow
Cannot form reaction center for light dependent stage
Carotenoids
Absorbs green blue and violet
Reflects red orange and yellow
Can transfer energy to chlorophyll a
Absorb excess light energy and dissipate it to avoid damage
When an electron becomes excited due to absorption ___ many things can happen
Three
Outcome 1
Electron drops back to ground state and energy is lost (released as heat)
Outcome 2
Electron drops back to ground state state but energy is transferred to neighbouring electrons
(Resonance)
Outcome 3
High energy electron is accepted by the primary electron acceptor (only done by chlorophyll a) electron leaves pigment and pigment becomes oxidized
light is converted to chemical energy
What is an antenna complex?
Shows several hundred pigments in the chloroplast (can illustrate outcomes 2/3)
Absorption spectrum
Peak- light absorbed
Low lines- light reflected
Shows the wavelengths that alignment is absorbing/absorbs best
Action spectrum
Shows how fast photosynthesis is happening in regards to the wavelength of light
Light dependent reaction parts
P680
PQ
Cytochrome complex
Plastocyanin
P700
Ferredoxin
NADP+ reductase
ATP synthase
How does light dependent reaction start
Sunlight hits the antenna complex, energy is funneled to chlorophyll a and e- is transferred to primary acceptor (light -> chemical)
Summary
P680->PQ->cytochrome complex ->plastocyanin->p700…..
As e- moves from each complex it___
Loses energy and that energy is used to pump H+ into the thylakoid’s lumen from the stroma
What happens when p700 gets a low energy e-
E- is re-energized through the antenna complex (suns photon) before it loses its e- to the electron acceptor
P700->…..
Ferredoxin->NADP+ reductase (NADPH takes 2e-)
What does H+ want to do?
Restore equilibrium by moving from [high] to [low] in stroma using ATP synthase
What does ATP synthase do?
Uses energy to make ATP from ADP + Pi
What replaces the lost e- in cycle
Water, breaks down by water splitting complex (called photolysis)
What does water do
An e- is donated to p680 and oxygen is released
What’s does the light dependent reaction make
Makes NADPH and ATP (both needed for light independed reaction)
Cyclic cycle
E- from p700 that’s excited goes to Ferredoxin but is donated back to PQ (NOT to NADP+)
Why does the cyclic cycle exist
Allows more H+ to be pumped across leading to more ATP productions calvin cycle needs 9ATP and 6NADPH to run
Or
Could run out of NADP+ to use at the end of the day
Where do light independent reactions happen
Happen in stroma
What do light independent reactions use?
Products of the light dependent rxn *totally endergonic
Step one:
Carbon fixation:
Done by Rubisco (enzyme) takes an inorganic C from atmosphere and make it apart of organic molecule
Makes five carbon sugar called ribulosbiphosphate (3 of them x2)
Why is every reaction multiplied by two?
Because although it’s written 3CO2 every glucose needs 6CO2 therefore everything is multipled by two
Rublosbiphosphate makes…..
Breaks down into 6 (x2) 3-phosphoglycerate
Step two
Reduction
(X2) 3-phosphoglycerate -> 6G3P (use 6 ATP and 6 NADPH) (both of those are made in light dependent reactions
Step three
Regeneration
6 G3P (x2) one leaves five stays in cycle (x2) (need 2 G3P to make one glucose)
Step four
Regeneration
5 G3P -> ribolosebiphosphate
Use 3ATP to make 3 (x2) five carbon molecules
Total ATP and NADPH used
18 and 12
Rubisco
Rubsico is the enzyme that helps catalyze the reaction between ribulose biphosphate and CO2
During the day the stomata are….
Open
CO2 diffuses into the leaf as it diffuses from [high] to [low]
If the soil is dry….
Stomata close to prevent water loss
Rubisco will bind with….
Oxygen instead of CO2 since oxygen is readily available due to photolysis in light dependent reactions
