Photosynthesis Flashcards
What does photosynthesis do?
Builds reduced organic molecules from CO2 and H2O
Is photosynthesis endergonic or exergonic?
Endergonic
Photosynthesis is done by ______ and eaten by ________
Photoautotrophs
Heterotrophs
What is reduced and what is oxidized?
Carbon is reduced
Oxygen is oxidized
What are the two major stages of photosynthesis?
Light reactions
Calvin Cycle
What are light reactions?
Capture light energy to energize electrons
Makes NADPH and ATP
What is the calvin cycle?
Uses energy from ATP and NADPH to reduce CO2 to make 3 carbon sugars which can be used to make glucose
Occurs in the light but can occur in the dark until NADPH and ATP run out
Where does photosynthesis occur?
The chloroplast
CO2 enters the plant via ________
The stomata
The fluid inside the mesophyll cell is called the ________?
Stroma
The calvin cycle occurs where?
The stroma
Inside the chloroplasts, ______ can be stacked to form ______.
Thylakoids
Grana
The thylakoid intermembrane space is called the _____which is where light reactions occur
Lumen
What is chlorophyll?
The pigment which absorbs and transforms the photon energy
Absorption spectrum vs Action spectrum
Shows the wavelengths of light that are absorbed by a substance
Shows the wavelengths of light that are used for a process, such as photosynthesis
When an excited electron quickly falls back to ground state, what may happen?
- Energy is released as heat
- Energy is re-emitted in a less energetic photon
- Energy may be transferred to another molecule
What is a porphyrin ring?
Light absorbing “head” of a molecule
What is a hydrocarbon tail?
Interacts with the hydrophobic regions of proteins inside thylakoid membranes of chloroplasts
Photosystems are composed of _______ surrounded by _________.
Reaction-centre complexes
Light harvesting complexes
Which photosystem comes first?
Photosystem ll
- Light is captured in the _______ and transferred to the reaction centre to the _______.
- The _________ captures the electron and takes it to _________.
- This oxidizes _______ to ______.
P680+ takes an _______ which reduces it back to P680 - The electron that gets ejected from PSll gets captured by _________.
- The electrons are passed to photosystem l where they are re-energized. The energy excited a pair of ______ chlorophyll molecules.
- Photoexcited electrons are passed to a second _______ called ________.
- Once ferredoxin has two electrons, it passes them to _______ to form ________.
Light harvesting complex, Pair of chlorophylls
Primary electron acceptor, photosystem ll
P680 to P680+
Water
The primary electron acceptor
P700-P700+
ETC, ferrodoxin
NADP+ reductase, NADPH
Which complex pumps H+ into the thylakoid lumen?
Cytochrome
Is ATP made directly?
No. Protons build up in the lumen by splitting water and by the cytochrome complex pumping protons into the lumen
Does the second electron transport chain generate a protein gradient?
No
Does the PSll energize an electron sufficiently to reduce NADP+ to form NADPH?
No. Both photosystems are needed
Cyclic electron flow
Recycles electrons from photosystem l
What is the disadvantage of cyclic electron flow?
No NADPH production and no O2
Light reactions summary
- Water is split in _____ on the _____.
- Pq transfers electrons to _______ while also transporting ______ into ______.
- H+ is removed from the stroma as _____ takes up an electron.
Photosystem ll/inner thylakoid membrane
The cytochrome complex/4 H+/thylakoid space
NADP+
The calvin cycle summary
Anabolic pathway of 11 enzymes that builds the _______.
The initial sugar (__________) is used and ________.
Each turn in the cycle fixes 1 molecule of ______.
3-carbon sugar (G3P)
Ribulose bisphosphate/regenerated
CO2
What are the 3 phases of the calvin cycle?
- Carbon fixation
- Reduction
- Regeneration of RuBP
What is carbon fixation?
CO2 is incorporated to the cycle by attatching to a 5C sugar (RuBP) via rubisco, and then split into 3C sugars
What is reduction?
Each 3C molecule is phosphorylated and reduced to G3P
What is regeneration of RuBP?
The skeletons of 5 molecules of G3P are rearranged into 3 molecules of RuBP using ATP
If CO2 is added to the 5C RuBP? How often does this happen?
Both 3PGs can continue in the calvin cycle
75% of the time
If O2 is added to RuBP? How often does this happen?
Photorespiration must occur to recycle the 2PGo produced which consumes ATP and is very wasteful
25% of the time
In a C3 plant, photosynthesis occurs where?
In mesophyll cells, in the middle of the leaf
In C4 plants, photosynthesis occurs where?
The bundle sheaths associated with the veins
_____ adds carbon from CO2 to PEP. The ______ export the 4-carbon products to the _______ where CO2 is released. CO2 then enters the calvin cycle where it operates normally with Rubisco
PEP carboxylase
Mesophyll cells
Bundle sheaths
How many ATPs does it cost to regenerate PEP?
1 ATP but it costs less than binding with O2 instead of CO2
CAM plant photosynthesis looks like C4 plants but they store ____ during _____ when stomata are open, and release them for the calvin cycle when stomata close during ______.
Organic intermediates
The night
The day
Rubisco mistakenly uses O2 if the temperature is higher. What will happen to the productivity of C3 plants?
It will go down since rubisco will be using Rubisco more than it should
