Photosynthesis Flashcards
What part of the light spectrum is primarily used in photosynthesis?
red and blue
Why is green light less effective for photosynthesis?
chlorophyl reflects green light
How does chlorophyll a differ from chlorophyll b in light absorption?
Chlorophyll a absorbs mostly red light, while chlorophyll b absorbs more blue light
Which color of light has the highest energy and why?
blue because it has the shortest wavelength
What is the role of carotenoids in photosynthesis?
absorb blue and green light
Why is the absorption of red and blue light crucial for photosynthesis?
provides energy for light dependent reactions
What happens to the absorbed light energy in chlorophyll?
The energy excites electrons, initiating the process of converting light into chemical energy.
What is the main function of chloroplasts?
site of photosynthesis
What is the outer structure of the chloroplast composed of?
double membrane
What is the fluid-filled space inside the chloroplast called?
stroma
What are the disk-shaped structures in chloroplasts called?
Thylakoids
Where do the light-dependent reactions of photosynthesis take place?
thylakoid membrane
Where do the light-independent (Calvin cycle) reactions occur in the chloroplast?
stroma
What is the role of the thylakoid membrane in photosynthesis?
It contains chlorophyll and other pigments to capture light energy and generate ATP and NADPH.
What is the purpose of the thylakoid lumen?
proton gradient needed for ATP synthesis.
What pigment is embedded in the thylakoid membranes?
chlorophyl
What is Photosystem II (PSII) and where is it located?
PSII is a protein complex in the thylakoid membrane that initiates photosynthesis by absorbing light and splitting water molecules.
What is Photosystem I (PSI) and where is it located?
PSI is a protein complex also located in the thylakoid membrane, responsible for producing NADPH by transferring electrons to NADP+.
What is the primary role of PSII?
splits water to produce oxygen and passes electrons to ETC
What is the primary role of PSI?
reduce NADP+ to NADPH
What is Förster resonant energy transfer (FRET)?
energy from an excited molecule (donor) is transferred to a nearby pigment molecule (acceptor) without the movement of electrons.
How is FRET important in photosynthesis?
allows for transfer of energy to chloroplast
What is the efficiency of FRET dependent on?
distance between donor and acceptor
What is charge separation in photosynthesis?
Charge separation occurs when an electron in the chlorophyll reaction center becomes excited by light and is transferred to an electron acceptor, leaving behind a positively charged chlorophyll.
In PSII, which molecules participate in charge separation?
The chlorophyll molecule P680 absorbs light and transfers an excited electron to a nearby plastoquinone molecule, initiating the electron transport chain.
What is the result of charge separation in PSI?
PSI’s P700 chlorophyll transfers an excited electron to ferredoxin, which is then used to reduce NADP+ to NADPH.
How is the H+ gradient generated in photosynthesis?
The movement of electrons through the electron transport chain causes protons (H+) to be pumped from the stroma into the thylakoid lumen, creating a proton gradient.
What role does the H+ gradient play in photosynthesis?
drives ATP synthesis
In which part of the thylakoid membrane is the H+ gradient the highest?
thylakoid lumen
What is the electron transport chain in photosynthesis?
The ETC is a series of protein complexes in the thylakoid membrane that transfer electrons from PSII to PSI and ultimately to NADP+ to form NADPH.
What role does plastoquinone (PQ) play in the electron transport chain?
PQ shuttles electrons from PSII to the cytochrome b6f complex and helps move protons into the thylakoid lumen
How does the cytochrome b6f complex contribute to the H+ gradient?
It transfers electrons from plastoquinone to plastocyanin and simultaneously pumps protons (H+) into the thylakoid lumen, strengthening the proton gradient.
What role does plastocyanin (PC) play in electron transport
transfers electrons from the cytochrome b6f complex to PSI.
How does ferredoxin (Fd) function in the electron transport chain?
Ferredoxin transfers electrons from PSI to the enzyme ferredoxin-NADP+ reductase (FNR), which reduces NADP+ to NADPH.
What is the final electron acceptor in photosynthesis?
NADP+
How do photosystem II (PSII) inhibitors work as herbicides?
block transfer of electrons
What is the effect of blocking electron transport in PSII?
causes a build up of reactive oxygen species that damages cell
How do Photosystem I (PSI) inhibitors work as herbicides?
They accept electrons from PSI and produce toxic reactive oxygen species (ROS), causing oxidative damage to the plant.
Name a herbicide that targets PSI.
paraquat
Which herbicide class inhibits Photosystem II (PSII)?
Triazines
What is the effect of inhibiting carotenoid synthesis in herbicide action?
plant cannot be protected from excess light leading to photo damage
How do chloroplasts respond to high light intensity?
NPQ dissipates excess light
What role do carotenoids play in protecting chloroplasts?
protects from ROS and dissipates excess light
how do chloroplasts deal with low light conditions?
increase LHC
What is photoinhibition, and how do chloroplasts cope with it?
Photoinhibition occurs when excess light damages PSII. Chloroplasts repair damaged D1 proteins in PSII to recover from this damage.
What is the role of chloroplast movement in coping with environmental changes?
In high light conditions, chloroplasts move to the sides of cells to minimize light absorption; in low light, they spread out to maximize exposure.
How do chloroplasts adjust to changes in temperature?
modulation of fluid and heat shock proteins
How does photorespiration help chloroplasts cope with low CO₂ conditions?
Photorespiration allows the chloroplast to process oxygen when CO₂ levels are low, though it reduces photosynthetic efficiency.
How do chloroplasts cope with water stress?
close stroma
