Photosynthesis
Chloroplasts (thylakoid membranes & stroma).
What are the primary inputs to the light-dependent reactions?
Photosynthesis fixes atmospheric into organic carbon, supports primary productivity and food webs, and sequesters carbon. If photosynthesis declines, atmospheric rises, primary productivity and crop yields drop, and ecosystems/food chains are disrupted.Light (photons), water (), NADP+, and ADP + .
What is the three-carbon sugar produced directly by the Calvin Cycle that can be used to build glucose?
Glyceraldehyde-3-phosphate (G3P).
P700 is the reaction center chlorophyll of which photosystem (I or II)?
Photosystem I (PSI).
P680 is the reaction center chlorophyll of which photosystem (I or II)?
Photosystem II (PSII).
Carbon dioxide + water (with light energy) → glucose + oxygen (and water rearrangements); formally: carbon dioxide + water + light energy → glucose + oxygen + water.
What important molecule is produced in the light-dependent reactions and used later in the Calvin Cycle?
NADPH (also ATP is produced).
What enzyme catalyzes the fixation of mathrum in the Calvin Cycle?
Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase).
Explain what happens when P700 absorbs light.
Electrons becomes excited to a higher energy level by absorbing more light energy and electrons are transferred.
What is the role of P680 in water splitting (photolysis)?
P680 (when excited) extracts electrons from water via the oxygen-evolving complex (photolysis), producing 02, H+ protons and electrons.
Name two major stages of photosynthesis and where each occurs in the chloroplast.
Light-dependent reactions (thylakoid membranes) and Calvin Cycle / light-independent reactions (stroma).
Name the two photosystems involved in the light-dependent reactions and state which one comes first in the electron flow.
Photosystem II (PSII, P680) first, then Photosystem I (PSI, P700) in noncyclic electron flow.
List the three main phases of the Calvin Cycle in order.
Carbon fixation → Reduction → Regeneration of RuBP.
Describe how P700 is involved in the production of NADPH.
Electrons becomes excited and donates an electron to NADP+.
Identify the immediate electron acceptor of excited P680 and describe its place in the electron transport chain.
The immediate acceptor is plastoquinone.
Explain why chlorophyll appears green (what happens to different wavelengths of light).
Chlorophyll absorbs red and blue wavelengths and reflects/transmits green, so leaves appear green.
Explain the role of the electron transport chain in the light-dependent reactions and how it helps form ATP.
The ETC transfers electrons through carriers (e.g., plastoquinone → cytochrome b6f → plastocyanin), pumping/providing conditions for proton accumulation in the thylakoid lumen; the proton gradient drives ATP synthase to produce ATP from
Explain how ATP and NADPH are used during the Calvin Cycle, including which steps they power.
ATP provides energy (phosphorylation steps, RuBP regeneration) and NADPH provides reducing power (reducing 1,3‑bisphosphoglycerate to G3P).
Explain why P700 is named “P700.”
P700 is named for its peak absorption at about 700 nm (700 = wavelength in nm)
Explain how the activity of P680 contributes to the proton gradient across the thylakoid membrane.
P680 activity (water splitting and electron transfer) contributes protons to the lumen (from water and via cytochrome b6f), creating the proton gradient used by ATP synthase to make ATP.
Describe how photosynthesis contributes to the global carbon cycle and one ecological consequence if plant photosynthesis rates decline.
Photosynthesis fixes atmospheric into organic carbon, supports primary productivity and food webs, and sequesters carbon. If photosynthesis declines, atmospheric rises, primary productivity and crop yields drop, and ecosystems/food chains are disrupted.
Compare cyclic and noncyclic electron flow: give one purpose of cyclic electron flow and one condition when a plant might favor it.
Cyclic electron flow returns electrons from PSI to the cytochrome b6f complex to make extra ATP without producing NADPH or splitting water. Plants favor it when the Calvin Cycle needs more ATP relative to NADPH or when NADP+ is limited.
How many molecules of G3P are formed during the Reduction phase?
How many are Counted?
6 molecules f G3P are formed during the Reduction phase and only one is counted as a net gain.
Predict the effect on NADPH production if P700 could not be reduced efficiently; include consequences for the Calvin Cycle.
If P700 could not be reduced efficiently, NADPH production would decline, limiting the Calvin Cycle’s reduction steps; plants might shift to cyclic flow (making ATP) but overall carbon fixation and carbohydrate synthesis would be impaired.
Describe the effect on O2 release if P680 were permanently unable to oxidize water. Include effects on ATP and NADPH production.
If P680 could not oxidize water, photolysis would stop, electrons to the ETC would cease, O2 release would stop, the proton gradient would collapse (less ATP), NADPH production would fall, and the Calvin Cycle would be unable to proceed.