Govt. Exams
Entrance Exams
ABA stress signaling involves activation of phospholipase C → IP3 generation → Ca2+ release from vacuoles → opening of anion channels (Cl-, malate) → efflux of anions and K+ → loss of turgor → stomatal closure. This is the canonical ABA-signaling pathway in guard cells.
The Kok cycle involves S0→S1→S2→S3→S4 states. Four electrons are removed sequentially from the Mn4CaO5 cluster before O2 is released at the S4→S0 transition.
The Emerson effect revealed the existence of two photosystems. Both PSI and PSII need to function sequentially for optimal electron transport and ATP/NADPH generation.
P700 (PSI) has a lower (more negative) reduction potential than P680 (PSII), making it easier to reduce and better suited for final electron acceptance and NADP+ reduction.
Without light-driven electron transport, no new protons are pumped into the thylakoid lumen. The existing gradient dissipates as protons leak back through ATP synthase or other pathways.
Higher CO2 increases the carboxylation of RuBP to form 3-PG faster, consuming RuBP more rapidly. As long as the reduction phase can regenerate RuBP, levels may remain relatively stable, but the consumption rate increases.
ATP synthase works in both processes using chemiosmotic gradient; F0 is the membrane-spanning unit; F1 synthesizes ATP from ADP.
The Pasteur effect describes how aerobic respiration inhibits the rate of fermentation, as aerobic respiration is more efficient.
The carboxylation of RuBP by RuBisCO is typically the slowest step in photosynthesis under normal light conditions.
The proton gradient (pH gradient) is established by water photolysis at PSII and the Q-cycle in cytochrome b6f complex, which pumps H+ into the thylakoid lumen.
