Govt Exams
The correct electron flow is: PSII (P680) → Plastoquinone → Cytochrome b6f complex → Plastocyanin → PSI (P700) → NADP+ reductase.
During drought, water loss causes cells to lose turgor pressure. ABA accumulation further reduces guard cell turgor by opening K+ efflux channels, closing stomata.
Carotenoids are accessory pigments that absorb light and protect against photoinhibition but do NOT participate directly in CO2 fixation.
CAM plants open stomata at night to fix CO2 as malic acid, stored in vacuoles. During the day, stomata close to reduce water loss while malic acid is decarboxylated for the Calvin cycle.
Photoinhibition occurs when light intensity exceeds the photosynthetic capacity, causing photodamage to PSII reaction center and photodissociation of D1 protein.
Light intensity directly affects photosynthesis but has no effect on respiration, which occurs in both light and dark conditions.
Quantum yield represents the photosynthetic efficiency, defined as the number of CO2 molecules fixed per photon absorbed (typically 8-10 photons per CO2).
Guttation occurs through specialized pores called hydathodes located at the leaf margins, allowing liquid water to be exuded when root pressure exceeds transpiration.
Light reactions do not require CO2. CO2 is used in the dark reaction (Calvin cycle). Light reactions produce ATP, NADPH, and O2.
At compensation point, the rate of CO2 fixation in photosynthesis equals the rate of CO2 release in respiration, resulting in net zero gas exchange.