Govt. Exams
Entrance Exams
Transpiration pull is the tension/negative pressure developed in xylem vessels due to continuous water loss (transpiration) from leaves. This creates a suction force that pulls water upward from roots. It can occur both day and night through lenticels and cuticles, though primarily during day.
White patches result from chloroplasts lacking chlorophyll or being non-functional, typically due to mutations in chloroplast DNA (maternal inheritance). Green patches have functional chloroplasts.
Phytochrome exists in two interconvertible forms (Pr and Pfr) and acts as a red/far-red light sensor, measuring day length for photoperiodic flowering responses.
Carotenoids absorb light energy in blue and green regions, transfer it to chlorophyll, and provide photoprotection by quenching singlet oxygen and excess excitation energy.
K+ accumulation in guard cells lowers the water potential, causing water influx and turgor increase, leading to stomatal opening. This is the primary mechanism.
CAM (Crassulacean Acid Metabolism) plants fix CO2 at night into malate and release it during the day for photosynthesis, reducing water loss in arid environments.
Photosystem II contains the oxygen-evolving complex (OEC) with a manganese cluster that catalyzes water splitting, releasing O2, H+, and electrons.
Guttation occurs when root pressure forces water out through hydathodes (water pores) as liquid water droplets, typically at night.
Grana are stacks of thylakoids arranged vertically, while stroma lamellae are unstacked thylakoids connecting different grana.
Q10 of 2.0-3.0 indicates that enzyme activity doubles or triples with every 10°C increase in temperature, typical for biological systems.
