Photomorphogenesis refers to light-dependent development processes including light-mediated seed germination. Phytochrome is the photoreceptor involved. This is distinct from photoperiodism (flowering response to day length).
In C4 plants, PEP carboxylase fixes CO2 into oxaloacetate (4-carbon compound), unlike C3 plants where RuBisCO produces 3-PGA. This adaptation reduces photorespiration and is efficient in hot climates.
Phytochrome exists in two interconvertible forms (Pr and Pfr) and absorbs maximally in red (~660 nm) and far-red (~730 nm) regions. It's crucial for seed germination and photoperiodism - important for UPSC agriculture-related questions.
Root pressure is generated by active transport of mineral ions into the xylem sap, creating a concentration gradient that draws water in osmotically. This is distinct from transpiration pull and is a key concept in plant physiology.
In hypertonic solutions, water moves out of the cell due to osmosis, causing protoplasm to shrink away from the cell wall - this is plasmolysis. This is a fundamental osmotic principle tested in SSC/Railway exams.
Double fertilization: one sperm fuses with egg nucleus (embryo), other fuses with polar nuclei (endosperm - 3n).
Physiological wilting occurs when transpiration rate exceeds water absorption rate, though soil moisture is sufficient.
Rhizobium bacteria in root nodules of legumes fix atmospheric nitrogen into ammonia through nitrogenase enzyme.
Cohesion-tension theory explains that water is pulled upward due to transpirational pull creating negative pressure in xylem.
CAM plants like pineapple, cactus, and agave fix CO2 at night into organic acids and release during day for photosynthesis.