The reduction phase of Calvin cycle requires 3 ATP per CO2 fixed. NADPH requirement is 2 molecules per CO2. These are stoichiometric ratios essential for understanding photosynthetic efficiency.

Ethylene is the senescence hormone that promotes leaf yellowing, abscission, and fruit ripening. Cytokinins antagonize ethylene effects. This hormone physiology is important for understanding plant development.

The correct radial arrangement in dicot stems is Epidermis (outermost) → Cortex → Vascular bundles (Phloem outer, Xylem inner) → Pith (center). This NCERT-based concept is frequently asked in SSC exams.

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.