In chloroplasts of leaves.

Chlorophyll a is the primary photosynthetic pigment that absorbs light in the blue and red regions of the electromagnetic spectrum.

Plant cell sap is slightly acidic due to organic acids like malic acid and citric acid, maintaining pH between 4-6.

Magnesium (Mg) is the central atom in the chlorophyll molecule, forming a coordinate bond with the porphyrin ring.

Auxin causes differential elongation of cells on the shaded side, resulting in phototropic response towards light.

Transpiration is the loss of water vapour from aerial parts of plants, primarily through stomata during daytime.

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.

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.

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.

Stomata generally close at night (except CAM plants) to reduce transpiration. Guard cells are rich in mitochondria and chloroplasts to provide ATP and regulate osmotic potential. This circadian regulation is fundamental to plant physiology.