Which of the following is a defining feature of all chordates at some stage of their life? MCQ with Answer and Explanation

Explanation:
Oxytocin, released from the posterior pituitary in response to suckling, causes contraction of myoepithelial cells around mammary alveoli, forcing milk into ducts (let-down reflex). Prolactin stimulates milk synthesis. Estrogen and progesterone inhibit milk secretion during pregnancy.

Explanation:
Vitamin C (ascorbic acid) is a water-soluble antioxidant that also acts as a cofactor for enzymes involved in collagen synthesis, carnitine synthesis, and neurotransmitter production. Deficiency causes scurvy. Vitamin A is for vision, D for bone, K for clotting. Smokers require higher vitamin C intake due to oxidative stress.

Explanation:
Azolla is an aquatic fern that harbors the nitrogen-fixing cyanobacterium Anabaena azollae in its leaf cavities. It is extensively used as a biofertilizer in rice paddies, adding organic nitrogen. Rhizobium fixes nitrogen in legume roots, Azotobacter is free-living in soil, mycorrhiza is a fungal association enhancing phosphorus uptake. Azolla multiplies rapidly and improves soil fertility.