The scientist who proposed the 'lock and key' model was: MCQ with Answer and Explanation

Explanation:
Vitamin B₁₂ contains a cobalt ion at the center of its corrin ring structure, hence the name cobalamin. It is essential for DNA synthesis and nervous system function. Iron is in heme, magnesium in chlorophyll, zinc in many enzymes. B₁₂ is unique in having a metal-carbon bond.

Explanation:
Photoperiodism is the physiological reaction of organisms, particularly plants, to the length of the day or a dark period. It is the mechanism by which plants measure the relative lengths of light and dark periods to regulate developmental processes, most notably the timing of flowering. Plants are classified as short-day plants, long-day plants, or day-neutral plants based on their flowering response to photoperiod. The photoreceptor pigment phytochrome is crucial in perceiving these light/dark signals.

Explanation:
Light reactions occur in thylakoid membranes, producing ATP, NADPH, and oxygen. Oxygen comes from water (photolysis), not CO₂. So statement 2 is incorrect. 1 and 3 are correct.