Which law of thermodynamics explains why heat cannot spontaneously flow from a colder body to a hotter body?

The correct answer is B: Second Law of Thermodynamics. The Second Law of Thermodynamics states that entropy of an isolated system increases or remains constant. Heat spontaneously flows from hot to cold, not vice versa, establishing the direction of processes.

Which phenomenon is responsible for the reddish appearance of the Sun at sunset?

The correct answer is B: Scattering of light. At sunset, light travels through a longer path in the atmosphere. Shorter wavelengths (blue) scatter more (Rayleigh scattering), leaving longer wavelengths (red) to reach the observer.

The process of nitrogen fixation in legumes is performed by which organism?

The correct answer is B: Rhizobium (Nitrogen-fixing bacteria in root nodules). Rhizobium bacteria form symbiotic associations with legume roots, fixing atmospheric N2 into ammonia. The bacteria live in root nodules. This symbiotic relationship is agriculturally significant and frequently tested in competitive exams.

The reduction phase of Calvin cycle produces which molecule as the final product?

The correct answer is C: Glyceraldehyde-3-phosphate. G3P (Glyceraldehyde-3-phosphate) is the final product of the reduction phase where 3-PG is reduced using ATP and NADPH from light reactions.

The casparian strip in plant roots is composed primarily of:

The correct answer is B: Suberin and lignin. The casparian strip is a hydrophobic barrier of suberin and lignin in the endodermis that prevents apoplastic transport and regulates ion uptake.