The phenomenon of a plant bending toward a light source is called: MCQ with Answer and Explanation

Explanation:
Earthworm (Pheretima) belongs to phylum Annelida, characterized by metameric segmentation (body divided into segments), a closed circulatory system, and setae for locomotion. Tapeworm is a platyhelminth (flatworm), roundworm is nematode (Ascaris), Planaria is a free-living platyhelminth. Annelids include polychaetes (Nereis), oligochaetes (earthworm), and hirudinea (leech).

Explanation:
Adenylyl cyclase converts ATP to cyclic AMP (cAMP), a second messenger. Phosphodiesterase breaks down cAMP, PKA is activated by cAMP, PLC produces IP₃ and DAG.

Explanation:
An operon is a functional unit of DNA in prokaryotes containing a cluster of genes under the control of a single promoter, transcribed as a single mRNA. Example: lac operon. It includes operator, promoter, and structural genes. Operons allow coordinate regulation. Eukaryotes generally lack operons.