Which branch of biology deals with the study of external form and structure of organisms? MCQ with Answer and Explanation

Explanation:
The spliceosome is a large, dynamic complex composed of five small nuclear ribonucleoproteins (snRNPs, pronounced 'snurps') and numerous other protein factors. It assembles on the pre-mRNA transcript in the nucleus. Its primary function is to catalyze the splicing of pre-mRNA: it precisely recognizes the splice sites at the boundaries of introns and exons, removes the non-coding intron sequences, and ligates (joins) the coding exons together to form a continuous, mature mRNA molecule that can be exported to the cytoplasm for translation.

Explanation:
Thyroxine (T₄) and triiodothyronine (T₃) are synthesized by thyroid follicular cells. They regulate basal metabolic rate, growth, and development. Iodine is essential for their synthesis.

Explanation:
Photolysis of water provides electrons and protons for the light reactions, releasing O₂; NADPH formed carries hydrogen to reduce CO₂ in the Calvin cycle. R correctly explains A.