The hormone that stimulates the reabsorption of water in the collecting duct is: MCQ with Answer and Explanation

Explanation:
In the lac operon, the 'i' gene (regulatory gene) constitutively produces a repressor protein. In the absence of lactose (the inducer), this active repressor binds specifically to the operator region of the operon. The operator overlaps with the promoter, physically blocking RNA polymerase from binding to the promoter or moving forward to transcribe the structural genes (z, y, a). When lactose is present, it binds to the repressor, inactivating it and allowing transcription.

Explanation:
Mature mammalian red blood cells (erythrocytes) are enucleated to maximize space for hemoglobin. Platelets (thrombocytes) are cell fragments crucial for the blood coagulation cascade. Blood plasma, the liquid component, constitutes about 55% of total blood volume, while the formed elements (RBCs, WBCs, platelets) make up the remaining 45%. Thus, statements 1 and 2 are correct.

Explanation:
The plasma membrane (cell membrane) is primarily composed of a phospholipid bilayer with embedded proteins, following the fluid mosaic model, regulating transport in and out of the cell. The nucleus is the membrane-bound organelle that houses the cell's genetic material (DNA) organized into chromosomes. Mitochondria are the site of aerobic cellular respiration and ATP production; chloroplasts are the organelles where photosynthesis occurs in plant cells. Thus, statements 1 and 2 are correct.