Consider statements about cell biology: 1. The cell membrane is selectively permeable. 2. The cell wall is present in all plant cells. 3. The nucleus is the control center of the cell. Which are correct? MCQ with Answer and Explanation

Explanation:
The juxtaglomerular apparatus (JGA) is a specialized structure where the distal convoluted tubule (DCT) comes into contact with the afferent arteriole. It consists of juxtaglomerular cells (modified smooth muscle cells in the afferent arteriole that secrete renin), macula densa cells (modified DCT cells that sense NaCl concentration), and extraglomerular mesangial cells. It plays a crucial role in regulating blood pressure and glomerular filtration rate via the renin-angiotensin-aldosterone system.

Explanation:
The fluid mosaic model, proposed by Singer and Nicolson (1972), describes the plasma membrane as a phospholipid bilayer with proteins floating like icebergs in a sea of lipids. It accounts for membrane fluidity and selective permeability. The cell wall is rigid, nucleus has a double membrane, ribosome is a ribonucleoprotein complex.

Explanation:
Creutzfeldt-Jakob disease (CJD) is a rare, fatal brain disorder caused by misfolded prion proteins (PrP^Sc), which are infectious protein particles lacking nucleic acid. Rabies, polio, and influenza are caused by viruses. Prions cause spongiform encephalopathies like mad cow disease (BSE).