The scientist who discovered the concept of 'natural killer' cells was: MCQ with Answer and Explanation

Explanation:
Peptide bond formation is a condensation (dehydration synthesis) reaction where the carboxyl group of one amino acid reacts with the amino group of another, releasing a water molecule. Hydrolysis breaks bonds by adding water. Oxidation/reduction involve electron transfer. Dehydration synthesis builds polymers.

Explanation:
The plasma membrane (cell membrane) is selectively permeable, regulating the entry and exit of substances into and out of the cell, maintaining internal homeostasis. The nucleus is the membrane-bound organelle that houses the cell's genetic material (DNA) organized into chromosomes, directing cellular activities. Mitochondria are the double-membrane-bound organelles known as the 'powerhouses of the cell' because they are the primary site of aerobic respiration, producing the majority of the cell's ATP (energy currency). All statements are correct.

Explanation:
Pellagra, characterized by dermatitis, diarrhea, dementia (three D's), results from niacin deficiency. Beriberi is due to B₁ deficiency, scurvy to C, rickets to D. Niacin is part of NAD and NADP, essential in redox reactions. Foods rich in niacin include meat, fish, whole grains. Pellagra historically associated with corn-based diets.