The 'Hershey-Chase' experiment in 1952 used radioactive isotopes to prove that DNA is the genetic material of bacteriophages. They used: MCQ with Answer and Explanation

Explanation:
The skin and mucous membranes form the first line of defense (innate immunity), acting as physical barriers that prevent pathogens from entering the body. White blood cells (leukocytes), including phagocytes and lymphocytes, are the cellular components of the immune system that identify, attack, and destroy pathogens. Antibiotics are drugs designed to kill or inhibit the growth of bacteria; they are completely ineffective against viruses, which lack the cellular machinery targeted by antibiotics. Thus, statements 1 and 2 are correct.

Explanation:
Gastrin is a peptide hormone produced by the G cells (gastrin cells) located in the pyloric antrum of the stomach. Its primary function is to stimulate the parietal cells of the gastric glands to secrete hydrochloric acid (HCl) and the chief cells to secrete pepsinogen. This prepares the stomach for the digestion of food. Gastrin also stimulates gastric motility and growth of the gastric mucosa. Secretin and CCK stimulate the pancreas and gall bladder.

Explanation:
Abscisic acid (ABA) is known as the stress hormone because it plays a crucial role in plant responses to environmental stresses, particularly drought. It induces the closure of stomata to reduce water loss (transpiration) and also inhibits seed germination and growth, helping the plant survive adverse conditions.