Assertion (A): The pituitary gland is connected to the hypothalamus by a stalk. Reason (R): This connection allows the hypothalamus to control pituitary hormone secretion. MCQ with Answer and Explanation

Explanation:
HIV is a retrovirus with two copies of single-stranded RNA as its genome. It uses reverse transcriptase to convert RNA into DNA upon infection. Double-stranded DNA is typical of many organisms. Single-stranded DNA viruses exist (e.g., parvovirus). Double-stranded RNA viruses include rotavirus. The viral RNA genome enables integration into host DNA via a DNA intermediate.

Explanation:
Crystallization is a property of non-living substances where molecules arrange in a definite pattern, e.g., salt crystals. Living organisms exhibit growth, reproduction, metabolism, cellular organization, and consciousness. Metabolism is a defining feature of all living organisms, occurring even in unicellular forms. Reproduction, though absent in sterile organisms like mules, is generally a characteristic. Growth in living beings is internal and intrinsic, unlike extrinsic accumulation in non-living things. Hence, crystallization is not a characteristic of life.

Explanation:
Sclerenchyma is a simple permanent tissue composed of dead cells with extremely thick, lignified, and pitted cell walls. These cells (fibers and sclereids) are narrow, elongated, and provide rigid mechanical strength, allowing plant parts to withstand bending and pressure. Collenchyma provides flexible support in growing parts, and parenchyma is for storage and photosynthesis (chlorenchyma).