Assertion (A): The menstrual cycle ceases during pregnancy. Reason (R): High levels of progesterone and estrogen inhibit FSH and LH release. MCQ with Answer and Explanation

Explanation:
Simple permanent tissues (parenchyma, collenchyma, sclerenchyma) consist of a single cell type. Meristematic tissues are dividing and have thin walls; xylem/phloem are complex; epidermis is dermal.

Explanation:
Innate immunity is the non-specific defense mechanism present by birth, including physical barriers and phagocytes. Vaccination introduces antigens to stimulate the body's own antibody production, conferring artificial active immunity. Antibodies (immunoglobulins) are produced and secreted by B-lymphocytes (plasma cells), not T-lymphocytes, which are involved in cell-mediated immunity. Thus, statements 1 and 2 are correct.

Explanation:
Biological magnification (or biomagnification) is the process where the concentration of persistent, non-biodegradable toxic substances (like DDT, mercury, or PCBs) increases progressively at each successive trophic level in a food chain. Because these substances are not metabolized or excreted, they accumulate in the tissues of organisms. Top predators end up with the highest, often lethal, concentrations of these toxins.