Which of the following is a defining characteristic of meiosis? MCQ with Answer and Explanation

Explanation:
Antonie van Leeuwenhoek was the first to observe and describe living microorganisms, including bacteria, using his single-lens microscopes. Robert Koch formulated Koch's postulates, a set of criteria to establish that a specific microorganism causes a specific disease. Alexander Fleming discovered penicillin; streptomycin was discovered by Selman Waksman. Thus, statements 1 and 2 are correct.

Explanation:
Natural passive immunity is transferred from mother to child via placental transfer of IgG antibodies (in utero) and IgA antibodies in breast milk (colostrum). It provides temporary protection without the infant's immune system being activated. Active immunity results from natural infection or vaccination.

Explanation:
The joints between skull bones are immovable fibrous joints called sutures, where bones are tightly connected by dense connective tissue. Hinge joint (elbow, knee) allows movement in one plane. Ball and socket (shoulder, hip) allows multi-directional movement. Pivot joint (atlas-axis) allows rotational movement. Sutures fuse completely in old age.