Final answer:
Anton van Leeuwenhoek observed bacteria in 1675, with serious scientific study starting in the 19th century. The 'Golden Age' of microbiology in the mid-1800s to early 1900s furthered our understanding of bacteria.
Explanation:
Bacteria were first observed by Anton van Leeuwenhoek in 1675, making option A. 1600s the closest choice among the given options. However, it wasn't until the 19th century that bacteria became the subject of serious scientific study as scientists realized their role in causing diseases. The 'Golden Age' of microbiology, from the mid-1800s to early 1900s, led to significant advancements in understanding and studying bacteria.
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