Final answer:
Antonie van Leeuwenhoek is credited with inventing the first single lens microscope and was also the first to observe "animalcules" using his microscopy techniques. He made significant contributions to biology by observing microbes, including bacteria.
Step-by-step explanation:
The first person credited with creating a microscope powerful enough to view microbes is Antonie van Leeuwenhoek. He was a Dutch tradesman and scientist born in Delft, who began his microscopy work as a fabric seller, possibly to inspect the quality of the threads. Leeuwenhoek's innovation in lens making allowed him to construct microscopes capable of observing microorganisms, which he did so in the 1670s, calling them "animalcules" or "wee little beasties."
Answering the student's question: Who invented the first single lens microscope? The correct choice is B) Anton van Leeuwenhoek. None of the other options, Robert Hooke, Louis Pasteur, or Joseph Lister were credited with this particular invention. While Hooke did make significant contributions to the field of microscopy, it was Leeuwenhoek who excelled in creating single lens microscopes that rivaled even those of more complex design.
Regarding who first observed "animalcules" under the microscope, the correct answer is A) Antonie van Leeuwenhoek, who accomplished this feat using his expertly crafted single lens microscope.