In 1665, Robert Hook discovered many "small chambers" that he called "celluae" by looking at slices of cork through a self-made microscope. In fact, what he saw were not living cells, but cells of the dead plant xylem.
In 1667, the Dutch scientist Leeuwenhoek observed a living ciliate through his self-made microscope, which was the first time that human observed a living cell. Because cell biology was still a novel subject at the time and his secrecy about microscopic techniques, no one succeeded his work for more than 100 years after his death.
Carl Linnaeus proposed the binomial nomenclature and Linnaean classification in the 18th century. He classified almost all organisms known in his time according to their characteristics, and all of them were uniquely named, ending the chaos of biological classification and nomenclature.
The optical microscope was owned by a few people until 19th century when it became popular and more people began to study cells. In 1838-1839, Schleiden and Schwann concluded that both animal and plant are composed of cells after summarizing previous research. In 1858, Rudolf Virchow summarized the work of predecessors to point out that all the cells were from cells. The establishment of the cell theory broke down the barriers between plant and animal and allowed life to be research in a more unified view.
During the 100 years from mid-19th century to mid-20th century, cells were studied by optical microscopy and stained sections. The cell membrane, protoplasm, nucleus and various organelles were observed. Amitosis, mitosis and meiosis were also discovered during this period. The study of cells was not limited to microscopic observation, experimental manipulation and in vitro culture techniques were also incorporated into biology. People can partially regulate the cell life activity according to their purpose.
Hertwig observed fertilization of animal cells in 1876. After this, plant fertilization and the phenomenon that germ cells had only half number of chromosomes were discovered. The genetic law that discovered by G. Mendel 34 years ago received attention again in 1900. People began to realize that chromosomes and genetic traits were somehow related. In 1910, after years of research on fruit flies, Morgan concluded the genes that determine the genetic traits were located on chromosomes. Classical gene theory described biology from a new perspective and was a prelude to molecular biology.
In 1953 Watson and Crick discovered the double helix structure of DNA based on the diffraction image of X-rays. Then they proposed the central dogma of biology, marking the birth of an emerging discipline—molecular biology.