Simplify the following text for a Grade 14 native English-speaking person.
Original: His discovery of mitosis and chromosomes is considered one of the 100 most important scientific discoveries of all times , and one of the 10 most important discoveries in cell biology ( together with August Weismann 's ( 1834 â `` 1914 ) discovery of meiosis , Theodor Schwann ( 1810 â `` 1882 ) and Matthias Schleiden 's ( 1804 â `` 1881 ) cell theory and Alfred Sturtevant 's ( 1866 â `` 1945 ) first genetic maps ) .
Simplified: His discovery of mitosis and chromosomes is considered one of the 100 most important scientific discoveries of all times , and one of the 10 most important discoveries in cell biology .