When a single cell undergoes many mitotic divisions in the nucleus, producing many daughter cells, it has conducted
binary fission
multiple fission
fragmentation
budding

When a single cell undergoes many mitotic divisions in the nucleus, producing many daughter cells, it has conducted B) Multiple fission. 

Multiple Fission is a type of asexual reproduction in which the parental body divides into many daughter cells simultaneously during the unfavorable conditions to increase the chances of survival of daughter cells.In this, the reproductive unit is whole parental body.

Hope this helps :)

That would be a working theory.

The answer to this will be from your lab notes/procedure. it would be best to ask another student who participated in the lab as we do not know what was done, what enzyme or if the temperature is celsius or fahrenheit. if i were to guess though i'd say the rate stopped due to enzyme denturing at high temperature