Who modified the cell theory in a final shape?

Assertion $A$: Every cell is a wonderful marvel of the world. Reason $R$: $A$ cell takes in nutrients,converts them into energy,and performs specialized functions. Which option is correct for Assertion $A$ and Reason $R$?

Matthias Schleiden $(1838)$ proposed that the cell is the structural and functional unit of life. His idea was a:

Unicellular organisms are capable of:
$(i)$ Having an independent life.
$(ii)$ Organ development.
$(iii)$ Performing metabolic activities for life.
$(iv)$ Tissue constitution.

The cell is a wonder of the world because ...........

Which scientist explained that all cells arise from pre-existing cells?