To solve this problem, we need to understand what happens during the 'S' phase of the cell cycle. Let's analyze each option:$\newline \bullet$Option 1: amount of DNA doubles in each cell.$\newline$ - During the 'S' (synthesis) phase, the cell replicates its DNA.$\newline$ - This means that the amount of DNA in the cell doubles, preparing the cell for division.$\newline$ - Therefore, this option is correct.$\newline \bullet$Option 2: amount of DNA remains same in each cell.$\newline$ - This is incorrect because the DNA is replicated during the 'S' phase, so the amount of DNA does not remain the same.$\newline \bullet$Option 3: chromosome number is increased.$\newline$ - The chromosome number does not increase during the 'S' phase.$\newline$ - Instead, each chromosome is duplicated, resulting in sister chromatids, but the number of chromosomes remains the same.$\newline \bullet$Option 4: amount of DNA is reduced to half in each cell.$\newline$ - This is incorrect because the DNA is not reduced during the 'S' phase; it is doubled.$\newline$Therefore, the correct answer is Option 1: \text{amount of DNA doubles in each cell.}