Complex sentence: Wee1 acts to keep Cdk1 inactive during early G2 when cells are still a size of a pea, the phosphatase Cdc25 removes the inhibitory phosphorylation, and thus activates Cdk1 to allow mitotic entry.
Split into simpler sentences: Wee1 acts to keep Cdk1 inactive during early G2 when cells are still small. When cells have reached sufficient size during G2, the phosphatase Cdc25 removes the inhibitory phosphorylation, and thus activates Cdk1 to allow mitotic entry.