B. The levels of unbound cyclin E are at their lowest when the cell transitions into the S phase. Cell reproduction operates cyclically, governed by the specific needs of the cell. For mitosis, the transition from G1 to S to G2 to M is overseen by proteins like cyclins. In particular, passing from G1 to S requires cdK2. Cyclins are synthesized and degraded continuously throughout the cell cycle.
The plasma membrane envelops the absorbed molecules.
1. rivers and streams 2. groundwater seepage
