AP Biology: Cell Reproduction – Part 1: Interphase

Every second, thousands of cells are dying throughout our bodies. Fortunately, the body replaces them at an amazing rate. In fact, epidermal (skin) cells die off and are replaced so quickly that the average 18-year-old grows an entirely new skin every few weeks. The body is able to maintain this unbelievable rate due to the mechanisms of cell division, which you need to know all about for the AP Biology exam.


Every cell has a life cycle – the period from the beginning of one division to the beginning of the next. The cell’s life cycle is known as the cell cycle, which is divided into two periods: interphase and mitosis.


Interphase is the time span from one cell division to another. This stage is called interphase because the cell has not yet started to divide. The cell carries out its regular activities, and all the proteins and enzymes it needs to grow are produced during interphase.

Interphase can be divided into three stages: G1, G2, and S phase.

S phase is the most important phase. This is when the cell replicates its genetic material. Firstly, the cell replicates all of its chromosomes. The original chromosome and the duplicate chromosome remain linked, like conjoined twins. The identical chromosomes are now called sister chromatids (each individual structure is called a chromatid). The chromatids are held together by the centromere.

During the G1 and G2 stages, the cell produces enzymes and proteins. For example, during G1, the cell prodces all of the enzymes required for DNA replication.


-          The cell cycle consists of two parts: interphase and mitosis

-          During the S phase of interphase, the chromosomes replicate

-          Growth and preparation for mitosis occur during the G1 and G2 stages of interphase.


Create an annotated flow diagram outlining the stages involved in interphase.

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