Cell Division Phases to Know for AP Biology

Cell division is crucial for growth, repair, and reproduction in living organisms. This process includes interphase, mitosis, and meiosis, each with distinct phases that ensure accurate genetic material distribution to daughter cells. Understanding these phases is key in AP Biology.

1. Interphase

   • The longest phase of the cell cycle, where the cell prepares for division.
   • Composed of three sub-phases: G1, S, and G2.
   • DNA is in the form of chromatin, making it less visible under a microscope.

2. Prophase

   • Chromatin condenses into visible chromosomes, each consisting of two sister chromatids.
   • The nuclear envelope begins to break down.
   • Spindle fibers start to form from the centrosomes, which move to opposite poles.

3. Metaphase

   • Chromosomes align at the cell's equatorial plane, known as the metaphase plate.
   • Spindle fibers attach to the centromeres of the chromosomes.
   • Ensures that each daughter cell will receive an identical set of chromosomes.

4. Anaphase

   • Sister chromatids are pulled apart toward opposite poles of the cell.
   • The cell elongates as the spindle fibers shorten.
   • Ensures that each new cell will have the correct number of chromosomes.

5. Telophase

   • Chromatids reach the poles and begin to de-condense back into chromatin.
   • The nuclear envelope re-forms around each set of chromosomes.
   • The spindle apparatus disassembles.

6. Cytokinesis

   • The final step of cell division, where the cytoplasm divides.
   • In animal cells, a cleavage furrow forms to separate the two daughter cells.
   • In plant cells, a cell plate forms, leading to the creation of a new cell wall.

7. G1 phase

   • The first sub-phase of interphase, where the cell grows and carries out normal functions.
   • The cell prepares for DNA replication by synthesizing proteins and organelles.
   • Critical checkpoint to assess if the cell is ready to proceed to the S phase.

8. S phase

   • The phase where DNA replication occurs, resulting in two identical sets of chromosomes.
   • Each chromosome is duplicated, forming sister chromatids.
   • Ensures that each daughter cell will have a complete set of genetic information.

9. G2 phase

   • The final sub-phase of interphase, where the cell continues to grow and prepares for mitosis.
   • The cell checks for DNA damage and ensures all DNA is replicated correctly.
   • Organelles are duplicated, and proteins necessary for mitosis are synthesized.

10. Mitosis

    • The process of nuclear division that results in two genetically identical daughter cells.
    • Consists of four main stages: prophase, metaphase, anaphase, and telophase.
    • Essential for growth, repair, and asexual reproduction in organisms.

11. Meiosis I

    • The first division in meiosis, reducing the chromosome number by half.
    • Homologous chromosomes pair up and exchange genetic material through crossing over.
    • Results in two haploid cells, each with half the original chromosome number.

12. Meiosis II

    • The second division in meiosis, similar to mitosis, where sister chromatids are separated.
    • Results in four genetically diverse haploid cells.
    • Essential for sexual reproduction, producing gametes (sperm and eggs).