Use models to explain how the cell cycle and mitosis produce genetically identical cells for growth, repair, and reproduction (North Carolina Standard Course of Study, Biology, LS.Bio.2).

What this topic is asking

North Carolina LS.Bio.2 asks you to model how the cell cycle and mitosis make genetically identical cells for growth, repair, and reproduction. For the Biology EOC you need to know the phases of the cell cycle (interphase then mitosis then cytokinesis), why the DNA is copied before division, that the daughter cells are identical to the parent, and that uncontrolled division causes cancer. Mitosis is also the contrast partner for meiosis.

The cell cycle and interphase

Most of a cell's life is spent in interphase, which has three jobs: the cell grows, it carries out its normal functions, and it copies its DNA by replication. Copying the DNA first is essential: it ensures that when the cell divides, each daughter cell can receive a complete, identical set of genetic information. If the DNA were not doubled beforehand, the two new cells would not both get a full set.

Mitosis: dividing the nucleus

After interphase, mitosis divides the nucleus so each new cell gets one complete set of chromosomes. The chromosomes (each now a doubled pair of identical copies) line up in the middle of the cell, then the copies are pulled apart to opposite ends, giving two identical sets. The cell then completes division with cytokinesis, when the cytoplasm splits to form two separate cells. You may meet the named stages (prophase, metaphase, anaphase, telophase), but the EOC focus is the outcome: two genetically identical daughter cells with the full chromosome number.

Why mitosis matters: growth, repair, and cancer

Mitosis is how multicellular organisms grow (more cells), repair damage (replace injured cells), and replace worn-out cells (such as skin and blood cells). In some organisms it is also the basis of asexual reproduction, producing offspring identical to the parent.

The cell cycle is normally tightly controlled by checkpoints that decide whether a cell should divide. When these controls fail, often because of mutations in the genes that regulate the cycle, cells divide without stopping. This uncontrolled division produces a mass of cells called a tumor, the basis of cancer. So the same process that builds and heals the body becomes dangerous when its controls break down, which the EOC links back to mutations and gene regulation.

Try this

Q1. State what happens to the DNA during interphase and why it is important. [2]

• Cue. The DNA is copied (replicated), so each daughter cell can receive a complete, identical set after division.

Q2. State two differences between mitosis and meiosis. [2]

• Cue. Mitosis makes two identical cells with the full chromosome number; meiosis makes four genetically different gametes with half the chromosome number.