ally identical daughter cells. Some textbooks call the preparation stage **interphase**, meaning the part of the cycle where the cell grows and copies DNA before mitosis. They may call the final split **cytokinesis**, meaning division of the cytoplasm, the jelly-like material inside the cell. You can use these terms, but the descriptions are what matter most for marks. Here is the whole cycle in one view. Focus on the order of events: prepare, separate chromosomes, then split into two cells. ![Diagram of the cell cycle showing growth and DNA replication, mitosis, and division into two genetically identical daughter cells.](https://assets.yesgenie.com/notes/9771f8ae-4acb-45f1-a628-5023124cdca9.png) During the cell cycle, the genetic material is **doubled first**, then the chromosome copies are **separated**, and finally the cell divides to make two genetically identical cells. Mitosis is only the stage where the copied chromosomes are separated and the nucleus divides. The cell must grow and copy its DNA **before** mitosis, and the cytoplasm and membrane divide **after** mitosis. ## Stage 1: growth and DNA replication Before a cell divides, it needs to get ready. It grows larger and makes more **sub-cellular structures**, which are smaller parts inside the cell. For this topic, the key examples are: - **Ribosomes**: tiny structures where proteins are made. - **Mitochondria**: structures where aerobic respiration transfers energy for cell processes. The cell also copies its DNA. **DNA replication** means making an exact copy of the DNA. In the cell cycle, DNA replicates to form two copies of each chromosome. This copying step matters because each daughter cell needs a complete set of chromosomes. If the DNA was not copied first, the new cells would not receive the full genetic instructions. For this first stage, exam answers often need both ideas: the cell **grows and increases sub-cellular structures**, and the **DNA replicates to form two copies of each chromosome**. ## Stage 2: mitosis separates the chromosomes **Mitosis** is the stage of the cell cycle where one set of copied chromosomes is pulled to each end of the cell and the nucleus divides. During mitosis, the cell makes sure each end receives one complete set of chromosomes. Then the nucleus divides, so each future daughter cell will have a nucleus containing the correct genetic information. You do **not** need to learn the detailed named phases inside mitosis for AQA GCSE Biology 8461. The important idea is that copied chromosomes are separated accurately. A body cell has 8 chromosomes before DNA replication. After the full cell cycle is complete, how many chromosomes will be in each daughter cell? 1. A genetically identical daughter cell must end with the same full chromosome set as the parent cell: 8 chromosomes. 2. DNA replication produces two copies of each chromosome before mitosis, so there are enough chromosome copies for two cells. 3. During mitosis, the copied chromosomes are separated so each end of the cell receives one copy of every chromosome. 4. After the cytoplasm and membrane divide, each daughter cell has 8 chromosomes and the same genetic information as the parent cell. After DNA replication, there are two copies of each chromosome temporarily. Mitosis separates those copies, so the final daughter cells have the normal chromosome set, not double the normal amount. ## Stage 3: the cell divides into two After mitosis, the cell still needs to physically split. The **cell membrane**, the thin boundary around the cell, divides. The cytoplasm divides too, sharing out the contents of the cell between the two new cells.