Cell division
2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis.
The first stage of cell division is interphase which is divided into 3 phases; G1, S and G2. The cell cycle starts with G1 (Gap phase 1) during which the cell grows larger. This is followed by phase S (synthesis) during which the genome is replicated. Finally, G2 (gap phase 2) is the second growth phase which separates the newly replicated genome and marks the end of interphase.
The fourth stage is mitosis which is divided into prophase, metaphase, anaphase and telophase. During mitosis the spindle fibers attach to the chromosomes and pull sister chromatids apart. This stage separates the two daughter genomes. Finally, cytokinesis is the last stage during which the cytoplasm divides to create two daughter cells. In animal cells the cell is pinched in two while plant cells form a plate between the dividing cells.
2.5.2 State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.
Tumors are formed when cell division goes wrong and is no longer controlled. This can happen in any organ or tissue.
2.5.3 State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.
Interphase is an active period in the life of a cell during which many metabolic reactions occur such as protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplast.
2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
During prophase the spindle microtubules grow and extend from each pole to the equator. Also chromosomes super coil and become short and bulky and the nuclear envelope breaks down.
During metaphase the chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides.
During anaphase the spindle microtubules pull the sister chromatids apart splitting the centromeres. This splits the sister chromatids into chromosomes. Each identical chromosome is pulled to opposite poles.
During telophase the spindle microtubules break down and the chromosomes uncoil and so are no longer individually visible. Also the nuclear membrane reforms. The cell then divides by cytokinesis to form two daughter cells with identical genetic nuclei.
2.5.5 Explain how mitosis produces two genetically identical nuclei.
Mitosis is divided into four stages; prophase, metaphase, anaphase and telophase. During prophase, the chromosomes become visible under a light microscope as they super coil and therefore they get shorter and more bulky. The nuclear envelope disintegrates and the spindle microtubules grow and extend from each pole to the equator. At metaphase the chromatids move to the equator. The sister chromatids are two DNA molecules formed by DNA replication and are therefore identical. These sister chromatids are then separated in anaphase as the spindle microtubules attaches to centromere and pulls the sister chromatids to opposite poles. As the sister chromatids separate they are called chromosomes. This means that each pole has the same chromosomes (same genetic material). Finally the microtubules break down, the chromosomes uncoil and the nuclear membrane reforms. The cell then divides into two daughter cells with genetically identical nuclei.
2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.
Growth, embryonic development, tissue repair and asexual reproduction involve mitosis.