Interphase consists of G1, S and G2.
G1 is the first growth phase. Cytoplasm are active and new organelles are formed. It is also a phase of intense biochemical activity of growing cells
S is the synthesis of DNA, this is the phase here chromosomes are copied or replicated. The process in which chromatids
G2 is the second growth phase. It prepares the cell to undergo mitosis by increasing the growth
In prophase, chromosomes become visible as long thin threads. At the end of prophase, it is possible to see two chromatids held together at the centromere. The nuclear membrane starts the break down.
In metaphase, the centrioles move to opposite ends of the cell. Microtubules in the cytoplasm starts to form into a spindle attached to the centromeres of each pair of chromatids at the equator.
In anaphase, the centromeres divide, the spindle fibre shorten, and the chromatids are pulled by their centromeres to opposite poles.
In telophase, the nuclear membrane reforms and the chromosomes decondense by uncoiling. They become chromatin again.
Cytokinesis follows telophase where it splits the cell into two daughter 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.
Uncontrolled cell division are various forms of different cancers affecting several tissues of the body. In cancer, cells divide by mitosis repeatedly, without control or regulation, forming an irregular mass of cells, called a tumour. Cancer is caused by damage to DNA of chromosomes. Mistakes of different types build up in the DNA of the body cells.
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 chloroplast.
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).
Prophase
Telophase
2.5.5 Explain how mitosis produces two genetically identical nuclei.
Daughter cells produced by mitosis have a set of chromosomes identical to each other and to the parent cell from which they were formed. This occurs because:
- An exact copy of each chromosomes is made by accurate replication during interphase, when two chromatids are formed
- Chromatids remain attached by their centromeres during metaphase of mitosis, when each becomes attached to a spindle fibre at the equator of the spindle
- Centromeres then divide during anaphase and the chromatids of each pairs are pulled apart to opposite poles of the spindle.
- The chromosomes at the poles form the new nuclei.
- Two cells are then formed by division of the cytoplasm at the midpoint.
2.5.6 State that growth, embryonic development, tissue repair, and asexual reproduction involve mitosis.
In growth and development of an embryo, it is important that all cells carry the same genetic information as the existing cells from which they are formed, and which they share with surrounding cells or tissues. Similarly, when repair of damaged or worn out cells occurs, they are exact copies what they replace. In fact, this essential for growth, development and repair, because otherwise different parts of our body might start working to conflicting blueprints. The results will be chaos.
Mitosis cell division is also the basis of all forms of asexual reproduction, in which the offspring produced are identical to the parent.
沒有留言:
張貼留言