Identify and describe What is the Cell Cycle?, Interphase: The Preparation Stage and Mitosis: Separating the Chromosomes in the context of mitosis and the cell cycle.
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GCSE Biology Revision
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GCSE Biology revision
Mitosis and the cell cycle
Cell division
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Explain the relationships between What is the Cell Cycle?, Interphase: The Preparation Stage and Mitosis: Separating the Chromosomes and how they contribute to mitosis and the cell cycle.
Apply and analyse knowledge of What is the Cell Cycle?, Interphase: The Preparation Stage and Mitosis: Separating the Chromosomes to interpret unfamiliar information about mitosis and the cell cycle.
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Key knowledge
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What is the Cell Cycle?
- The cell cycle is the series of stages a cell goes through to duplicate and divide, and it occurs continuously to replace dead cells, support growth, and repair tissues.
- The length of the cell cycle varies between organisms and cell types, with rapidly replaced cells such as skin and hair follicle cells having a faster cycle.
Interphase: The Preparation Stage
- Interphase is the longest stage of the cell cycle, during which the cell prepares for division by growing in size, replicating its DNA, and producing new organelles.
- DNA replication during interphase ensures the cell doubles its genetic material so each daughter cell receives a complete set of chromosomes.
- The number of mitochondria increases during interphase to provide the extra energy needed for protein synthesis and cell division.
- Ribosomes increase in number during interphase because they are the site of protein synthesis, and large amounts of new protein are needed to form two daughter cells.
- The cell surface membrane extends outwards as the cytoplasm grows, allowing the cell to increase in size before division.
Mitosis: Separating the Chromosomes
- Mitosis is the stage of cell division in which the parent cell's nucleus divides to produce two genetically identical sets of chromosomes.
- At the start of mitosis, the duplicated chromosomes line up along the equator of the cell.
- Spindle fibres attach to the chromosomes and pull them to opposite poles of the cell, ensuring each new nucleus receives a complete set of genetic material.
- Once the chromosomes reach opposite poles, new nuclear membranes form around each set, creating two separate nuclei and marking the end of mitosis.
Cytokinesis: Splitting into Two Daughter Cells
- Cytokinesis follows mitosis and is the process by which the cytoplasm divides and new cell membranes form around each nucleus to produce two separate daughter cells.
- The two daughter cells produced are genetically identical to each other and to the original parent cell.
Chromosomes During the Cell Cycle
- Chromosomes are found in pairs in body cells, with one chromosome in each pair inherited from the mother and one from the father.
- After DNA replication in interphase, each chromosome exists as two identical copies, giving the cell double its usual number of chromosomes before division.
- Following mitosis and cytokinesis, each daughter cell contains the same number and type of chromosomes as the original parent cell.
Key Definitions to Remember
- Mitosis is defined as the division of a parent cell into two genetically identical daughter cells.
- Cytokinesis refers to the division of the cytoplasm and cell membrane to enclose the two new nuclei, completing cell division.
- Interphase is the preparatory phase of the cell cycle during which growth, DNA replication, and organelle production occur.
Mitosis and Growth
- Mitosis is essential for the growth of multicellular organisms, as all organisms begin as a single fertilised egg cell and develop into complex organisms through repeated rounds of cell division.
- Because mitosis produces genetically identical daughter cells, the new cells carry the same genetic instructions as the original, ensuring consistent development.
- Each round of mitosis doubles the number of cells, so one parent cell produces two daughter cells, and four parent cells undergoing mitosis produce eight daughter cells.
Mitosis and Cell Replacement
- Mitosis is vital for replacing worn-out or damaged cells, such as skin cells that are constantly lost through everyday contact with surfaces.
- An actively dividing layer of skin cells beneath the outer surface layer continuously replaces lost skin cells through mitosis.
- Mitosis also plays a key role in repairing damaged tissues throughout the body.
Mitosis and Asexual Reproduction
- Mitosis is the basis of asexual reproduction in single-celled organisms, where one organism divides to produce two genetically identical daughter organisms.
- Unlike sexual reproduction in humans, asexual reproduction produces offspring that are genetically identical to the parent organism.
- An example of asexual reproduction by mitosis is seen in single-celled organisms such as algae, which divide to produce two new daughter organisms.