Cell Division
Cell division and cell enlargement is used by multicellular organisms to grow and reproduce. Plants can also grow via differentiation into branches, leaves, etc.
From the moment of fertilisation cell division begins, when the zygote replicates itself exactly through mitosis. Later in its life cycle an organism may use cell division to produce sex cells (gametes) in a different type of division called meiosis.
The stages of cell division make up the cell cycle of an organism.
Chromosomes
Chromosomes are found in the nucleus of eukaryotic cells. Chromosomes exist as pairs called homologues and are made of DNA and carry a large number of genes.
For the exact duplication of cells is it essential that all of the genetic material is duplicated. Chromosomes form a key part of a sequence of events that ensures the genetic code is transmitted exactly and appears in the new daughter cells.
DNA replication
DNA replication occurs during the cell cycle; the genetic material is doubled and then divided between the identical daughter cells.
The diagram below shows DNA replication:
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- DNA helix starts to unzip
- Bases added to form new strands
- The new DNA molecule
- Two identical strands of DNA are formed
Mitosis and Meiosis are the two types of cell division.
Mitosis enables growth and repair to occur. Meiosis is for the production of sex cells.
Mitosis is used in asexual reproduction. Meiosis is used to produce gametes for sexual reproduction
Mitosis prodcues cells with identical number of chromosomes and genetic information are produced (46 in humans). Meiosis produces daughter cells with half the number of chromosomes of the parent (23 in humans)
Mitosis (Asexual)
Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell.
The daughter cells are identical to one another and to the original parent cell.
Each chromosome replicates.
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This video looks at Mitosis
Meiosis (Sexual)
Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced.
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This video looks at Meiosis
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