Biology
Cell division
Key words
Learning objectives:
daughter cell mitosis stem cells
• describe the process of mitosis in growth, and mitosis as part of the cell cycle • describe how the process of mitosis produces cells that are genetically identical to the parent cell.
As an adult, we are made up of 37 trillion (3.7 × 1013) cells. To produce these cells, the fertilised egg needs to undergo many cell divisions. 1
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Chromosomes As we grow, the cells produced by cell division must all contain the same genetic information.
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The genetic information of all organisms is contained in chromosomes, made of DNA. The DNA in resting cells is found in the nucleus as long, thin strands. For cell division, these strands form condensed chromosomes.
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Human body cells have 46 chromosomes, or 23 pairs. Each chromosome in a pair has the same type of genes along its length. How many chromosomes are found in human body cells?
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How are the chromosomes arranged in a karyotype?
Mitosis New cells have to be produced for growth and development, and to replace worn out and damaged body cells.
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When new cells are produced they must be identical to the A photograph is taken of a dividing cell. parent cell. Cells divide to produce two new ones. This type of cell division is called mitosis. Two daughter cells are produced from the parent cell.
The chromosomes in the photograph are cut out and arranged into pairs. The pairs are arranged so that Pair 1 has the longest chromosomes; Pair 22 the shortest Pair 23 is the sex chromosomes.
For some cell types, new cells are produced by the division of stem cells (discussed later in the chapter).
Figure 1.19 A profile of a set of chromosomes, called a karyotype
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When are new cells produced?
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In this type of cell division: • how many chromosomes do daughter cells have? • how many daughter cells are produced?
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MAKING CONNECTIONS To come up with a figure for how many cells there are in the human body, scientists must estimate the number by adding up cell counts from different organs.
AQA GCSE Biology for Combined Science: Trilogy: Student Book
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The chromosom cut out and arra The pairs are ar longest chromos Pair 23 is the se
A photograph is taken of a dividing cell.
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