B2: Cell Division


B2.1: Cell Division

  • in body cells, chromosomes are found in pairs.
  • body cells divide in a series of stages called the cell cycle. 
  • during the cell cycle the genetic material is doubled. it then divides into two identical nuclei in a process called mitosis.
  • before a cell can divide it needs to grow, replicate the DNA to form two copies of each chromosome and increase the number of sub-cellular structures. 
  • in mitosis one set of chromosomes is pulle to each end of the cell and then the nucleus divides.
  • finally the cytoplasm and cell membranes divide and form two identical cells.
  • mitotic cell division is important for the growth, repair and development of multicellular organisms.
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B2.2: Growth and Differentiation

  • in plant cells, mitosis takes place throughout life in the meristems found in the shoot and root tips.
  • many types of plant cells retain the ability to differentiate throughout life.
  • most types of animal cells differentiate at an early stage of development. 
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B2.3: Stem Cells

  • embryonic stem cells are from human embryos and adult stem cells are from adult bone marrow.
  • they can be cloned and made to differentiate into different types of cells.
  • treatment with stem cells may be able to help conditions such as paralysis and diabetes.
  • stem cells from plant meristems are used to produce new plant closed quickly and economically for research, horticulture and agriculture. 
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B2.4: Stem Cell Dilemmas

  • treatment with stem cells, from embryos or adult cell cloning may be able to help with conditions such as diabetes.
  • in theraputic cloning, an embryo is produced with the same genes as the patient so the stem cells produced are not rejected and may be used for medical treatment.
  • the use of stem cells has potential risks and some people have religious or ethical objections. 
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