B3 - D

  • Created by: zoolouise
  • Created on: 02-06-15 19:38
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  • Cell division
    • Becoming multicellular
      • There are a number of advantages of being multicellular, humans are
        • It allows an organism to become larger and more complex
        • It allows different cells to take on different jobs, cell differentiation.
      • When an organism becomes multicullular, it needs to have certain systems.
        • They need to allow communication between all cells in the body.
          • They need to supply all cells with enough nutrients and control exchanges with the environment such as heats and gases.
    • Mitosis
      • The process that produces new cells for growth is called mitosis.
      • Cells made by mitosis are genetically identical. Before cells divide, DNA replication must take to ensure that each cell still has two copies of each chromosome.
      • Body cells in mammals have 2 copies of each chromosome, they're called diploid cells.
      • Before mitosis happens, DNA's replicated and this involves two strands of the DNA molecule unzipping to form single strands and the new double strands forming by DNA bases lining up in complementary pairings.
        • After this, mitosis occurs. Chromosomes line up along the center of the cell and divide. The copies then move to the opposite poles of the cell.
    • Meiosis
      • The type of cell division that produces gametes is called meiosis.
        • In mitosis there's 2 divisions, first the single strands are copied to make X-shaped chromosomes and chromosomes with  the same genes pair up.
          • In the first division, 1 chromosome from each pair move to opposite poles of the cell. in the second division, the copies of each chromosome come apart and move to opposite poles of the cell.
      • Gametes are haploid cells as they contain only 1 chromosome from each pair. This means the zygote only gets 1 copy of each gene from one parent and one from the other parent. Produces genetic variation.
      • Structure of a sperm cell is adapted to its function, it has many mitochondria to provide energy to swim to the egg, an chromosome releases enzymes to digest the egg membrane.


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