2.2 All cells arise from other cells

• Why is mitosis so important?

  It allows the replacement of cells and allows the number of cells in an organ/tissue to increase
• What percentage of the cell cycle does mitosis take up?

  10%
• What happens during interphase?

  DNA replicates, protein synthesis occurs, ATP is produced, organelles are replicated and accumulated in the cytoplasm.
• What is a centromere?

  The protein that holds together the chromatid
• How do you calculate the mitotic index?

  Mitotic index = number of cells undergoing mitosis (PMAT) / total number of cells
• How do you work out percentage increase?

  (new value - old value) / old value

  It's the same for percentage decrease too.
• What is the equation to work out the end number of cells after binary fission?

  End number of cells = start number of cells x 2 *to the power of * number of divisions

  You times by 2 as it produces two daughter cells.
• Describe interphase including visuals.

  Chromosomes are not visible. Cell grows more cytoplasm, DNA replicates, organelles replicate, ATP builds up and protein synthesis occurs (any two or more of these).

  
• Why do we need control groups?

  They allow comparison
• What must we do with control groups, in terms of ethics? [2]

  We must still treat them, with another known to be safe drug.
• What are two problems with using mice in drug trails?

  Ethics and they may respond differently to human cells
• What are the three stages of the cell cycle?

  Interphase (longest) Nucleur division (mitosis or meiosis) Cell division (kytokinesis - splitting of the cytoplasm)
• Why is sample size important? [2]

  A larger sample size gives more reliable and reprosentative results, however can be expensive
• How can the results of the mitotic index be used to diagnose cancer and why does the result mean they have cancer?

  The mitotic index would increase as the duration of the cell cycle is shorter in cancerous cells.
• Describe what happens during telophase including visuals [2]

  A new nucleur envelope starts to form and chromosomes uncoil

  
• Describe prophase including visuals

  Chromosomes condense and become visible. Nuclear envelope breaks down, centrioles move to the poles and begin to form spindle fibres

  
• How do bacterial calls divide? Descibe the process. [3]

  Through the process of binary fission ⁽¹⁾. DNA replicates while cytoplasm divides to make two daughter cells (cytokinesis) ⁽¹⁾. Each new cell has a single copy of circular DNA and a variable number of plasmids ⁽¹⁾.
• Why do you times by two when working out the end number of cells after binary fission?

  As two daughter cells are produced.

  End number of cells = start number of cells x 2 ^number of divisions
• Which of these is after replication, before mitosis and after mitotic division?

  Fill in the following:

  A) Before mitosis

  B) After replication

  C) After mitotic division

  
• Describe metaphase including visuals.

  Chromosomes line up on the equator of the spindle, spindle fibres attach to chromosomes at the centromere

  
• Describe anaphase including visuals.

  Spindle fibres contract and pull sister chromatids towards opposite poles (ignore the word early)