Chromosomes And Mitosis

• What is mitosis?

  Mitosis is a stage in the cell cycle when the nucleus divides
• What is the cell cycle?

  The cell cycle is a series of stages in the life cycle of a cell
• What happens during the growth phase of the cell cycle?

  The genetic material of the cell (chromosomes) is doubled
• How many copies of each chromosome are produced during the growth phase?

  Two copies of each chromosome are produced
• What are the strands called that remain attached to each other after chromosome duplication?

  Each strand is called a chromatid
• What happens to the chromatids during cell division?

  The chromatids will eventually be divided between the two genetically identical daughter cells
• What happens to the number of subcellular structures during the growth phase?

  The number of subcellular structures (such as ribosomes and mitochondria) also increases
• Why is cell division by mitosis important for multicellular organisms?

  It is important for the growth and development of multicellular organisms
• What occurs when a sperm cell fertilizes an egg cell in human reproduction?

  The resulting zygote cell divides by mitosis
• What happens to the cells produced from the zygote during development?

  Each subsequent cell produced divides by mitosis to form an embryo
• What forms as the embryo continues to grow in size?

  A fetus forms as the embryo continues to grow
• How does mitosis contribute to the growth of multicellular organisms?

  Mitosis produces an increase in cell number for growth
• Why do chromosomes condense?


  In preparation for mitosis
• When a chromosome replicates, what is the name given to each ’arm’


  Chromatid
• What shape does a chromosome look like when replicated 


  An ‘X’ shape
• Chromosomes are usually uncoiled, when a cell prepares to divide they fold up into ‘worm-like‘ structures that we recognise
• What are chromosomes 


  They are coiled up lengths of DNA molecules
• What does each chromosomes carry


  A large number of genes
• What do different genes control


  Different genes control different characteristics ( e.i. Hair colour )
• Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle
• What is mitosis


  The stage of the cell when the cell divides forming two identical diploid cells
• What does the cell have to do before mitosis occurs in a body cell?


  The grouth and DNA replication happens before mitosis
• What is a multicellular organism 


  Organisms that are made up of more than one cell ( e.i. Humans )
• Multicellular organisms use mitosis to grow or replace cells that have been damaged
• The end of the cell cycle results in two new cells that are identical to the original and includes the same amount of chromosomes
• What are the names of the stages called during the cell division

  -interphase

  -prophase

  -metaphase

  -anaphase

  -telophase

  -cytokinesis
• What happens during interphase?


  This is where a cell would be for most of its life, in this stage the DNA replicates and other sub cellular structures are copied to prepare the cell for division
• What happens during prophase?


  The chromosomes starts to become visible as the nucleus membrane breaks down
• What happens during metaphase?


  The chromosomes line up in the middle of the cell where the chromosomes are still in an ‘X’ shape
• What happens during anaphase?


  The cell fibres form and pulls the chromosomes apart to opposite sides, where the chromosomes are no longer in an ‘X’ shape as it has been separated so both new cells in the end have a form of genetic material
• What happens during telophase?


  The nucleus membrane reforms causing the chromosomes to not be visible anymore as it also de-condenses
• What happens during cytokinesis?


  The cytoplasm and cell membrane splits (end of cell division) the cell splits into two new identical daughter cells as a result
• Give a brief summary of what happens in the growth and DNA replication of a cell


  -DNA is spread out in long strings if it isn’t dividing

  -before it divides it has to grow and increase the anount of sub cellular structures (e.i. Ribosomes)

  -then DNA duplicates, so there will be one copy of DNA for each cell

  -when it divides by cytokines the chromatid will have the same amount of genetic material as they are identical
• Give a brief summary of what happens during mitosis


  -chromosomes line up in the centre of the cell

  -cell fibres pull them apart

  -each chromatid to to opposite ends of the cell

  -membranes forms around each sets of chromosomes, those become nuclei of the two new cells (nucleus has divided)

  -lastly cytoplasm and cell membrane divide
• What is mitosis required for


  -growth

  -repairing of damaged cells

  -asexual reproduction
• What does a pair of chromosomes have


  Maternal chromosomes and paternal chromosomes
• Cells move through the cell cycle multiple times
• What does the term ‘diploid’ mean


  That a cell has 2 sets of chromosomes
• What does the term ‘haploid’ mean


  That a cell has 1 set of chromosomes
• What is the formula to work out the length of time in a stage


  Length of time in a stage = observed number of cells in a stage/ total number of cells observed, times this number by the total length of the cell cycle