Cell division and cycle

• What stage of mitosis is cell a?


  prophase

  
• What evidence is there that cell b is in anaphase?


  Sister chromatids have moved apart

  
• cell c is in interphase. Give 2 processes which occur during interphase so cell division will occur?.


  increase in volume

  synthesis of proteins
• how would you calculate the magnification of the photograph?


  divide the real length of the bar in mm by 0.02

  
• the number of cells at each stage of mitosis was counted the results are shown in the table.One cycle is 24 hours. The number of cells at each stage is proportional to the time spent at that stage, calculate the length spent in metaphase.One cycle is 24 hours. The number of cells at each stage is proportional to the time spent at that stage, calculate the length spent in metaphase.


  12/200 x 24

  Number of cells In metaphase/ amount of cells x 24
• describe the appearance of the chromosome


  Two dna strands that are coiled to make sister chromatids

  
• What is happening in this stage?

  Stage A - anaphase as the sister chromatids are moving to opposite poles

  
• what is happening at this stage?

  Stage B - metaphase as the chromosomes are on the equator and are attaching to a spindle fibre

  
• What happens in the stages of mitosis?

  Prophase - chromosomes become visible

  Metaphase - chromosomes align at the centre of the cell atttached to spindle fibres

  Anaphase - chromatids move towards the poles

  telophase - chromatids are in groups at the poles
• What letter represents when the cells are being replicated ?

  Q

  
• Explain the change in dna content during s.

  Nucleus has divided

  
• What are stages a and b?

  A is prophase as the chromosomes are becoming more visible

  B is anaphase as the Sister chromatids are moving to opposite poles

  
• What are the two events that occur during interphase?

  dna replicates and protein synthesis
• Describe and explain how the structure of dna results in accurate replication.

  1. Two strands of dna because of replication of dna
  2. Hydrogen bonds hold the strands together
  3. Hydrogen bonds are weak so the strands seperate
  4. Bases are exposed so then they can be copied
  5. a,t,c and g as a complementary copy
  6. There ends up being dna from one parent and a new strand of dna
• Describe the behaviour of chromosomes during mitosis and explain how this results in the production of 2 genetically identical cells.

  1. Chromosomes shorten
  2. the sister chromatids form due to replication
  3. Chromatids move to the equator of the cell
  4. Attach to spindle fibres
  5. Sister chromatids then separate
  6. Move to opposite poles
  7. Each pole has a group of chromosomes
  8. Nuclear envelope forms around each group of chromosomes
• What is stage a?

  Anaphase

  
• what is the order of the process?

  C(prophase) b( metaphase) a(anaphase) d(telophase)

  
• describe and explain the appearance of one of the chromosomes in stage b

  DNA has been replicated snd made sister chromatids which attach at the centromere.

  
• What’s happens to chromosome number?

  Doubled

  
• Why is there a change of chromosome number?

  DNA has been replicated but not gone through cell division
• what is this stage of mitosis?

  anaphase

  because it shows sister chromatids move to opposite poles

  
• What process occurs in interphase?

  Protein synthesis
• What evidence is there that the cells are multiplying rapidly?

  The short duration of interphase
• Why would a biologist chose to examine 200 cells?

  For a representative sample
• What evidence is there of the different phases?

  meta phase - chromosomes lie on the equator

  Anaphase - chromatids are moving to opposing poles
• what are the events of the cell cycle?

  Chromosomes condense and become visible

  Nuclear envelopes disappear

  Chromosomes on the equator attached to the spindle fibres

  Chromatids seperate

  Cytoplasm divides
• metaphase is..


  Chromosomes on the equator attached to spindle fibres
• what is the phase where dna replication occurs?

  interphase
• What is the importance of meiosis?


  Halves chromosome number

  Restored at fertilisation the full number
• describe The appearance and behaviour of chromosomes during mitosis.


  Prophase

  • chromosomes become visible and appear as sister chromatids joined at the centromere
  • Metaphase
  • Chromosomes line up at the equator attached to spindle fibres by the centromere
  • Anaphase
  • Centromere splits and sister chromatids are pulled To opposite poles
  • Telophase
  • Chromstids become longer
• describe what happens in metaphase


  chromatids attach to spindle fibres and line up across the equator
• describe what occurs at anaphase


  chromatids are pulled to opposite poles of the cell
• Explain the advantage of cells completing the cell cycle in short time


  Able to replace cells quickly
• explain why she was given an instruction to push down hard on the cover slip not push the cover slip sideways.


  Pushing too hard would squash the tissue

  dont push sideways to avoid breaking chromosomes
• The student concluded it was anaphase. Is she correct?


  Yes as it shows sister chromatids at opposite poles being pulled apart from their centromeres

  
• Why take cells from root tip?


  region where mitosis occurs
• why firmly squash the tip?


  To allow light to pass through by making a thin layer of tissue
• describe how dna is replicated


  Strands seperate As hydrogen bonds break

  Both strands act as a template

  Free nucleotides attach

  complementary base pairing occurs

  Hydrogen bonds reform

  New dna molecules contain one old strand and one new strand of dna
• how could a doctor recognise that cells were in interphase?


  no visible chromosomes
• What sample would have traits from a cancerous tumour?


  higher Percentage of cells in mitosis so more cells dividing quicker so uncontrolled cell division