Cell division

Question 1

what are the 3 stages of interphase ?

Answer 1

• G1 phase - first growth phase = protein synthesis, organelles replicate, size of cell increases
• S phase = DNA replication
• G2 phase - cell continues to increase + duplicated DNA checked for errors + ATP synthesis

Question 2

what is mitosis ?

Answer 2

• asexual reproduction = genetically identical
• produces 2 genetically identical daughter cells = diploid cells (2n)

Question 3

what are the 4 stages of mitosis ?

Answer 3

1. Prophase = chromatin fibres coil + condense to form chromosomes
   = nucleolus disappears
   = nuclear envelope disintegrates
   = microtubules form spindle fibres
   = centrioles duplicate + move to opposite poles of the cell
2. Metaphase = spindle fibres attach to centromere + position chromosomes along equator of the cell.
3. Anaphase = centromeres in each chromosome divide
   = spindle fibres shorten + pull sister chromatids apart
   = sister chromatids move to opposite end of pole
4. Telophase = chromatids have reached poles + now called chromosomes
   = nuclear envelope reforms
   = chromosomes uncoil + nucleolus reappears
   = cell divides into 2 by cytokinesis.

Question 4

What is meiosis?

Answer 4

• sexual reproduction = produces gametes
• starts with diploid cells and makes 4 haploid cells + NOT genetically identical.

Question 5

Explain the difference between meiosis I and meiosis II ?

Answer 5

meiosis I = reduction division = homologous chromosomes are separated
meiosis II = sister chromatids from each chromosome are separated

Question 6

Describe the 4 stages of meiosis I ?

Answer 6

• prophase I = chromosomes condense
  = nucleolus disappears + nuclear envelope disintegrates
  = homologous chromosomes pair up forming the bivalent
  = crossing over occurs
• metaphase I = spindle fibres move homologous pair on equator
  = independent assortment occurs resulting in genetic variation
• anaphase I = spindle fibres shorten + homologous chromosomes pulled to opposite
  poles / (sister chromatids are no longer identical )
• telophase I = 1 chromosome at each end of pole
  = nuclear envelope reforms + chromosomes uncoil
  = cytokinesis occurs

Question 7

Describe the 4 stages of meiosis II ?

Answer 7

• prophase II = chromosomes condense
  = nuclear envelope disintegrates
• metaphase II = individual chromosome line up on equator of cell
  = independent assortment
• anaphase II = centromere divides
  = spindle fibres shorten + pull chromatids apart
• telophase II = chromosomes uncoil + nuclear envelope reforms + nucleolus visible
  = cytokinesis occurs = 4 cells form