Mitosis

Question 1

what is mitosis?

Answer 1

nuclear division

Question 2

when is mitosis necessary?

Answer 2

when all the daughter cells have to be identical.

• growth
• replacement
• repair
• asexual reproduction

Question 3

what is asexual reproduction?

Answer 3

the production of genetically identical offspring from one parent in multicellular organisms.

Question 4

how do prokaryotic organisms divide?

Answer 4

binary fission

Question 5

what is each chromosome converted into before mitosis?

Answer 5

two identical DNA molecules called chromatids.

Question 6

what joins the two chromatids together?

Answer 6

a centromere

Question 7

why is it necessary to keep chromatids together?

Answer 7

so they can be precisely manoevred and segregated equally, one each into the two new daughter cells.

Question 8

how is chromatin formed?

Answer 8

DNA combines with proteins called histones to form a dense complex called chromatin.

Question 9

what are the stages of mitosis?

Answer 9

• prophase
• metaphase
• anaphase
• telophase.

Question 10

what happens during prophase?

Answer 10

• chromatin fibres begin to coil and condense to form chromosomes
• the nucleolus disappears
• nuclear membrane begins to break down.
• protein microtubules form spindle-shaped structures linking the poles of the cell.
• centrioles migrate to the opposite poles of the cell.
• spindle fibres attach to specific areas on the centromeres and start to move the chromosomes to the centre of the cell
• by the end the nuclear envelope has disappeared.

Question 11

what happens during metaphase?

Answer 11

• chromosomes are moved by spindle fibres to form a plane in centre of the cell (metaphase plate) and then held in position.

Question 12

what happens during anaphase?

Answer 12

• centromeres holding pairs of chromatids divide.
• chromatids are seperated (pulled to opposite poles of the cell by shortening spindle fibres.)
• characteristic v shape formed as chromatids are dragged by their centromeres through the liquid cytosol.

Question 13

what happens during telophase?

Answer 13

• chromatids have reached the poles and are now called chromosomes.
• two new sets of chromsomes assemble at each pole and the nuclear envelope reforms around them.
• the chromosomes start to uncoil
• nucleolus reformed
• cytokinesis begins.

Question 14

how does cytokinesis occur in animal cells?

Answer 14

• a cleavage furrow forms around the middle of the cell.
• cell surface membrane is pulled inwards by the cytoskeleton until is it close enough to be fused around the middle, forming two cells.

Question 15

why cant plants form a cleavage furrow?

Answer 15

plant cells have a cell wall so it is not possible.

Question 16

how do plants divide by cytokinesis?

Answer 16

1. vesicles from the golgi apparatus begin to assemble in the same place as where the metaphase plate was formed.
2. the vesicles fuse together and with the cell surface membrane, dividing the cell in two.
3. new sections of the cell wall form along the new sections of membrane.

Question 17

why are plant root tips a good source of cells to examine mitosis?

Answer 17

plant root tips contain actively dividing cells; the root tips are responsible for growth and development. They contain meristematic tissue that is actively diving.