mitosis

Question 1

define mitosis

Answer 1

nuclear division stage in mitotic phase of cell cycle

Question 2

define chromosome

Answer 2

condensed and coiled DNA in the form of chromatin

Question 3

define chromatids

Answer 3

one of the two halves of a replicated chromosome

Question 4

define sister chromatids

Answer 4

identical copies formed by DNA replication of a chromosome with both copies joined together by a common centromere

Question 5

define centromere

Answer 5

region at which two chromatids are held together

Question 6

define spindle fibres

Answer 6

structures composed of microtubules that organise chromosomes and pull them apart to opposite poles during mitosis

Question 7

define homologous pairs

Answer 7

matching pair of chromosomes, one inherited from each parent

Question 8

describe how DNA is packaged in a chromosome

Answer 8

• DNA is associated with proteins (histones)
• DNA wraps around making it more compact (chromatin)
• interphase: chromatin is decondensed
• mitosis - chromatin is condensed (chromosomes)

Question 9

list the stages of mitosis in order

Answer 9

• prophase
• metaphase
• anaphase
• telophase

Question 10

describe what happens during interphase

Answer 10

• chromatin fibers coil & condense = chromosomes (visible if stained)
• nucleolus disappears, nuclear membrane breaks down
• microtubules form spindle fibers
• centrioles migrate to opposite poles of cells
• spindle fibers attach to specific areas on centromeres, start moving chromosomes to center
• nuclear envelope has disappeared by end

Question 11

describe what happens during metaphase

Answer 11

chromosomes are moved by spindle fibers + line up along the equator of the cell

Question 12

describe what happens during anaphase

Answer 12

• centromeres holding pairs of chromatids in each chromosome divide
• chromatids pulled to opposite ends by shortening of spindle fibers

Question 13

describe what happens during telophase

Answer 13

• chromatids have reached the poles as chromosomes
• two new sets of chromosomes assemble at each pole
• nuclear envelope reforms around chromosomes
• chromosomes uncoil, nucleolus is formed
• cytokinesis begins

Question 14

explain the role of centrioles in mitosis

Answer 14

organise spindle fibres which are attached to them

Question 15

explain the role of spindle fibres in mitosis

Answer 15

pull chromatids to opposite poles and ensure even chromosome distribution between daughter cells

Question 16

describe the process of cytokinesis in animal cells

Answer 16

• cleavage furrow forms around middle of the cell
• plasma membrane pulled inwards by cytoskeleton until close enough to fuse
• two cells are formed as a result

Question 17

describe the process of cytokinesis in plant cells

Answer 17

• vesicles from Golgi assemble on metaphase plate
• vesicles fuse with each other + CSM, dividing cell into two
• new sections of cell wall form along new sections of membrane

Question 18

what is osmotic lysis

Answer 18

if dividing cell wall forms before daughter cells have separated, surrounding water causes osmotic lysis

Question 19

why does a cleavage furrow not form in plant cells?

Answer 19

due to the cell walls

Question 20

compare animal and plant cytokinesis.

Answer 20

• animal cells: form cleavage furrow, plant cells do not bc of cell wall + high internal pressure
• plant cells: use vesicles for cytokinesis, animal cells do not

Question 21

describe the purpose of mitotic cell division

Answer 21

• ensures both daughter cells produced when a parent cell divides are genetically identical
• necessary when all of the daughter cells have to be identical

Question 22

list 4 roles of mitosis

Answer 22

• growth of organisms
• repair/Replacement of tissues
• embryo development
• asexual reproduction

Question 23

what is the mitotic index?

Answer 23

ratio between number of cells in mitosis and total number of cells

Question 24

how would you calculate the mitotic index of a sample of dividing cells

Answer 24

• count number of cells in sample and number of cells in mitosis
• divide number of cells in mitosis by total number of cells

Question 25

how would you calculate how many cells have been produced during mitosis from one cell given the number of cell cycles that have taken place.

Answer 25

2(^x) where x is the number of cell cycles

Question 26

explain how to calculate length of time each stage in cell cycle takes given a sample of cells undergoing mitotic cell division and total duration of the cell cycle.

Answer 26

• calculate mitotic index
• multiply that by total duration - calculates amount of time mitosis takes up in cell cycle
• subtract mitosis time from total cell cycle time to get time in interphase