6.2. MITOSIS

Question 1

What does mitosis refer to?

Answer 1

• nuclear division

Question 2

What does mitosis ensure?

Answer 2

• both daughter cells produced when a parent cell divides are genetically identical (except when mutations occur - rare)
• each new cell will have an exact copy of the DNA present in the parent cell and the same number of chromosomes

Question 3

What is mitosis also necessary for, other than for the creation of daughter cells?

Answer 3

• asexual reproduction

Question 4

What is asexual reproduction?

Answer 4

• production of offspring (daughter cells) from ONE parent in multicellular organisms

Question 5

How do prokaryotic cells reproduce?

Answer 5

Binary fission
- don’t have a nucleus so can’t undergo mitosis

Question 6

What is Chromatin?

Answer 6

during interphase, a nucleus contains chromosomes as chromatin
- chromatin is a tangle of unwound chromosomes

Question 7

What does chromosomes being in the structure of chromatin allow?

Answer 7

• genes to be exposed

Question 8

What are chromosomes?

Answer 8

A molecule of DNA

Question 9

What is chromatid? [see textbook and notes for better explanation of chromosomes and chromatids]

Answer 9

one of the two identical halves of a chromosome that has been replicated in preparation for cell division.

Question 10

What joins two chromatids together to form one chromosome?

Answer 10

centromere

Question 11

What are the stages of mitosis?

Answer 11

• prophase (before stage)
• metaphase (next stage)
• anaphase (movement stage)
• telophase (distant/ end stage)

Question 12

How is the haploid number defined?

Answer 12

• number of DIFFERENT chromosomes
• i.e. length/ position of centromeres/ band

Question 13

What is the difference between diploid and haploid numbers?

Answer 13

• diploid is double the haploid number

Question 14

What happens during Early Prophase?

Answer 14

1. chromosomes have replicated and condensed, and now exist as a pair of sister chromatids held by the centromere.
2. centrioles begin to produce spindle fibres/ microtubules, one centriole moves to the opposite pole.
3. nuclear envelopes begin to disappear.
4. spindle fibres grow and bind to the centromeres so that the spindle fibres can move chromosomes around.

Question 15

What happens during Late Prophase?

Answer 15

1. nuclear envelope is nearly digested.
2. spindle fibres bind to the centromeres and start to move the chromosomes around, ready for the metaphase checkpoint.

Question 16

What happens during metaphase?

Answer 16

1. spindle fibres move the chromosome so that they line up on the equator of the cell (metaphase plate).
2. cell only proceeds to Anaphase if the conditions of the Metaphase checkpoint are met.

Question 17

What does the Metaphase Checkpoint check for?

Answer 17

• all chromosomes are attached to a spindle fibre
• all chromosomes are on the Metaphase Plate

Question 18

What happens during Anaphase?

Answer 18

1. spindle fibres contract and pull apart the sister chromatids, so that they are called chromosomes again.
2. chromosomes are pulled to the poles of the cell, the “arms” of each chromosome trail behind as they are pulled through the cytoplasm

Question 19

What happens during Telophase?

Answer 19

1. nuclear envelope begins reforming around each new set of chromosome.
2. cytoskeleton begins to separate the cytoplasm and pulls in the plasma membrane (cleavage furrow begins to form).
   - This is now a single cell, but with two nuclei, each nucleus is a copy/ clone of original cell.

Question 20

What is cytokinesis?

Answer 20

• last stage of ‘mitotic phase’

Question 21

What happens during cytokinesis in animal cells?

Answer 21

1. cytoskeleton pulls the plasma membrane in (cleavage furrow).
2. cells separate to form two daughter cells.
3. chromosomes unpackage/ uncoil to form chromatin
4. one out of the two cells enters G1.

Question 22

Why is cytokinesis different in plants than it is in animals?

Answer 22

• plant cells are not bathed in tissue fluid, like animal cells, so they need their cell walls to stop Lysis by osmosis from the water surrounding plant cells.

Question 23

What happens during cytokinesis in plant cells?

Answer 23

1. vesicles line up on the equator of the cell (where the Metaphase Plate was).
2. vesicles will fuse to form 2 separate plasma membranes.
3. on the cell plate, a cell wall forms for each cell, so 2 cell walls form along the cell plate.
4. enter G1 phase.