6.2 Mitosis

Question 1

When is mitosis used?

Answer 1

When daughter cells have to be identical - growth, repair of tissues and replacement

Question 2

What organisms require mitosis?

Answer 2

Plants, fungi, some animals

Question 3

What happens to DNA before mitosis?

Answer 3

Before mitosis, DNA is replicated in the nucleus during interphase.
- Each DNA molecule/chromosome is converted into 2 identical DNA molecules/chromosomes, called chromatids

Question 4

Where are the 2 chromatids produced before mitosis during interphase joined?

Answer 4

Centromere

Question 5

Why is it important for chromatids to be kept together during mitosis?

Answer 5

So they can be precisely moved and segregated, one each into each new daughter cell

Question 6

How is chromatin formed during interphase?

Answer 6

When DNA combines with histones

Question 7

What are the 4 stages of mitosis?

Answer 7

PMAT

Prophase, Metaphase, Anophase, Telophase

Question 8

.

Answer 8

.

Question 9

What are the 5 stages of prophase?

Answer 9

1. Chromatin fibres coil + condense to form chromosomes.
   - Nucleolous disappears
   - Nuclear membrane begins to break down
2. Microtubules form spindle fibres, which link the poles of the cell. (Fibres needed to move chromosomes to right position before division.)
3. Two centrioles move to opposite poles of the cell. (Centrioles - cylyndrical bundles of protein - role in spindle formation)
4. Spindle fibres attach to specific areas on centromeres + move chromosomes to centre of cell
5. By the end of prophase, nuclear envelope disappears

Question 10

What happens during metaphase?

Answer 10

Spindle fibres move chromosomes to centre of cell to form metaphase plate + hold them in place

Question 11

What happens during anaphase? 2 steps

Answer 11

1. Centromeres holding pairs of chromatids in each chromosome divide
2. Chromatids are separated + pulled to opposite poles of the cell due to the shortening spindle fibres

Question 12

What happens during telophase? 3 steps

Answer 12

1. Chromatids have reached poles and are now chromosomes
2. Two new sets of chromosomes assemble at each pole + nuclear envelope reforms around them
3. Chromosomes uncoil + nucleolus is formed. Cytokinesis begins

Question 13

What stage does cytokinesis begin in?

Answer 13

Telophase

Question 14

How does cytokinesis in animal cells work?

Answer 14

1. Cleavage furrow forms around the middle of the cell

2. Plasma membrane is pulled inwards by cytoskeleton until it’s close enough to fuse around the middle, forming 2 cells

Question 15

How does cell division work in plant cells?

Answer 15

1. Vesicles from golgi apparatus assemble in the same place where the meta phase plate was formed
2. Vesicles fuse w/ each other + cell surface membrane, dividing the cell into 2
3. New sections of cell wall form along new sections of the membrane

Question 16

Why doesn’t a cleavage furrow form in plant cells?

Answer 16

Due to the presence of cell walls

Question 17

In plant cells, what would happen if the dividing cell wall were formed before the daughter cells separated?

Answer 17

Cells would undergo osmotic lysis from the surrounding water.
In simple terms, the cell will burst