Chapter 3 Mitosis (3.7-3.8)

Question 1

How do eukaryotic divide

Answer 1

Meiosis or mitosis

Question 2

How do prokaryotic cells divide

Answer 2

Binary fission

Question 3

Why can’t viruses undergo cell division

Answer 3

As they are non living

Question 4

How do viruses replicate

Answer 4

By injecting their nucleic acid into a the host cell they invade to replicate virus particles

Question 5

Stages of cell division

Answer 5

1) interphase (G1,S,G2)
2) mitosis (M phase)
3) cytokinesis (M phase)

Question 6

What happens in interphase

Answer 6

• G1 phase= size of cell increases, transcription and translation occurs and organelles replicate
• S phase = DNA synthesis occurs so that chromosomes replicate to form sister chromatids joined together by a centromere
• G2 = repairs damaged chromosomes, energy stores are replicated , transcription and translation occurs, size of cell increases

Question 7

Stages of mitosis

Answer 7

Prophase
Metaphase
Anaphase
Telophase

Question 8

What happens in Prophase

Answer 8

1) chromosomes condenses and become visible when in the nucleus
2) nucleolus breaks down
3) a pair of centrioles move to opposite poles of the cell
4) proteins form spindle fibres which attach to the centromere of each chromosome
5) the spindle fibres start to move towards the centre of the cell

Question 9

What happens in metaphase

Answer 9

1) spindle apparatus is completely formed and the chromosomes line up at the equator of the cell

Question 10

What happens in anaphase

Answer 10

1) the centromeres divide into two and the spindle fibres to start to retract, pulling the sister chromatids towards the opposite poles with the help of motor proteins
2) this results in each pole getting a full set of chromosomes which are identical to each other

Question 11

What happens in telophase

Answer 11

1) the chromosomes are at opposite poles and become longer and thinner so become invisible under a microscope
2) the spindle apparatus breaks down and the nuclear membrane starts to reform
3) the nucleolus reappears in each nucleus

Question 12

What happens in cytokinesis

Answer 12

The cytoplasm splits in two
The central cell membrane is pulled inwards by the cytoskeleton creating a groove which deepens and the membranes fuse to form two independent cells

Question 13

How to calculate the mitotic index

Answer 13

Number of cells in mitosis/ total number of cells x 100

Question 14

What does the mitotic index tell us

Answer 14

A percentage of cells that are undergoing mitosis

Question 15

How many pairs of chromosomes do humans have

Answer 15

23 pairs

Question 16

What do we use mitosis for

Answer 16

• growth - all cells grow from other cells and therefore are genetically identical and mitosis ensures that this happens
• repairs - if a cell is damaged or dies it is important that new cells are produced and have an identical structure and function to the one that is lost
• asexual reproduction

Question 17

How is the cell cycle different in plant cells

Answer 17

• They don’t have centrioles but do have a spindle apparatus that forms straight from the cytoplasm
• when a plant cell undergoes cytokinesis the cell membrane cannot form a groove so instead vesicles from the Golgi apparatus form membrane structures down the centre of the cell, which the fuse together to form a new cellulose cell wall and a central cell membrane down the centre dividing the cytoplasm into two

Question 18

What happens if there is a mutation to the gene that controls the rate of mitosis

Answer 18

Leads to uncontrolled cell division formimg tumours

Question 19

How do drugs that treat cancer (chemotherapy) disrupt the cell cycle

Answer 19

• prevent DNA from replicating
• inhibit the metaphase stage of mitosis by interfering with spindle formation

Question 20

Problems with chemotherapy (drugs that treat cancer)

Answer 20

Can disrupt the cell cycle of normal cells
They damage rapidly dividing cells to a great degree such as hair producing cells (and cancer cells)

Question 21

Why can’t prokaryotic cells undergo mitosis

Answer 21

As mitosis is a nuclear division and prokaryotic cells do not have a nucleus

Question 22

Why does size of the cell need to increase in interphase

Answer 22

To ensure when the cell divides the daughter cells are the correct size

Question 23

Why would cells exit the cell cycle and enter the G0 phase

Answer 23

• if the cell is a fully differentiated cells so stays in G0permanently
• if the DNA in cells is damaged, so can no longer divide ( called senescent cell) and stay in G0 permanently
• some cells are temporarily stored in the G0 phase to be let out if there is any infection or disease in the cell cycle

Question 24

Why does the chromosomes in chromatin have a loose open structure in interphase

Answer 24

So that the DNA is accessible for transcription and replication

Question 25

How do the chromosomes condense and become visible in prophase

Answer 25

the chromatids supercoils around the DNA winding tightly around the histone protein (of the DNA) so it is no longer long and stringy, forming a more condensed structure

Question 26

Why do we use HCL in root tip squash practical

Answer 26

• separate cells
• to allow stain to diffuse into cells
• to stop mitosis

Question 27

Why do we use acetic orcein stain in root tip squash practical

Answer 27

To make the chromosomes visible
To distinguish chromosomes

Question 28

Why do we use a mounted needle in root tip squash practical

Answer 28

To prevent air bubbles under the cover slip

Question 29

Why do we use the root tip in root tip squash practical

Answer 29

The root tip is a growing region therefore mitosis should be occurring here

Question 30

Why do you squash your root tip

Answer 30

To get a single layer of cells so light can pass through it

Question 31

describe how to prepare squares of cells from plant root tips

Answer 31

1) cut a thin slice of root tip
2) soak the tip in hydrochloric acid then rinse
3) stain for DNA with toluidine blue
4) lower coverslip using a mounted needle without trapping air bubbles
5) squash by firmly pressing down in glass slip but do not push sideways

Question 32

why don’t you push the coverslip sideways

Answer 32

to avoid breaking chromosomes

Question 33

describe how to set up and use an optical microscope

Answer 33

1) clip slide onto stage and turn in light
2) select lowest power objective lens
3) use a coarse focusing dial to move stage closer to the lens until image comes into focus
4) adjust fine focusing dial to get a clear image
5) swap to higher power objective lens then refocus