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A Level Bio > Chapter 3 Mitosis (3.7-3.8) > Flashcards

Chapter 3 Mitosis (3.7-3.8) Flashcards

1
Q

How do eukaryotic divide

A

Meiosis or mitosis

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2
Q

How do prokaryotic cells divide

A

Binary fission

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3
Q

Why can’t viruses undergo cell division

A

As they are non living

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4
Q

How do viruses replicate

A

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

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5
Q

Stages of cell division

A

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

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6
Q

What happens in interphase

A
  • 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
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7
Q

Stages of mitosis

A

Prophase
Metaphase
Anaphase
Telophase

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8
Q

What happens in Prophase

A

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

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9
Q

What happens in metaphase

A

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

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10
Q

What happens in anaphase

A

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

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11
Q

What happens in telophase

A

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

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12
Q

What happens in cytokinesis

A

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

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13
Q

How to calculate the mitotic index

A

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

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14
Q

What does the mitotic index tell us

A

A percentage of cells that are undergoing mitosis

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15
Q

How many pairs of chromosomes do humans have

A

23 pairs

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16
Q

What do we use mitosis for

A
  • 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
17
Q

How is the cell cycle different in plant cells

A
  • 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
18
Q

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

A

Leads to uncontrolled cell division formimg tumours

19
Q

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

A
  • prevent DNA from replicating
  • inhibit the metaphase stage of mitosis by interfering with spindle formation
20
Q

Problems with chemotherapy (drugs that treat cancer)

A

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)

21
Q

Why can’t prokaryotic cells undergo mitosis

A

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

22
Q

Why does size of the cell need to increase in interphase

A

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

23
Q

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

A
  • 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
24
Q

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

A

So that the DNA is accessible for transcription and replication

25
Q

How do the chromosomes condense and become visible in prophase

A

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

26
Q

Why do we use HCL in root tip squash practical

A
  • separate cells
  • to allow stain to diffuse into cells
  • to stop mitosis
27
Q

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

A

To make the chromosomes visible
To distinguish chromosomes

28
Q

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

A

To prevent air bubbles under the cover slip

29
Q

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

A

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

30
Q

Why do you squash your root tip

A

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

31
Q

describe how to prepare squares of cells from plant root tips

A

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

32
Q

why don’t you push the coverslip sideways

A

to avoid breaking chromosomes

33
Q

describe how to set up and use an optical microscope

A

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

A Level Bio (15 decks)

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