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as biology (sme) > 2.3 (cell structure) > Flashcards

2.3 (cell structure) Flashcards

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1
Q

within multicellular organisms, not all cells retain the ability to

A

divide

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2
Q

eukaryotic cells that do retain the ability to divide show a

A

cell cycle

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3
Q

mitosis is part of a precisely controlled process known as the

A

cell cycle

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4
Q

the cell cycle is the

A
  • regulated sequence of events
  • that occurs between one cell division and the next
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5
Q

the cell cycle has three phases

A
  • interphase
  • nuclear division (mitosis)
  • cell division (cytokinesis)
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6
Q

nuclear division is also known as

A
  • mitosis
  • mitosis is a process of nuclear division in eukaryotic cells that occurs when a parent cell divides to produce two identical daughter cells, during cell division, mitosis refers specifically to the separation of the duplicated genetic material carried in the nucleus
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7
Q

the physical process of cell division is

A
  • cytokinesis
  • which divides the cytoplasm of a parental cell into two daughter cells
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8
Q

the length of the cell cycle is very variable depending on

A
  • environmental conditions
  • the cell type
  • and the organism
  • for example, onion root tip cells divide once every 20 hours (roughly) but human intestine epithelial cells divide once every 10 hours (roughly)
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9
Q

the movement from one phase to another is triggered by chemical signals called

A

cyclins

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10
Q

the cell cycle diagram

A
  • S: synthesis (of DNA)
  • G: gap
  • M: mitosis
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11
Q

during Interphase the cell increases in

A

mass and size

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12
Q

during Interphase the cell increases in mass and size and

A
  • carries out its normal cellular functions
  • eg. synthesising proteins and replicating its DNA ready for mitosis
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13
Q

interphase consists of three phases

A
  • G1 phase
  • S phase
  • G2 phase
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14
Q

at is at some point during the G1 phase a

A

signal is received telling the cell to divide again

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15
Q

it is at some point during the G1 phase a signal is received telling the cell to divide again, the DNA

A
  • in the nucleus replicates
  • (resulting in each chromosome consisting of two identical sister chromatids)
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16
Q

this phase of the interphase stage of the cell cycle, when DNA in the nucleus replicates is called the

A
  • S phase: S stands for synthesis (of DNA)
  • the S phase is relatively short
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17
Q

the gap between the previous cell division and the S phase is called the

A
  • G1 phase : G stands for growth or gap
  • cells make the RNA, enzymes and other proteins required for growth during the G1 phase
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18
Q

during the G1 phase cells make the

A
  • RNA
  • enzymes
  • and other proteins required for growth
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19
Q

between the S phase and the next cell division event the

A

G2 phase occurs

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20
Q

during the G2 phase, the

A
  • cell continues to grow
  • and the new DNA that has been synthesised is checked
  • and any errors are usually repaired
  • other preparations for cell division are made (eg. the production of tubulin protein, which is used to make microtubules for the mitotic spindle)
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21
Q

interphase =

A

G1 + S + G2

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22
Q

main events of the G1 stage of interphase

A
  • cell grows
  • and receives a signal to divide
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23
Q

main events of the S stage of interphase

A

synthesis of new DNA

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24
Q

main events of the G2 stage of interphase

A
  • further cell growth
  • error checking of newly synthesised DNA
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25
Q

events of interphase table

A
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26
Q

nuclear division (mitosis) follows

A

interphase

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27
Q

nuclear division (mitosis) referred to as the

A

M phase: M stands for mitosis

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28
Q

during the M phase what stops

A

cell growth stops

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29
Q

cell growth stops during the

A

M phase

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30
Q

cytokinesis follows

A

M phase

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31
Q

during cytokinesis, once the nucleus has

A
  • divided into two genetically identical nuclei
  • the whole cell divides
  • and one nucleus moves into each cell
  • to create two genetically identical daughter cells
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32
Q

during cytokinesis, once the nucleus has divided into two genetically identical nuclei the whole cell divides and

A
  • one nucleus moves into each cell
  • to create two genetically identical daughter cells
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33
Q

during cytokinesis, once the nucleus has divided into two genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create

A

two genetically identical daughter cells

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34
Q

in animal cells, cytokinesis involves

A

constriction of the cytoplasm between the two nuclei

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35
Q

in plant cells, cytokinesis involves

A

a new cell wall is formed

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36
Q

mitosis is the process of

A
  • nuclear division by which
  • two genetically identical daughter nuclei are produced
  • that are also genetically identical to the parent nucleus
  • (they have the same number of chromosomes as the parent cell)
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37
Q

the process of mitosis is fundamental to three main biological processes

A
  • growth of multicellular organisms
  • replacement of cells & repair of tissues
  • asexual reproduction
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38
Q

with growth of multicellular organisms the two daughter cells produced are

A
  • genetically identical to one another (clones)
  • and have the same number of chromosomes as the parent cell
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39
Q

growth of multicellular organisms by mitosis enables

A

unicellular zygotes (as the zygote divides by mitosis) to grow into multicellular organisms

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40
Q

multicellular organisms growth may occur across the whole body of the organism or be

A
  • confined to certain regions
  • such as in the meristems (growing points) of plants
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41
Q

damaged tissues can be repaired by

A

mitosis followed by cell division

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42
Q

as cells are constantly dying they need to be

A

continually replaced by genetically identical cells

43
Q

in humans, for example, cell replacement occurs particularly rapidly in

A
  • the skin
  • and the lining of the gut
44
Q

some animals can regenerate body parts, for example

A
  • zebrafish can regenerate fins and axolotls regenerate legs
  • and their tail amongst other parts
45
Q

asexual reproduction is

A
  • the production of new individuals of a species by a single parent organism
  • the offspring are genetically identical to the parent
46
Q

for unicellular organisms such as Amoeba, cell division results in

A

the reproduction of a genetically identical offspring

47
Q

gor multicellular organisms (as seen with many plant species) new individuals grow from

A
  • the parent organism (by cell division) and then detach (‘bud off’) from the parent in different ways.
  • some examples of these are budding in Hydra and yeast and runners from strawberries
48
Q

although mitosis is, in reality, one continuous process, it can be divided into four main stages

A
  • prophase
  • metaphase
  • anaphase
  • telophase
49
Q

during prophase
chromosomes

A

condense and are now visible when stained

50
Q

during prophase the chromosomes consist of

A
  • two identical chromatids called sister chromatids (each containing one DNA molecule)
  • that are joined together at the centromere
51
Q

during prophase the two centrosomes (replicated in the G2 phase just before prophase)

A

move towards opposite poles (opposite ends of the nucleus)

52
Q

during prophase spindle fibres (protein microtubules)

A

begin to emerge from the centrosomes (consists of two centrioles in animal cells)

53
Q

during prophase the nuclear envelope (nuclear membrane)

A

breaks down into small vesicles

54
Q

prophase process

A
  • chromosomes condense and are now visible when stained
  • the chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA molecule) that are joined together at the centromere (a constricted region of a chromosome)
  • the two centrosomes (replicated in the G2 phase just before prophase) move towards opposite poles (opposite ends of the nucleus)
  • spindle fibres (protein microtubules) begin to emerge from the centrosomes (a cellular structure involved in the process of cell division) (consists of two centrioles in animal cells)
  • the nuclear envelope (nuclear membrane) breaks down into small vesicles
55
Q

centromere diagram

A
56
Q

centrosome diagram

A
57
Q

prophase diagram

A
58
Q

duirng metaphase centrosomes

A

reach opposite poles

59
Q

during metaphase

A

spindle fibres (protein microtubules) continue to extend from centrosomes

60
Q

during metaphase chromosomes

A

line up at the equator of the spindle (also known as the metaphase plate) so they are equidistant to the two centrosome poles

61
Q

during metaphase spindle fibres (protein microtubules)

A

reach the chromosomes and attach to the centromeres

62
Q

during metaphase each sister chromatid

A

is attached to a spindle fibre originating from opposite poles

63
Q

metaphase diagram

A
64
Q

during anaphase the sister chromatids

A

separate at the centromere (the centromere divides in two)

65
Q

during anaphase the spindle fibres (protein microtubules)

A

begin to shorten

66
Q

during anaphase the separated sister chromatids (now called chromosomes)

A

are pulled to opposite poles by the spindle fibres (protein microtubules)

67
Q

anaphase diagram

A
68
Q

during telophase chromosomes

A

arrive at opposite poles and begin to decondense

69
Q

during telophase the nuclear envelopes (nuclear membranes)

A

begin to reform around each set of chromosomes

70
Q

during telophase the spindle fibres

A

break down

71
Q

telophase diagram

A
72
Q

during cytokinesis
although not regarded as a phase of mitosis, cytokinesis is an important

A
  • final step in the cell cycle
  • because during this stage the cytoplasm is divides forming two genetically identical cells
  • and it takes place after the telophase stage of mitosis
73
Q

cytokinesis is

A
  • this is the physical separation of the parent cell into two genetically identical daughter cells
  • and occurs once a new nucleus has completely re-formed at each pole of the parent cell at the end of telophase
74
Q

during cytokinesis the process differs slightly in animal and plant cells: in animal cells, a

A

cleavage furrow forms and separates the daughter cells

75
Q

during cytokinesis the process differs slightly in animal and plant cells: in plants, a

A
  • cell plate (the precursor to a new cell wall) forms at the site of the metaphase plate
  • once the cell plate reaches the cell walls of the parent cell, new cell walls are produced, separating the new daughter cells
76
Q

cytokinesis in an animal cell diagram

A
77
Q

cytokinesis in a plant cell diagram

A
78
Q

recognising the stages of mitosis from images: prophase

A
  • chromosomes are visible
  • the nuclear envelope is breaking down
79
Q

recognising the stages of mitosis from images: metaphase

A

chromosomes are lined up along the middle of the cell

80
Q

recognising the stages of mitosis from images: anaphase

A

chromosomes are moving away from the middle of the cell, towards opposite poles

81
Q

recognising the stages of mitosis from images: telophase

A
  • chromosomes have arrived at opposite poles of the cell
  • chromosomes begin to decondense
  • the nuclear envelope is reforming
82
Q

recognising the stages of mitosis from images: cytokinesis

A
  • animal cells: a cleavage furrow forms and separates the daughter cells
  • plant cells: a cell plate forms at the site of the metaphase plate and expands towards the cell wall of the parent cell, separating the daughter cells
83
Q

micrograph showing a cell undergoing prophase (P)

A
84
Q

micrograph showing cells undergoing metaphase (M) and anaphase (A)

A
85
Q

micrograph showing cells undergoing metaphase (M) and anaphase (A)

A
86
Q

micrograph showing a cell undergoing anaphase (A)

A
87
Q

growth in plants occurs in specific regions called

A

meristems

88
Q

the root tip meristem can be used to study

A

mitosis

89
Q

the root tip meristem can be found

A

just behind the protective root cap

90
Q

in the root tip meristem, there is a

A

zone of cell division that contains cells undergoing mitosis

91
Q

pre-prepared slides of root tips can be studied or temporary slides can be prepared using the

A
  • squash technique (root tips are stained and then gently squashed,
  • spreading the cells out into a thin sheet and allowing individual cells undergoing mitosis to be clearly seen)
92
Q

micrograph showing a stained root tip

A
93
Q

Required Practical: Identifying Mitotic Stages method

A
  • garlic or onion (Allium cepa) root tips are most commonly used (the bulbs can be encouraged to grow roots by suspending them over water for a week or two)
  • remove the tips of the roots (about 1cm) and place them in ethanoic alcohol
  • this helps to “fix” the tissue and prevent mitosis from continuing in the cells
  • place the root tips in warm (60oC) dilute hydrochloric acid
  • this separates the cells
  • transfer the root tip to a microscope slide
  • using a pipette, add a suitable stain (eg. acetic orcein, which stains chromosomes a deep purple)
  • place a coverslip on top of the root tip and press down firmly using a paper towel
  • this spreads out the cells so they are only one layer thick
  • view the cells under a microscope
94
Q

Required Practical: Identifying Mitotic Stage limitations

A
  • the preparation of tissue for microscope slides can damage cells and alter their appearance
  • during preparation, a sample is often squashed or stained, which can generate artefacts
  • the occurrence of artefacts can be decreased by more careful preparation of samples
  • the size of cells or structures of tissues may appear inconsistent in different specimen slides
  • cell structures are 3D and the different tissue samples will have been cut at different planes resulting in inconsistencies when viewed on a 2D slide
  • optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that can not be seen
95
Q

the mitotic index is

A

the proportion of cells (in a group of cells or a sample of tissue) that are undergoing mitosis

96
Q

the mitotic index can be calculated using the formula

A

mitotic index = number of cells with visible chromosomes ÷ total number of cells

97
Q

if you need to give the mitotic index as a percentage you can multiply the answer by

A

100

98
Q

a student who wanted to observe mitosis prepared a sample of cells, they counted a total of 42 cells in their sample, 32 of which had visible chromosomes, calculate the mitotic index for this sample of cells (give your answer to 2 decimal places)

A
99
Q
A
100
Q
A
101
Q

the images (micrographs) taken of slides containing root tip cells can be used to calculate the actual size of root tip cells, the magnification equation:

A

actual size = size of image ÷ magnification

102
Q

there are 1000 nanometers (nm) in a

A

micrometre (µm)

103
Q

there are 1000 micrometres (µm) in a

A

millimetre (mm)

104
Q

there are 1000 millimetres (mm) in a

A

metre (m)

as biology (sme) (8 decks)

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