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biology - component 2 > cell division > Flashcards

cell division Flashcards

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1
Q

define gene

A

small section of DNA which code for specific proteins

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2
Q

define gametes

A

haploid cells produced by the ovaries and testes

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3
Q

what is the longest part of the cell cycle?

A

interphase

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4
Q

what occurs during interphase?

A
  • DNA replication
  • ATP synthesis
  • protein synthesis
  • production of organelles
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5
Q

define centrioles

A

move to opposite poles of the cell and produce protein microtubule during prophase

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6
Q

define chromosome

A

made of DNA, protein and a small amount of RNA

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7
Q

define cytokenesis

A

constriction of the centre of the parent cell after telophase
in plant cells, a cell plate is formed first

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8
Q

the number of chromosomes present in a human somatic cell?

A

46

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9
Q

define metaphase

A

chromosomes arrange themselves at the equator during this phase of mitosis

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10
Q

define chromatin

A

this condenses during cell division to form chromosomes

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11
Q

the number of chromosomes present in a human gamete?

A

23

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12
Q

what is the name of the region where chromatids are joined?

A

centromere

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13
Q

what occurs during telophase?

A
  • nuclear envelope reforms
  • nucleoli reappear
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14
Q

define sister chromatids

A

identical copies of a chromosome, joined at the centromere

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15
Q

what occurs during anaphase?

A

spindle fibres contract and pull the sister chromatids to opposite poles

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16
Q

define fertilisation

A

haploid gametes fuse to form a zygote, restoring the diploid chromosome number

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17
Q

define chromatin

A
  • when a cell is not dividing the DNA exists as chromatin within the nucleus
  • chromatin is a complex of DNA and histone proteins found in the nucleus of eukaryotic cells
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18
Q

where do the chromosomes in each homologous pair come from?

A

one from the mother and one from the father

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19
Q

what are the four phases of mitosis?

A
  • prophase
  • metaphase
  • anaphase
  • telophase
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20
Q

outline what occurs during prophase

A
  • chromatin condenses and becomes visible as two sister chromatids joined at the centromere
  • centrioles move to opposite poles. protein microtubules form from each centriole and the spindle develops
  • nuclear envelope disintegrates, the nucleolus disappears and chromosomes move towards the equator of the cell
  • prophase is the longest stage of mitosis
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21
Q

outline what occurs during metaphase

A

chromosomes arrange themselves along the equator of the cell and becomes attached to spindle fibres and the centromere

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22
Q

outline what occurs at anaphase

A
  • a very rapid stage where the spindle fibres contract and shorten
  • centromere splits
  • sister chromatids pulled apart
  • chromatids then drawn towards opposite poles with the centromere leading
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23
Q

outline what occurs during telophase

A
  • chromosomes uncoil and lengthen
  • spindle fibres break down
  • nucleoli and nuclear membranes reform
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24
Q

outline cytokenesis

A
  • in animal cells, cytokinesis occurs by the constriction of the parent cell from the outside inwards, forming a cleavage furrow
  • in plant cells, a cell plate forms across the equator of the parent cell from the inside outwards, and a new cellulose cell wall is laid down
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25
Q

identify the differences between mitosis in plant and animal cells

A

SHAPE:
animal cells - cells become elongated before mitosis
plant cells - no shape change

CENTRIOLES:
animal cells - present
plant cells - absent

CYTOKENESIS:
animal cells - cleavage furrow develops from the outside inwards, pinching the cytoplasm
plant cells - cell plate develops from the centre outwards forming a new cell

SPINDLE:
animal cells - degenerates at telephase
plant cells - remains throughout new cell wall formation

OCCURRENCE:
animal cells - in epithelia, bone marrow and other sites
plant cells - meristems

26
Q

what is the significance of mitosis?

A
  • gives genetic stability
  • growth and repair of an organism
  • replacement of dead cells
27
Q

describe genetic stability arising from mitosis

A
  • mitosis produces 2 daughter cells with the same number of chromosomes as the parent cell.
  • each chromosome is an exact replica of one of the original
  • mitosis produces cells that are genetically identical to the parent cell
  • this gives genetic stability
28
Q

where does mitosis take place in plants?

A

root tips and growing points of shoots

29
Q

why does mitosis occur in human skin?

A

so that dead surface cells are replaced by genetically identical cells from below

30
Q

describe asexual reproduction

A
  • produces offspring that are genetically identical to the parent as a result of mitosis
  • in certain flowering plants, large numbers of identical offspring are produced
  • no genetic variation between offspring
  • they are clones
31
Q

advantage of asexual reproduction?

A
  • offspring are genetically identical to parent, so they are able to survive successfully if environmental conditions are stable
  • less time and energy is wasted as organisms do not need to find a reproductive partner
  • the population can rapidly increase in number, providing the environmental conditions are stable
32
Q

disadvantages of asexual reproduction?

A

lack of genetic variation would mean offspring are unable to adapt to a change in environmental conditions

33
Q

what is the length of the cell cycle controlled by?
why is this important?

A

genes which ensure that mitosis happens where and when it is needed
- this allows for timely repair and replacement of tissues in adults and correct development in embryos

34
Q

what are carcinogens?

A

radiation, certain chemicals, and some viruses can mutate DNA and affect the genes which control the cell cycle

35
Q

what are proto-oncogenes?

A

genes which control the cell cycle, they tell the cell when to divide.
- if mutated, uncontrollable cell division can occur to form a tumour

36
Q

what are the mutated form of proto-concogenes called?

A

oncogenes

37
Q

what type of tumours form and describe them?

A
  • benign - non-cancerous and wont invade nearby tissues
  • malignant - cancerous and can spread to other tissues
38
Q

describe meiosis

A
  • used to produce gametes in sexually reproducing organisms
  • meiosis produces four genetically different daughter cells
39
Q

how many cell division stages are there in meiosis?
what are they? describe them.

A

2 cell division stages:
MEIOSIS I - chromosome number is halved
MEIOSIS II - the new haploid cells divide again to produce 4 genetically different daughter cells (identical to mitosis)

40
Q

outline what occurs during prophase I

A
  • chromosomes condense and become visible as two sister chromatids joined at the centromere
  • homologous chromosomes pair up in a bivalent
  • chromatids wrap around each other and then partially repel each other, but remain joined at points called at the chiasmata. Here, homologous chromosomes can exchange equivalent sections of DNA - this is called crossing over
  • nuclear envelope disintegrates
  • nucleolus disappears
  • centrioles move to opposite poles and microtubules form the spindle
41
Q

outline what occurs during metaphase I

A
  • microtubules of spindle attach to centromere
  • bivalents align randomly along the spindle at the equator (independent assortment of chromosomes takes place)
  • this results in a random combination of paternal and maternal chromosomes in each daughter cell
42
Q

outline what occurs during anaphase I

A
  • spindle fibres contract and shorten, bivalents separate and chromosomes are pulled to opposite poles
  • each pole receives one of each homologous pair of chromosomes
  • there is a random mixture of maternal and paternal chromosomes as a result of independent assortment
43
Q

outline what occurs during telophase I

A
  • in some species, the nuclear envelope reforms around the haploid group of chromosomes, and the chromosomes unwind and so are no longer visible
  • in many species, the chromosomes stay in their condensed form
44
Q

outline what occurs during prophase II

A

centrioles migrate and new spindle develops at right angles to the previous ones

45
Q

outline what occurs during metaphase II

A
  • chromosomes align on the equator
  • spindle fibres attach to centromere
  • independent assortment happens because the chromatids of the chromosomes can face either pole
46
Q

outline what occurs during anaphase II

A
  • spindle fibres shorten
  • centromeres split and sister chromatids are pulled to opposite poles
47
Q

outline what occurs during telophase II

A
  • chromosomes are uncoil and lengthen and are no longer visible under a microscope
  • spindle breaks down
  • nuclear membrane and nucleoli reform
  • cytokinesis gives rise to 4 haploid daughter cells
48
Q

why are sources of variation essential?

A

for a species to survive in a constantly changing environment

49
Q

what are the 3 ways of creating genetic variation as a result of meiosis?

A
  1. crossing over
  2. independent assortment
  3. random fusion of haploid gametes
50
Q

describe crossing over as a source of genetic variation

A
  • during prophase I, chromosomes condense and homologous pairs form a bivalent; this is called synapsis
  • the chromatids in the bivalent join at points called chiasmata
  • parts of the chromosome may be exchanged at chiasmata
  • this is crossing over
51
Q

describe independent assortment as a source of genetic variation

A
  • during metaphase I and II, the chromosomes distribute themselves randomly at the equator of the spindle
  • the random distribution leads to independent assortment of chromosomes
52
Q

describe random fusion of haploid gametes as a source of genetic variation

A
  • at fertilisation, the diploid chromosome number is restored when the nuclei of haploid gametes fuse to form a zygote
  • half of the chromosomes come from the mother and half from the father
53
Q

what is the advantage of sexual reproduction?

A
  • allows offspring to adapt to a changing environment, allows natural selection to occur
  • spores produced by fungi and seeds by plants are dispersed widely to help reduce interspecific competition
54
Q

suggest an organ present in a mammal which contains cells capable of dividing by both mitosis and meiosis

A

ovary

55
Q

how does the mass of DNA change over time starting with a diploid cell that undergoes mitosis and meiosis

A
  1. the DNA content doubles as the DNA is replicated during interphase
  2. DNA content halves from 4 to 2 as a result of mitosis - DNA is divided into the nuclei of 2 daughter cells
  3. DNA content doubles as DNA is replicated during a second interphase
  4. DNA content halves from 4 to 2 during meiosis I as the chromosome number in each nucleus is halved
  5. DNA content halves during meiosis II, as DNA is divided into nuclei of 4 daughter cells
56
Q

explain how mitosis maintains genetic stability (1 MARK)

A

2 genetically identical daughter cells produced, clones of parent cell

57
Q

describe two ways in which the process of cell division differs between plant cells and animal cells ( 2 MARKS )

A
  • cell wall grows from inside outwards
  • no centrioles
58
Q

explain two ways by which the process of meiosis contributes to genetic variation in an organism (2 MARKS)

A
  • crossing over has occurred
  • independent assortment of bivalents
59
Q

describe two differences between metaphase II and metaphase I

A
  • metaphase I has bivalents, whereas metaphase II does not
  • in metaphase II, centromeres are on the equator whilst in metaphase I they are not
  • in metaphase I, chromosomes either side of equator. however in metaphase II, chromosomes are on the equator
  • in metaphase I, chiasmata are present but metaphase II has no chiasmata
60
Q

describe two differences between anaphase I and anaphase II

A
  • anaphase I is diploid and anaphase II is haploid
  • in anaphase I, chromosomes are being pulled to opposite poles, whereas in anaphase II, chromatids are being pulled to opposite poles
  • in anaphase I, centromeres do not divide and in anaphase II they do divide.
61
Q

state how meiosis contributes to genetic variation in the species and explain why this is important

A
  • chiasmata formation is taking place in prophase I
  • independent assortment is occurring in metaphase I
  • genetic variation allows the species to adapt in changeable environment

biology - component 2 (7 decks)

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