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Biology Form 4 > Chapter 6 > Flashcards

Chapter 6 Flashcards

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1
Q

What is karyokinesis & cytokinesis?

A

Karyokinesis: division of nucleus
cytokinesis: division of cytoplasm that occurs immediately after the nucleus is formed (after telophase)

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2
Q

Organism’s body cells are divided into somatic cells & reproductive cells/gametes. What is somatic cell? (4)

A
  • body cells apart from gametes
  • produced through mitosis
  • contains diploid number of chromosomes [each cell contains 2 sets of chromosomes/2n: 1 set from male aka paternal chromosomes, 1 set from female aka maternal chromosomes, both have same structural characteristics]
  • in humans somatic cells,2n=46
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3
Q

Organism’s body cells are divided into somatic cells & reproductive cells/gametes. What are gametes? (4)

A
  • reproductive cells
  • produced through mitosis
  • contains haploid number of chromosomes [each cell contain 1 set of chromosomes/n
  • in human gametes, n=23
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4
Q

What are homologous chromosomes & chromatin?

A

Homologous chromosomes: a pair of chromosomes, 1 set of paternal chromosome & 1 set of maternal chromosome that have the same structural characteristics.
Chromatin: chromosome that looks like a thread

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5
Q

What is a cell cycle (1) and the stages (2)?

A
  • sequence of events that involves DNA multiplication & cell division to produce 2 daughter cells
    stages:
  • interphase (longest phase in cell cycle, made up of G1, S & G2 phase)
  • M phase (made up of mitosis & cytokinesis)
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6
Q

Explain the G1 phase of a cell cycle. (5)

A
  • cells grow
  • mitochondrion & endoplasmic reticulum are produces
  • proteins synthesised
  • nucleus looks big
  • chromosome in chromatin form
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7
Q

Explain the S phase. (4)

A
  • DNA synthesis
  • DNA replication in the nucleus
  • chromosomes multiply into 2 identical chromosome aka sister chromatids
  • both chromatids contains same copy of DNA molecule & joined at centromere
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8
Q

Explain the G2 phase. (2)

A
  • cells continue to grow, remain metabolically active

- cells gather energy & make final arrangements to enter the next stage of cell division

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9
Q

Explain the M Phase. (2)

A
  • made up of mitosis (division of nucleus) & cytokinesis (division of cytoplasm)
  • mitosis involves prophase, metaphase, anaphase & telophase
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10
Q

What is mitosis? (2)

A
  • division of nucleus of parents cell into 2 nuclei

- each nucleus contains the same number of chromosomes & genetic content with the nucleus of parent cell

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11
Q

Explain the processes in prophase (5)

A
  • chromatin shortens & thicken to form chromosome structure
  • chromosome made up of sister chromatids
  • both sister chromatids are joined at the centromere
  • nucleus membrane disintegrates & nucleus disappears,
  • centriole moves to opposite poles & spindle fibres starts to form
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12
Q

Explain the processes in metaphase. (4)

A
  • centrioles are at the opposite poles of cell
  • spindle fibres maintain the chromosomes at the equatorial plane
  • chromosomes align in a single row on the equatorial plane
  • ends when the centromere begins to divide
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13
Q

Explain the processes in anaphase (3)

A
  • centromere divides into 2, sister chromatids separate
  • spindle fibres shorten, sister chromatids are attracted to opposite poles
  • ends when chromatid arrives at the pole of the cell
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14
Q

Explain the processes in telophase. (5)

A
  • chromatids at opposite poles are called daughter chromosome
  • each pole contain 1 set of complete & identical chromosomes
  • chromosomes reformed as fine chromatin threads
  • nucleoli formed again, new nucleus membrane is formed
  • spindle fibres disappear
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15
Q

Explain the cytokinesis process in animal cells. (3)

A
  • plasma membrane constricts in the middles o the cell between the 2 nuclei
  • microfilaments at the point of constriction will contract
  • cell constricts until it splits to form 2 daughter cells
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16
Q

Explain the cytokinesis process in plant cells.

[p.s plant cells do not contain centrioles but can still form spindle fibres during mitosis]

A
  • begins when formed vesicles combine to form cell plates at the centre of cell
  • cell plates surrounded by new plasma membrane & new cell wall
  • cell plates expand outwards until combine with the plasma mebrane
  • at the end, cells produce cellulose fibres to strengthen the new cell walls
  • 2 daughter cells are formed, each has diploid condition
17
Q

What is the importance of mitosis? (7)

A
  • ensures rapid cell growth for embryo development
  • produce new cells to replace dead/damaged cells
  • lizards are able to grow a new tail if it breaks off (regeneration)
  • aids hydra in the formation of new buds to produce new individuals
  • culturing technique uses stem cells from animal cells which are then cultured in labs to produce meat
  • stem cell therapy uses stem cells from bone marrows to treat damaged cartilage
  • culturing plant tissues to produce young plants without fertilisation process
18
Q

What is meiosis and where does it occur (2)?

A
  • process of cell division that occurs in reproductive organs to produce gametes that contain half the number of chromosomes of the parent cells (diploid)
  • occurs in testis for males and ovary for females
    [p.s meiosis is divided into meiosis I and meiosis II]
    [meiosis I - prophase 1,metaphase 1, anaphase 1, telophase 1]
    [meiosis II -prophase 1,metaphase 1, anaphase 1, telophase 1]

*interphase form Meiosis I is short, DNA doesn’t replicate

19
Q

What is the importance of meiosis? (3)

A
  • forms gametes through gametogenesis
  • ensures diploid chromosome number that carry out sex reproduction is always maintained from 1 generation to the next
  • produces genetic variation
20
Q

Explain the process in Prophase I of Meiosis I. (6)

A
  • chromatin shortens, thickens & form visible chromosomes
  • pairing of homologous chromosomes (synapsis) forms bivalent/tetrad ( 4 chromatids for each homologous chromosome)
  • crossing over (exchange of genetic materials between non-identical chromatids) [produces new combination of genes in chromosomes]
  • point of chromatids crossing over is called chiasma
  • nucleus membrane & nucleoli disappears
  • centrioles move to opposite poles, spindle fibres forms
21
Q

Explain the process in metaphase I of Meiosis I (3)

A
  • homologous chromosomes arranged at the equatorial plane
  • one chromosome from each pair is tied to spindle fibres from one pole cell, its homologous tied to spindle fibres from the opposite pole cell
  • sister chromatids still tied together (centromere has not separated)
22
Q

Explain the process in anaphase I of Meiosis I (2)

A
  • spindle fibres contract, each homologous chromosome separate from its homologous pair & pulled to opposite poles
  • each chromosome still made up of a pair of sister chromatids tied to a centromere & moves as 1 unit
23
Q

Explain the process in telophase I of Meiosis I (4)

A
  • chromosomes arrive at opposite polar sites
  • each polar cell contains a number of haploid chromosomes made up of 1 set of chromosomes only
  • spindle fibres disappear, nucleoli reappear, nuclear membrane formed
  • succeeded by cytokinesis, produces 2 daughter cells [haploid condition]
24
Q

Explain the process in prophase II of Meiosis II (3)

A
  • nucleoli & nuclear membrane disappear
  • chromosome made up of sister chromatids joined at centromere
  • spindle fibres form
25
Q

Explain the process in metaphase II of Meiosis II (3)

A
  • chromosomes arranged randomly on equatorial plane

- each chromatid tied to spindle fibres at centromere

26
Q

Explain the process in anaphase II of Meiosis II (2)

A
  • centromere of sister chromatids start to separate

- sister chromatids separate & moves towards opposite polar cells

27
Q

Explain the process in telophase II of Meiosis II (6)

A
  • chromosomes at opposite pole of cell
  • spindle fibres disappear, nucleoli & nuclear membrane reform
  • ends with cytokinesis that produces 4 daughter cells that are haploid
  • each haploid cell contains half the number of parent cell chromosomes, genetic content different from diploid parent cell, develops into gametes
28
Q

What are the similarities between mitosis and meiosis? (1)

A
  • DNA replicates only once
29
Q

What are the differences between mitosis and meiosis? (5)

A

Mitosis
- occurs in somatic cells
- synapsis does not occur
- crossing over between sister chromatids does not occur
- 2 diploid (2n) daughter cells produced
- genetically identical from parent cell, no genetic variation
Meiosis
- occurs in gametes
- synapsis occurs
- crossing over between sister chromatids does occurs
- 4 haploid (n) daughter cells produced
- different from parent cell, got genetic variation

30
Q

What is the importance of meiosis? (2)

A
  • ensures diploid number of chromosomes maintained from one generation to next
  • provides genetic variation :
    [ crossing over in prophase I results in exchange of genetic material between non-identical sister chromatids]
    [ homologous chromosome arranged randomly (independent assortment) at equatorial plane]
31
Q

What is an effect of uncontrolled mitosis? (6)

A
  • uncontrolled cell division can lead to formation of tumours
  • tumours divided into 2: benign & malignant

Benign:
-not dangerous, can be removed surgically

Malignant (cancer) :

  • caused by radiation, chemicals carcinogens, genetic factors, bacteria, viruses
  • spread & destroy normal cells around them
  • cancer not identified in early stage can cause organ damage & finally death
32
Q

Explain the development of breast cancer. (4)

A

1) tumour grows from a single cell
2) cancer cells compete to get nutrients from other tissues around them
3) cancer cells spread through the lymph vessels & blood vessels to other parts of the body
4) a new tumour develops on other organs

33
Q

What happens if there is an abnormality during the division of meiosis? (7)

A
  • causes genetic disease :
    Down syndrome
  • happens because spindle fibres fail to function during anaphase I/II
  • causes nondisjunction (chromosomes fail to separate)
  • gametes with abnormal number of chromosomes (22/24 chromosomes)
  • fertilisation between normal gamete (23 chromosomes) & abnormal gamete (24 chromosomes) forms zygote with 47 chromosomes (abnormal)
  • individual with Down syndrome has 47 chromosomes [extra chromosomes at 21st set], known as trisomy 21
  • causes mental retardation, slanted eyes, slightly protruding tongue

Biology Form 4 (13 decks)

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