Chapter 6

Question 1

What is karyokinesis & cytokinesis?

Answer 1

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

Question 2

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

Answer 2

• 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

Question 3

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

Answer 3

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

Question 4

What are homologous chromosomes & chromatin?

Answer 4

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

Question 5

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

Answer 5

• 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)

Question 6

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

Answer 6

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

Question 7

Explain the S phase. (4)

Answer 7

• 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

Question 8

Explain the G2 phase. (2)

Answer 8

• cells continue to grow, remain metabolically active

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

Question 9

Explain the M Phase. (2)

Answer 9

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

Question 10

What is mitosis? (2)

Answer 10

• 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

Question 11

Explain the processes in prophase (5)

Answer 11

• 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

Question 12

Explain the processes in metaphase. (4)

Answer 12

• 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

Question 13

Explain the processes in anaphase (3)

Answer 13

• 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

Question 14

Explain the processes in telophase. (5)

Answer 14

• 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

Question 15

Explain the cytokinesis process in animal cells. (3)

Answer 15

• 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

Question 16

Explain the cytokinesis process in plant cells.

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

Answer 16

• 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

Question 17

What is the importance of mitosis? (7)

Answer 17

• 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

Question 18

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

Answer 18

• 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

Question 19

What is the importance of meiosis? (3)

Answer 19

• 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

Question 20

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

Answer 20

• 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

Question 21

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

Answer 21

• 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)

Question 22

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

Answer 22

• 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

Question 23

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

Answer 23

• 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]

Question 24

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

Answer 24

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

Question 25

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

Answer 25

- chromosomes arranged randomly on equatorial plane | - each chromatid tied to spindle fibres at centromere

Question 26

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

Answer 26

- centromere of sister chromatids start to separate | - sister chromatids separate & moves towards opposite polar cells

Question 27

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

Answer 27

- 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

Question 28

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

Answer 28

- DNA replicates only once

Question 29

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

Answer 29

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

Question 30

What is the importance of meiosis? (2)

Answer 30

- 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]

Question 31

What is an effect of uncontrolled mitosis? (6)

Answer 31

- 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

Question 32

Explain the development of breast cancer. (4)

Answer 32

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

Question 33

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

Answer 33

- 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