Chapter 6 Flashcards
What is karyokinesis & cytokinesis?
Karyokinesis: division of nucleus
cytokinesis: division of cytoplasm that occurs immediately after the nucleus is formed (after telophase)
Organism’s body cells are divided into somatic cells & reproductive cells/gametes. What is somatic cell? (4)
- 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
Organism’s body cells are divided into somatic cells & reproductive cells/gametes. What are gametes? (4)
- reproductive cells
- produced through mitosis
- contains haploid number of chromosomes [each cell contain 1 set of chromosomes/n
- in human gametes, n=23
What are homologous chromosomes & chromatin?
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
What is a cell cycle (1) and the stages (2)?
- 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)
Explain the G1 phase of a cell cycle. (5)
- cells grow
- mitochondrion & endoplasmic reticulum are produces
- proteins synthesised
- nucleus looks big
- chromosome in chromatin form
Explain the S phase. (4)
- 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
Explain the G2 phase. (2)
- cells continue to grow, remain metabolically active
- cells gather energy & make final arrangements to enter the next stage of cell division
Explain the M Phase. (2)
- made up of mitosis (division of nucleus) & cytokinesis (division of cytoplasm)
- mitosis involves prophase, metaphase, anaphase & telophase
What is mitosis? (2)
- 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
Explain the processes in prophase (5)
- 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
Explain the processes in metaphase. (4)
- 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
Explain the processes in anaphase (3)
- 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
Explain the processes in telophase. (5)
- 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
Explain the cytokinesis process in animal cells. (3)
- 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
Explain the cytokinesis process in plant cells.
[p.s plant cells do not contain centrioles but can still form spindle fibres during mitosis]
- 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
What is the importance of mitosis? (7)
- 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
What is meiosis and where does it occur (2)?
- 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
What is the importance of meiosis? (3)
- 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
Explain the process in Prophase I of Meiosis I. (6)
- 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
Explain the process in metaphase I of Meiosis I (3)
- 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)
Explain the process in anaphase I of Meiosis I (2)
- 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
Explain the process in telophase I of Meiosis I (4)
- 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]
Explain the process in prophase II of Meiosis II (3)
- nucleoli & nuclear membrane disappear
- chromosome made up of sister chromatids joined at centromere
- spindle fibres form
Explain the process in metaphase II of Meiosis II (3)
- chromosomes arranged randomly on equatorial plane
- each chromatid tied to spindle fibres at centromere
Explain the process in anaphase II of Meiosis II (2)
- centromere of sister chromatids start to separate
- sister chromatids separate & moves towards opposite polar cells
Explain the process in telophase II of Meiosis II (6)
- 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
What are the similarities between mitosis and meiosis? (1)
- DNA replicates only once
What are the differences between mitosis and meiosis? (5)
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
What is the importance of meiosis? (2)
- 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]
What is an effect of uncontrolled mitosis? (6)
- 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
Explain the development of breast cancer. (4)
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
What happens if there is an abnormality during the division of meiosis? (7)
- 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
