biology question

11

https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/AQA/2-Cells/Set-C/2.2%20Cell%20Cycle%20and%20Mitosis%20QP.pdf

can someone explain the last question please a and b

(edited 1 year ago)

Reply 1

BankaiGintoki

21

Original post by cr7090121

https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/AQA/2-Cells/Set-C/2.2%20Cell%20Cycle%20and%20Mitosis%20QP.pdf

can someone explain the last question please a and b

The placing the stages in order question
Since we are given D - it is in interphase as nucleus is present with nucleosomes, chromosomes are not visible
Next is prophase - chromosome visible, still in nucleus as nuclear envelope is still partially present so is C
Than metaphase - chromosomes align on metaphase plate so is B
Than anaphase - chromosome pulled to opposite poles so E
Than telophase/cytokinesis happen together with cytokinesis starting in late telophase so is A - 2 nuclei in the 2 cells

Part b)
Taking cells from root tip - remember apical (tip of) roots/shoots and vascular cambium contain meristem cells. Stem cells are not differentiated, and divide by mitosis. Specialised cells generally do not divide by mitosis, as they are in G0 of the cell cycle (unless stimulated into G1).
Squashing - enables you to see the chromosomes

See https://www.leicabiosystems.com/en-gb/knowledge-pathway/an-introduction-to-specimen-preparation/ To gain more knowledge on sample preparation

Reply 2

cr7090121

OP

11

Original post by BankaiGintoki

The placing the stages in order question
Since we are given D - it is in interphase as nucleus is present with nucleosomes, chromosomes are not visible
Next is prophase - chromosome visible, still in nucleus as nuclear envelope is still partially present so is C
Than metaphase - chromosomes align on metaphase plate so is B
Than anaphase - chromosome pulled to opposite poles so E
Than telophase/cytokinesis happen together with cytokinesis starting in late telophase so is A - 2 nuclei in the 2 cells

Part b)
Taking cells from root tip - remember apical (tip of) roots/shoots and vascular cambium contain meristem cells. Stem cells are not differentiated, and divide by mitosis. Specialised cells generally do not divide by mitosis, as they are in G0 of the cell cycle (unless stimulated into G1).
Squashing - enables you to see the chromosomes

See https://www.leicabiosystems.com/en-gb/knowledge-pathway/an-introduction-to-specimen-preparation/ To gain more knowledge on sample preparation

thank you for your explanation but I asked for the last question on that pdf I am not that stupid I know the steps of mitosis and meiosis the last question is about the behaviour of chromosomes causes these changes in the amount of DNA per cell between F and G.which at first looks easy but mark scheme made me soo confused

Reply 3

BankaiGintoki

21

Original post by cr7090121

thank you for your explanation but I asked for the last question on that pdf I am not that stupid I know the steps of mitosis and meiosis the last question is about the behaviour of chromosomes causes these changes in the amount of DNA per cell between F and G.which at first looks easy but mark scheme made me soo confused

Semi conservative replication increases from 2 to 4 in S phase. Shortening microtubule pull sister chromatids of homologous chromosome from bivalent in meiosis I - each daughter cell has 2 chromosome. In meiosis II, sister chromatids are pulled from metaphase plate to the pole, each daughter cell has 1 chromosome.

Fertilisation of 2 haploid cells, the 2 gametes, produce a diploid cell, Doubles from 1 to 2.

(edited 1 year ago)

Reply 4

username5885174

12

Original post by cr7090121

thank you for your explanation but I asked for the last question on that pdf I am not that stupid I know the steps of mitosis and meiosis the last question is about the behaviour of chromosomes causes these changes in the amount of DNA per cell between F and G.which at first looks easy but mark scheme made me soo confused

maybe next time clarify that its c you need help with, not a and b....

Original post by cr7090121

https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/AQA/2-Cells/Set-C/2.2%20Cell%20Cycle%20and%20Mitosis%20QP.pdf

can someone explain the last question please a and b

(edited 1 year ago)

Reply 5

cr7090121

OP

11

Original post by h4nn4

maybe next time clarify that its c you need help with, not a and b....

oh I apologise I had a different pdf open and the question was a and b my bad @BankaiGintoki apologies

Reply 6

cr7090121

OP

11

Original post by BankaiGintoki

Semi conservative replication increases from 2 to 4 in S phase. Shortening microtubule pull sister chromatids of homologous chromosome from bivalent in meiosis I - each daughter cell has 2 chromosome. In meiosis II, sister chromatids are pulled from metaphase plate to the pole, each daughter cell has 1 chromosome.

Fertilisation of 2 haploid cells, the 2 gametes, produce a diploid cell, Doubles from 1 to 2.

so when chromosomes are split the amount of dna goes down ?

Reply 7

BankaiGintoki

21

Original post by cr7090121

so when chromosomes are split the amount of dna goes down ?

Let me clarify in terms of number of chromosomes
Cell cycle: G1 -> S -> G2 this will occur before mitosis and meiosis
Before S phase: 46 chromosomes (23 pairs) 1 chromatid per chromosome
After S phase: 92 chromosomes (23 pairs) 2 chromatid per chromosome (called sister chromatids). The replicated chromosome associate with the centromere of the identical chromatid.
In mitosis: each pair of sister chromatid align on metaphase plate - one chromatid pulled to each pole by the centrosome by shortening microtubule
Resulting in 2 genetically identical daughter cells with 46 chromosomes
In meiosis I: sister chromatid of homologous chromosome (chromosome from ‘mum and dad’) form bivalent (containing 4 chromatids)
Bivalent align on metaphase plate, pair of sister chromatid pulled to pole. Resulting in cells with 46 chromosomes (23 sister chromatids) but are haploid - a diploid has chromosomes from ‘mum and dad’ but these cells have a chromosomes from either parent.
Meiosis II - the 23 sister chromatids align and are pulled…
So before mitosis: 46 chromosome. After S phase: 92 chromosome. After mitosis: 46 chromosome in 2 daughter cell
Before meiosis: 46 chromosome. After S phase: 92 chromosome. After meiosis I : 46 chromosome in 2 daughter cell. After meiosis II: 23 chromosome in each daughter cell (4 total)

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