cell division and cell cycle

Question 1

describe appearance and behaviour of chromosomes during mitosis

Answer 1

p: chromosomes condense to become visible

p: chromosomes appear as two identical sister chromatids joined at centromere

m:chromosomes line up on equator of cell

m:spindle fibres attach at chromosomes at centromere

a:spindle fibres contract splitting the centromere and sister chromatids are pulled to opposite poles of cell making V shape

t:chromatids uncoil and become thinner

prophase,metaphase,anaphase,telophase

Question 2

describe how the process of meiosis results in haploid cells

Answer 2

Dna replicates

there are two divisions

in the first division, there is a separation of homologous chromosomes

in the second division, there is a separation of sister chromatids

this results in 4 haploid cells

Question 3

describe the process of independent segregation and explain how it increases genetic diversity

Answer 3

the homologous chromosomes randomly pair up along the equator of the cell

independent segregation leads to maternal and paternal chromosomes being reshuffled in any combination

Question 4

what is the importance of mitosis for organisms

Answer 4

growth and repair of tissues

asexual reproduction-2n to 2n
or n to n

Question 5

what is the importance of meiosis for organisms

Answer 5

create genetically different gametes, diploid to haploid cells, to be used in sexual reproduction

Question 6

describe the purpose of the following genes:

tumour suppressor genes
proto-oncogenes

Answer 6

tumour suppressor genes code for polypeptides that stop cell division

proto-oncogenes code for polypeptides that start cell division

Question 7

describe the process of crossing over and explain how it increases genetic diversity

Answer 7

the homologous chromosomes form a bivalent

chiasmata form between non sister chromatids of homologous chromosomes

equal lengths of non sister chromatids/alleles are exchanged

producing new combinations of alleles

Question 8

contrast mitosis and meiosis

Answer 8

mitosis 1 division whereas meiosis 2 divisions

mitosis has genetically identical daughter cells whereas meiosis has genetically different daughter cells

mitosis produces 2 cells whereas meiosis produces 4 cells

mitosis is diploid-diploid or haploid-haploid whereas meiosis is diploid-haploid

mitosis is separation of sister chromatids whereas meiosis is separation of homologous chromosomes (1st division)

there is no crossing over in mitosis whereas there is crossing over in meiosis

there is no independent segregation in mitosis whereas there independent segregation in meiosis

Question 9

describe binary fission in bacteria
(also how chloroplasts/mitochondria replicate)

Answer 9

replication of circular dna

replication of plasmids

division of cytoplasm (to produce daughter cells)

Question 10

describe the function of cholesterol

Answer 10

cholesterol controls membrane fluidity

the more cholesterol, the less fluid and permeable the membrane becomes