Cell division and Cell cycle A1

Question 1

What is mitosis?
(3)

Answer 1

1. cell division
2. which increases cell growth and repair
3. to produce two genetically identical daughter cells

Question 2

Why must DNA replication take place before cell division?

Answer 2

because the two daughter cells need one copy of each of DNA it cannot be halved as there wouldn’t be a full set.

Question 3

Define chromosone.

Answer 3

an independent DNA molecule which has folded into a condense form (contains genes) (two sister chromatids together)

Question 4

Define gene.

Answer 4

a section of DNA coding for one polypeptide protein

Question 5

Define sister chromatids.

Answer 5

two identical copies of the same chromosome formed in DNA replication

Question 6

Define homologous chromosomes.

Answer 6

have the same genes in same position but different alleles (version) of the genes

Question 7

Define…
-diploid
-haploid

Answer 7

diploid - two copy of each chromosome
haploid - one copies of each chromosome (one from each parent)

Question 8

Name the phases of mitosis in order.

Answer 8

1. prophase
2. metaphase
3. anaphase
4. telophase

Question 9

Describe the features of prophase.
(3)

Answer 9

1. nuclear membrane begins to break down
2. centrioles move to poles of the cell
3. chromosomes condense

Question 10

Describe the features of metaphase.
(4)

Answer 10

1. spindle fibres form
2. spindle fibres attach
3. to the centromere of chromosomes
4. chromosomes align at the equator

Question 11

Describe the features of anaphase.
(4)

Answer 11

1. spindle fibres shorten
2. centromere splits
3. sister chromatids are separated
4. pulled to opposite poles of the cell

Question 12

Describe the features of telophase.
(2)

Answer 12

1. nuclear membrane begins to reform
2. chromosomes unwind

Question 13

Describe and explain the stages of the phase that occurs before mitosis.
(4)

Answer 13

1. interphase (stages of interphase below)
2. G1 phase - cell increases in size and new biomass is made
3. S phase - DNA replicates
4. G2 phase - cell gets ready for division, it makes stores of ATP and new organelles

Question 14

What comes after mitosis?
(2)

Answer 14

1. cell division (cytokinesis)
2. period when cell divides into two, each daughter cell receiving one of the nuclei

Question 15

Define the end product of mitosis.
(4)

Answer 15

1. daughter cells are genetically identical to each other
2. and to original parent cell
3. no variation occurs
4. they have the same number of chromosomes as the parent cell

Question 16

Describe the appearance and behaviour of chromosomes during mitosis.
(8)

Answer 16

1. during prophase, chromosomes supercoil and condense to become visible
2. chromosomes appear as two identical sister chromatids joined by a centromere
3. during metaphase, chromosomes line up on equator of cell
4. chromosomes attach to spindle fibres
5. by their centromere
6. during anaphase, the centromere splits
7. sister chromatids are pulled to opposite sides of the cell making a V shape
8. during telophase, chromatids uncoil and become thinner

Question 17

How is cancer caused?
(4)

Answer 17

1. mutation occurs in a control gene
2. so cell division continues uncontrollable
3. division is rapid and cells produced are abnormal
4. a tumour develops (cancer)

Question 18

How may cancer be treated?
(2)

Answer 18

1. drugs that stop cell division (mitosis)
2. the drugs may stop DNA replication, spindle formations, cytokinesis or other processes linked to mitosis

Question 19

What is binary fission?
(4)

Answer 19

1. splitting in two (asexual reproduction of prokaryotes eg. bacteria)
2. DNA and plasmids replicated
3. cell elongates in middle, separating DNA molecules, new cell wall is formed
4. its very fast and simple

Question 20

What is the endosymbiont theory?

Answer 20

the theory that mitochondria and chloroplasts were once prokaryotic as they replicate via binary fission like prokaryotes.

Question 21

How do viruses replicate?
(4)

Answer 21

1. the protein molecules on capsid attach to cell surface membrane of host cells
2. the virus enters the cell as its genetic material hijacks the machinery of the cell
3. the cell copies the viruses DNA or RNA (using reverse transcriptase), makes new proteins coat and assembles the new virus
4. eventually these burst out the cell destroying it

Question 22

name the conversions for…
- nanometers (nm) to micro-meters (μm)
- micro-meters to milli-meters
- milli-meters to meters

Answer 22

• 1000 nm in a micro-meter
• 1000 micro-meters in a milli-meter
• 1000 mm in a meter

Question 23

What’s the purpose of the root tip squash experiment?
(5)

Answer 23

1. growth in plants occurs in specific regions called meristems
2. the root tip meristem can be used to study mitosis
3. the root tip meristem can be found just behind the protective root cap
4. in the root tip meristem, there is a zone of cell division that contains cells undergoing mitosis
5. pre-prepared slides of root tips can be studied or temporary slides can be prepared using the squash technique (root tips are stained and then gently squashed spreading the cells out into a thin sheet and allowing individual cells undergoing mitosis to be clearly seen)

Question 24

What’s the equation for mitotic index?

Answer 24

mitotic index = (number of cells with visible chromosomes ÷ total number of cells)
X
100 (to get a %)

Question 25

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. (7)

Answer 25

1. homologous chromosomes pair up 2. maternal and paternal chromosomes are arranged in any order 3. independent segregation 4. crossing over 5. portions of chromatids are swapped between chromosomes 6. produces new combinations of alleles 7. chromatids separate at meiosis II/ later

Question 26

Explain crossing over and how it leads to a varied population. (3)

Answer 26

1. crossing over leads to exchange of parts/segments of non-sister chromatids/alleles 2. between homologous chromosome pairs 3. this creates new combinations of alleles in the gametes

Question 27

Explain independent segregation and how it leads to a varied population. (5)

Answer 27

1. during metaphase of first division 2. homologous chromosomes attach to spindle fibres and pair up side by side 3. they are shuffles into any recombination 4. this produces new combinations of characteristics 5. meaning the members of species with advantageous alleles will be able to survive if environment changes

Question 28

How do you calculate the number of different combinations possible during independent segregation?

Answer 28

1. n = number of chromosomes 2. 2 to the power of n 3. eg if n = 3, 2 to the power of 3 = 8

Question 29

Describe and explain the process that occurs during meiosis that increases genetic variation. (5)

Answer 29

1. homologous chromosomes pair up 2. independent segregation 3. maternal and paternal chromosomes are re-shuffled in any combination 4. crossing over leads to exchange of parts/segments of (non-sister) chromatids/alleles between homologous chromosomes 5. both create new combinations of alleles

Question 30

Describe binary fission in bacteria. (3)

Answer 30

- replication of circular DNA - replication of plasmids - division of cytoplasm