Cell Division

Question 1

Give 2 reasons why mitosis of different garlic root tip was different?

Answer 1

• Temperature
• Genetic differences

Could be more

Question 2

Describe and explain what the student should have done when counting cells to amke sure the mitotic index obtained for garlic root tip was accurate?

What is mitotic index?

Answer 2

Examine large number of cells
To ensure representative sample

Proportion of cells undergoing cell division

Question 3

A student investigated the stages of mitosis in a garlic root. This was placed on a slide with a stain. Explain why:

• A root tip was used
• A stain was used
• Root tip was firmly squashed

Answer 3

• Mitosis occurs more rapidly
• Chromosomes not visible without stain
• To let light through as is a thin layer

Question 4

What is a tumour? (2)

Answer 4

Mass of cells/tissue
Uncontrolled mitosis/cell division

Question 5

Describe the process of crossing over + explain how it increases genetic diversity? (4)

Answer 5

• Homologous pairs of chromosomes form a bivalent
• Chiasmata forms
• Equal lengths of chromatids are exchanged
• Producing new combinations of alleles

Question 5

Describe binary fission in bacteria? (3)

Answer 5

• Replication of circular DNA
• Replication of plasmids
• Division of cytoplasm

Question 6

What is independent segregation?

Answer 6

The random order of maternal + paternal chromosomes lining up on equator during meiosis 1 to produce genetic variation

Question 6

Explain how meiosis results in cells that have the haploid number of chromosomes + show genetic variation? (6)

Answer 6

• Homologous chromosomes pair up
• Maternal + paternal chromosomes are arranged in any order
• Independent segregation + crossing over occurs
• Equal lengths of chromatids are swapped between chromosomes
• Produces new combination of alleles
• Chromatids separate at meiosis

Question 6

How do you calculate the number of possible combinations of chromosomes?

Answer 6

2^n

n = number of different pairs of homologous chromosomes

Question 7

Describe the features of telophase? (2)

Answer 7

• Nuclear membrane begins to reform
• Chromosomes unwind

Question 8

Describe the featuresof anaphase? (4)

Answer 8

• Spindle fibres shorten + contract
• Centromere splits
• Sister chromatids are separated
• Chromatids are pulled to opposite poles of cell

Question 9

Describe the features of metaphase (2)

Answer 9

• Spindle fibres form + attach to centromere of chromosomes
• Chromosomes align on equator of cell

Question 10

Describe the features of prophase? (3)

Answer 10

• Nuclear membrane begins to breakdown
• Centrioles move to poles of the cell
• Chromatin supercoil + condense in chromosomes

Question 11

Stages of meiosis? Draw?

Answer 11

P1, M1 —–> crossing over + independent segragation occurs
A1
T1 —–> each daughter cell in now haploid (n)

P2 —–> each daughter cell only contains 1 chromosome from each homologous pair
M2
A2
T2 —–> genetically different haploid daughter cells are produced

https://www.pinterest.co.uk/pin/400679698104511229/

Question 12

How to calculate length of time on each stage of mitosis?

Answer 12

Total number of cells in mitosis (visible chromosomes)
—————————————— X time of 1 cell cycle (minutes)
total number of cells

Question 13

What control genes can switch cell division on + off? What do they do? (2)

Answer 13

• Tumour suppressor genes - code for proteins that slow down the cell cycle
• Proto-onco genes - code for proteins that speed up the cell cycle

Question 13

How is cancer treated?

Answer 13

The drug inhibits cell division (mitosis) which stops DNA replication, cytokinesis, spindle formation

Question 14

Differences between mitosis + meiosis? (4)

Answer 14

Mitosis:

• One division
• Genetically identical
• Two produced
• Crossing over/independent segregation only in meiosis

Question 15

What is a homologous pair of chromosomes?

Answer 15

2 chromosomes that carry the same genes in the same loci

Question 16

What is mitosis used for? (3)

Answer 16

Increasing cell numbers + growth of organism
Repair of damaged cells
Replacement of dead cells

Question 17

Diagram of chromosome?

Answer 17

https://www.thesciencehive.co.uk/the-cell-cycle-mitosis-and-meiosis-a-level

Question 18

Difference between diploid + haploid cells?

Answer 18

Diploid = 2n —–> 46
Haploid = n —–> 23 (gametes)

Question 19

What are chromosomes?

Answer 19

Independant DNA molecule thats coiled into condensed form

Question 20

What happens at the end of the cell cycle?

Answer 20

Cytokinesis - division of cytoplasm to produce new cells (not all cells go through this)

Question 21

What are the 3 stages of interphase + what do they do?

Answer 21

G1 - Cell increases in size + new biomass is made (proteins)
S - DNA replicates by semi-conservative replication
G2 - Cell prepares for division, synthesis + stores ATP