Topic 2 Cell Cycle and Mitosis

Question 1

Stages of Mitosis

Answer 1

Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 2

What happens in Interphase?

Answer 2

G1 - cell grows
S - DNA synthesis
G2 - cell grows

Question 3

What happens in Prophase?

Answer 3

• Nuclear envelope breaks down.
  -Nucleolus disappears
  -Chromosomes coil more tightly
• Chromosomes become shorter and fatter
• centrioles move to opposite poles of cell
  -microtubules form the mitosis spindle between the centrioles.

Question 4

What happens in Metaphase?

Answer 4

• Chromosomes line up along equator of cell - they are maximally condensed
• they are attached to the spindle by the centromere

Question 5

What happens in anaphase?

Answer 5

• chromosomes break into two chromatids - separate at the centromere
  -spindles contract + pull chromatids to poles of cell.

Question 6

What happens in telophase?

Answer 6

• chromatids reach poles and begin to decondense
• nuclear envelope reforms
• cytoplasm splits

Question 7

How many daughter cells does mitosis produce?

Answer 7

2

Question 8

Describe binary fission in bacteria.

Answer 8

• replication of circular DNA
• replication of plasmids
• division of cytoplasm

Question 9

Suggest how two environmental variables increase the growth rate of bacteria by binary fission

Answer 9

• temperature -> inc temp, incs enzyme activity so bacteria grows better
• inc conc of nucleotides -> inc DNA synthesis occurring in binary fission

Question 10

what is the name of a fixed position occupied by a gene on a DNA molecule?

Answer 10

locus. / loci.

Question 11

why are eggs produced by meiosis genetically different? (1 reason)

Answer 11

• crossing over

Question 12

Why are offspring produced from diploid egg cells sterile?

Answer 12

• too many chromosomes
• homologous chromosomes do not pair so no meiosis

Question 12

Why does preventing the formation of spindle fibres stop the cell cycle?

Answer 12

• chromosomes cannot attach to spindle
• chromatics cannot separate

Question 13

If a substance stops spindle fibres forming why could it be used as a treatment for cancer even if it affects healthy cells?

Answer 13

• cancer cells divide more rapidly than healthy cells so good treatment

Question 14

Why did the student only use first 5mm of root tip when measuring mitosis?

Answer 14

• dividing cells found there

Question 16

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

Answer 16

repeat count ensure figures are correct

Question 17

Explain how the named chemical may stop the growth of cells and roots in the plant.

Answer 17

• if chromatids are prevented from separating
• its because anaphase is stopped by preventing spindle fibres forming
• so chromatids can’t be separated

Question 18

Suggest one way the structure could differ along its length to result in the stain binding more in some areas.

Answer 18

Different base repeats

Question 19

What is a homologous pair of chromosomes?

Answer 19

Chromosomes with different alleles of the same gene

Question 20

Two aseptic techniques when transferring broth bacterial culture onto agar plate? And why?

Answer 20

• sterile equipment
• to maintain pure culture of bacteria
• wear gloves
• to prevent bacteria contamination from hands

Question 21

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 21

Prophase
-> chromosomes condense - appear as chromatids joined together by the centromere.
Metaphase
-> chromosomes line up at the equator of the cell and are attached to spindle fibres by centromere
Anaphase
-> chromatids pulled to poles of cell by spindle fibres
Telophase
-> chromosomes uncoil
Cytoplasm splits