Cell Division, Diversity and Organisation - Chromosomes and Cell Cycle

Question 1

how is each chromatid held together

Answer 1

by the centromere

Question 2

describe chromosomes during interphase

Answer 2

each DNA molecule makes a copy of itself
chromosomes are then composed of two identical chromatids

Question 3

what are homologous pairs

Answer 3

one of each pair come from the father and from the mother (same genes, but possibly different alleles)

Question 4

what are autosomes

Answer 4

the remaining chromosomes that aren’t sex chromosomes

Question 5

how many sets of chromosomes do gametes have

Answer 5

one (haploid)

Question 6

how many sets of chromosomes do body cells have

Answer 6

two (diploid)

Question 7

what are the phases of the cell cycle

Answer 7

interphase (G1, S, G2)
prophase
metaphase
anaphase
telophase

Question 8

describe interphase

Answer 8

• DNA is uncoiled and not visible during interphase
• DNA replication occurs (S) and DNA is checked for errors
• centrioles replicate (animal cells only) (G1 and G2)
• cell increases in size (more cytoplasm)
• new organelles produced
• cell is very active and large amounts of ATP required
• protein synthesis occurs

Question 9

describe prophase

Answer 9

• chromosomes become visible as they shorten and thicken
• centrioles move to opposite ends (poles) of the cell
• microtubules develop from pole to pole forming spindle fibres
• nucleolus disappears (forms part of several chromosomes)
• nuclear envelope breaks down

Question 10

describe metaphase

Answer 10

• centrioles reach the two poles
• chromosomes line up at the equator of the cell
• the spindle fibres attach to the centromere on each chromosome and pull the chromosomes to arrange them along the equator of the cell

Question 11

describe anaphase

Answer 11

• the centromeres divide
• the spindle fibres contract and shorten, pulling the chromatids apart, centromere leading, towards opposite ends of the cell

Question 12

describe telophase

Answer 12

• the chromatids have now reached the poles and can be regarded as distinct chromosomes
• the nuclear envelope reforms around each group of chromosomes
• the nucleolus reappears
• the chromosomes uncoil to form chromatin

Question 13

describe cytokinesis in an animal cell

Answer 13

cell division involves furrowing and cleavage of the cytoplasm

Question 14

where does cytokinesis begin in an animal cell

Answer 14

the edge of the cell

Question 15

describe cytokinesis in a plant cell

Answer 15

cell division involves formation of a cell plate

Question 16

where does cytokinesis begin in a plant cell

Answer 16

the middle of the cell

Question 17

what are the four functions of mitosis

Answer 17

• asexual reproduction
• growth in multicellular organisms
• repair of tissues (same marking point)
• replacement of cells (same marking point)

Question 18

why is it important that gametes contain the haploid number of chromosomes

Answer 18

• restores diploid number
• prevents doubling of chromosomes

Question 19

What are checkpoints of the cell cycle

Answer 19

Monitor whether each stage of the cell cycle has been completed before the cell can proceed to the next step

Question 20

What are the purposes of checkpoints

Answer 20

• prevent uncontrolled cell division leading to tumours
• detect and repair damage to DNA
• ensure cell cycle is not reversed
• ensure DNA is only copied once during each cell cycle

Question 21

What are the three checkpoints of the cell cycle

Answer 21

• G1 checkpoint
• G2 checkpoint
• spindle assembly checkpoint

Question 22

What does the G1 checkpoint check for

Answer 22

• cell size
• nutrients
• growth factors
• DNA damage

Question 23

What does the G2 checkpoint check for

Answer 23

• DNA replication (no DNA damaged)
• cell size

Question 24

What does the spindle assembly checkpoint check for

Answer 24

Chromosome attached to spindle fibre

Question 25

What does the cell enter if a problem is found or DNA is damaged

Answer 25

G0 phase

Question 26

What is G0 or resting phase

Answer 26

Cells leave the cell cycle permanently or temporarily

Question 27

What happens during resting phase/why does it happen

Answer 27

- cell differentiation, once specialised some cells won’t undergo mitosis again - if DNA is damaged (majority of cells have limited number of times they divide) - lymphocytes, can start dividing again and re enter cell cycle

Question 28

What happens if the damage can’t be repaired

Answer 28

Apoptosis

Question 29

Where does mitosis take place in animal cells

Answer 29

Many cells are capable of mitosis

Question 30

Where does mitosis take place in plant cells

Answer 30

Only special regions called meristems can undergo mitosis

Question 31

Why can only meristems perform mitosis

Answer 31

Meristem cells have very thin cell walls. Older cell walls are thicker, meaning unable to undergo cytokinesis

Question 32

Give examples of meristems

Answer 32

- Just behind root tips - just behind shoot tips - cambium - buds

Question 33

Compare cell division in plants and animal cells

Answer 33

- no centrioles present vs centrioles present - cytokinesis starts from middle of the cell vs cytokinesis starts at edge of the cell - occurs at meristems vs occurs throughout the body

Question 34

How do yeast cells reproduce

Answer 34

Budding/asexual reproduction

Question 35

Describe the process of cell division in yeast cells

Answer 35

- nucleus divides by mitosis - cell swells on the side (bud develops) - one nucleus moves into the swelling - unequal distribution of cytoplasm - cell wall forms - two new cells formed (genetically identical)

Question 36

How do prokaryote cells divide

Answer 36

Binary fission

Question 37

Describe cell division in prokaryote cells

Answer 37

- the cell grows to its limit - DNA replicates - two new loops of DNA pulled to opposite poles of the cell - cell divides into 2 - a new cell wall forms

Question 38

What organelles within eukaryotes divide by binary fission

Answer 38

Chloroplasts, mitochondria

Question 39

Suggest what might happen if the genetic information is not checked

Answer 39

- mutations - faulty DNA - daughter cell may not have identical genetic information - do not function

Question 40

Explain why the nuclei of most human cells contain 46 chromosomes

Answer 40

- two sets of chromosomes - one from each parent

Question 41

Explain why prokaryotic cells do not undergo meiosis

Answer 41

- no nucleus - single chromosome - need homologous chromosomes for meiosis