CELL DIVISION, DIVERSITY, CELLULAR ORGANISATION (2.1.6)

Question 1

State the stages of the cell cycle

Answer 1

• interphase
• m phase

Question 2

State and describe the stages of interphase

Answer 2

G1 Phase:
- organelles replicated
- protein synthesis
- cell grows
S Phase:
- DNA replicated
G2 Phase
- cell grows
- ATP production increases
- protein synthesis for spindle fibres

Question 3

State and describe the checkpoints within interphase

Answer 3

G1 checkpoint
- checks that required chemicals are present for replication
- checks for DNA damage
G2 checkpoint
- checks DNA has been replicated without damage

Question 4

State G0 Phase’s position in the cell cycle and its purpose

Answer 4

• after G1 phase
• exit from the cell cycle
• fully differentiated cells permanently enter
• senescent cells enter permanently
• some enter temporarily, late triggered to re-join cell cycle

Question 5

State the stages within M phase

Answer 5

• mitosis
• cytokinesis

Question 6

State and explain the checkpoint in M phase

Answer 6

• Metaphase checkpoint
• checks that chromosomes are correctly assembled on mitotic spindle

Question 7

State purpose of mitosis

Answer 7

• growth
• repair of damaged cells
• asexual reproduction

Question 8

What is the centromere and its purpose

Answer 8

• “round” structure
• after replication, 2 sister chromatids are attached at the centromere
• attach to spindle fibres during metaphase

Question 9

Describe prophase in mitosis

Answer 9

• chromosomes condense, become visible
• centrioles move to opposite ends of the cell for spindle formation
• nuclear envelope breaks down, meaning chromosomes are free in the cytoplasm

Question 10

Describe metaphase in mitosis

Answer 10

• chromosomes line up along the middle at the spindle equator
• become attached to spindle fibres at their centromere
• MPHASE CHECKPOINT

Question 11

Describe anaphase in mitosis

Answer 11

• spindle fibres contract/shorten
  -centromere divides
• sister chromatically pulled to opposite ends of the cell

Question 12

Describe telophase in mitosis

Answer 12

• spindle fibres disintegrate
• chromatids reach opposite poles
• chromosomes no longer visible
• nuclear envelope forms around each group of chromosomes

Question 13

Describe cytokinesis after mitosis

Answer 13

• animal cells, cleavage furrow forms
• divides cell membrane
• cytoplasm divides
• produces 2 genetically identical daughter cells

Question 14

What is a zygote

Answer 14

• formed after fertilisation
• diploid, 46 chromosomes
• divides through mitosis to form a new organism

Question 15

What is a gamete

Answer 15

• sex cell (sperm or egg)
• haploid, 23 chromosomes
• join to produce zygote

Question 16

Describe chromosomes in a normal body cell

Answer 16

• 23 homologous pairs of chromosomes (46 overall)
• 1 chromosome in each pair from mother, the other from the father

Question 17

What are homologous chromosomes

Answer 17

• same size chromosome for the same gene
• one from the mother, one from the father
• may have different alleles (versions of the same gene)

Question 18

State the purpose of meiosis

Answer 18

• occurs in sex organs only
• produce gametes (haploid)
• forms 4 genetically different daughter cells with different combinations of chromosomes

Question 19

State the stages of meiosis

Answer 19

MEIOSIS 1: occurs with original diploid cell
-prophase 1 -metaphase 1 -anaphase 1 -telophase 1
MEIOSIS 2:
-prophase 2 -metaphase 2 -anaphase 2 -telophase 2

Question 20

Describe what happens during recombination/crossing over

Answer 20

PROPHASE 1
- homologous pairs of chromosomes pair up
- chromatids twist around each other, swapping parts
- chromatids contain the same gene, but different alleles
- means daughter cells in meiosis 2 have chromatids w/ different alleles

Question 21

Describe what happens during independent assortment of chromosomes

Answer 21

ANAPHASE 1
- after maternal and paternal chromosomes line up, it is random as to how they are separated
- daughter cells have different combinations of maternal and paternal chromosomes
- leads to genetic variation in offspring

Question 22

State what is different about anaphase 2 to anaphase 1

Answer 22

Sister chromatids are separated rather than chromosomes