Cell division

Question 1

Phases of the cell cycle

Answer 1

Interphase and mitotic phase

Question 2

What happens during interphase?

Answer 2

DNA is replicated and checked for errors in the nucleus
protein synthesis occurs in the cytoplasm
mitochondria grow and divide
chloroplast grow and divides in the plant
normal metabolic processes occur

Question 3

What happens in each of the 3 phases of interphase?

Answer 3

G1 - first growth phase: proteins from which organelles are synthesised are produced and organelles replicate, cell increases in size
S - synthesis phases: DNA is replicated
G2 - 2nd growth phase: cell continues to grow in size, energy stores increase and replicated DNA is checked

Question 4

What are the 2 stages of the mitotic phase?

Answer 4

Mitosis - nucleus divides
Cytokinesis - cytoplasm divides and 2 cells are produced

Question 5

What is G0?

Answer 5

when a cell leaves the cell cycle indefinitely
reasons:
differentiation - specialised cells carry out a specific function and will no longer divide
DNA may be damaged, in which case its no longer viable to divide and enters permanent cell arrest
age

Question 6

When are the checkpoints in the cell cycle?

Answer 6

G1 checkpoint - end of G1 phase, before entering S phase. checking cell size, nutrients, growth factors and DNA damage
G2 checkpoint - end of G2 before mitosis, checking cell size, DNA replication and DNA damage
Metaphase checkpoint - checking that the spindle fibres are attached to the chromosomes

Question 7

What are the stages of mitosis?

Answer 7

Prophase
Anaphase
Telophase
Metaphase

Question 8

What happens during prophase?

Answer 8

• Nucleus membrane begins to break down
• Protein microtubules form spindle fibres
• 2 centrioles migrate to opposite poles in the cell and hellp the formation of spindle fibres
• Spindle fibres attach to the centromere of the chromosomes
• By the end of prophase, the nuclear envelope has disappeared

Question 9

What happens during metaphase?

Answer 9

• chromosomes are moved to the centre of the cell to form a plane call the metaphase plate

Question 10

What happens during anaphase?

Answer 10

• the centromere holding the pairs of chromatids in each chromosomes divides
• the separated chromatids are pulled to opposite ends of the cell

Question 11

What happens during telophase?

Answer 11

• the chromatids have reached opposite ends of the cell
• two new sets of chromosomes assemble at each pole
• a nuclear envelope form around each set and the nucleolus form
• cytokinesis begins

Question 12

Stages of meiosis

Answer 12

Meiosis 1 - the first division where the homologous chromosomes are separated into 2 haploid cells
Meiosis 2 - similar to mitosis, the pairs of chromatids are separated forming 2 more cells

Question 13

Prophase 1

Answer 13

chromosomes condense, nucleus envelope disintegrates, nucleolus disappears and spindle fibres formation begins
homologous chromosomes pair up forming bivalents and cross over

Question 14

Metaphase 1

Answer 14

same a metaphase but the pairs line up on the metaphase plate but not the the lone chromosomes

Question 15

anaphase 1

Answer 15

homologous chromosomes are pulled to opposite ends
sister chromatids become entangled and exchange DNA
causing genetic variations

Question 16

telophase 1

Answer 16

same as mitosis

Question 17

prophase 2

Answer 17

2 chromatids condense and become visible, nuclear envelope breaks down and spindle formation begins

Question 18

metaphase 2

Answer 18

same as mitosis but there is independent assortment and genetic variation

Question 19

anaphase 2

Answer 19

same as mitosis