Module 2 Section: 6 - Cell division

Question 1

What are the 3 phases of interphase?
2 phases of mitosis and explain what happens?

Answer 1

Interphase:
- growth phase 1
- synthesis
- growth phase 2
Mitotic phase:
- mitosis= nucleus divides
- cytokinesis= cytoplasm divides & 2 daughter cells produced

Question 2

What is G0? Why might a cell enter G0?

Answer 2

The resting phase, in which the cell leaves the cycle temporarily or permanently
When a cell is specialized it no longer needs to divide, hence entering G0

Question 3

Which cells DON’T divide?

Answer 3

DNA damaged cells and senescent cells

Question 4

What happens at each checkpoint of the cell cycle? (3)

Answer 4

G1 checkpoint checks for:
cell size, nutrients, growth factors, DNA damage

G2 checkpoint checks for:
cell size, DNA replication, DNA error

Spindle assembly checkpoint checks for:
all chromosomes attached to spindles and being aligned

Question 5

What happens at G1 phase?

Answer 5

• proteins synthesised
• organelles replicated
• cell enlarges

Question 6

What happens at synthesis phase?

Answer 6

• DNA replicated

Question 7

What happens at G2 phase?

Answer 7

• energy stores are increased
• DNA checked for errors
• cell enlarges

Question 8

what are the uses of mitosis

Answer 8

-growth
-repair
-asexual reproduction
-Production of new stem cells

Question 9

what are the 4 division stages of mitosis in order

Answer 9

-prophase
-metaphase
-anaphase
-telophase

Question 10

what happens in prophase

Answer 10

-chromosomes condense and become visible
-nuclear envelope breaks down
-nucleolus disappears
-centrioles move to opposite poles and release spindle fibres

Question 11

what are the parts of the chromosomes called and where are they in the chromosome

Answer 11

• the separate strands are called chromatids
  -the middle part that joins the strands together is called the centromere

Question 12

what happens in metaphase

Answer 12

-chromosomes line up on the metaphase plate (equator)
-spindle fibres attach to centromere

Question 13

what happens during the anaphase

Answer 13

-centromeres divide separating each pair of sister chromatids
-spindle fibres contract pulling the chromatids to opposite poles

Question 14

what happens during telophase

Answer 14

-chromosomes begin to grow and become longer and thinner
-spindle fibres begin to disintegrate
-nucleus reforms
-cytoplasm splits(cytokinesis)

Question 15

what does meiosis produce

Answer 15

gametes

Question 16

what are all the stages of mitosis and in order

Answer 16

-prophase I
-Metaphase I
-Anaphase I
-Telophase I
-Prophase II
-Metaphase II
-Anaphase II
-Telophase II

Question 17

what happens in Prophase I

Answer 17

-Chromosomes condense and become visible as sister chromatids
-nuclear envelope breaks down
-nucleolus disintegrates
-Homologous Chromosomes pair up and crossing over occurs
-Centrioles migrate to opposite poles and start to make spindle fibres

Question 18

what are homologous chromosomes

Answer 18

are pairs of chromosomes that have the same genes but possibly different versions (called alleles) of those genes.

Question 19

what is crossing over

Answer 19

where homologous chromosomes (the ones from your mother and father) swap some of their genetic material. This creates new combinations of genes.

Question 20

What happens during crossing over in meiosis?

Answer 20

During crossing over, homologous chromosomes (chromosomes from both parents) line up next to each other in prophase I of meiosis. They exchange genetic material by swapping sections of their chromatids. This creates new combinations of genes, leading to genetic variation in offspring.

Question 21

what happens in meta phase I

Answer 21

-Homologous Chromosomes align at the metaphase plate
-Independent assortment occurs
-spindle fibres attach to sister chromatid centromere

Question 22

what is independent assortment

Answer 22

how chromosomes are randomly distributed to gametes

Question 23

what is the process of independent assortment (answer from marksheet)

Answer 23

-(homologous
chromosomes) line up,
across the centre of the cell
on the equator / on the
metaphase plate
- maternal or paternal
chromosomes / either one
of the homologous pair,
can end up, facing either
pole / in either (daughter) cell

Question 24

what is a sister chromatid

Answer 24

two identical copies of a single chromosome formed during DNA replication

Question 25

what is the Chiasmata

Answer 25

point where crossing over occurs

Question 26

what occurs in anaphase I

Answer 26

Spindle fibre contract and Homologous Chromosomes separate and move to opposite sides of the cell

Question 27

What happens in Telophase I

Answer 27

-nuclear envelope reforms
-spindle fibres breakdown
-cytokinesis

Question 28

What happens in Prophase II

Answer 28

-nuclear envelope breaks down
-Chromosomes condense and become visible
-Centrioles move to opposite poles and release spindle fibres

Question 29

what happens in metaphase II

Answer 29

-Chromosomes line up on the metaphase plate
-Spindle fibres attach to the centromeres

Question 30

what happens in anaphase II

Answer 30

-Spindle fibres attach back to centromere causing the centromere to divide and chromatids to go to each pole

Question 31

what happens in telophase II

Answer 31

-Chromosomes start to grow and become longer and thinner
-spindle fibres begin to disintegrate
-Cytoplasm reforms

Question 32

what 2 events in meiosis lead to genetic variation

Answer 32

-crossing over and Independent assortment

Question 33

what are senescent cells

Answer 33

cells that have stopped dividing and have reached a stage of permanent growth but don’t die