Chapter 6- Cell Cycle, Mitosis, Meisois

Question 1

What is the cell cycle?

Answer 1

The cell cycle is the process that all body cells in multicellular organisms use to grow and divide.

Question 2

What are the phases and checkpoint in the cell cycle?

Answer 2

G1 phase
G1 checkpoint
S phase
G2 phase
M Phase

From G1 to G2, it is interphase

Question 3

What happens in the G1 phase?

Answer 3

The cell grows and new organelles and proteins are made

Question 4

What happens at the G1 checkpoint?

Answer 4

The cell checks that the chemicals needed for replication are present and for any damage ti the DNA before entering S phase

Question 5

What happens at the S phase.

Answer 5

This is synthesis. The cell replicates its DNA ready to divide by mitosis

Question 6

What happens at the G2 phase?

Answer 6

The cell keeps growing and proteins needed for cell division are made

Question 7

What happens at the G2 checkpoint?

Answer 7

The cell checks whether all the DNA has been replicated without any damage, if it has, the cell can enter mitosis.

Question 8

What happens at the M phase?

Answer 8

Mitosis and cytokinesis

Question 9

What is the G0 phase?

Answer 9

This is when the cell moves out of the cell cycle and this can be permanent or temporary.

Question 10

Why do cells enter the G0 phase?

Answer 10

1) differentiation - a cell becomes specialised to carry out a specific function

2) dna has been damaged so cell can no longer divide

Question 11

What are the functions of mitosis?

Answer 11

1) needed for growth in multicellular organisms

2) repairs damaged tissues

3) a method of asexual reproduction for some plants, animals and fungi.

4) production of new stem cells

5) producing gametes from haploid cells.

Question 12

What are the four stages of mitosis?

Answer 12

1) Prophase
2) metaphase
3) anaphase
4) telophase

Question 13

What stage comes before mitosis in the cell cycle?

Answer 13

Interphase

Question 14

What happens during interphase ?

Answer 14

The cell carries out normal functions but also prepares to divide. The cell’s dna unravels and replicates and organelles are also replicated and it’s ATP content is increased to provide energy for cell division.

Question 15

What happens during prophase?

Answer 15

1) the chromosomes condense getting shorter and fatter and become visible

2) Centrioles start moving to opposite ends of the cell, forming a network of spindle fibres across.

3) the nuclear envelope breaks down and chromosomes lie free in the cytoplasm.

Question 16

What happens during metaphase?

Answer 16

1) the chromosomes line up along the middle of the cell and become attached to the spindle by their centromere.

2) at the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue.

Question 17

What happens during anaphase?

Answer 17

1) the centromeres divide, separating each pair of sister chromatids.

2) the spindles contract, pulling chromatids to opposite ends of the cell, centromere first.

Question 18

What happens during telophase?

Answer 18

1) the chromatids reach opposite poles of the cell.

2) they uncoil and become long and thin again and are now called chromosomes.

3) a nuclear envelope forms around each group of chromosomes so now there are two nuclei.

Question 19

What happens during cytokinesis?

Answer 19

1) the cytoplasm divides. In animal cells, a cleavage furrow forms to divide the cell membrane.

2) there are now two daughter cells that are genetically identical to original cell and to each other.

Question 20

Where does meiosis occur?

Answer 20

A type of cell division that occurs in the reproductive organs to produce gametes.

Question 21

What type of cell does meiosis produce?

Answer 21

Genetically different haploid cells

Question 22

What are the two divisions in meiosis?

Answer 22

Meiosis 1- reduction division
Meiosis 2

Question 23

What occurs before meiosis 1?

Answer 23

Interphase.

Question 24

What happens in interphase before meiosis?

Answer 24

The dna unravels and replicates to produce double armed chromosomes called sister chromatids

Question 25

What happens in prophase 1?

Answer 25

Prophase 1- the chromosomes condense, getting shorter and fatter. They arrange themselves in homologous pairs and crossing over occurs. Centrioles move to opposite ends of the cell, forming spindle fibres. The nuclear envelope breaks down.

Question 26

What happens in metaphase 1?

Answer 26

The homologous pairs like up across the centre and attach to the spindle fibres by their centromeres and independant assortment could occur.

Question 27

What happens in anaphase 1?

Answer 27

The spindles contract, separating the homologous pairs, one chromosome goes to each end of the cell

Question 28

What happens in telophase 1 + cytokinesis ?

Answer 28

A nuclear envelope forms around each group of chromosomes. Then cytokinesis occurs and two haploid daughter cells are produced.

Question 29

What happens in meiosis 2?

Answer 29

The two daughter cells undergo prophase, metaphase, anaphase, telophase 2 and cytokinesis like mitosis. In anaphase 2, the pairs of sister chromatids are seperated and each new daughter cell inherits one chromatid from each chromosome. Four genetically different haploid daughter cells are produced. These are gametes.

Question 30

What leads to genetic variation in meiosis?

Answer 30

1) crossing over 2) independent assortment 3) random fertilisation

Question 31

What is crossing over in meiosis?

Answer 31

During prophase 1 of meiosis 1, homologous pairs of chromosomes come together and pair up. The chromatids twist around each other and bits of chromatids swap over. The chromatids still contain the same genes but now have a different combination of alleles.

Question 32

What is independent assortment of chromosomes?

Answer 32

1) when homologous pairs line up in metaphase 1 ans are seperated in anaphase 1, it’s completely random which chromosome ends up in which daughter cells so the four daughter cells produced have different combinations of maternal and paternal chromosomes.