Chapter 6 - Cell Division

Question 1

What are the 2 main stages of the cell cycle of eukaryotic cells?

Answer 1

Interphase + Mitotic Phase

Question 2

What is Interphase?

Answer 2

The long period in which the cell is not dividing

Question 3

What is the Mitotic Phase?

Answer 3

The period of cell division - split into 2 stages: Mitosis, where the nucleus is divided, and Cytokinesis, in which the cytoplasm divides and two new cells are produced.

Question 4

List 3 things that occur during interphase

Answer 4

• Protein Synthesis occurs in cytoplasm.
• mitochondria grow and divide within the cytoplasm.
• normal metabolic processes of cells occur.

Question 5

What are the 3 stages of interphase?

Answer 5

G1 - cell increases in size
S - (synthesis) - DNA replicated in nucleus
G2 - 2nd growth phase - the cell continues to increase in size, duplicated DNA checked for errors.

Question 6

What is the G0 phase for?

Answer 6

When a cell leaves the cell cycle, either temporarily or permanently.

Question 7

Why does the G0 phase occur?

Answer 7

Differentiation - A cell that becomes specialised to carry out a particular function (differentiated) is no longer able to function / divide.
Damaged DNA - damaged cells can no longer divide and enter state of permanent cellular arrest (G0)

Question 8

What are Checkpoints?

Answer 8

Control mechanisms of the cell cycle

Question 9

What is the G1 checkpoint?

Answer 9

At the end of the G1 phase, if cell satisfies requirements of checkpoint, then DNA replication (S) is triggered.

Question 10

What is the G2 checkpoint?

Answer 10

For the cell to pass this checkpoint, it must satisfy a number of requirements, e.g. if DNA has been replicated without error; if these are satisfied, then cell is signalled to begin mitosis.

Question 11

What is Spindle Assembly checkpoint?

Answer 11

At metaphase in mitosis, where the spindle fibres should have formed - Mitosis cannot proceed until this checkpoint is passed.

Question 12

What is Mitosis?

Answer 12

The division of the nucleus, ensuring that both daughter cells produced are genetically identical.

Question 13

True or False - mitosis is necessary for asexual reproduction.

Answer 13

True

Question 14

How do prokaryotic cells divide?

Answer 14

Binary Fission

Question 15

What are the four stages of mitosis?

Answer 15

Prophase, Metaphase, Anaphase, Telophase.

Question 16

What occurs during prophase?

Answer 16

• Nucleolus dissapears
• chromatin fibres condense to form chromosomes
• Protein microtubules form spindle-shaped structures
• centrioles are cylindrical bundles of proteins - they migrate to opposite poles of the cell.
• By the end of prophase, the nuclear envelope has dissappeared.

Question 17

What occurs during metaphase?

Answer 17

• Chromosomes are moved by the spindle fibres to form a plane in the middle of the cell.
• this is called the metaphase plate.

Question 18

What occurs during anaphase?

Answer 18

• Centromeres divide, and chromatids are seperated to oppposite sides of cell.
• chromatids form ‘v’ shape due to being dragged by centromeres through liquid cystol.

Question 19

What occurs during Telophase?

Answer 19

• chromatids have now reached poles and have become chromosomes
• nuclear envelope reforms around them
• cytokinesis can begin.

Question 20

What is cytokinesis?

Answer 20

The actual division of the cell into 2 seperate cells.

Question 21

How does cytokinesis work in animal cells?

Answer 21

• Cleavage furrow forms.

- cell-surface membrane pulled inwards by cytoskeleton until it fuses at the middle, creating 2 cells.

Question 22

How does cytokinesis work in plant cells?

Answer 22

• vesicles created by golgi apparatus fuse with one another to the cell membrane, which divides the cell into 2
• new sections of cell wall form around the new sections of membrane.

Question 23

Why can plant cells not form a cleavage furrow?

Answer 23

They have strong cellulose cell walls, so it is not possible for them to be manipulated by the cytoskeleton.