Cell Division - 16.2

Question 1

How many cells does mitosis produce?

Answer 1

Two new cells

Question 2

What are the three important functions of mitosis?

Answer 2

*Growth - organism can mature from single celled zygote

• Maintenance - cells replace worn out cells
• Repair - Cells regenerate damaged tissues

Question 3

How are the three functions (growth, maintenance, repair) accomplished

Answer 3

Each daughter cell must have correct genetic information

Question 4

What are the cellular events that must take place for daughter cells to be produced?

Answer 4

• Genetic material of one of the parents must be replicated
• The replicated chromatin must be condensed and organized in the nucleus
• One complete set of chromosomes must be divided into each of the two nuclei
• Cytoplasm must divide to produce two complete and functional daughter cells

Question 5

When does DNA replication take place?

Answer 5

S phase of interphase

Question 6

What is prophase?

Answer 6

When the chromatin condenses into tightly packed chromosomes.

Question 7

What are the events that happen in prophase?

Answer 7

• Nuclear membrane breaks down - chromosome is released into the cytoplasm - nucleus disappears
• Centrioles move apart to opposite poles of the cell
• Network of spindle fibers forms between the centrioles
• Microtubules (hollow tubes of protein that facilitate movement of chromosomes within a cell).
• Spindle fibres lengthen with the addition of microtubule subunits (removal will cause them to shorten)

Question 8

What is metaphase?

Answer 8

The spindle fiber guides the chromosomes to the equator or the centre line of the cell.

Question 9

What are the events that happen in metaphase ?

Answer 9

• Spindle fires from opposite poles attach to the centromere of each chromosome
• attach in a way that one sister chromatid faces one pole while the other faces the opposite pole
• Each pair of sister chromatid is considered to be a single chromosome (as long as they are joined at centromere)

Question 10

What is anaphase?

Answer 10

When the centromere splits apart and the sister chromatids separate from one another.

Question 11

What are the events that happen in anaphase?

Answer 11

• The spindle fibre that link the centromeres to the poles of the cell shorten
• as they shorten, sister chromatids are pulled to opposite poles
• Other microtubules in the spindle apparatus lengthen and force the poles of the cell away from each other
• At the end of this phase - one complete diploid set of chromosomes has been gathered at each pole of the elongated cell

Question 12

What happens in Telophase?

Answer 12

Telophase begins when chromatids have reached the opposite poles of the cell.

Question 13

What are the events in telophase?

Answer 13

• The chromatids begin to unwind into longer less visible strands of chromatin
• Spindle fibre breaks down
• Nuclear membrane forms around each new set of chromosomes - nucleous forms within each nucleus

Question 14

What process happens after mitosis?

Answer 14

Cytokenesis

Question 15

What happens during cytokinesis in animal cells?

Answer 15

• Indentation form in the cell membrane along the equator
• Idenation deepens until the cell is pinched into two

Question 16

When does cytokinesis end?

Answer 16

With the separation of two genetically identical daughter cells

Question 17

What is the difference with mitosis and cytokensis in plants and animals?

Answer 17

• Plants do not have centrioles but they have spindle apparatus
• Cell wall does not furrow - cell plate forms between the two daughter nuclei
• Cell plate extends across the diameter of the cell - reinforced by addition of cellulose and proteins

Question 18

What are external factors that “start” and “stop” cell divison?

Answer 18

• Presence of particular hormones
• Availability of nutrients
• Contact with other cells

Question 19

What is a group of diseases that are associated with rapid, uncontrolled cell division?

Answer 19

Cancer

Question 20

What is a tumor?

Answer 20

Fast growing non functional cells as a result of cancer.

Question 21

What allows us to understand the cell cycle better?

Answer 21

• Staining
• Light microscope