Cell Division

Question 1

What are the two types of cell divisions carried out by eukaryotic cells?

Answer 1

1. Mitosis

2. Meiosis

Question 2

Mitosis

Answer 2

Cell division carried out by eukaryotic cells which produces two genetically identical daughter cells

Question 3

Define “genetically identical”

Answer 3

Exact same copy of DNA as parent cell

Question 4

Uses of mitosis

Answer 4

1. Growth and development

2. Repair of damaged tissue

Question 5

Cell Cycle

Answer 5

Multi-cellular organisms divide following the cell cycle:

1. Interphase (G1, S1, G2)
2. Mitosis (PMAT)

Question 6

Interphase

Answer 6

Gap Phase 1: Cell grows, makes new organelles + proteins
Synthesis Phase: DNA replication (DNA “unravels”)
Gap Phase 2: Cell grows more, + produces more proteins
Cell increases ATP content. ATP provides energy for cell division

Question 7

Prophase

Answer 7

1. Chromosomes condense (become shorter + fatter)
2. Centrioles move to opp ends of cell forming spindle
3. Nuclear envolope breaks down releasing chromosomes into cytoplasm. Chromosomes now freee floating in cytoplasm

Question 8

Metaphase

Answer 8

1. Chromosomes (2 chromatids) line up in middle of cell. Attach to spindle via centromere

Question 9

Anaphase

Answer 9

1. Centromeres divides and the two sister chromatids seperate
2. Spindle contracts and chromatids pulled to opp ends of spindle
3. Chromatids now “V” shaped

Question 10

Telophase

Answer 10

1. Chromatids now at opposite ends of spindle
2. Chromatids uncoil, decondence and become more long and thin, now called chromosomes again
3. Nuclear envolope forms around each set of chromosomes forming 2 new nuclei
4. Cytoplasm divides via cytokenesis.
5. Two new daughter cells form which are genetically identical to each other and the parent cell

Question 11

Cancer

Answer 11

Cancer occurs when a tumour invades surrounding tissue

Question 12

Tumour

Answer 12

This is a result of uncontrolled cell division. This can happen when there is a mutation to a gene which controls the cell cycle

Question 13

Cancer Treatment

Answer 13

Cancer is usually treated by controlling the rate of cell division by interupting the cell cycle which kills tumour cells

The specific stages of the cell cycle which are interrupted include:

Gap Phase 1: This is where cell grows and proteins (e.g. enzymes) are synthesised. Drugs are used (chemotherapy) to prevent the synthesis of enzymes involved in DNA replication which prevents the cell from entering S phase, interupting cell cycle, forcing cell to kill itself

Synthesis Phase: This is where DNA replication occurs. Radiation is used to damage the DNA. During cell cycle, DNA is checked at sevral points. If severe damage deteced, cell kills itself

Question 14

Disadvantages of Cancer Treatment

Answer 14

1. It is difficult to distinguish between cancer cells and normal body cells.
2. Although cancer cells divide much more frequently, some normal body cells do as well (e.g. hair cells)
3. So, it is very likley that some normal body cells will also be killed. Not just tumour cells

Question 15

Mitotic index

Answer 15

The proportion of cells undergoing mitosis

Question 16

Mitotic index formula

Answer 16

mitotic index = no. of cells with visible chromosomes / total no. of cells observed

Question 17

Interpretating mitotic index value

Answer 17

1. Higher mitotic index means lots of cells undergoing mitosis
2. This could mean
   - Lots of repair of damaged tissue
   - Cancerous growth