3.2.2 All cells arise from other cells

Question 1

What are the two types of nuclear division.

Answer 1

Mitosis and meiosis

Question 2

What are the four stages of mitosis.

Answer 2

Prophase, metaphase, anaphase, telophase

Question 3

What happens in prophase?

Answer 3

1. Chromatins coils up and condenses back into chromosomes (becomes visible)
2. Two centrosomes move to each end of the cytoplasm of cell, spindle fibres (long thin tubes filled with proteins) start growing from them, forming a network
3. Old nuclear membrane breaks down, chromosomes lie freely in the cytoplasm

Question 4

What happens in metaphase?

Answer 4

1. Chromosomes line up in the middle (equator), one on top of the other
2. Spindle fibres attach to the centromere of the chromosome - which holds the two chromatids together

Question 5

What happens in anaphase?

Answer 5

1. Centromere divide, splitting the two chromatids.
2. Spindle fibres attached to chromosomes pull chromatids towards the two opposite centrosomes - chromatids appear V-shape

Spindle fibres not attached to chromosomes push against each other to elongate the cell

Question 6

What happens in telophase?

Answer 6

1. Chromatids reach opposite poles on the spindle, chromosomes unwind back into chromatin
2. A nuclear membrane forms around each group of chromosomes - two nuclei forms - they are genetically identical

Question 7

What is the cell cycle and what are the stages?

Answer 7

The process in which a cell divides.
Interphase
Nuclear division

Question 8

What are the three growth stages of interphase?

Answer 8

G1 - Cell doubles in size, making new organelles and proteins, small number of cells may enter G0
(G0) - Cell is resting, not dividing or preparing to divide

S - Synthesis of DNA, cell replicates, ready to divide by mitosis

G2 - Cells keep growing, new centrosome forms - now two in cytoplasm

Cells now wait for signal to start mitosis

Question 9

What is cytokinesis?

Answer 9

The physical process of cell division - centrosomes pull away until cell membrane separates the two cytoplasm

Question 10

What is a tumour caused by?

Answer 10

A mutation in the gene that controls cell division, leading to cells dividing uncontrollable

Question 11

What is cancer?

Answer 11

A tumour that invades surrounding tissues

Question 12

What are the two types of tumours?

Answer 12

Benign - has a boarder, not harmful, doesn’t replace healthy cells

Malignant - cancerous, no boarder, metastasis (spread), replaces healthy cells

Question 13

What are cancer treatments and why are there drawbacks?

Answer 13

Controls the rate of cell division in tumour cells by disrupting the cell cycle

They kill healthy cells as well because they cannot distinguish between tumour and normal cells

However, since tumour cells divide more frequently than healthy cells, it’s more likely to kill tumour cells

Question 14

What are the types of cancer treatment

Answer 14

1. Prevention of synthesis of enzymes needed in DNA replication using chemical drugs - cells can no longer enter synthesise phase, disrupting cell cycle and forcing cell to kill itself
2. Prevention of DNA replication - S phase: DNA will be damaged by radiation/drugs, if severe DNA is detected, the cell will kill itself, preventing further tumour growth
3. Inhibition of spindle formation - prevent metaphase and anaphase as spindles won’t be attached to centromeres

Question 15

Why are cells taken from the root tip when observing mitosis?

Answer 15

There’s a zone of cell division which contains cells undergoing mitosis

Question 16

Why is the root tip firmly squashed when observing mitosis?

Answer 16

Flatten the specimen- making it thin so that individual cells could be absorbed