1.6

Question 1

What is mitosis?

Answer 1

The division of the nucleus to form two genetically identical daughter nuclei, divided into 4 phases; 
Prophase
Metaphase
Anaphase
Telophase

Question 2

Outline the 4 stages of mitosis:

Answer 2

Prophase - chromosomes supercoil & condense to form chromatids, nucleolus disappears, centrioles move to opposite poles, microtubules grow spindles

Metaphase - chromosomes align in the metaphase plate, then attach to spindle fibres by centrosomes

Anaphase - sister chromatids are pulled apart at centromeres by shortening microtubules

Telophase - nuclear membrane forms around each set of chromatid, chromatids uncoil to form chromatin, nucleoli reappear, spindles disintegrate

Question 3

How is cytokinesis different in animal cells than in plant cells?

Answer 3

In animal cells:

• plasma membrane pulled apart by ring of contractile protein microfilaments, forming a cleavage furrow
• when furrow reaches the centre, the cell is pinched apart, forming 2 daughter cells

In plant cells:

• vesicle from Golgi move to the centre & fuse to form a large vacuole which becomes the plasma membrane of the 2 new cells
• cellulose is then divided by exocytosis b/w the 2 new membranes to form new cell wall
• occurs in the cell plate

Question 4

What occurs during interphase?

Answer 4

3 stages
G1: cell growth, metabolic reactions take place like respirations and protein synthesis
S: DNA doubles, chromosomes replicate
G2: more cell growth, mitochondria increase in number, new organelles synthesised

Question 5

What are cyclins?

Answer 5

Cyclins are involved in controlling the cell cycle, they tell the cell when it’s time for division.

Cyclins must reach a threshold in order to move to the next stage

Question 6

What are mutagens, oncogenes and metastasis?

Answer 6

Mutagens: agents which cause genetic mutations, e.g. radiation, chemicals, viruses

Oncogenes: mutation in genes that can be cancerous

Metastasis: when cells from primary tumours get carried to a different part of the body and divide out of control, forming a secondary tumour

Question 7

How can mutations cause cancer?

Answer 7

Several mutations are needed in the same cell for it to become cancerous & divide out of control, forming a mass of cells called a primary tumour