3.2.2 ALL CELLS ARISE FROM OTHER CELLS (MITOSIS)

Question 1

Stages of mitosis in order:

Answer 1

1) prophase
2) metaphase
3) anaphase
4) telophase
(5. Cytokinesis)

Question 2

What happens in prophase?

Answer 2

• chromosomes become visible as they shorten and thicken
• centrioles move to opposite poles, from which spindle fibres form from pole to pole
• together the spindle fibres form spindle apparatus
• nuclear envelope disappears along with nucleolus- chromosomes are left free in the cytoplasm
• plant cells lack centrioles but still form spindle apparatus

Question 3

What happens in metaphase?

Answer 3

• chromosomes pulled to equator of the cell by spindle fibres
• attached to spindle by centromere

Question 4

What happens in anaphase?

Answer 4

• centromeres divide into 2, spindle fibres pull the sister chromatids apart moving to opposite poles
• sister chromatids turn to sister chromosomes
• energy supplied by mitochondria

Question 5

What happens in telophase?

Answer 5

• chromosomes have reached their poles, becoming larger and thinner, eventually not being able to be seen by microscopes
• spindle fibres break down
• nuclear envelope and nucleolus re-forms
• cytoplasm divides into two (cytokenesis)

Question 6

What cells can’t undergo cytokenisis?

Answer 6

Fungal cells

Question 7

What does cytokenisis include in an animal cell?

Answer 7

• involves the formation of a cleavage furrow which pinches the cell into two

Question 8

Mitosis is a…

Answer 8

Controlled process

Question 9

What does uncontrolled cell division lead to?

Answer 9

The formation of tumours and cancers

Question 10

When does a tumour become cancerous?

Answer 10

If it changes from benign to malignant

Question 11

Treatment of cancer:

Answer 11

Chemotherapy and radiotherapy
Directed at controlling the rate of division

Question 12

Cell division in prokaryotes is called….

Answer 12

Binary fission

Question 13

What happens in binary fission?

Answer 13

1. Circular DNA replicates and both copies attach to the cell membrane
2. Plasmids also replicate
3. Cell membrane grows between two DNA molecules and pinches inwards, dividing the cytoplasm into two
4. The new cell wall forms between the two DNA molecules
5. New cells are identical daughter cells each with the same copy of circular DNA but a variable number of plasmids

Question 14

Simple version of binary fission:

Answer 14

• replication of circular DNA and plasmids
• division of the cytoplasm to produce two daughter cells
• each with a single copy of the circular DNA but a variable number of copies of plasmids

Question 15

Viruses are…

Answer 15

Not alive so cannot replicate by themselves

Question 16

How to viruses replicate?

Answer 16

1. Attach to a hosts cell using attachment proteins on their surface
2. Inject their nucleic acid into the host cell
3. The genetic information from the injected viral nucleic acid provides the instructions for the hosts cells metabolic processes to start producing viral components
4. These include nucleic acids, enzymes and structural proteins
5. These can be assembled into a new virus

Question 17

When does DNA replication occur?

Answer 17

During the interphase of the cell cycle

Question 18

Importance of mitosis?

Answer 18

• growth
• repair
• replacement