3.2.2 All cells arise from other cells

Question 1

what is the purpose of mitosis?

Answer 1

• asexual reproduction
• growth of tissues
• replacement of lost cells
• repairing damaged tissue

Question 2

what are the three stages of the cell cycle?

Answer 2

• interphase
• mitosis
• cytokinesis

Question 3

what happens during interphase?

Answer 3

• cell grows/elongates
• DNA is uncondensed and replicated so each cell will have the same amount
• organelles are replicated

Question 4

what are the three stages of interphase?

Answer 4

• G1 (gap 1)
• S (synthesis)
• G2 (gap 2)

Question 5

chromosomes are not ____ during interphase because?

Answer 5

• visible
• DNA is uncondensed

Question 6

what happens during the G1 phase?

Answer 6

cell elongates and new organelles and proteins are made

Question 7

what happens during the S phase?

Answer 7

cell replicates its DNA

Question 8

what happens during the G2 phase?

Answer 8

cell keeps elongating and proteins needed for cell division are made

Question 9

what is a centromere?

Answer 9

holds two sister chromatids together

Question 10

what are the four stages of mitosis?

Answer 10

• prophase
• metaphase
• anaphase
• telophase

Question 11

what happens during prophase?

Answer 11

• chromosomes condense and become visible (DNA is coiled tightly around proteins called histones)
• nucleolus disappears
• nuclear envelope breaks down
• centrioles separate and move to opposite poles of the cell
• centrioles start to produce spindle fibres

Question 12

what happens during metaphase?

Answer 12

• chromosomes align along the equator of the cell
• spindle fibres released from centrioles attach to the centromere and chromatids

Question 13

what happens during anaphase?

Answer 13

• spindle fibres retract and pull the centromere and chromatids towards the opposite poles
• this causes the centromere to divide in two and the individual chromatids are pulled to each opposite pole
• CHROMATIDS SEPARATE, CHROMOSOMES DO NOT SEPARATE
• requires ATP which is provided by respiration

Question 14

what happens during telophase?

Answer 14

• chromosomes are now at each end of the cell and become longer and thinner again
• nuclear envelope begins to reform around each new group of chromosomes

Question 15

what happens during cytokinesis?

Answer 15

• cytoplasm divides
• two genetically identical diploid cells are formed

Question 16

what happens during binary fission?

Answer 16

• circular DNA loop is replicated
• plasmids are replicated
• cytoplasm divides

Question 17

what is cancer?

Answer 17

mutations in the genes that control cell division can cause cells to grow out of control

Question 18

what is a mutation?

Answer 18

a change to the base sequence of DNA

Question 19

what causes mutations?

Answer 19

• mutagens such as ionising radiation from UV rays
• carcinogenic chemicals

Question 20

how are cancer cells different to normal cells in structure and function?

Answer 20

they either die through apoptosis or can be destroyed by the immune system

Question 21

how are tumours formed?

Answer 21

uncontrolled cell division causes cells to keep on dividing and they layer on top of each other

Question 22

how tumours can harm the body?

Answer 22

• can cause blockages which damage organs they grow in
• they can cause damage to other organs

Question 23

why do tumours need their own blood supply?

Answer 23

• rate of cell division is very high which requires lots of oxygen
• however, blood supply often cannot meet oxygen demand
• so tumours suffer from low oxygen

Question 24

what are the two types of tumours?

Answer 24

benign and malignant

Question 25

what are the characteristics of benign tumours?

Answer 25

• tumour grows slowly and is kept in one place
• do not invade other tissues and start tumours in other organs

Question 26

what are the characteristics of malignant tumours?

Answer 26

• grows quickly
• will invade other tissues and can break off and spread around the body causing tumours in other organs (metastasis)

Question 27

what is the key difference between benign and malignant tumours?

Answer 27

malignant tumours metastasise, benign tumours do not

Question 28

how do cancer treatments generally work?

Answer 28

they control the rate of cell division by targeting the cell cycle to try to stop it

Question 29

what is the problem with cancer treatments?

Answer 29

• they cannot distinguish between cancer cells and normal body cells so kill both
• however, cancer cells have a faster rate of cell division so are more likely to be affected by cancer treatment

Question 30

what are 3 examples of cancer treatments?

Answer 30

• chemotherapy
• radiotherapy (and some chemotherapy drugs)
• drugs which prevent spindle fibres from forming

Question 31

how does chemotherapy work?

Answer 31

• prevents the synthesis of enzymes required for DNA replication
• stops the cell cycle before the S phase

Question 32

how does radiotherapy work?

Answer 32

• damage DNA
• so the cell will not pass through the checkpoints in the S phase
• forces the cell to kill itself (apoptosis)

Question 33

how do viruses replicate (long)?

Answer 33

• virus detects host cell by recognising protein markers on its membrane
• virus attaches itself to the cell using attachment proteins
• virus injects genetic material into the cell
• cell replicates the genetic material and makes new viral proteins
• virus leaves cells by bursting it (lysis) using some of the cell’s membrane to form itself

Question 34

how do viruses replicate (short)?

Answer 34

• inject their nucleic acid into the host cell
• infected host cell replicates the virus particles