3.2.2 | ALL CELLS ARISE FROM OTHER CELLS

Question 1

describe the stages of the cell cycle in eukaryotes

Answer 1

interphase:
- (S phase) DNA replicates semi-conservatively
- (G1/G2) number of organelles + volume of cytoplasm increases
mitosis:
- nucleus divides to produce two nuclei with identical copies of DNA produced by the parent cell
cytokinesis:
- cytoplasm and cell membrane divides to form two new genetically identical cells

Question 2

describe the behaviour of chromosomes and role of spindle fibres in mitosis

Answer 2

prophase:
- chromosomes condense become thicker, appear as two sister chromatids joined by centromere
- nuclear envelope breaks down
metaphase:
- spindle fibres attach to chromosomes by their centromere, chromosomes align along equator
anaphase:
- spindle fibres contract, centromere divides and chromatids are pulled to opposite poles of the cell
telophase:
- chromosomes uncoil, nuclear envelopes reform and spindle fibres break down

Question 3

explain the importance of mitosis in an organism

Answer 3

growth of multicellular organisms, replacing cells to repair damaged tissue and asexual reproduction

Question 4

describe how tumours and cancers form

Answer 4

mutations in DNA/genes controlling mitosis can lead to uncontrolled cell division
tumour formed if this results in mass of abnormal cells

Question 5

suggest how cancer treatments control rate of cell division

Answer 5

some disrupt spindle fibre formation/activity so chromosomes can’t attach to spindle by their centromere so chromatids can’t be separated to opposite poles so prevents/slows mitosis
some prevent DNA replication in interphase so can’t make two copies of each chromosomes so prevents/slows mitosis

Question 6

describe how prokaryotes replicate

Answer 6

replication of circular DNA then plasmids
division of cytoplasm to produced 2 daughter cells with single copies of circular DNA and variable number of copies of plasmids

Question 7

describe how viruses replicate

Answer 7

attachment proteins attach to complementary receptors on host cell
inject viral nucleic acid (DNA/RNA) into host cell
infected host cell replicates virus particles:
nucleic acid replicated, cell produces viral protein/capsid/enzymes and virus assembled then released

Question 8

what is a malignant tumour

Answer 8

cancerous tumour which grows quickly, invades other tissues and can break off and spread around the body

Question 9

what is a benign tumour

Answer 9

non-cancerous tumour which grows slower than malignant tumours, kept in one place as it produces adhesions and does not invade other tissues

Question 10

what are the products of mitosis

Answer 10

two genetically identical diploid cells