3.2.2 All Cells Arise From Other Cells

Question 1

interphase

Answer 1

• DNA replicates semi-conservatively (S phase), leading to 2 sister chromatids joined at a centromere (genetic content doubled)
• organelles increased
• volume of cytoplasm increased
• protein syntehsis

Question 2

prophase

Answer 2

longest phase in mitosis
- chromosomes condense, becoming shorter/thicker so visible - appear as 2 sister chromatids joined by a centromere
- centrioles move to opposite poles (ends of the cell) forming spindle network
- spindle fibres start to attach to chromosomes by their centromeres
- nuclear envelope disintegrates + nucleolus disappears

Question 3

metaphase

Answer 3

• spindle fibres attach to chromosomes by their centromeres
• chromosomes line up single file along the equator (middle) of cell

Question 4

anaphase

Answer 4

• very fast
• spindle fibres shorten/contract
• contromere divides
• pulling chromatids (from each pair) to opposite poles of cells - centromere first

Question 5

telophase

Answer 5

• chromosomes uncoil, becoming longer/thinner
• nuclear envelope reforms = 2 nuclei
• spindle fibres/centrioles break down

Question 6

cytokinesis

Answer 6

• cytoplasm + cell membrane (normally) divide
• to form 2 new genetically identical daughter cells

Question 7

stages of cell cycle

Answer 7

interphase
(mitosis)
prophase
metaphase
anaphase
telophase
(mitosis ends)
cytokinesis

Question 8

why do some eukaryotic cells not undergo the cell cycle?

Answer 8

• within multicellular organisms, not all cells retain the ability to divide e.g. neurons
• only cells that do retain this ability go through a cell cycle

Question 9

explain the importance of mitosis in the life of an organis

Answer 9

• growth of multicellular organisms by increasing cell number
• replacing cells to repair damaged/replaceworn tissues
• asexual reproduction - identical copies of cells

Question 10

describe how tumours and cancers form

Answer 10

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

Question 11

malignant tumour

Answer 11

cancerous, can spread (metastasis)

Question 12

benign tumour

Answer 12

non-cancerous

Question 13

suggest how cancer treatments control the rate of cell division

Answer 13

some disrupt spindle fibre activity/formation
- so chromosomes can’t attach to spindle by their centromere
- so chromatids can’t be separated to opposite poles (no anaphase)
- so prevents/slows mitosis

some prevent DNA replication during interphase
- so can’t make 2 copies of each chromosome (chromatids)
- so prevents/slows mitosis

Question 14

describe how prokaryotic cells replicate

Answer 14

1. replication of circular DNA
2. replication of plasmids
3. division of cytoplasm to produce 2 daughter cells
   - single copy of circular DNA
   - variable number of copies of plasmids

Question 15

how do viruses replicate

Answer 15

1. attachment proteins attach to complementary receptors on host cell
2. inject viral nucleic acid (DNA/RNA) into host cell
3. infected host cell replicates virus particles:
   - nucleic acid replicates
   - cell produces viral protein/capsid/enzymes
   - virus assembled then released