Cell Division in Eukaryotic + Prokaryotic Cells

Question 1

Describe cell division in multicellular organisms.

Answer 1

• not all cells retain ability to divide
• eukaryotic cells that do retain ability to divide show a cell cycle

Question 2

What are the 3 stages of the eukaryotic cell cycle?

Answer 2

• interphase (G1, S, G2)
• nuclear division (mitosis or meiosis)
• cell division (cytokinesis)

Question 3

What is the movement from 1 stage of the cell cycle to another triggered by?

Answer 3

• chemical signals called cyclins thus making mitosis a controlled process

Question 4

What are the 3 phases (stages) of interphase?

Answer 4

• G1 (growth 1) phase
• S (DNA synthesis) phase
• G2 (growth 2) phase

Question 5

Describe interphase in the cell cycle.

Answer 5

• during G1 phase, cell makes RNA, enzymes + other proteins needed for growth
• during S phase, DNA in nucleus replicates
• during G2 phase, cell continues to grow + new synthesised DNA is checked + any errors repaired

Question 6

Describe what occurs during nuclear division.

Answer 6

• either a eukaryotic cell divides by mitosis to form 2 identical, diploid daughter cells w identical DNA for growth + repair, during DNA replication
• or cell divides by meiosis to form 4 genetically diff. haploid cells (gametes)

Question 7

Why is mitosis important?

Answer 7

• forms 2 genetically identical daughter cells enabling unicellular zygotes to grow into multicellular organisms
• allows damaged cells to be replaced by genetically identical cells so repairs tissues
• allows organisms to reproduce asexually + produce genetically identical offspring

Question 8

What are the 4 key stages of mitosis?

Answer 8

• prophase
• metaphase
• anaphase
• telophase

Question 9

Describe prophase.

Answer 9

• chromosomes condense + become visible
• in animal cells, centrioles separate + move to opposite poles of cell + are responsible for creating spindle fibres, released from both poles
• the nuclear envelope also starts to disintegrate

Question 10

Describe metaphase.

Answer 10

• chromosomes line up along equator of cell + spindle fibres, released from centrioles at each pole, attach to centromere + chromatid

Question 11

Describe anaphase.

Answer 11

• spindle fibres start to retract + pull centromere + chromatids towards opposite poles causing centromere to divide in 2 + pull individual chromatids to opposite poles
• this requires energy from ATP provided by respiration in mitochondria

Question 12

Describe telophase.

Answer 12

• chromosomes at opposite poles of cell start to decondense, becoming longer + thinner
• spindle fibres disintegrate + nuclear envelope starts to reform around each set of chromosomes

Question 13

Describe cell division (cytokinesis).

Answer 13

• cytoplasm splits in 2, forming 2 new genetically identical cells in final stage of cell cycle
• in animal cells a cleavage furrow forms, separating daughter cells
• however in plants, a cell plate forms which expands towards cell wall + fuses w it, separating daughter cells

Question 14

Describe a method for identifying mitotic stages.

Answer 14

• remove tips of garlic roots + place in ethanoic alcohol to prevent mitosis from continuing
• place root tips in warm dilute HCl to soften + loosen root tissue
• transfer root tip to a microscope slide + add a stain (so chromosomes r visible) using a pipette
• place a coverslip on top of root tip + press down to spread out cells so is 1 cell thick meaning light can pass through
• view cells under a microscope

Question 15

What is the equation for mitotic index?

Answer 15

• mitotic index = (NO° of cells in mitosis / total NO° of cells) x100

Question 16

How do you calculate the actual size of root tip cells?

Answer 16

• actual size = size of image / magnification
• nm (x1000) = μm (x1000) = mm (x1000) = m

Question 17

Explain how tumours + cancer are formed.

Answer 17

• an oncogene (mutation in genes that control cell division + cause cancer), causes cell to divide repeatedly + uncontrollably to form a tumour
• benign tumours don’t spread or cause cancer
• malignant tumours spread through body, invading + destroying tissues, + cause cancer
• if cells break off malignant tumour + travel through blood/lymphatic system they can form secondary cancers (metastasis)

Question 18

What are carcinogens?

Answer 18

• agents that may cause cancer (e.g. UV light, tar in tobacco, smoke + X-rays)

Question 19

How do most cancer treatments/drugs work?

Answer 19

• by controlling rate of cell division (mitosis)

Question 20

Describe binary fission (cell division) of prokaryotic cells.

Answer 20

• circular DNA molecule + any plasmids present undergo DNA replication + move to opposite poles of cell
• the cytoplasm divides to produce 2 daughter cells each containing a single copy of circular DNA + a variable NO° of plasmids

Question 21

Why don’t viruses undergo cell division?

Answer 21

• bc they’re non-living

Question 22

What is the structure of a virus?

Answer 22

• a nucleic acid core (DNA or RNA)
• a capsid (protein coat)
• some have an envelope formed from phospholipids of membrane from cell they were made in

Question 23

Describe viral particle replication.

Answer 23

• attachment proteins on surface of virus binds to complementary receptor proteins on surface of host cell
• virus injects its nucleic acid (DNA or RNA) into host cell which uses its nucleic acid + ribosomes to produce new viral particles
• eventually, either host cell bursts open, releasing new viral particles or viral particles leave individually through host cell membrane
• this damages host cell, causing disease