Cell division

Question 1

4 phases in the cell cycle

Answer 1

G1 , S , G2 , Mitosis + cytokineses

Question 2

What happens at the G1 checkpoint

Answer 2

• Growth phase
• Check for following :
  cell size, nutrients, growth factors and DNA damage

Question 3

What happens during G1?

Answer 3

• First growth phase
• Organelles synthesised and produced
• Organelles replicate
• Cell grows in size

Question 4

What happens at the G2 checkpoint?

Answer 4

• Checks DNA replication and damage
• Check cell size
• Cell initiates molecular process that signals the beginning of mitosis

Question 5

What happens during the synthesis phase?

Answer 5

DNA is replicated in the nucleus

Question 6

What happens during interphase?

Answer 6

• DNA replicated and checked
• Protein synthesis occurring in cytoplasm
• Mitochondria grow + divide increase amount
• Chloroplasts grow + divide in plant + algal
• Normal metabolic processes of cells occur (respiration)

Question 7

What happens during G0?

Answer 7

• When cell leaves the cycle temporarily or permanently

Question 8

Reasons why G0 can happen

Answer 8

• Differentiation : cell differentiated so no longer able to divide
• DNA of cell is damaged : cell enters a period of permanent cell rest (G0) Majority of cells divide limited times until senescent
• Growing number of senescent cells = age related diseases

Question 9

What is the cell cycle?

Answer 9

• Highly ordered sequence of events resulting in division of cells and formation of two genetically identical daughter cells

Question 10

Why are checkpoints needed?

Answer 10

Control mechanisms of the cell cycle

Question 11

Spindle assembly checkpoint (metaphase checkpoint)

Answer 11

• Happens during mitosis where all chromosomes should be attached to spindles
• Mitosis can not pass until this has happened

Question 12

Copying and separating DNA

Answer 12

• DNA wrapped around proteins called histones (condensed)
• DNA and histone together called chromatin
• Before cell division, DNA of each chromosome must be replicated

Question 13

What happens during prophase (Mitosis)

Answer 13

• Chromatin fibres coil and condense
• Nuclear membrane begins to break down
• Chromosomes shorten and thicken
• Centrioles divide into two and move to opposite ends of cell - spindle formed
• Nuclear envelope disappears

Question 14

What happens during Metaphase (Mitosis)

Answer 14

• Chromosomes moved by spindle fibres to form plane in centre of the cell, Metaphase plate

Question 15

What happens during anaphase (Mitosis)

Answer 15

• Centromeres holding the pair of chromatids in each chromosome divide
• Chromatids moving towards poles, dragged by centromeres the the liquid cytosol

Question 16

What happens during telophase (Mitosis)

Answer 16

• Chromatids reach poles + now called chromosomes
• Two new sets of chromosomes assemble at each pole, nuclear envelope reforms
• Chromosomes start to uncoil and nucleolus is formed

Question 17

What happens during cytokinesis?

Answer 17

Actual division of two cells
Cytoplasm and membrane divide

Question 18

Why is mitosis important?

Answer 18

• Asexual reproduction, offspring produced
• Growth
• Repair (when cells are damaged, replaced)
  e.g. red blood cells + skin cells regularly replaced by new cells

Question 19

What happens during meiosis

Answer 19

• 4 daughter cells which are not identical produced
• Have half the number of chromosomes as parent cell : haploid

Question 20

Why is meiosis important?

Answer 20

• Takes place in sex organs
• Gametes are produced here
• Important to have genetically different gametes
• Promote genetic variation and allow for Natural Selection to take place

Question 21

Prophase 11

Answer 21

• Chromosome condense and become visible again
• Nuclear envelope breaks down and spindle formation

Question 22

Metaphase 11

Answer 22

• Individual chromosomes assemble on metaphase plate
• Independent assortment and more genetic variation

Question 23

Anaphase 11

Answer 23

• Chromatids of individual chromosomes pulled to opposite poles after division of centromeres

Question 24

Telophase 11

Answer 24

• As telophase in mitosis
• Chromosome uncoil and form chromatin again
• Nuclear envelope reforms
• Nucleolus becomes visible

Question 25

What is independent assortment?

Answer 25

• Process where the chromosomes move randomly to separate poles during meiosis

Question 26

What is crossing over?

Answer 26

• Exchange of DNA between paired homologous chromosomes

Question 27

What is a homologous chromosome?

Answer 27

• Paired chromosomes

Question 28

What is an allele?

Answer 28

• Alternative forms of a gene occupying a position on a chromosome

Question 29

Examples of specialised animal cells

Answer 29

• Erythrocytes (biconcave, no nuclei, flexible)
• Neutrophils (multi-lobed nucleus can squeeze through, many lysosomes)
• Sperm cells (flagella, mitochondria, acrosome containing digestive enzymes)

Question 30

Examples of specialised plant cells

Answer 30

• Palisade cells (absorb light, packed, vacuole is large turgor pressure, chloroplasts move)
• Root hair cells (at surface, long extensions)
• Guard cells (lose water during day, change shape prevent further water loss)

Question 31

4 main categories of tissues in animals

Answer 31

• Nervous tissue (transmission of electrical impulses)
• Epithelial cells (cover body surface)
• Muscle tissue (adapted to contract)
• Connective tissue (transport + joining)

Question 32

Different tissues in plants

Answer 32

• Epidermis tissue (cover plant surfaces)
• Vascular tissue (transport of water + nutrients)

Question 33

Stem cell potency

Answer 33

• Totipotent (differentiate into any type and may become a whole organism)
• Pluripotent (form all tissue cells not whole organisms)
• Multipotent (range of cells within a certain type of tissue)