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OCR A LEVEL BIOLOGY > M2, C6 Cell Divisions > Flashcards

M2, C6 Cell Divisions Flashcards

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1
Q

what happens during interphase

A
  • DNA is replicated and checked for errors in the nucleus
  • protein synthesis occurs in the cytoplasm
  • mitochondria grow and divide, increasing in number
  • in plant cells chloroplasts grow and divide
  • normal metabolic process occur like respiration
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2
Q

what are the three stages of interphase

A

G1 - protein synthesis, organelles replicate, cell increases in size
S - synthesis phase: DNA is replicated in the nucleus
G2 - cell continues to increase in size, energy stores increase and duplicated DNA is checked for errors

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3
Q

what stages does the mitotic phase include

A

mitosis - nucleus divides

cytokinesis - cytoplasm divides and two cells are produced

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4
Q

why would a cell enter G0 phase

A
  • for a cell that becomes specialised and no longer is able to divide
  • the DNA could be damaged so is no longer viable
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5
Q

what does it mean if a cell is senescent

A

it can no longer divide

you get more of these cells as you age which leads to the risk of disease

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6
Q

why are their checkpoints in the cell cycle

A

ensure the cell only divides when it has grown to the right size, there are no errors and the chromosomes are in the correct positions

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7
Q

what does the G1 checkpoint check for

A

cell size
nutrients
growth factors
DNA damage

if these are there then the cell enters S phase
if not it enters G0

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8
Q

what does the G2 checkpoint check for

A

cell size
DNA replication
DNA damage

if satisfactory then the cell enters the mitotic phase
if not then it enters resting state

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9
Q

what does the spindle assembly checkpoint check for

A

chromosome attachment to spindle

mitosis doesn’t proceed unless this checkpoint is passed

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10
Q

define mitosis

A

a type of cell division that resuslts in 2 daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth

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11
Q

why is mitosis important

A

growth
repair tissues
asexual reproduction

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12
Q

what is the centromere

A

the region of a chromosome to which the microtubules of the spindle attach during cell division.

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13
Q

what are chromatids

A

each of the two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.

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14
Q

what are the phases of mitosis

A 
prophase
metaphase
anaphase
telophase
cytokinesis
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15
Q

what happens in prophase in mitosis

A

mitosis begins
chromatin condenses and becomes inactive
centrioles migrate in pairs to opposite poles and the nuclear evelope and nucleolus break up

the chromosomes are now tightly coiled and visible as separate bodies under the microscope
the mitotic spindle begins to form at the centrioles

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16
Q

what is chromatin

A

the material of which the chromosomes of organisms other than bacteria (i.e. eukaryotes) are composed, consisting of protein, RNA, and DNA.

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17
Q

what happens during the metaphase in mitosis

A

the mitotic spindle grows further and attaches to the centromere of each chromosome
the fibres then arrange the chromosomes to line up along the cell equator

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18
Q

what happens during anaphase in mitosis

A

the centromere of each chromosome breaks
sister chromatids separate into daughter chromosomes
the cell starts to elongate as cytokinesis begins

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19
Q

what happens during telophase in mitosis

A

new nuclear membranes and nucleoli form

the chromosomes start to unwind back into chromatin and are no longer visible under the microscope

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20
Q

what happens during cytokinesis in animal cells

A

the cytoplasm is divided between the 2 daughter cells to finish the cycle
each new cell enters interphase and resumes its normal functions

Cleavage furrow formed in the middle of the cell. cell-surface membrane pulled inwards by cytoskeleton and fuse forming two cells.

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21
Q

what happens during cytokinesis in plant cells

A

vesicles from the Golgi apparatus begin to assemble between the two nuclear envelopes
the vesicles fuse with each other and the cell surface membrane divides the cell into 2
new sections of the cell wall then form along the new membrane which splits the cell

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22
Q

how are gametes formed

A

meiosis

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23
Q

why is a gamete said to be haploid

A

contains half the chromosome number of the parent cell

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24
Q

what are homologous chromosomes

A

a pair of same chromosomes, one from each parent

have the same genes but can different alleles of each gene

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25
Q

what are alleles

A

different versions of the same gene

the genes have the same locus and the centromeres will be in the same position

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26
Q

in meiosis 1 what happens during prophase

A 
chromosomes condense
nuclear envelope disintegrates
nucleolus disappears
spindle formation begins
homologous chromosomes pair up, forming bivalents
chromatids entangle - crossing over
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27
Q

in meiosis 1, what happens during metaphase

A

homologous pairs of chromosomes assemble along the metaphase plate
the orientation of the pair is random
the maternal or paternal chromosomes can end up facing either pole - independent assortment - leads to genetic variation

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28
Q

in meiosis 1, what happens during anaphase

A

homologous chromosomes are pulled to opposite poles and chromatids stay joined together
the entangled chromatids break off and rejoin - sometimes exchanges DNA
when exchange occurs, recombinant chromatids form
genetic variation arises from a new combination of alleles - sister chromatids are no longer identical

29
Q

in meiosis 1, what happens during telophase

A

chromosome assemble at each pole
nuclear membrane reforms
chromosomes uncoil
cell undergoes cytokinesis and divides into 2 cells

the reduction of chromosome number from diploid to haploid is complete

30
Q

in meiosis 2, what happens during prophase

A

chromosomes that have 2 chromatids condense and become visible again
nuclear envelope breaks down
spindle formation begins

31
Q

in meiosis 2, what happens during metaphase

A

the individual chromosome assemble on the metaphase plate

due to crossing over, chromatids are no longer identical so there is independent assortment and more genetic variation

32
Q

in meiosis 2, what happens during anaphase

A

chromatids of the individual chromosomes are pulled to opposite poles after division of the centromeres

33
Q

in meiosis 2, what happens during telophase

A

chromatids assemble at the poles
chromosomes uncoil and form chromatin again
nuclear envelope reforms and the nucleolus becomes visible
cytokinesis results in division of the cells forming 4 daughter cells
the cells will be haploid due to the reduction division
they are all genetically different from each other and the parent cell

34
Q

what does a differentiated cell mean

A

they are specialised to carry out very specific functions

35
Q

how are erythrocytes specialised

A

have a flattened biconcave shape
increases surface area : volume
essential for transporting oxygen
no nucleus or organelles to maximise space for haemoglobin
flexible to squeeze through narrow capillaries

36
Q

how are neutrophils (type of white blood cell) specialised

A

have a multi-lobed nucleus so they can squeeze through small gaps to get to the site of infection
contain many lysosomes to attack pathogens

37
Q

how are sperm cells specialised

A

tail or flagellum for movement
lots of mitochondria to supply energy
acrosome on the head contains digestive enzymes to break through the egg

38
Q

how are palisade cells specialised

A

contain lots of chloroplasts which can move in the cytoplasm to absorb large amounts of light for photosynthesis
rectangular box shape to tightly pack in a continuous layer
thin cell walls for increased diffusion of co2
large vacuole to maintain turgor pressure

39
Q

how are root hair cells specialised

A

long extensions called root hairs to increase surface area

maximises uptake of water and minerals from the soil

40
Q

how are guard cells specialised

A

when guard cells lose water and become less swollen as a result of osmotic forces - they change shape and the stoma closes to prevent further water loss

cell wall is thicker on one side so cell doesn’t change shape symmetrically as its volume changes

41
Q

what are the 4 main categories of animal tissues

A

nervous tissue
epithelial tissue
muscle tissue
connective tissue

42
Q

how is squamous epithelium tissue specialised

A

very thin - one cell thick
for rapid diffusion
forms the lining of the lungs for diffusion of oxygen into the blood

43
Q

how is ciliated epithelium tissue specialised

A

cilia that move in a rhythmic manner to move mucus along

goblet cells are also present to release mucus to trap pathogens

44
Q

how is cartilage tissue specialised

A

connective tissue
contains elastin and collagen
firm and flexible
prevents ends of bones rubbing together

45
Q

how is muscle tissue specialised

A

able to shorten in length in order to move bones

contains contractile proteins and myofibrils

46
Q

how is epidermis tissue specialised

A

covered by a waxy, waterproof cuticle to reduce loss of water
closely packed cells
contains stomata which can open and close due to the guard cells
allows water, oxygen and carbon dioxide in and out

47
Q

how is xylem tissue specialised

A

composed of dead cells
walls are strengthened by lignin which is waterproof
structural support for plants

48
Q

how is phloem tissue specialised

A

composed of columns of sieve tube cells separated by perforated walls called sieve plates
transported organic nutrients from leaves and stems to parts of the plant where it’s needed

49
Q

define an organ

A

collection of tissues that are adapted to perform a particular function in an organism

50
Q

give examples of animal organ systems

A 
digestive system
cardiovascular system (movement of blood)
gaseous exchange system
51
Q

what organs are involved in the digestive system

A 
oesophagus
rectum
stomach
large intestine
small intestine
liver
mouth
anus
52
Q

what organs are involved in the nervous system

A

nerves

brain

53
Q

what organs are involved in the urinary system

A

bladder
ureter
kidneys
urethra

54
Q

what organs are involved in the circulatory system

A

veins
arteries
heart
capillaries

55
Q

what organs are involved in the respiratory system

A

trachea
bronchi
bronchioles
lungs

56
Q

what organs are involved in the musculoskeletal system

A

muscles

bones

57
Q

what are stem cells

A

undifferentiated cells so they don’t have a specific function
they have the potential to differentiate into a specialised cell

58
Q

what is the term for a stem cells ability to differentiate

A

potency

59
Q

define totipotent

A

these stem cells can differentiate into any type of cell, forming a whole organism
eg. a fertilised egg

60
Q

define pluripotent

A

these stem cells can form all tissue types but not whole organism

61
Q

define multipotent

A

these stem cells can only form a range of cells within a certain type of tissue

62
Q

what stem cells have blood cells derived from

A

stem cells in the bone marrow

63
Q

what are the sources of animal stem cells

A

embyros - these are totipotent

tissues like bone marrow - these are multipotent

umbilical cords - multipotent

64
Q

what are the sources of plant stem cells

A

meristematic tissue (meristems) - found wherever growth is occurring in plants or between xylem and phloem - it is pluripotent

65
Q

what are the potential uses of stem cells

A

heart disease - repair muscle tissue in the heart
type 1 diabetes - for insulin-producing cells
Parkinson’s disease - for dopamine-producing cells in the brain
Alzeihmer’s disease - brain cells
macular degeneration - treat blindness
birth defects
spinal injuries

66
Q

what are stem cells currently being used for

A

treatment of burns - new skin
drug trials - can be tested on stem cells before animals
developmental biology

67
Q

what are the reasons for using stem cells

A
  • saves lives
  • improves peoples lives
  • embryos have been donated, were going to be discarded of anyway
  • could save NHS lots of money as people wouldn’t need medicine or operations
68
Q

what are the reasons against using stem cells

A
  • embryos are destroyed
  • religious objections - belief life begins at conception so destroying embryos is murder
  • costs a lot of money - too much of a risk

OCR A LEVEL BIOLOGY (23 decks)

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