2.1.6 Cell division, cell diversity and cellular organisation Flashcards
(108 cards)
1
Q
what is the cell cycle
A
- highly ordered sequence of events that takes place in a cell resulting in the division of the cell and forming 2 genetically identical daughter cells
2
Q
what are the stages that the cell cycle is divided into
A
- interphase (G1, G2, S)
- mitosis
- cytokinesis
3
Q
what is interphase
A
- the phase when cells aren’t dividing but rather growing and carrying out major functions like producing enzymes or hormones
> they are actively preparing for cell division
4
Q
what stage does a cell spend majority of its time in
A
- interphase
5
Q
what happens in G1 of interphase
A
- first growth phase:
> proteins needed for organelles to synthesise are produce and organelles replicate
> cell increased in size
6
Q
what happens in G2 of interphase
A
- synthesis phase:
> DNA is replicated in the nucleus
7
Q
what happens in G3 of interphase
A
- second growth phase:
> cell continues to increase in size
> energy stores are increased
> duplicated DNA checked for errors
8
Q
name some of the things that happen in interphase
A
- DNA replication + checking for errors in nucleus
- protein synthesis in cytoplasm
- mitochondria grow + divide
- chloroplast grow + divide in plant
- normal metabolic processes of cells occur
9
Q
what is the mitotic phase
A
- period of cell division
- involves 2 stages:
> mitosis
> cytokinesis
10
Q
what is G0
A
- phase when cell leaves the cycle temporarily or permanently
11
Q
what are some of the reasons G0 can happen
A
- differentiation: cell becomes specialised and no longer able to divide
- DNA of cell may be damaged, so no divide
> some cells that enter G0 can be stimulated to go back into cell cycle and start dividing (lymphocytes in immune response)
12
Q
why is it important that cell only divides when its grown to right size, repl DNA is error free and chromosomes are in correct position during mitosis
A
- to ensure the accuracy of the cell division
> that 2 genetically identical daughter cells are created from the parent
13
Q
what are checkpoints in cell cycle
A
- they are the control mechanisms of cell cycle
- they monitor and verify that processes at each stage of cell cycle have been accurately completed before cell is allowed to progress into next phase
14
Q
what does the G1 checkpoint do + where found
A
- at end of G1 phase
- check for cell size, nutrients, growth, DNA damage
- if requirements satisfied then triggers DNA replication
> if not then enters resting state (G0)
15
Q
what does the checkpoint G2 do + where found
A
- end of G2 phase
- check cell for DNA replication without error
- if checkpoint passed, cell initiates molecular processes signaling beginning of mitosis
16
Q
what does the S checkpoint do
A
- checks whether all chromosomes have been replicated
17
Q
what does metaphase checkpoint do
A
- aka spindle assembly checkpoint
- checks whether all chromosomes have been attached to spindle fibres and are aligned
> mitosis can’t proceed until checkpoint is passed
18
Q
what is mitosis
A
- the nuclear division, to produce 2 genetically identical daughter cells
19
Q
why is mitosis neccessary
A
- for growth
- replacement + repair of tissues in multicellular organisms
- asexual reproduction in plants, animals and fungi
20
Q
before mitosis can occur all the DNA in nucleus is replicated during interphase, how does this happen
A
- a DNA molecule (chromosome) uncoils and replicates producing a pair of sister chromatids held by a centromere
> chromatin now becomes supercoiled + forms visible chromosomes
21
Q
what is chromatin
A
- the DNA wrapped around histone proteins + linear chromosomes is called chromatin
22
Q
name the 4 stages of mitosis
A
- prophase
- metaphase
- anaphase
- telophase
23
Q
describe what happens during prophase
A
- chromatin fibres coil + condense to form chromosomes
- nucleolus (resp for RNA synthesis) disappears
- nuclear membrane breaks down
- centrioles move to each end of cell
- spindle fibres begin to form + attach to centromere
24
Q
describe what happens during metaphase
A
- spindle fibres begin to move chromosomes to the centre of the cell (metaphase plate) and hold them in position
25
describe what happens during anaphase
- centromere divides
- sister chromatids separated + pulled to each end of cell
26
describe what happens in telophase
- chromatids reach poles + now called chromosomes
- 2 new sets of chromosomes assemble and nuclear envelope reforms + creates 2 new nuclei
- chromosomes slowly uncoil + nucleolus formed
- spindle fibres break down
27
describe what happens in cytokinesis
- cell membrane pinches off to form 2 genetically identical daughter cells
28
describe what happens in cytokinesis in animal cells
- cleavage furrow forms around middle of cell
- cell surface membrane pulled inwards by cytoskeleton until it's close enough to fuse around the middle to form 2 cell
29
describe what happens in cytokinesis in plant cells
- Golgi apparatus + secretary vesicle assemble at the same place as the metaphase plate
- vesicles fuse with each other + cell surface membrane + cell divides into 2
- new sections of cell wall form along new sections of membrane
30
what does it mean if a cell is diploid
- have 2 chromosomes of each type
> one from each parent
31
what does it mean if a cell is haploid
- have half the number of chromosomes from parent cell
32
what are alleles
- different versions of the same gene
33
what are gametes formed by
- cell division called meiosis
> nucleus divides to produce 4 daughter cells
> each gamete contains half of the chromosome of parent cell (haploid)
34
what happens in meiosis 1 (general)
- first division
> reduction division when pairs of homologous chromosomes are separated into 2 cells
> each intermediate cell will only contain one full set of genes instead of 2 (haploid)
35
what happens in meiosis 2 (general)
- second division
> pairs of chromatids present in each daughter cell are separated, forming 2 more cells
> 4 haploid daughter cells are produced in total
36
what happens in prophase 1
- chromosomes condense + supercoil
- nuclear envelope breaks
- centrioles move to opposite ends of cell + spindle fibres of tubulin protein start to form
37
what happens in metaphase 1
- bivalents line up at equator
- orientation of each homologous pair on metaphase plate is random
- spindle fibres attach to centromeres
- crossing over of non sister chromatids + alleles are swapped
> independent assortment as homologous pairs arranged randomly (results in genetic variation)
38
what happens in anaphase 1
- members of each pair of homologous chromosomes pulled apart by motor proteins dragging them along tubulin threads to opposite poles
> sections of DNA on sister chromatids that became entangled during crossing over now break off + rejoin (exchange DNA)
> each chromosome consists of 2 chromatids
39
what happens in telophase 1
- nuclear membrane reforms
- 2 new nuclear envelopes form
40
what happens in cytokinesis 1
- cell splits as cytoplasm gets pinched + separated
> forms 2 genetically different daughter cells
41
what happens in prophase 2
- nuclear envelope breaks
- chromosomes condense + coil
- spindle formation begins
42
what happens in metaphase 2
- individual chromosomes assemble on metaphase plate
- due to crossing over, chromatids no longer identical so independent assortment + more genetic variation produced
43
what happens in anaphase 2
- chromatids of individual chromosomes pulled to opposite poles after centromere divides
> dragged by motor proteins along tubulin threads of spindle
> chromatids randomly segregated
44
what happens in telophase 2
- nuclear envelope forms around each of 4 haploid nuclei
45
what happens in cytokinesis 2
- 2 cells split to give 4 haploid cells
> genetically different from each other + parent cell due to process of crossing over + independent assortment
46
what is bivalent
- pair of joined homologous chromosomes present during prophase + metaphase 1 of meiosis
47
in asexually reproducing organisms, where would variation in phenotype likely have come from
- environmental influences
48
what are the 3 opportunities for variation to arise in sexually reproducing organisms
1. crossing over
2. independent assortment
3. random fusion of gametes
49
how does crossing over cause variation
- in prophase 1 crossing over occurs between non-homologous pairs of sister chromatids
> they cross over at points called chiasmata where genes from one chromatid swap with genes from the other chromatid
50
how does independent assortment cause variation
- in metaphase 1 + anaphase 1, homologous bivalents randomly line up + segregate (independent assortment)
> forms varies combinations
51
how does random fusion of gametes cause variation
- random fertilisation during reproduction further diversifies offspring
> as any sperm can fertilize any egg
52
what is differentiation
- the process of a cell becoming specialised
53
what are stem cells
- undifferentiated cell
54
what are specialised cells
- cell that have been differentiated to carry out a specific function
55
where are stem cells found in animals
- embryo
- tissue
56
what are the 2 types of animal stem cells
- embryonic stem cells
- tissue (adult) stem cell
57
what do stem cells divide by + to produce what
- mitosis
- produce identical stem cells or specialised cells
58
what does stem cell self renewal mean
- when a stem cell divided by mitosis to renew itself
> maintains the stem cell pool (so stem cells don't run out)
59
what does it mean when stem cells undergo differentiation
- stem cell divided by mitosis to become differentiated
> replaces dead or damaged cells throughout your life
> important to carry out specific functions
60
where are embryonic stem cells found
- in blastocysts (early stage embryos)
> embryonic stem cells taken from the inner cell mass
61
what type of cells are embryonic stem cells
- at first they're totipotent (very early embryo stage)
- after a while when the blastocyst has formed the cells are now pluripotent so can differentiate into all possible types of specialised cells
62
what does it mean if a stem cell is totipotent
- it can be used to make any cell in the body plus the umbilical cord + placenta
63
where are tissue stem cells found
- skin, brain, bone marrow, muscle, breasts, testicles, intestines, surface of eyes
64
what type of cells are tissue stem cells
- multipotent so can differentiate into certain types of cells
65
what are Induced pluripotent stem cells
- cell taken from body + you add certain genes (genetic reprogramming)
- IPS cell behaves like an embryonic stem cell
> cultures in lab --> differentiation --> all possible types of specialised cells
66
what are some advantages of induced pluripotent stem cells
- patient's own cells used so no risk of rejection
> unlike when using stem cells from embryo where risk of rejection if immune system views stem cell as foreign
67
what is potency
- a measure of how many types of specialised cells a stem cell can make
68
what does it mean if a stem cell is pluripotent
- can make all types of specialised cells in body
69
what does it mean if a stem cell is multipotent
- can make multiple types of specialised cells but not all types
70
what are the levels of organisation in a multicellular organism
specialised cell ---> tissue ---> organs ---> organ system ---> whole organism
71
name some specialised animal cells
- erythrocytes
- neutrophils
- spermatozoa
- epithelial cells
72
describe some features of erythrocytes
- very small (7.5 micrometers)
- flattened biconcave disc shape (large SA:V ratio)
- no nucleus, mitochondria, EPR, cytoplasm
- flexible + well developed cytoskeleton
73
why do erythrocytes having no organelles useful
- most of organelles lost at differentiation
- inc space for haemoglobin molecules that are synthesised within immature erythrocytes whilst they still have all their organelles
> inc oxygen transportation around body
74
why do erythrocytes having a developed cytoskeleton a good feature
- allows them to change shape so can twist + turn + travel through narrow capillaries
75
what are neutrophils
- type of white blood cell making up 50% of white blood cells in body
> play essential role in immune system
76
describe some features of neutrophils
- 10-14 micrometers size + contains multi-lobes nucleus
- attracted + travels through infection sites by chemotaxis
- granular cytoplasm contains many lysosomes that contain enzymes to attack pathogens by phagocytosis
77
why is a lobed nucleus in neutrophils useful
- makes it easier to squeeze through gaps + get to site of infection by allowing twisting + turning
78
what is the function of spermatozoa
- male gametes function is to deliver genetic information to the female game, ovum
79
what are some features of sperm
- many mitochondria
- acrosome (specialised lysosome)
- head of sperm contains haploid male gamete nucleus + very little cytoplasm
80
why do sperm have many mitochondria
- to carry out aerobic respiration + ATP supplies energy for the undulipodium (tail) to move + propel the cell towards the ovum
81
why do sperms having acrosome a good feature
- acrosome (specialised lysosome) contains digestive enzymes that are released to digest the outer protective layer around the ovum, allowing the sperm head to penetrate
82
name some specialised plant cells
- palisade cells
- root hair cells
- guard cells
83
what are palisade cells
- present in mesophyll of leaves + well adapted for photosynthesis
84
what are some features of palisade cells + why is it good
- long + cylindrical : closely pack to form continuous layer with little space for air to circulate
- many chloroplast: light for photosynthesis
- large vacuole: maintain turgor pressure
- thin walls: reduce distance for diffusion of CO2
- cytoskeleton threads + motor proteins to move chloroplasts near upper surface of leaf when light intensity is low
85
what are root hair cells
- epidermal cells on outer layer of young plant roots
86
what are some useful features of root hair cells + why is it good
- hair like projections: inc SA for maximising uptake of water + mineral ions from soil
- special carrier proteins in plasma membrane to actively transport mineral ions
- produce ATP for active transport
87
what are guard cells
- pair of specialised cells within lower epidermis containing chloroplast but can't carry out photosynthesis
> forms small openings called stomata
88
what are some useful features of guard cells + why are they good
- cell wall thicker on one side
- light energy needed to produce ATP that actively transports potassium ions from surrounding epidermal cells into guard cells
> lowers wp so water enters guard cells via osmosis so they can swell + stomata closes
89
what is a tissue
- tissue made up of collection of differentiated cells that have a specialised function
> each tissue adapted for a particular function within the organism
90
what are the 4 main categories of tissues in animals
- nervous tissue: adapted to support transmission of electrical impulses
- epithelial tissue: adapted to cover body surfaces, internal + external
- muscle tissue: adapted to contract + cause movement
- connective tissue: adapted to hold structures together + provide support or as a transport medium
91
what are epithelial tissue made of
- made up of cells that form continuous sheets as cells are bond together by lateral contacts
92
what are some features of epithelial tissue
- no blood vessels: cells receive nutrients by diffusion from tissue fluids in underlying connective tissue
- short cell cycles + divide up to 2/3x a day to replace worn/damaged tissue
- specialised to carry out its functions of protection, absorption, filtration, excretion + secretion
93
describe features of squamous epithelial tissue
- very thin + one cell thick
> forms linings of lungs + allows rapid diffusion of oxygen into blood
94
describe features of ciliated epithelial cells
- have cilia that move in rhythmic manner + line trachea
> sweeps mucus away from lungs
95
describe features of cartilage
- contains fibres of proteins elastin + collagen
- firm, flexible connective tissue composed of chondrocyte cells embedded in an extracellular matrix
96
where can cartilage be found
- outer ear
- nose
- ends of (and between) bones
97
what are the 3 types of cartilage
- hyaline forms embryonic skeleton covering ends of long bones in adults, joins ribs to sternum, found in nose, trachea + larynx (voice box)
- fibrous occurs in discs between vertebrae in back bone (spine) + knee joint
- elastic makes up outer ear (pinna) + epiglottis (flap cover over larynx when swallowing)
98
what are some features of muscle tissue
- well vascularised (many blood vessels)
- muscle cells are celled fibres that elongated + contain special organelles called myofilament allowing muscle to contract (shorten in length)
> needed in order to move bones which move diff parts of body
99
what are the 3 diff types of muscle tissue
- skeletal muscles: packaged by connective tissue sheets + joined to bones by tendon, contains myofibrils that contain contractile proteins
- cardiac muscle: makes up wall of heart allowing it to beat + pump blood
- smooth muscle: occurs in walls of intestine, blood vessels etc + allows substances to move along the tracts
100
what is epidermal tissue + features
- consists of flattened cells, apart from guard cells + no chloroplast
- forms protective layer over leaves, stems + roots
- usually covered by waxy, waterproof cuticle, reducing water loss
101
what is vascular tissue
- concerned with transport of water + mineral in plants
- xylem + phloem present in vascular bundles
102
what are some features of xylem tissue
- transports water + mineral ions throughout plant
- tissue composed of vessel elements which are elongated dead cells
- walls strengthened with waterproof lignin providing structural support for plants
103
what are some features of phloem tissue
- transports organic nutrients (sucrose) from leaves + stems to other parts of plants'
- composed of sieve tube elements separated by perforated walls called sieve plates
104
what is meristematic tissue
- contains stem cells from which other plant tissues can be derived by cell differentiation
105
where is meristematic tissue found
- root + shoot tips
- in cambium of vascular bundles
106
what is an organ
- a collection of tissues that are adapted to perform a particular function in an organism
107
what are some plant organs + functions
- leaf: photosynthesis
- roots: anchors in soil, absorption of mineral ions + water, storage
- stem: support, transportation of substances, storage
- flower: sexual reproduction
108
what are some examples of organs in animals
- digestive system: breaks molecules, absorbs nutrients, removes waste (undigested material)
- cardiovascular system: transports blood around body, effective transport system for substances
- gaseous exchange system: air into body, O2 for respiration, CO2 removal
