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OCR A-Level Biology > Chap 6 - Cell Division > Flashcards

Chap 6 - Cell Division Flashcards

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1
Q

List the stages of the cell cycle in order and outline what happens at each stage.

A
  • interphase –> period of normal functioning, growth and DNA replication
  • mitotic phase (nucleus and cytoplasm divide) –> mitosis and cytokinesies - period of cell division
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2
Q

List 3 stages of interphase in order and describe what happens at each stage.

A
  • G1 - proteins from which organelles are synthesised are produced, organelles replicate and cell increases in size
  • S - synthesis phase - DNA is replicated in the nucleus
  • G2 - cell continues to increase in size, energy stores increased, duplicated DNA checked for errors
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3
Q

List 2 stages of mitotic phase, outline what happens at each stage.

A
  • mitosis - nucleus divides
  • cytokinesis - cytoplasm divides and two cells are produced
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4
Q

What 3 reasons might a cell enter G0

A
  • damaged DNA - damaged cells cannot divide
  • differentiation - specialised cells that carry out specific function cannot divide
  • as you age, cells need to be regulated
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5
Q

Define the G0 stage

A

the phase when cell leaves the cell cycle temporarily or permanently

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6
Q

Outline the role of checkpoints to control the cell cycle.

A
  • ensures that a cell only divides when it has grown to the right size
  • ensures that the replicated DNA is error free
  • ensures that chromosomes are in correct positions during mitosis
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7
Q

Give 3 examples of cell cycle checkpoints.

A
  • G1 checkpoint
  • G2 checkpoint
  • M checkpoint (spindle assembly checkpoint)
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8
Q

State where G1 checkpoint occurs, what is checked at the checkpoint and what happens if cell passes/fails.

A
  • checks: cell size, nutrients, growth factors, DNA dmg
  • if requirements satisfied - DNA replication begins
  • if requirements not satisfied - cell enters G0
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9
Q

State where G2 checkpoint occurs, what is checked at the checkpoint and what happens if cell passes/fails.

A
  • checks: cell size, DNA replication, DNA damage
  • if requirements satisfied - molecular processes that signal beginning of mitosis initiated
  • if requiremetns not satisfied - cell pauses at G2 to try and repair, if irreparable cell undergoes apoptosis
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10
Q

State what is checked at M checkpoint, and what happens if cell passes/fails.

A
  • checks if all chromatids are correctly attached to spindle fibers
  • if requirements satisfied - cell continues with mitosis
  • if requirements not satisfied - mitosis paused, repair attempted
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11
Q

Define mitosis

A

nuclear division stage in mitotic phase of the cell cycle

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12
Q

Define chromosome

A
  • structure of condensed and coiled DNA in the form of chromatin
  • become visible under light microscope when preparing to divide
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13
Q

Define chromatids

A

one of two halves of a replicated chromosome

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14
Q

Define sister chromatids

A

identical copies formed by DNA replication of a chromosome with both copies joined together by a common centromere

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15
Q

Define centromere

A

region at which two chromatids are held together

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16
Q

Define spindle fibres

A

structures made of microtubules that organise chromosomes and pull them apart to opposite poles during mitosis

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17
Q

Define homologous pairs

A

matching pair of chromosomes, one inherited from each parent

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18
Q

Describe how DNA is packaged in a chromosome

A
  • DNA is wound around proteins (histones) making it more compact - chromatin
  • During interphase, chromatin is decondensed
  • During mitosis - chromatin is condensed - chromosomes
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19
Q

List the stages of mitosis in order

A
  • prophase
  • metaphase
  • anaphase
  • telophase
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20
Q

Describe what occurs during prophase.

A
  • chromatin fibers begin to coil & condense forming chromosomes (visible if stained)
  • nucleolus disappears, nuclear membrane starts breaking down
  • protein microtubules form spindle fibers
  • if cell has centrioles, they migrate to opposite poles of cells
  • spindle fibers attach to specific areas on centromeres, start moving chromosomes to center
  • by the end, nuclear envelope has disappeared
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21
Q

Describe what occurs during metaphase

A

chromosomes are moved by spindle fibers and line up along the equator of the cell

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22
Q

Describe what occurs during anaphase

A
  • centromeres holding pairs of chromatids in each chromosome divide
  • chromatids separated - pulled to opposite ends by shortening of spindle fibers
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23
Q

Describe what occurs during telophase

A
  • the two new sets of chromosomes asemble at each pole
  • nuclear envelope reforms around chromosomes
  • chromosomes start to uncoil, nucleolus is formed
  • cytokinesis begins
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24
Q

Explain the role of centrioles and spindle fibers in mitosis.

A
  • centrioles organise spindle fibers which are attached to them
  • spindle fibers pull chromatids to opposite poles and ensure even chromosome distribution between daughter cells
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25
Q

Describe the process of cytokinesis in animal cells.

A
  • cleavage furrow forms around middle of the cell
  • plasma membrane pulled inwards by cytoskeleton until close enough to fuse around middle
  • two cells are formed as a result
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26
Q

Describe the process of cytokinesis in plant cells.

A
  • vesicles from Golgi assemble along equator (metaphase plate)
  • vesicles fuse with each other and cell surface membrane, dividing the cell into two
  • new sections of cell wall form along new sections of membrane
  • (cleavage furrow cannot form because plant cells have cell walls)
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27
Q

Compare animal and plant cytokinesis.

A
  • animal cells: cleavage furrow, plant cells do not because of cell wall and high internal pressure
  • plant cells: vesicles for cytokinesis
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28
Q

Describe the purpose of mitotic cell division.

A
  • ensures that both daughter cells produced when a parent cell divides are genetically identical
  • necessary when all of the daughter cells have to be identical
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29
Q

List 4 roles of mitosis.

A
  • growth of organisms
  • repair/Replacement of tissues
  • embryo development
  • asexual reproduction (production of genetically identical offspring from one parent in multicellular organisms)
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30
Q

Define diploid

A

two complete sets of chromosomes, one from each parent

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31
Q

Define haploid

A

containing one chromosome from each homologous pair

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32
Q

Define gamete

A

haploid sex cell produced by meiosis in organisms that reproduce sexually

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33
Q

Define zygote

A
  • initial diploid cell formed when two gametes are joined by sexual reproduction
  • earliest stage of embryonic development
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34
Q

Define meiosis

A
  • nuclear division for the purpose of gamete production
  • nucleus divides twice resulting in forming four haploid cells from one diploid cell
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35
Q

Define meiosis

A
  • nuclear division for the purpose of gamete production
  • nucleus divides twice resulting in forming four haploid cells from one diploid cell
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36
Q

Define reduction division

A

where the chromosome number is halved from diploid to haploid (first meiotic division)

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37
Q

Explain the role of meiosis in life cycles.

A
  • production of gametes which allows sexual reproduction
  • ensures all organisms produced via sexual reproduction contain correct # of chromosomes - if this didn’t occur: # of chromosomes would double with every round of reproduction
  • produces genetic variation
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38
Q

State the ways in which meiosis produces variation.

A
  • crossing over during prophase 1
  • independent assortment of chromosomes in metaphase 1
  • independent assortment of chromatids in metaphase 2
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39
Q

Suggest the importance of the creation of different allele combinations in populations.

A
  • different phenotypes will be produced
  • reduces the chances of a population going extinct - more likely that some individuals posess advantageous characteristics to help them survive and adapt
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40
Q

Define homologous chromosomes.

A

matching pair of chromosomes, one inherited from each parent

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41
Q

Define bivalent

A

a pair of homologous chromosomes during (crossing over)

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42
Q

Define crossing over

A

exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring

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43
Q

Define chiasmata

A

points at which chromatids break and rejoin

44
Q

Define recombination

A
  • process where pieces of DNA are broken and recombined to produce new combinations of alleles
  • formed by crossing over of chiasmata in meiosis
45
Q

State the stages of meiosis in order

A
  • prophase 1
  • metaphase 1
  • anaphase 1
  • telophase 1
  • prophase 2
  • metaphase 2
  • anaphase 2
  • telophase 2
46
Q

What happens at P1?

A
  • chromosomes condense, nuclear envelope disintegrates, nucleolus disappears
  • spindle formation begins
  • homologous chromosomes pair up, forming bivalents & crossing over occurs
47
Q

What happens at M1?

A
  • homologous pairs assemble along metaphase plate
  • independent assortment occurs
48
Q

What happens at A1?

A
  • homologous chromosomes pulled to opposite poles and chromatids stay joined to each other
  • entangled sections of DNA on non-sister chromatids break off and rejoin at chiasmata, resulting in formation of recombinant chromatids
49
Q

What happens at T1?

A
  • chromosomes assemble at each pole, nuclear membrane reforms
  • chromosomes uncoil
  • cytokinesis occurs, cell divides into two
  • reduction of chromosome number from diploid to haploid is complete
50
Q

What happens at P2?

A
  • chromosomes that still consist of two chromatids condense and become visible
  • nuclear envelope breaks down, spindle formation begins
51
Q

What happens at M2?

A
  • individual chromosomes assemble on metaphase plate
  • due to crossing over, chromatids are not identical - independent assortment occurs
52
Q

What happens at A2?

A

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

53
Q

What happens at T2?

A
  • chromatids assemble at poles, uncoil and form chromatin
  • nuclear envelope reforms, nucleolus is visible again
  • cytokinesis results in division of the cells forming four daughter cells in total
  • daughter cells will be haploid and genetically different from each other & from parent cell
54
Q

Describe the process of crossing over and explain how it produces genetic variation.

A
  • homologous chromosomes pair up, forming a bivalent
  • non-sister chromatids become entangled at points called chiasmata
  • they break off and re-join, sometimes resulting in an exchange of DNA forming recombinant chromatids with different combinations of alleles and therefore genetic variation
55
Q

Describe the process of random independent assortment and explain how it produces genetic variation.

A
  • orientation of each homologous pair on metaphase plate is random and independent of any other homologous pair
  • maternal or paternal chromosomes can end up facing either pole
  • this means that the daughter cells can end up with any combination of maternal and paternal chromosomes hence why it produces genetic variation
56
Q

Outline the levels of organisation of a multicellular organism in order.

A

specialised cells - tissues - organs - organ systems - whole organisms

57
Q

Define specialised.

A

having particular structure to serve a specific function

58
Q

Define differentiated

A

specialised to carry out very specific functions

59
Q

Define cell

A

the smallest structural and functional unit of an organism

60
Q

Define tissue

A

a collection of cells, of one or more types, working together to perform a function

61
Q

Define organ

A

a collection of different tissues working together to perform a function

62
Q

Define organ system

A

a collection of organs working together to perform a function

63
Q

Explain why multicellular organisms have specialised cells.

A
  • multicellular organisms are complex and require different organ systems to function
  • specialised cells carry out their functions very efficiently
64
Q

Describe how erythrocytes are specialised for their function.

A
  • flattened biconcave shape - increases SV ratio
  • flexible - able to squeeze through narrow capillaries
  • no nuclei & many other organelles in mammals - more space for haemoglobin that carries oxygen
  • these features are all essential for their role of transporting oxygen around the body
65
Q

Describe how neutrophils are specialised for their function.

A
  • multi-lobed nucleus to squeeze through small gaps to get to the site of infection
  • granular cytoplasm contains many lysosomes to contain enzymes used to attack pathogens
  • these features allow neutrophils to combat infections as part of the immune system
66
Q

Describe how sperm cells are specialised for their function.

A
  • tail/flagellum - capable of movement
  • many mitochondria - energy supply for swimming
  • acrosome - contains digestive enzymes to allow sperm to penetrate the ovum and fertilise
  • these features all allow the sperm cell to deliver genetic information to the female gamete
67
Q

Describe how palisade cells are specialised for their function.

A
  • chloroplasts - absorb large amounts of light for photosynthesis
  • rectangular box shape - closely packed to form continuous layer
  • thin cell walls - increased rate of diffusion of CO2
  • large vacuole - maintain turgor pressure
  • chloroplasts able to move within cytoplasm to absorb more light
  • these features allow the cells to maximise the rate of photosynthesis of the plant
68
Q

Describe how root hair cells are specialised for their function.

A
  • long extensions (root hairs) - increase surface area of cell
  • this feature maximises the uptake of water and minerals from the soil - its function
69
Q

Describe how guard cells are specialised for their function.

A
  • they form small openings on surfaces of leaves - stomata
  • stomata allow CO2 to enter plants but also allow water to exit plants
  • when the cells lose water, they become less swollen due to osmotic forces, change shape and stoma closes to prevent further water loss from plant
  • cell wall is thicker on one side so the cell does not change shape symmetrically as volume changes
70
Q

State the 4 main categories of tissues in animals.

A
  • nervous tissue - support transmission of el. impulses
  • epithelial tissue - cover body surfaces, internal and external
  • muscle tissue adapted to contract
  • connective tissue - adapted to hold tissues together/as a transport medium
71
Q

Describe how squamous epithelium is specialised for its function.

A
  • made up of specialised squamous epithelial cells
  • very thin bc it is one cell thick & the cells are flat - small diffusion distance
  • its present when rapid diff. across a surface is essential (lining of lungs)
72
Q

Describe how ciliated epithelium is specialised for its function.

A
  • made up of ciliated epithelial cells & goblet cells
  • cilia (hair-like structures) - move in rythmic manner, causing mucus to be swept away from the lungs
  • goblet cells - release mucus to trap unwanted particles from the air
  • the function of the tissue is to prevent particles & pathogens from reaching the alveoli once inside lungs
  • found in the trachea
73
Q

Describe how ciliated epithelium is specialised for its function.

A
  • made up of ciliated epithelial cells & goblet cells
  • cilia (hair-like structures) - move in rythmic manner, causing mucus to be swept away from the lungs
  • goblet cells - release mucus to trap unwanted particles from the air
  • the function of the tissue is to prevent particles & pathogens from reaching the alveoli once inside lungs
  • found in the trachea
74
Q

Describe how cartilage is specialised for its function.

A
  • firm, flexible connective tissue composed of chondrocyte cells embedded in extracellular matrix containing elastin & collagen
  • this helps prevent ends of bones from rubbing together & causing damage
  • found in outer ear, nose, ends of & between bones
75
Q

Describe how muscle tissue is specialised for its function.

A

skeletal muscle fibres contain myofibrils that contain contractile proteins - allow muscle tissue to contract in order to move bones - moves diff parts of the body

76
Q

Describe how epidermis tissue is specialised for its function.

A
  • single layer of closely packed cells that covers surface of plants
  • covered by waxy waterproof cuticle - reduces loss of water
  • stomata (formed by guard cells) - allow CO2, H2O and O in and out
77
Q

Describe how xylem tissue is specialised for its function.

A
  • vascular tissue responsible for transport of water and minerals throughout plants
  • vessel elements (elongated dead cells) walls of them strengthened with lignin - structural supoport for plants
78
Q

Describe how phloem tissue is specialised for its function.

A
  • vascular tissue in plants responsible for transport of organic nutrients (sucrose) from leaves and stems where it is made to other parts of the plant
  • composed of columns of sieve tube cells separated by perforated walls (sieve plates)
79
Q

State 3 examples of organ systems in animals and for each describe their funciton.

A
  • digestive system - takes in food, breaks down large insoluble molecules into small soluble ones, absorbs nutrients into the blood, retains water needed by body and removes undigested material from body
  • cardiovascular system - moves blood around the body to provide a transport system for the substance it carries
  • gaseous exchange system - brings are into the body so O can be extracted for respiration and CO2 can be expelled
80
Q

Define stem cell

A

undifferenciated cell with the potential to differentiate into a variety of the specialised cell types of the organism

81
Q

Define undifferentiated

A

unspecialised cell originating from mitosis or meiosis

82
Q

Define totipotent

A

stem cells capable of dividing to produce all the cell types to form a whole organism

83
Q

Define pluripotent

A

stem cells capable of dividing to produce all cell types but not the extra-embryonic membranes so not a whole organism

84
Q

Define multipotent

A
  • stem cells capable of dividing to produce several cell types
  • adult stem cells are an example
85
Q

Define embryonic stem cell

A

also known as pluripotent stem cells

86
Q

Define tissue (adult) stem cells.

A

also known as multipotent stem cells

87
Q

Describe the characteristic abilities of stem cells compared to specialised cells.

A
  • stem cells are able to undergo cell division again and again indefinitely, specialised cells are not able to undergo cell division at all
  • they are able to differentiate into other cell types, specialised cells are not
88
Q

Explain the importance of stem cells and why their activity must be carefully controlled.

A
  • they are the source of new cells for growth, development and tissue repair
  • if they dont divide fast enough - tissues not efficiently replaced - ageing
  • if they too quickly without control - tumors which could lead to cancer
89
Q

State the 3 types of stem cell and give examples of where they occur in animals.

A
  • totipotent - zygote and the 8/16 cells from its first few mitotic divisions
  • pluripotent (embryonic stem cells) - early embryos
  • multipotent (adult stem cells) - bone marrow
90
Q

State where stem cells occur in plants and state which potency they have.

A
  • found in meristematic tissue (meristems) - wherever growth is occurring in plants
  • this tissue also found between xylem and phloem - vascular cambium
  • they’re pluripotent
91
Q

Outline how a cell becomes specialised.

A
  • stem cells in the cell cycle replicate indefinitely until
  • at one point, specific genes within a stem cell activate, causing it to differentiate by expressing features required for its function and become specialised
  • this cell has entered G0 once specialised and cannot divide anymore
92
Q

Explain why it is important for erythrocytes and neutrophils to be constantly produced.

A
  • erythrocytes are essential for transport of oxygen around the body, since they have no nucleus - short lifespan (120 days) so they need to be replaced constantly
  • neutrophils have an important role in immune system and only live about 6 hours so they must constantly be replaced (even more produced when infected)
93
Q

Outline how xylem vessels and phloem sieve tubes are produced from meristems.

A
  • meristematic tissue located between xylem and phloem tissues - vascular cambium
  • cells originating from this region differentiate into diff cells present in xylem and phloem tissues
94
Q

List 7 diseases that stem cells have the potential to treat.

A
  • heart disease
  • type 1 diabetes
  • parkinson’s disease
  • alzheimer’s disease
  • macular degeneration
  • birth defects
  • spinal injuries
95
Q

Suggest how stem cells could be used to treat heart disease.

A

can use stem cells to repair damage in muscle tissue in heart caused by heart attack

96
Q

Suggest how stem cells could be used to treat type 1 diabetes.

A

stem cells could replace insulin-producing cells in the pancreas that were destroyed by the body’s own immune system

97
Q

Suggest how stem cells could be used to treat parkinson’s disease.

A

stem cells could replace dead dopamine-producing cells in the brain

98
Q

Suggest how stem cells could be used to treat Alzheimer’s disease.

A

replacing brain cells destroyed due to buildup of abnormal proteins

99
Q

Suggest how stem cells could be used to treat macular degeneration.

A

replacing cells in the retina to prevent blindness in elderly and diabetics

100
Q

Suggest how stem cells could be used to treat spinal injuries.

A

replacing damaged spinal cords using stem cell implants

101
Q

Describe how stem cells may be useful for treating burns.

A
  • stem cells grown on biodegradable meshes can produce new skin for burn patients
  • quicker than taking graft from another part of body
102
Q

Describe two ways in which stem cells may be useful in research.

A
  • drug trials - new drugs can be tested on cultures of stem cells before being tested on animals and humans
  • developmental biology - can divide indefinitely and differentiate into various types of cells they can be used to study changes that occur as multicellular organisms grow and develop from a single cell and why things go wrong
103
Q

Describe arguments for the use of embryonic stem cells for research and medicine.

A
  • allow us to find treatments for incurable diseases
  • allow us to study developmental biology more closely
  • embryoes used were donated from those left over after fertility treatment so they were gna be discarded anyway
104
Q

Define the term induced pluripotent stem cell

A

adult stem cells that have been genetically modified to act like embryonic stem cells and so they are plurpotent

105
Q

Explain why induced pluripotent stem cells may be very useful in research and medicine.

A

this could be useful as a replacement for actually harvesting embryonic stem cells as it is not as controversial

OCR A-Level Biology (16 decks)

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