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BIOLOGY OCR A > 2.6 Cell division > Flashcards

2.6 Cell division Flashcards

1
Q

What is the cell cycle?

A

Sequence of events that take place, resulting in the division of the cell

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2
Q

What are the two main phases in the cell cycle

A

Interphase and mitotic phase

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3
Q

What is interphase

A

Long periods of growth and normal workings

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4
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, (chloroplasts grow and divide), Normal metabolic processes if cells occur

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5
Q

What are the three stages of interphase?

A

G1
S
G2

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6
Q

What occurs during G1 of interphase

A

Proteins from which organelles are synthesised and produced, organelles replicate, increasing cell size

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7
Q

What occurs during S of interphase?

A

DNA is replicated in the nucleus

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8
Q

What occurs in G2 of interphase

A

Cell increases in size, energy stores are increased and duplicated, DNA is checked for errors

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9
Q

What is the difference between mitosis and cytokinesis

A

Mitosis - nucleus divides
Cytokinesis - cytoplasm divides, two cells are produced

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10
Q

What is G0

A

During stage G1 Cell leaves the cycle, either temporarily or permanently

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11
Q

Why might a cell enter G0?

A

Differentiation - cell becomes specialised and is no longer able to divide (does not re-enter)
DNA of a cell may be damaged - No longer viable, normal cells can only divide a limited number of times, eventually becoming senescent (does not re-enter)

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12
Q

What are checkpoints in the cell cycle

A

Monitor and verify whether the processes have been accurately completed, before the cell can progress

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13
Q

Where is the G1 checkpoint? What do this check for? Where does an unsatisfactory cell go?

A

G1 checkpoint - end of G, before entry into S, checks for cell size, nutrients, growth factors, DNA damage
Cell travels to G0 (resting state)

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14
Q

Where is the G2 checkpoint? What do this check for? Where does an unsatisfactory cell go?

A

End of G2 phase, before mitotic phase, checks for cell size, DNA replication, DNA damage

If not cell goes to resting state

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15
Q

Where is the Spindle assembly (metaphase) checkpoint? What do this check for? Where does an unsatisfactory cell go?

A

During metaphase, all chromosomes should be attached to spindles, Mitosis cannot occur until this checkpoint is passed

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16
Q

What enzyme allows the passing of a cell cycle checkpoint? What does this enzyme do?

A

Kinases
Catalyse the addition of a phosphate group to a protein (cyclins), Forming a CDK (cyclin dependent kinase) changing the tertiary structure

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17
Q

What is cancer? What is a tumour

A

Uncontrolled division of cells, abnormal mass

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18
Q

What is the difference between benign and malignant tumours

A

Benign - Stop growing and do not travel to other locations
Malignant - Does not stop growing, can break off and spread to other areas

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19
Q

What can cause tumors?

A

Damage or mutation of genes that encode proteins needed to regulate cell cycle.

Overexpression of cyclin gene, disrupts cell cycle, leading to uncontrolled division

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20
Q

Why is mitosis important?

A

Growth, replacement and repair, asexual reproduction

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21
Q

What is a chromatid? What is a centromere

A

Chromatid - identical DNA molecules
Centromere - area that joins the chromatids

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22
Q

What are the four stages of mitosis?

A

PMAT
Prophase
Metaphase
Anaphase
Teleophase

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23
Q

What is Prophase? Draw a diagram

A

Chromosomes condense, Nucleolus disappears and the nuclear membrane begins to break down, Spindle structures at poles of cell formed, centrioles migrate to poles. Spindle fibres attach to centromere and begin to pull them to the centre of the cell

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24
Q

What is metaphase. Draw a diagram

A

Chromosomes are moved by spindle fibres, chromosomes line up in the middle of a cell, caused the metaphase plate

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25
Q

What is anaphase. Draw a diagram

A

Centromeres divide, chromatids are separated due to the shortening of spindle fibres

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26
Q

What is telophase. Draw a diagram

A

Chromatids have reached the poles, and are now called chromosomes, two new sets of chromosomes assemble, nuclear envelope reforms, chromosomes start to uncoil and the nucleolus is formed

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27
Q

What is cytokinesis

A

Actual division of cell into two separate cells

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28
Q

What is a cleavage furrow?

A

In animal cells, a cleavage furrow forms around the middle of the cell, cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to close enough to fuse

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29
Q

What happens in plant cells during cell division?

A

Cell wall prevent formation of a cleavage furrow, Vesicles from the Golgi apparatus assemble and fuse with one another, cell surface membrane divides in two, cell wall forms along cell membrane

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30
Q

Compare diploid cells and haploid cells

A

Diploid - two chromosomes of each type (one from each parent)
Haploid - One chromosome of each type (gamete)

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31
Q

What is a gamete? What is a Zygote

A

Gamete - Haploid sex cell (sperm or egg)
Zygote - fertilised egg, combination of two gametes

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32
Q

How are gametes formed? What division is this?

A

Formed by meiosis, reduction division

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33
Q

What are homologus chromosomes

A

matching sets of chromosomes, has the same genes at the same loci

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34
Q

What is the loci of genes

A

Position of genes on a chromosome

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35
Q

What is an allele

A

Different versions of the same gene. (eg different eye colours)

36
Q

Compare Meiosis and mitosis

A

Mitosis - 2 identical daughter cells
1 division
PMAT
Meiosis - 4 genetically different daughter cells
2 divisions
PMAT PMAT

37
Q

What is the stages in meiosis

A

Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

38
Q

What happens in Meiosis I

A

First division, each cell only contains one full set of genes, instead of two, cells are haploid

Prophase I, Metaphase I, Anaphase I, Telophase I

39
Q

What happens in Meiosis II

A

Second division, forming 2 new cells, four haploid cells are produced

40
Q

When does crossing over of chromosomes occur, What does this cause

A

Crossing over occurs in Prophase I, this causes genetic variations

41
Q

What happens in Prophase I

A

Chromosomes condense, nuclear envelope disintegrates, nucleolus disappears.
Homologous chromosomes pair up, forming bivalents, chromosomes entangle, causing crossing over

42
Q

What happens in Metaphase I

A

same as mitosis, but
Orientation of each pair of homologous pairs is random, maternal (female parent of parent) or parental (male, parent of parent) chromosomes can end up facing either pole, resulting in independent assortment

43
Q

What happens in Anaphase I

A

Homologous chromosomes are pulled to poles, chromatids remain joined.
Sister chromatids become entangled, break of and re-join, (break is called chiasmata), if exchange occurs, this forms recombinant chromatids (alleles are exchanged). This leads to genetic variation

44
Q

What happens in telophase I, and after telophase I

A

Chromosomes assemble at poles, nuclear membrane reforms, chromosomes uncoil.

After - cytokinesis - reduction in chromosome number, from diploid (two chromatids) to haploid (One chromatid)

45
Q

What happens in Prophase II

A

Chromosomes (two chromatids) condense and become visible, nuclear envelope breaks down, spindle formation begins

46
Q

What happens during Metaphase II

A

Individual chromosomes assemble on the metaphase plate. Due to crossing over, chromatids are no longer identical so there is independent assortment and more genetic variation

47
Q

What happens in Anaphase II

A

Chromatids are pulled apart

48
Q

What happens in Telophase II, What happens after

A

Chromatids assemble at the poles, chromosomes uncoil and and form chromatin, nuclear envelope reform and nucleolus becomes visible

Cytokinesis - divisions of cells form four genetically different haploid daughter cells.

49
Q

Why are the four daughter cells at the end of meiosis genetically diffrent?

A

Independent assortment - Maternal and parental chromosomes face either poles during metaphase
Crossing over - Chromosomes entangle, during Prophase I and anaphase I, During anaphase I, parts of the chromatids break of and re-join (called Chiasmata), these are recombinant chromatids, with genes being exchanged
Mutation - random mutation can cause genetic variation

50
Q

What is specialisation?

A

unspecialised cells become specialised and have different roles

51
Q

How are Erythrocytes (red blood cells) specialised

A

flattened biconcave shape - increases surface area to volume ratios
no nucleus - increases space for haemoglobin, so more oxygen can be carried
Flexible - able to fit through capillaries

52
Q

How are Neutrophils (white blood cells) specialised?

A

Multi-lobed nucleus - easier for them to move through small gaps and get to site of infection
Granular cytoplasm - contain many lysosomes used to attack pathogens

53
Q

How are sperm cells specialised?

A

Flagellum - capable of movement
Contain many mitochondria - supply energy for swimming
Acrosome (head) contains digestive enzymes - digest protective layers around the ovum

54
Q

How are palisade cells specialised?

A

Contain chloroplasts - absorb large amounts of light
Rectangular shaped - closely packed together
Thin cell walls - increase rate of diffusion of CO2
Large vacuole - maintain turgor pressure
Chloroplasts can move in the cytoplasm to absorb more light

55
Q

How are root hair cells specalised?

A

Long extensions - increase surface area, maximising uptake of water and minerals

56
Q

How are guard cells specialised?

A

When guard cells lose water and becomes less swollen they change shape - stomata closes to prevent further water loss

57
Q

What is a tissue?

A

Collection of differentiated cells that have specialised function

58
Q

What are the four main category’s of tissues in animals

A

Nervous - electrical impulses
Epithelial tissues - cover body surfaces (internal and external)
Muscle tissue - adapted to contract
Connective tissue - adapted to hold other tissues together or act as a transport medium

59
Q

What is the squamous epithelium, how is it adapted? One example

A

Flat and Thin - one cell thick, allows for rapid diffusion
Alveoli - needs diffusion of oxygen and carbon dioxide

60
Q

What is the ciliated epithelium , how is it adapted? One example

A

Hair-like structures called cilia
Goblet cells - release mucus to trap unwanted particles
Bronchi - prevent pathogens or bacteria reaching the alveoli

61
Q

What is the cartilage , how is it adapted? One example

A

Contains fibres of of elastin and collagen
Firm and flexible - prevents end of bones rubbing together
Trachea - prevents collapse

62
Q

What is the muscle , how is it adapted? One example

A

Need to contract and relax

63
Q

What is the Epidermis, how is it adapted?

A

layer of cells on surface of plants,
covered by a waxy cuticle - prevents water loss
Stomata - allow for movement of gasses

64
Q

What is the Xylem tissue , how is it adapted?

A

responsible for transport of water and minerals
Composed of dead cells and strengthened by lignin - provides structural support

65
Q

What is the phloem tissue, how is it adapted?

A

Responsible for transport of nutrients
Composed of sieve tube cells

66
Q

What is an organ

A

collection of tissues that are adapted to perform a particular function

67
Q

What is an organ system?

A

composed of many organs working together working together to carry out a function in the body

68
Q

What are three examples of organ systems

A

Digestive system
Cardiovascular system
Gaseous exchange system

69
Q

What are stem cells

A

Undifferentiated cells

70
Q

Stem cells loose the ability to do what once they become specialised

A

Divide, they enter the G0 phase of the cell cycle

71
Q

What is stem cell potency

A

Cells ability to differentiate into different cells

72
Q

What is totipotent?

A

Cell can differentiate into any type of cell.

73
Q

Give an example of a totipotent cell

A

A zygote, or the first 8-16, egg cells from the first few mitotic divisions

74
Q

What is a pluripotent cell

A

Can form all tissue types but not the whole organisms

75
Q

Give an example of a pluripotent cell

A

Early embryos

76
Q

What is a multipotent cell

A

Can only form a range of cells within a certain types of tissue

77
Q

Give an example of a multipotent cell

A

Hematopoietic stem cells in bone marrow, produce various types of blood cell

78
Q

Why is it important that cells differentiate?

A

They can become adapted to a specific role, and become more efficient

79
Q

Why is it important that red blood cells be replaced? How many are made per day

A

short lifespan - around 120 days
Around 3 billion per kilogram per day

80
Q

Why is it important white blood cells are replaced. How many are made per hour, why might this increase?

A

Short life span - 6 hours. Produce 1.6 billion per hour, increases during infections

81
Q

What are two sources of Animal stem cells

A

Embryonic stem cells - very early stage = totipotent, After 7 days, a blastocyst has formed = pluripotent
Adult stem cells - found in specific areas, multipotent

82
Q

Where are plant stem cells found, what type of stem cells are these?

A

Meristem tissue - wherever growth occurs in plants (roots and shoots)
Between phloem and xylem tissues, these are pluripotent

83
Q

What could stem cells be used for?

A

Heart disease, type 1 diabetes, Parkinson’s disease, Alzheimer’s disease, macular degeneration, birth defects, spinal injuries, burns, drug trials, development biology

84
Q

How are embryonic stem cells harvested

A

Left over embryos from IVF

85
Q

Why are embryonic stem cells better then adult stem cells

A

Pluripotent, so can differentiate into any stem cell

86
Q

Give both sides of embryonic stem cells

A

For - can help cure life altering diseases, like Alzheimer’s and type 1 diabetes
Against - involves destruction of ‘possible life’.

87
Q

What are the medical uses of plant stem cells

A

Medical drugs can be created from stem cells, for cheap

BIOLOGY OCR A (6 decks)

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