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BIOLOGY OCR A > 2.6 Cell division > Flashcards

2.6 Cell division Flashcards

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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
What is anaphase. Draw a diagram
Centromeres divide, chromatids are separated due to the shortening of spindle fibres
26
What is telophase. Draw a diagram
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
27
What is cytokinesis
Actual division of cell into two separate cells
28
What is a cleavage furrow?
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
29
What happens in plant cells during cell division?
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
30
Compare diploid cells and haploid cells
Diploid - two chromosomes of each type (one from each parent) Haploid - One chromosome of each type (gamete)
31
What is a gamete? What is a Zygote
Gamete - Haploid sex cell (sperm or egg) Zygote - fertilised egg, combination of two gametes
32
How are gametes formed? What division is this?
Formed by meiosis, reduction division
33
What are homologus chromosomes
matching sets of chromosomes, has the same genes at the same loci
34
What is the loci of genes
Position of genes on a chromosome
35
What is an allele
Different versions of the same gene. (eg different eye colours)
36
Compare Meiosis and mitosis
Mitosis - 2 identical daughter cells 1 division PMAT Meiosis - 4 genetically different daughter cells 2 divisions PMAT PMAT
37
What is the stages in meiosis
Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II
38
What happens in Meiosis I
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
What happens in Meiosis II
Second division, forming 2 new cells, four haploid cells are produced
40
When does crossing over of chromosomes occur, What does this cause
Crossing over occurs in Prophase I, this causes genetic variations
41
What happens in Prophase I
Chromosomes condense, nuclear envelope disintegrates, nucleolus disappears. Homologous chromosomes pair up, forming bivalents, chromosomes entangle, causing crossing over
42
What happens in Metaphase I
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
What happens in Anaphase I
Homologous chromosomes are pulled to poles, chromatids remain joined. Sister chromatids cross over, leads to genetic variation
44
What happens in telophase I, and after telophase I
Chromosomes assemble at poles, nuclear membrane reforms, chromosomes uncoil. After - cytokinesis - reduction in chromosome number, from diploid (two chromatids) to haploid (One chromatid)
45
What happens in Prophase II
Chromosomes (two chromatids) condense and become visible, nuclear envelope breaks down, spindle formation begins
46
What happens during Metaphase II
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
What happens in Anaphase II
Chromatids are pulled apart
48
What happens in Telophase II, What happens after
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
Why are the four daughter cells at the end of meiosis genetically diffrent?
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
What is specialisation?
unspecialised cells become specialised and have different roles
51
How are Erythrocytes (red blood cells) specialised
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
How are Neutrophils (white blood cells) specialised?
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
How are sperm cells specialised?
Flagellum - capable of movement Contain many mitochondria - supply energy for swimming Acrosome (head) contains digestive enzymes - digest protective layers around the ovum
54
How are palisade cells specialised?
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
How are root hair cells specalised?
Long extensions - increase surface area, maximising uptake of water and minerals
56
How are guard cells specialised?
When guard cells lose water and becomes less swollen they change shape - stomata closes to prevent further water loss
57
What is a tissue?
Collection of differentiated cells that have specialised function
58
What are the four main category's of tissues in animals
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
What is the squamous epithelium, how is it adapted? One example
Flat and Thin - one cell thick, allows for rapid diffusion Alveoli - needs diffusion of oxygen and carbon dioxide
60
What is the ciliated epithelium , how is it adapted? One example
Hair-like structures called cilia Goblet cells - release mucus to trap unwanted particles Bronchi - prevent pathogens or bacteria reaching the alveoli
61
What is the cartilage , how is it adapted? One example
Contains fibres of of elastin and collagen Firm and flexible - prevents end of bones rubbing together Trachea - prevents collapse
62
What is the muscle , how is it adapted? One example
Need to contract and relax
63
What is the Epidermis, how is it adapted?
layer of cells on surface of plants, covered by a waxy cuticle - prevents water loss Stomata - allow for movement of gasses
64
What is the Xylem tissue , how is it adapted?
responsible for transport of water and minerals Composed of dead cells and strengthened by lignin - provides structural support
65
What is the phloem tissue, how is it adapted?
Responsible for transport of nutrients Composed of sieve tube cells
66
What is an organ
collection of tissues that are adapted to perform a particular function
67
What is an organ system?
composed of many organs working together working together to carry out a function in the body
68
What are three examples of organ systems
Digestive system Cardiovascular system Gaseous exchange system
69
What are stem cells
Undifferentiated cells
70
Stem cells loose the ability to do what once they become specialised
Divide, they enter the G0 phase of the cell cycle
71
What is stem cell potency
Cells ability to differentiate into different cells
72
What is totipotent?
Cell can differentiate into any type of cell.
73
Give an example of a totipotent cell
A zygote, or the first 8-16, egg cells from the first few mitotic divisions
74
What is a pluripotent cell
Can form all tissue types but not the whole organisms
75
Give an example of a pluripotent cell
Early embryos
76
What is a multipotent cell
Can only form a range of cells within a certain types of tissue
77
Give an example of a multipotent cell
Hematopoietic stem cells in bone marrow, produce various types of blood cell
78
Why is it important that cells differentiate?
They can become adapted to a specific role, and become more efficient
79
Why is it important that red blood cells be replaced?
short lifespan cannot divide via mitosis - no nucleus
80
Why is it important white blood cells are replaced. why might this increase?
Short life span increases during infections
81
What are two sources of Animal stem cells
Embryonic stem cells - very early stage = totipotent, After 7 days, a blastocyst has formed = pluripotent Adult stem cells - found in specific areas, multipotent
82
Where are plant stem cells found, what type of stem cells are these?
Meristem tissue - wherever growth occurs in plants (roots and shoots) Between phloem and xylem tissues, these are pluripotent
83
What could stem cells be used for?
Heart disease, type 1 diabetes, Parkinson's disease, Alzheimer's disease, macular degeneration, birth defects, spinal injuries, burns, drug trials, development biology
84
How are embryonic stem cells harvested
Left over embryos from IVF
85
Why are embryonic stem cells better then adult stem cells
Pluripotent, so can differentiate into any stem cell
86
Give both sides of embryonic stem cells
For - can help cure life altering diseases, like Alzheimer's and type 1 diabetes Against - involves destruction of 'possible life'.
87
What are the medical uses of plant stem cells
Medical drugs can be created from stem cells, for cheap

BIOLOGY OCR A (25 decks)

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