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A-level Biology > 6 - Cell Division ➗ > Flashcards

6 - Cell Division ➗ Flashcards

1
Q

What is the cell cycle?

A

A highly ordered sequence of that take place in a cell resulting in division

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2
Q

Why is mitosis important?

TOAD

A

Tissue repair/replacement
Organism growth
Asexual reproduction
Development (zygotes)

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3
Q

Summarise what happens in interphase

DOCTOR

A

DNA replication
Organelle duplication
Cell growth
Transcription/translation
Obtain nutrients
Respiration

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4
Q

What phase does a cell spend the majority of its time?

A

Interphase

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5
Q

List the three stages of interphase

A

G1, S and G2

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6
Q

What happens in G1 (gap/growth1)

A
  • cell grows and prepares for DNA replication
  • synthesis of proteins for organelle production
  • growth of cell size (increase cytoplasm size)
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7
Q

What happens in S (synthesis)?

A

DNA is replicated in the nucleus ready for mitosis

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8
Q

What happens in G2 (gap/growth2)?

A
  • continuing increase in cell size
  • energy stores (ATP) increase
  • duplicated DNA is checked for errors
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9
Q

What are the 2 stages of the mitotic phase?

A

Mitosis - the nucleus divides
Cytokinesis - the cytoplasm divides

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10
Q

What are the matching sets of chromosomes known as during S?

A

Sister chromatids

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11
Q

What is G0?

A

The phase when the cell leaves the cycle either temporarily or permanently from G1

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12
Q

Why would a cell enter G0 because of differentiation?

A

a specialised cell is no longer able to divide will carry out its function indefinitely and not enter the cell cycle again

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13
Q

Why would a cell enter G0 because of damage?

A

DNA of a cell may be damaged, in which case it is no longer viable, so will not divide

Enters a period of permanent cell arrest = G0

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14
Q

What is it called when a cell enters G0 due to ageing?

A

A senescent cell

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15
Q

Why would a cell enter G0 temporarily and be stimulated to re-enter G1?

A

If they are not needed and are dormant = quiescent cells

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16
Q

Give an example of a quiescent cell leaving G0 and entering G1

A

Lymphocytes in an immune response will be needed to fight a pathogen, but not needed any other time

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17
Q

Give an example of a differentiated cell that is arrested in G0

A

Neurons - these cells are amitotic (can’t divide)

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18
Q

Why are there checkpoints in the cell cycle?

A

To ensure the fidelity of cell division

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19
Q

What are checkpoints?

A

Control mechanisms of the cell cycle to monitor and verify whether the process at each phase is accurately completed

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20
Q

What does the end of G1 checkpoint check for?

A
  • cell size
  • nutrients
  • growth factors
  • DNA damage
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21
Q

What does the end of G2 checkpoint check for?

A
  • cell size
  • DNA replication
  • DNA damage
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22
Q

What does the spindle assembly / metaphase checkpoint check for?

A
  • chromosome spindle attachment
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23
Q

What happens when a cell passes G1 checkpoint?

A

Enters S phase for DNA replication

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24
Q

What happens when a cell fails G1 checkpoint?

A

Enters G0

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25
What happens when a cell passes G2 checkpoint?
Starts mitosis
26
What happens when a cell fails G2 checkpoint?
Repairs damaged DNA to prevent it from being transmitted to daughter cells
27
What happens when a cell passes the metaphase checkpoint?
Mitosis proceeds
28
What happens when a cell fails the metaphase checkpoint?
Arrests cell cycle at metaphase until all chromosomes are aligned on spindle (keeps retrying until they attach)
29
What is the level of organisation in multicellular organisms?
Specialised cells - tissues - organs - organs systems - whole organism
30
In multicellular organisms, eukaryotic cells can have structural adaptations such as:
- the shape of the cell - the organelles the cell contains (or doesn’t)
31
Specialised Animal Cells Red blood cells - adaptation + function
Flattened biconcave shape = increased SA:V In mammals no nuclei / organelles = increases space for haemoglobin Flexible = squeeze through capillaries
32
Specialised Animal Cells What type of cells are neutrophils?
A type of white blood cell that plays an essential role in the immune system
33
Specialised Animal Cells Neutrophils - Adaptation + Function
Multi-loved nucleus = easier to squeeze through small gaps to get to infection sites Granular cytoplasm containing lysosomes = contains enzymes to attack pathogens Glycogen = used as a source of energy
34
Specialised Animal Cells Sperm cells - adaptation + function
Flagellum = capable of movement Many mitochondria in mid piece = supply of energy to swim Acrosome full of digestive enzymes = digests protective layers around ovum (egg) to penetrate
35
Specialised Plant Cells Palisade cells - adaptation + function
Chloroplasts = absorbs light for photosynthesis Large Vacuole = maintains turgor pressure Rectangular shape = pack tightly together in a continuous layer Thin cell walls = increasing rate of diffusion of CO2
36
Specialised Plant Cells Root hair cells - adaptation + function
Thin cell walls = shortens diffusion pathway Long extensions (root hairs) = increases SA:V to maximise water/mineral ion uptake
37
Specialised Plant Cells Guard cells - adaptation + function
Forms openings called stomata = allows diffusion Thicker cell wall in one side = cell doesn’t change shape symmetrically as it’s volume changes
38
Specialised Plant Cells Guard cells - what happened when they lose water?
Become less swollen (due to osmosis), changes shape and the stoma closes to prevent further water loss
39
Give an example of a cell
Amoeba Sperm cell Phagocyte Erythrocyte
40
Define tissue
A collection of differentiated cells that’s have a specialised function(s). Each tissue is adapted to a particular function
41
4 main categories of tissues in animals
Nervous tissue Epithelial tissue Muscle tissue Connective tissue
42
Tissues in Animals What does nervous tissue do?
Adapted to support the transmission of electrical impulses
43
Tissues in Animals What does epithelial tissue do?
Adapted to cover body surfaces, interns and external
44
Tissues in Animals What does muscle tissue do?
Adapted to contract
45
Tissues in Animals What does connective tissue do?
Adapted either to hold other tissues together or as a transport medium
46
What are the 6 principle plant tissues?
Photosynthetic tissue Epidermis tissue Vascular tissue Meristem tissue Packing tissue Strengthening tissue
47
Animal Tissues What is the function of squamous epithelia / pavement epithelium?
Provides a flat surface covering or outer layer to line organs
48
Animal Tissues Squamous Epithelium - Adaptation + Help
Very thin due to flat cells = reduces diffusion pathway Permeable = allows diffusion easily Basement membrane of a single layer of cells = helps diffusion/separates tissues/protects cells
49
Animal Tissues What is the function of ciliated epithelia?
To move substances from one place to another in a rhythmic manner
50
Animal Tissues Ciliated Epithelium - Adaptation + Help
Goblet cells that release mucus = traps unwanted particles (bacteria) Hair like structures - cilia = beat rhythmically to move substances up to throat to be swallowed
51
Animal tissues What is the function of cartilage?
Connective tissue found in the outer ear, nose and at the end or inbetween bones
52
Animal tissues Cartilage - Adaptation + Help
Contains chondrocyte cells = produce collagen Contains fibres of elastin/collagen = prevents end of bones rubbing by acting as a buffer Matrix = provides nourishment as no blood vessels in cartilage
53
Animal tissues What is the function of muscle?
A tissue that needs to contact in order to move bones, which in then moves body parts
54
Animal Tissues Muscle - Adaptation + Help
Skeleton muscle containing myofibrils = myofibrils contain contractile proteins to help tissue contract Different types of muscle fibres = allowed for wide range of capabilities Contains connective tissue between muscle fibres = protects cells allowing them to withstand force
55
Plant Tissues What type of tissue is xylem?
Type of vascular tissue responsible for transport
56
Plant Tissues Xylem - Adaptation + Help
Contains lignin = waterproof material/structural support Thick-walled xylem parenchyma packs around xylem vessels = stores food and tannin Has bordered pits = allows water to leave xylem tubes
57
Plant Tissues What type of tissue is phloem?
Vascular tissue responsible for transport of organic nutrients
58
Plant Tissues Phloem - Adaptation + Help
Sieve tubes made of unlignified cells = allows substances to flow through plates Surrounded by companion cells = completes metabolic functions for tubes Surrounded by phloem parenchyma = stores nutrients and tannin
59
Define an organ
A collection of tissues that are adapted to perform a particular function in an organism
60
What is an organ system?
A number of organs working together to carry out a major function in the body
61
Examples of animal organ systems
- digestive system - cardiovascular system - gaseous exchange system
62
Define asexual reproduction
The production of genetically identical offspring from one parent in multicellular organisms including plants, fungi, Ameoba
63
How do prokaryotes reproduce?
Binary fission
64
Before mitosis can occur, what happens to DNA?
Each DNA molecule is converted into two identical DNA molecules, called chromatids
65
Where are two chromatids joined?
At the centromere
66
Why is it necessary to keep chromatids together during mitosis?
So they can be precisely manoeuvred and segregated equally, one each into the two new daughter cells
67
What are the 4 stages of mitosis?
Prophase, metaphase, anaphase and telophase
68
What makes homologous chromosomes the same?
- same loci - same size - same genes
69
Mitosis - Prophase What happens to DNA and the nucleolus?
Chromatin coils and condenses (will take up stain more) Nucleolus disappears and the nuclear membrane breaks down
70
Mitosis - Prophase What happens with spindle fibres?
- Spindle-shaped structures form linking the poles of the cell - they attach to specific areas on the centromeres and start to move the chromosomes to the centre of the cell
71
Mitosis - Prophase In animal and some plant cells, what happens to centrioles?
Two centrioles migrate to opposite poles of the cell
72
Mitosis - Prophase What are centrioles?
Cylindrical bundles of proteins that help in the formation of the spindle
73
Mitosis - Metaphase What happens to chromosomes
Chromosomes are moved by the spindle fibres to form a metaphase plate along the equator
74
Mitosis - Metaphase What happens to spindle fibres?
Spindle fibres attach to centromere - longest phase as they have to align correctly
75
Mitosis - Anaphase What happens to the centromere and chromosomes?
- Centromere divides causing chromatids to separate
76
Mitosis - Anaphase What happens to spindle fibres?
Contract, pulling chromatids to separate poles, forming V shape as they are dragged by their centromeres
77
Mitosis - Telophase What happens with the chromatids?
Reach the poles and are now called chromosomes - the two new sets of chromosomes assemble at each pole, beginning to uncoil
78
Mitosis - Telophase What happens to the nuclear membrane?
Nuclear envelope reforms and nucleolus is formed
79
What actually is cytokinesis?
The actual division of the cell into two separate cells, beginning during telophase
80
Cytokinesis What happens in animals?
A cleavage furrow forms around the middle of the cell, as the cell surface membrane is pulled inwards by the cytoskeleton until it’s close enough to fuse around the middle
81
Cytokinesis Why can’t plant cells form a cleavage furrow?
They have cell walls
82
Cytokinesis How is a plant cell divided initially?
Vesicles from the Golgi assemble in the same place as where metaphase plate was - they then fuse with each other and the cell surface membrane
83
Cytokinesis How does the cell wall form around the cell surface membrane?
New sections form along the new section of membrane
84
Cytokinesis Plants If the dividing cell wall was formed before the daughter cells separated, what would happen?
They would immediately undergo osmotic lysis from the surrounding water
85
What do all cells begin as and known as?
Undifferentiated cells are known as stem cells
86
What two qualities makes a stem cell?
Self renewal and potency
87
What is self renewal in stem cells?
They can continuously divide and replicate
88
What is potency in stem cells?
They have the capacity to differentiate into specialised cell types
89
What happens when cel division is too slow and too rapid?
Too slow = ageing Too rapid = tumours
90
Define a stem cell
An unspecialised cell that is capable of diffusion and differentiation to become other cell types
91
What happens to stem cells once they become specialised?
They lose the ability to divide and enter G0
92
Why is self-renewal in stem cells important?
For the body to maintain a pool of stem cells to use in life so they don’t run out
93
Why is cell differentiation important?
As specialised cels are used up, damaged or die, they can’t divide so they need to be replaced
94
What is a stem cell’s potency?
A stem cell’s ability to differentiate into different cell types
95
What does it mean if a cell has a great potency?
It can differentiate into many cell types
96
Stem Cell Potency What is totipotent?
Differentiate into any cell type
97
Stem Cell Potency What cells are totipotent?
Fertilised egg / zygote / 8-16 first mitotic divisions
98
Stem Cell Potency What is pluripotent?
They can differentiate into all tissue types but not whole organisms
99
Stem Cell Potency Where can pluripotent cells be found?
In early embryos and are the origin of the different types of tissue within an organism
100
Stem Cell Potency What is multipotent?
Can form a range of cells within a certain type of tissue
101
Stem Cell Potency Where can multipotent cells in blood cells?
Haematopoetic stem cells in bone marrow are multipotent because this gives rise to the various types of blood cell.
102
Stem Cell Potency What other cells are mutlipotent?
Bone marrow, cord blood, adipose tissue, skin, MSCs
103
Erythrocytes and neutrophils are both present in blood. How is this differentiation?
They are both adapted to their specific function
104
Where are all blood cells derived from?
Bone marrow
105
How long is the blood cell of a mammalian erythrocyte?
120 days
106
The stem cell colonies in bone marrow produce how many erythrocytes to keep up with demand?
3 billion per kg of body mass per day
107
How long do neutrophils live for?
6 hours
108
The stem cell colonies in bone marrow produce how many neutrophils to keep up with demand?
1.6 billion per kg per hour This figure increases during infection
109
Embryonic stem cells are present when?
At an early stage of embryo development and are totipotent
110
What must be destroyed and when to get embryonic stem cells?
After about seven days, a blastocyst (mass of cells) has formed and cells are now pluripotent
111
Tissue / adult stem cells are present when and where?
From birth in bone marrow
112
What potency do adult stem cells have?
Multipotent, but there is new evidence that they can be artificially triggered to become pluripotent
113
Where can stem cells be harvested from that’s not bone marrow?
Umbilical cord of newborn babjes
114
Advantages of getting stem cells from umbilical cords?
- Plentiful supply of umbilical cords - Invasive surgery isn’t needed
115
Where are stem cells present in plants?
Meristematic tissue - this is found wherever growth is occurring in plants (roots/shoots)
116
Where is meristematic tissue found that’s not in roots and shoots?
Sandwiched between the phloem and xylem issues called the vascular cambium
117
Stem cells transplanted into specific areas have what potential?
To treat certain diseases
118
What diseases can stem cells treat in the future?
Heart disease Type 1 diabetes Parkinson’s disease Alzheimer’s disease Macular degeneration Birth defects Spinal injuries
119
How are stem cells already used to treat burns?
Stem cells grown on biodegradable meshes can produce new skin Whicker than the normal process of taking a graft from another body part
120
How are stem cells used in drug trials?
Potential new drugs can be tested on cultures of stem cells before being tested on humans/animals
121
How are stem cells used in developmental biology?
The study of the changes that occur as multicellular organisms grow and develop from a single cell (fertilised egg)
122
Where were embryonic stem cells first used?
Donated from those left over after fertility treatment
123
What is the UK law most recently on embryonic stem cells?
Embryos can be specifically created in a lab as a source of stem cells
124
What are the ethical oppositions against embryonic stem cells?
- religion - many people begin life begins at conception, so you’re killing a life
125
What are induced pluripotent stem cells (iPSCs)?
Adult age cells that have been genetically modified to act like embryonic stem cells and so are pluripotent
126
What happens to cambium cells that differentiate to form xylem?
- they lose their cytoplasm - deposit lignin in their cell walls - lose their end cell walls
127
What happens to cambium cells that differentiate to form phloem?
- lose some of their cytoplasm - lose organelles - develop sieve plates
128
What are haematopoetic stem cells?
A multipotent blood stem cell located in bone marrow (in colonies)
129
What can haematopoetic stem cells differentiate into?
Several types of blood cell types like lymphocytes, monocytes, neutrophils
130
What can haematopoetic stem cells not differentiate into?
Brain cells, bone cells, or other non-blood cell types
131
What are cells with two chromosomes?
Diploid
132
What are sex cells called?
Gametes
133
What is a fertilised egg called?
Zygote
134
Each characteristic of a gene is coded for by what?
Two copies of each gene, one from each parent
135
What are homologous chromosomes?
Matching sets of chromsomes
136
What is an allele?
Different versions of the same gene
137
What qualities do homologous chromosomes have?
- same loci - same shape - same size - same position of centromeres
138
Mitosis VS Meiosis How many daughter cells?
Mitosis = 2 Meiosis = 4
139
Mitosis VS Meiosis How many divisions?
Mitosis = 1 nuclear, 1 cytoplasmic Meiosis = 2 nuclear, 2 cytoplasmic
140
Mitosis VS Meiosis Gamete / Somatic (body) cell?
Mitosis = somatic Meiosis = gamete
141
Mitosis VS Meiosis Does crossing over occur?
Mitosis = no Meiosis = yes
142
Mitosis VS Meiosis Reason for cell division
Mitosis = TOAD Meiosis = sexual reproduction
143
What do you not get from asexual reproduction?
Variation because the offspring are clones of the parent
144
What is a male gametocyte (sperm) called?
Spermatocyte
145
What is a female gametocyte (egg) called?
Oocyte
146
Meiosis What happens in interphase?
Same as mitosis with G1, S and G2 phases
147
Meiosis What happens in Meiosis 1?
Reduction division where homologous chromosomes separate into two cells
148
Meiosis What happens in Meiosis 2?
Pairs of chromatids are separated like in mitosis
149
Meiosis What suggests meiosis evolved from mitosis?
First stage as mitosis is the same (interphase)
150
Meiosis Why is it helpful to have duplicate chromatids?
Increases potential for genetic variation
151
Meiosis What happens in Prophase 1?
- DNA condenses = visible chromosomes - nuclear envelope disintegrates - nucleolus disappears - spindle fibres formation begins
152
Meiosis Prophase 1 What is a pair of homologous chromosomes called?
A bivalent = homologous chromosomes undergo a process called synapsis
153
Meiosis Prophase 1 What is chiasma (chiasmata; plural)?
The point at which the crossing over occurs
154
Meiosis Prophase 1 What is crossing over?
Crossing over of genetic material between non-sister chromatids as they are very close together and become entangled
155
Meiosis Prophase 1 What does crossing over result in?
Recombinant DNA = exchange of genetic material creates new combinations on chromatids
156
Meiosis Metaphase 1 Where does the bivalent go?
Lines up along the equator of the spindle, with spindle fibres attached to the centromeres
157
Meiosis Metaphase 1 What do the maternal and paternal chromosomes in each pair do?
They position themselves independently of the others = independent assortment
158
Meiosis Metaphase 1 What does independent assortment mean?
That the proportion of paternal/maternal chromosomes that end up on each side of the equator is random and due to chance
159
Meiosis Metaphase 1 What does independent assortment result in?
Genetic variation
160
Meiosis What generally happens Metaphase 1?
- nuclear membrane breaks down fully - spindle fibres move towards chromosomes - spindle fibres from one pole attach to one chromosomes of each pair (sister chromatids)
161
Meiosis Metaphase 1 What is the equator also called that homologous chromosomes line up along?
Metaphase plate
162
Meiosis What happens in Anaphase 1?
- homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite end of the spindle - centromeres do not divide
163
Meiosis What happens in telophase 1?
- chromosomes arrive at opposite poles - spindle fibres break down - nuclear envelope reforms
164
Meiosis What do plant cells sometimes do at the end of Meiosis 1?
Skip telophase 1 and go straight into meiosis 2
165
Meiosis What happens in plant cells during the start of cytokinesis in Meiosis 1?
vesicles from the Golgi gather along the equator of the spindle
166
Meiosis How does a cell surface membrane form in plants in cytokinesis 1?
- vesicles merge with each other to form new cell surface membrane and also secrete a layer of calcium pectate which becomes the middle lamella
167
Meiosis How is the cell walls of plant cells created during cytokinesis 1?
Layers of cellulose are laid upon the middle lamella to form the walls
168
Meiosis What doesn’t happen between Meiosis 1 and 2?
Interphase so DNA isn’t replicated
169
Meiosis What happens in Prophase 2?
- nuclear envelope breaks down and chromosomes condense - a spindle forms at a right angle to the old one
170
Meiosis What happens in Meiosis 2?
Chromosomes (not in pairs) line up in single file along the equator of the spindle
171
Meiosis What does not happen in Prophase 2?
Crossing over
172
Meiosis What happens in Anaphase 2?
- centromeres divide and individual chromatids are pulled to opposite piles - this creates 4 groups of chromosomes that are haploid
173
Meiosis What happens in Telophase 2?
Nuclear membranes form around each group of chromosomes
174
Meiosis What happens in cytokinesis 2?
Cytoplasm divides as new cell surface membrane are formed creating 4 haploid cells
175
Meiosis What is the key difference between metaphase 1 and 2?
Metaphase 1 = homologous chromosomes pair up at the metaphase plate Metaphase 2 = single chromosomes line up at the metaphase plate
176
Meiosis When does independent assortment happen?
Metaphase 1 and 2
177
Meiosis Chromosomal numbers before and after mitosis
Before interphase = 46 chromosomes = 46 chromatids After interphase = 46 chromosomes = 92 chromatids
178
Meiosis Chromosome numbers after meiosis 1 and meiosis 2
Meiosis 1 = 23 chromosomes = 46 chromatids Meiosis 2 = 23 chromosomes = 23 chromatids
179
Meiosis Summarise chromosomal numbers
46 —> 23 —> 23

A-level Biology (23 decks)

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