Cell Division and Cellular Organisation Flashcards
(127 cards)
1
Q
How many pairs of chromosomes does a normal human have?
A
23
2
Q
What does a gene do?
A
Code for a characteristic
3
Q
For what 3 reasons does mitosis occur?
A
Growth, repair and asexual reproduction
4
Q
What occurs during the G1 phase of the cell cycle?
A
- Proteins are synthesised 2. ATP is produced 3. Key organelles (including centrioles) grow larger, then duplicate
5
Q
Why is the G1 checkpoint important?
A
The cell must be checked to make sure that it is ready for division, as once the chromosomes are duplicated the process cannot be reversed
6
Q
What happens if the cell is rejected at the G1 checkpoint?
A
It passes into a resting state called G0
7
Q
What are some reasons for passing into G0?
A
Cell age/senescence, damage, lack of need for them to reproduce
8
Q
Is G0 temporary or permanent?
A
It can be both
9
Q
What happens if a cell passes the G1 checkpoint?
A
It passes into the S phase
10
Q
What occurs during the S phase?
A
Each chromosome is duplicated in the nucleus
11
Q
Which stages of the cell cycle make up interphase?
A
G1, S and G2
12
Q
What occurs during the G2 phase of cell division?
A
The duplicated chromosomes are checked for damage, and repaired/replaced if possible and necessary
13
Q
What is checked at the G2 checkpoint?
A
Cell size, DNA condition (integrity, i.e. is any damaged?, and replication, i.e. is it fully replicated?)
14
Q
What happens if a problem is detected at the G2 checkpoint?
A
The cell will pause at the checkpoint to undergo repairs
15
Q
What happens if any problem is fixed at the G2 checkpoint?
A
The cell re-enters the cell cycle, and proceeds with division as normal
16
Q
What happens if damage found at the G2 checkpoint is irreparable, and why is this important?
A
The cell may undergo apoptosis, which is important in preventing cancer by stopping errors being passed to daughter cells
17
Q
What is apoptosis?
A
Programmed cell death
18
Q
What happens if a cell passes the G2 checkpoint without any problems?
A
It proceeds to mitosis
19
Q
How many chromatids is a chromosome made up of?
A
Either 1, or two genetically identical ones
20
Q
What is a chromatid?
A
A strand of DNA
21
Q
How many chromatids does each chromosome have during G1?
A
1 chromatid
22
Q
How many chromatids does each chromosome have from S phase to the beginning of mitosis?
A
2
23
Q
How do chromosomes condense?
A
The DNA (in the form of chromatin fibres) is supercoiled around histone proteins
24
Q
What are the 4 stages of Mitosis?
A
Prophase, Metaphase, Anaphase, Telophase
25
What is a chromosome?
A strip of tighlly coiled DNA
26
What 6 things occur during Prophase in mitosis?
1. Chromatin fibres begin to coil and condense to form chromosomes. 2. Nucleolus disappears 3. Nuclear envelope begins to break down, and fully disappears by the end of Prophase 4. Microtubules begin to form spindle fibres linking the poles of the cell 5. Centrioles migrate to opposite poles of the cell 6. Spindle fibres attach to centromeres, begin to move chromosomes to cell centre
27
What is a centromere?
The point on a chromosome onto which a spindle fibre attaches
28
What occurs in Metaphase in mitosis?
Chromosomes are moved by the spindle fibres to form a plane in the cell's centre, called the Metaphase Plate, and are then held in position
29
What occurs in Anaphase in mitosis?
Centromeres holding pairs of chromatids together in chromosomes divide. Sister chromosomes separated and pulled to opposite poles of the cell by shortening spindle fibres
30
What shape do chromatids tend to be in during Anaphase?
A 'v' shape because of them being pulled by the spindle fibres
31
What occurs during telophase during mitosis?
Chromatids, which have now reached the poles of the cell, are referred to as chromatids. Each new set of chromosomes assembles at its respective pole, nuclear envelope and nucleolus reform. Chromosomes start to uncoil.
32
When does cytokinesis start in both animals and plants?
During telophase
33
How does cytokinesis occur in animals?
The cytoskeleton pulls the cell surface membrane inwards, causing it to invaginate (pinch in). This causes a cleavage furrow to form, until the cell surface membrane pinches off and two new cells are formed
34
What is osmotic lysis?
When a cell membrane bursts (and so, essentially, does the cell) due to the movement of water into the cell via osmosis
35
What do homologous chromosomes have the same of?
They have the same gene loci, so they have genes which code for the same thing. They also have the same length
36
What happens to homologous chromosomes before cell division?
They are copied
37
What is a bivalent?
Where pairs of homologous chromosomes attach to each other at points called chaisma (singular) or chaismata (plural)
38
What occurs during Prophase 1 of meiosis?
1. Chromosomes condense 2. Homologous chromosomes pair up to form bivalents (resulting in crossing over of chromatids) 3. Nuclear envelope disintegrates 4. Centrioles migrate to poles of cell 5. Spindle fibres begin to form
39
What is independent assortment?
Where pairs of homologous chromosomes line up with random alignments along the metaphase plate during metaphase in meiosis
40
What occurs during Metaphase 1 during meiosis?
1. Homologous pairs assemble along metaphase plate with random orientations (independent assortment) 2. Spindle fibres from each centriole attach to centromeres
41
What occurs during Anaphase 1 during meiosis?
1. Homologous chromosomes pulled to opposite poles of cell by spindle fibres, sister chromatids stay attached. 2. Sections of DNA entangled during crossing over break off and rejoin, with recombinant chromatids being formed by this exchange of genes
42
What is a recombinant chromatid?
One with a different genetic makeup to either the father or the mother's chromatid due to sections of DNA entangled during crossing over being exchanged.
43
What occurs during Telophase 1 during meiosis?
1. Chromsomes assemble at the pole of each cell and uncoil 2. Nuclear envelope reforms 3. Centrioles move back into cytosol 4. Cell surface membrane invaginates and pinches off to form 2 daughter cells, each with the same amount of genetic information as the parent cell
44
What happens during Prophase 2 during meiosis?
1. Chromosomes condense and become visible again 2. Nuclear envelope disintegrates 3. Centrioles migrate to poles of cell, spindle fibres begin to form
45
What happens during Metaphase 2 in meiosis?
"1. Individual chromosomes line up along metaphase plate, again with independent assortment 2. Spindle fibres attach to centromeres "
46
What happens during Anaphase 2 in meiosis?
Chromatids of individual chromosomes pulled to poles of cell by shortening spindle fibres after division of centromeres
47
What happens during Telophase 2 in meiosis?
1. Chromosomes assemble at poles, then uncoil and form chromatin again 2. Nuclear envelope reforms 3. Each cell's cell surface membrane invaginates and pinches off to form two new daughter cells, each with half the genetic information of the original parent cell
48
Why is mitosis used in repair?
Old and damaged cells can be replaced by new, identical ones
49
Why is mitosis used in growth?
Allows accelerated growth to increase the size of the organism
50
What is a diploid number of chromosomes?
The full number of chromosomes in a normal cell (46 in humans)
51
What is a haploid number of chromosomes?
Half the normal amount of chromosomes (23 in humans)
52
How does meiosis ensure variation within a species? (methods)
1. Crossing over between homologous chromosomes 2. Fertilisation (1/2 of genetic information from both mother's and father's gametes) 3. Independent assortment and segregation of both homologous and non-identical sister chromatids
53
What is a specialised cell?
A cell which has adaptations which help it carry out a specific function
54
What is a tissue?
A group of the same specialised cells, which work together to carry out a function
55
What is another name for an erythrocyte?
A red blood cell
56
What shape do erythrocytes have and why?
A flattened biconcave shape to increase their surface area and SA:V ratio
57
What are the 3 adaptations which erythrocytes have in order to help them transport oxygen round the body?
1. Flattened biconcave shape 2. Flexible, to fit through narrow capillaries 3. In mammals, they lack nuclei or other organelles, to leave more space for haemoglobin
58
What is the function of a sperm cell?
To deliver genetic information to the female gamete, the ovum
59
What adaptations does a sperm cell have?
1. A flagellum containing microtubules and many mitochondria, giving them the ability and energy to swim. 2. An acrosome on its head containing digestive enzymes, which are released to digest the protective layers around the ovum and allow the sperm to penetrate 3. Protein fibres to strengthen the tail
60
What type of nucleus does a sperm cell have?
A haploid nucleus
61
What adaptations does a palisade mesophyll have?
1. Contain many chloroplasts to absorb lots of light for photosynthesis. 2. Cells rectangular, so can be closely packed to form continuous layer 3. Thin cell walls, increasing rate of CO2 diffusion 4. Chloroplasts can move in cytoplasm to absorb more light 5. Large vacuole to maintain turgor pressure
62
What is a neutrophil a type of?
Type of white blood cell
63
Why do neutrophils have a multi-lobed nucleus?
To make it easier for them to squeeze through small gaps to get to the site of infections
64
What adaptations does a neutrophil have?
Multi-lobed nucleus, granular cytoplasm, many lysosomes in cytoplasm
65
What is the function of a palisade mesophyll cell?
Take in light via chlorophyll for photosynthesis
66
What is the function of a neutrophil?
Plays an important role in the immune system
67
What is the function of a root hair cell?
Uptakes water and minerals from the soil
68
Where are root hair cells found?
Surface of the roots near the growing tips
69
What adaptations does a root hair cell have?
Long, thin extension to maximise SA:V ratio, vacuole containing cell sap (solution of ions and sugars) to lower water potential and maximise concentration gradient to take up water by osmosis
70
What is the function of a pair of guard cells?
To open and close one stoma
71
What happens once a guard cell loses water?
It becomes less swollen and changes shape, closing the stoma to prevent further water loss.
72
Why does a guard cell not change shape symmetrically?
Because the cell wall is thicker on the inside and thinner on the outside
73
What is the hole between two guard cells called?
Stomatal aperture
74
Where are totipotent stem cells found?
A fertilized egg, zygote or the first 8-16 cells made from the fertilized egg
75
What type of cells can totipotent stem cells divide into?
Any type of cell
76
Where are pluripotent stem cells found?
Early embryos
77
What can totipotent stem cells produce apart from cells for the embryo?
Cells for the amnion (amniotic sac) or umbilicus (umbilical cord)
78
What are undifferentiated cells called?
Stem cells
79
Why does the replication of stem cells have to be tightly controlled?
If they do not divide quickly enough then tissues will be replaced inefficiently, leading to aging, but if there is uncontrolled division then they can form tumours
80
What can be created from pluripotent stem cells?
Any type of tissue, but not whole new organisms
81
How can scientists produce pluripotent stem cells?
By genetically manipulating cells found in umbilical cords, and some parts of adults (these would be multipotent stem cells before manipulation)
82
Where are the stem cells which create all blood cells located?
The bone marrow
83
What can be created from multipotent stem cells?
A few cells types, such as erythrocytes
84
What is the name for the type of stem cell which blood cells are created from?
Haematopoetic stem cells
85
What are the new cells created from stem cells necessary for?
Growth, development and tissue repair
86
What is the name for the ability of a stem cell to differentiate?
Potency
87
What is the average lifespan of a human erythrocyte?
120 days
88
What 3 steps occur for a haematopoetic stem cell to be converted to an erythrocyte?
1. Nucleus and organelles lost 2. Haemoglobin made 3. Cell shape changed
89
What is the average lifespan of a human neutrophil?
6 hours
90
What 3 steps occur for a haematopoetic stem cell to be converted to an neutrophil?
1. More lysosomes created 2. Nucleus becomes multi-lobed 3. Extensive cytoskeleton created
91
When are more neutrophils produced from stem cells?
During infection
92
What are the two broad sources of human stem cells?
Adult and embryonic stem cells
93
What are some advantages of taking stem cells from the umbilical cord?
No invasive surgery needed, plentiful supply of umbilical cords, cells could be stored if owner of umbilicus ever needed them (with no risk of rejection)
94
Where are stem cells found in plants?
Meristems, which are found in the cambium between the xylem and phloem, as well as at the tips of roots/shoots or anywhere else growth is occurring in the plant
95
What is the term for meristems found at the tips of roots and shoots?
Apical meristems
96
What 4 steps occur for a plant stem cell to be converted into a xylem cell?
1. Loss of cytoplasm and contents 2. Lignin deposited 3. Elongation of cells 4. End walls lost
97
What 2 steps occur for a plant stem cell to be converted to a phloem cell?
1. Some loss of cytoplasm and organelles 2. Sieve plate development
98
What potency of stem cells are plant stem cells all through the plant's adult life?
Pluripotent
99
What diseases could stem cells have the potential to be used in the treatment of?
1. Heart disease 2. Alzheimer's 3. Type 1 diabetes 4. Parkinson's 5. Macular degeneration (causes blindness in the elderly and diabetics) 6. Birth defects 7. Spinal injuries
100
What other areas can stem cells be used in? (apart from disease treatment)
1. Burns treatment (growing stem cells on a biodegradable mesh instead of a skin graft) 2. Drug trials (testing drugs on cultures instead of organisms) 3. Developmental biology studies
101
How have stem cells been used in medicine for years already?
In the form of bone marrow transplants
102
What causes most ethical issues with the use of embryonic stem cells?
The fact that extracting stem cells from embryos usually involves destroying the embryo
103
What are some ethical objections to/issues with the use of embryonic stem cells?
1. Religious objections 2. Moral objections i.e. life begins at conception, therefore harvesting embryo is murder 3. Lack of consensus on rights of embryo 4. Lack of consensus on who holds genetic material taken from embryos
104
Why is using embryonic stem cells better and worse than using umbilical stem cells?
Embryonic stem cells are pluripotent, so can divides into more things than multipotent umbilical stem cells, but use of umbilical stem cells removes many ethical issues assosciated to embryonic stem cells.
105
What are induced pluripotent stem cells?
Adult stem cells genetically modified to act like embryonic (and therefore pluripotent) stem cells
106
What are some disadvantages of using adult stem cells instead of umbilical stem cells?
They do not divide as well and are more likely to have acquired mutations
107
What is an organ?
A collection of tissues which are adapted to perform a function
108
What is an organ system?
A number of organs working together to carry out a major function in the body
109
What are the 4 main categories of tissue in animals?
1. Nervous tissue 2. Epithelial tissue 3. Muscle tissue 4. Connective tissue
110
What is nervous tissue adapted to do?
Support the transmission of electrical impulses
111
What is epithelial tissue adapted to do?
Cover internal and external body surfaces
112
What is muscle tissue adapted to do?
Contract
113
What is connective tissue adapted to do?
Hold other tissues together, or act as a transport medium
114
What is the structure of squamous epithelial tissue?
A single layer of squamous cells attached to a basement membrane
115
How is squamous epithelial tissue adapted to aid diffusion?
Very thin due to only being 1 cell thick
116
What is the structure of the ciliated epithelial tissue?
Ciliated epithelial cells (with cilia) mixed with goblet cells, all on a basement membrane
117
What type of tissue is cartilage?
Connective
118
What two protein fibres does cartilage contain?
Elastin and collagen
119
What are two types of muscle fibres?
Skeletal and cardiac
120
What is special about cardiac muscle fibres?
They can contract without stimulation from the nerves, instead basing their rhythm on pacemaker cells
121
Why does muscle need to be able to contract?
In order to move bones, which in turn move the parts of the body
122
What do skeletal muscles contain?
Myofibrils, which contain contractile proteins
123
How are cells connected in muscle fibres?
By collagen- when the cell contracts, it pulls on the collagen, causing tension which can cause movement
124
What organelles do muscle cells have more of?
Mitochondria and ribosomes (to produce actin and myosin fibres)
125
What are two broad types of tissue in plants?
1. Epidermis tissue, adapted to cover plant surfaces 2. Vascular tissue, adapted for transport of water and nutrients
126
What are 3 specific specialised plant tissues?
Xylem, phloem, epidermal
127
What is the structure of the epidermis?
A single layer of closely packed cells, usually covered by a waxy cuticle to reduce water loss, with stomata in them to allow gas exchange
