Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is mitosis important?

TOAD

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Summarise what happens in interphase

DOCTOR

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

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

A

Interphase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

List the three stages of interphase

A

G1, S and G2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What happens in S (synthesis)?

A

DNA is replicated in the nucleus ready for mitosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens in G2 (gap/growth2)?

A
  • continuing increase in cell size
  • energy stores (ATP) increase
  • duplicated DNA is checked for errors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the 2 stages of the mitotic phase?

A

Mitosis - the nucleus divides
Cytokinesis - the cytoplasm divides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

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

A

Sister chromatids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is G0?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

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

A

A senescent cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why are there checkpoints in the cell cycle?

A

To ensure the fidelity of cell division

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does the end of G1 checkpoint check for?

A
  • cell size
  • nutrients
  • growth factors
  • DNA damage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What does the end of G2 checkpoint check for?

A
  • cell size
  • DNA replication
  • DNA damage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What does the spindle assembly / metaphase checkpoint check for?

A
  • chromosome spindle attachment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What happens when a cell passes G1 checkpoint?

A

Enters S phase for DNA replication

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What happens when a cell fails G1 checkpoint?

A

Enters G0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What happens when a cell passes G2 checkpoint?

A

Starts mitosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What happens when a cell fails G2 checkpoint?

A

Repairs damaged DNA to prevent it from being transmitted to daughter cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What happens when a cell passes the metaphase checkpoint?

A

Mitosis proceeds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What happens when a cell fails the metaphase checkpoint?

A

Arrests cell cycle at metaphase until all chromosomes are aligned on spindle

(keeps retrying until they attach)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the level of organisation in multicellular organisms?

A

Specialised cells - tissues - organs - organs systems - whole organism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

In multicellular organisms, eukaryotic cells can have structural adaptations such as:

A
  • the shape of the cell
  • the organelles the cell contains (or doesn’t)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Specialised Animal Cells

Red blood cells - adaptation + function

A

Flattened biconcave shape = increased SA:V

In mammals no nuclei / organelles = increases space for haemoglobin

Flexible = squeeze through capillaries

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Specialised Animal Cells

What type of cells are neutrophils?

A

A type of white blood cell that plays an essential role in the immune system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Specialised Animal Cells

Neutrophils - Adaptation + Function

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Specialised Animal Cells

Sperm cells - adaptation + function

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Specialised Plant Cells

Palisade cells - adaptation + function

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Specialised Plant Cells

Root hair cells - adaptation + function

A

Thin cell walls = shortens diffusion pathway

Long extensions (root hairs) = increases SA:V to maximise water/mineral ion uptake

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Specialised Plant Cells

Guard cells - adaptation + function

A

Forms openings called stomata = allows diffusion

Thicker cell wall in one side = cell doesn’t change shape symmetrically as it’s volume changes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Specialised Plant Cells

Guard cells - what happened when they lose water?

A

Become less swollen (due to osmosis), changes shape and the stoma closes to prevent further water loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Give an example of a cell

A

Amoeba
Sperm cell
Phagocyte
Erythrocyte

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Define tissue

A

A collection of differentiated cells that’s have a specialised function(s). Each tissue is adapted to a particular function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

4 main categories of tissues in animals

A

Nervous tissue
Epithelial tissue
Muscle tissue
Connective tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Tissues in Animals

What does nervous tissue do?

A

Adapted to support the transmission of electrical impulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Tissues in Animals

What does epithelial tissue do?

A

Adapted to cover body surfaces, interns and external

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

Tissues in Animals

What does muscle tissue do?

A

Adapted to contract

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Tissues in Animals

What does connective tissue do?

A

Adapted either to hold other tissues together or as a transport medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What are the 6 principle plant tissues?

A

Photosynthetic tissue
Epidermis tissue
Vascular tissue
Meristem tissue
Packing tissue
Strengthening tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Animal Tissues

What is the function of squamous epithelia / pavement epithelium?

A

Provides a flat surface covering or outer layer to line organs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

Animal Tissues

Squamous Epithelium - Adaptation + Help

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

Animal Tissues

What is the function of ciliated epithelia?

A

To move substances from one place to another in a rhythmic manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Animal Tissues

Ciliated Epithelium - Adaptation + Help

A

Goblet cells that release mucus = traps unwanted particles (bacteria)

Hair like structures - cilia = beat rhythmically to move substances up to throat to be swallowed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Animal tissues

What is the function of cartilage?

A

Connective tissue found in the outer ear, nose and at the end or inbetween bones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

Animal tissues

Cartilage - Adaptation + Help

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

Animal tissues

What is the function of muscle?

A

A tissue that needs to contact in order to move bones, which in then moves body parts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

Animal Tissues

Muscle - Adaptation + Help

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

Plant Tissues

What type of tissue is xylem?

A

Type of vascular tissue responsible for transport

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

Plant Tissues

Xylem - Adaptation + Help

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Plant Tissues

What type of tissue is phloem?

A

Vascular tissue responsible for transport of organic nutrients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

Plant Tissues

Phloem - Adaptation + Help

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

Define an organ

A

A collection of tissues that are adapted to perform a particular function in an organism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

What is an organ system?

A

A number of organs working together to carry out a major function in the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

Examples of animal organ systems

A
  • digestive system
  • cardiovascular system
  • gaseous exchange system
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

Define asexual reproduction

A

The production of genetically identical offspring from one parent in multicellular organisms including plants, fungi, Ameoba

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

How do prokaryotes reproduce?

A

Binary fission

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

Before mitosis can occur, what happens to DNA?

A

Each DNA molecule is converted into two identical DNA molecules, called chromatids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

Where are two chromatids joined?

A

At the centromere

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

Why is it necessary to keep chromatids together during mitosis?

A

So they can be precisely manoeuvred and segregated equally, one each into the two new daughter cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

What are the 4 stages of mitosis?

A

Prophase, metaphase, anaphase and telophase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

What makes homologous chromosomes the same?

A
  • same loci
  • same size
  • same genes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

Mitosis - Prophase

What happens to DNA and the nucleolus?

A

Chromatin coils and condenses (will take up stain more)

Nucleolus disappears and the nuclear membrane breaks down

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Mitosis - Prophase

What happens with spindle fibres?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

Mitosis - Prophase

In animal and some plant cells, what happens to centrioles?

A

Two centrioles migrate to opposite poles of the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

Mitosis - Prophase

What are centrioles?

A

Cylindrical bundles of proteins that help in the formation of the spindle

73
Q

Mitosis - Metaphase

What happens to chromosomes

A

Chromosomes are moved by the spindle fibres to form a metaphase plate along the equator

74
Q

Mitosis - Metaphase

What happens to spindle fibres?

A

Spindle fibres attach to centromere - longest phase as they have to align correctly

75
Q

Mitosis - Anaphase

What happens to the centromere and chromosomes?

A
  • Centromere divides causing chromatids to separate
76
Q

Mitosis - Anaphase

What happens to spindle fibres?

A

Contract, pulling chromatids to separate poles, forming V shape as they are dragged by their centromeres

77
Q

Mitosis - Telophase

What happens with the chromatids?

A

Reach the poles and are now called chromosomes - the two new sets of chromosomes assemble at each pole, beginning to uncoil

78
Q

Mitosis - Telophase

What happens to the nuclear membrane?

A

Nuclear envelope reforms and nucleolus is formed

79
Q

What actually is cytokinesis?

A

The actual division of the cell into two separate cells, beginning during telophase

80
Q

Cytokinesis

What happens in animals?

A

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
Q

Cytokinesis

Why can’t plant cells form a cleavage furrow?

A

They have cell walls

82
Q

Cytokinesis

How is a plant cell divided initially?

A

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
Q

Cytokinesis

How does the cell wall form around the cell surface membrane?

A

New sections form along the new section of membrane

84
Q

Cytokinesis

Plants

If the dividing cell wall was formed before the daughter cells separated, what would happen?

A

They would immediately undergo osmotic lysis from the surrounding water

85
Q

What do all cells begin as and known as?

A

Undifferentiated cells are known as stem cells

86
Q

What two qualities makes a stem cell?

A

Self renewal and potency

87
Q

What is self renewal in stem cells?

A

They can continuously divide and replicate

88
Q

What is potency in stem cells?

A

They have the capacity to differentiate into specialised cell types

89
Q

What happens when cel division is too slow and too rapid?

A

Too slow = ageing
Too rapid = tumours

90
Q

Define a stem cell

A

An unspecialised cell that is capable of diffusion and differentiation to become other cell types

91
Q

What happens to stem cells once they become specialised?

A

They lose the ability to divide and enter G0

92
Q

Why is self-renewal in stem cells important?

A

For the body to maintain a pool of stem cells to use in life so they don’t run out

93
Q

Why is cell differentiation important?

A

As specialised cels are used up, damaged or die, they can’t divide so they need to be replaced

94
Q

What is a stem cell’s potency?

A

A stem cell’s ability to differentiate into different cell types

95
Q

What does it mean if a cell has a great potency?

A

It can differentiate into many cell types

96
Q

Stem Cell Potency

What is totipotent?

A

Differentiate into any cell type

97
Q

Stem Cell Potency

What cells are totipotent?

A

Fertilised egg / zygote / 8-16 first mitotic divisions

98
Q

Stem Cell Potency

What is pluripotent?

A

They can differentiate into all tissue types but not whole organisms

99
Q

Stem Cell Potency

Where can pluripotent cells be found?

A

In early embryos and are the origin of the different types of tissue within an organism

100
Q

Stem Cell Potency

What is multipotent?

A

Can form a range of cells within a certain type of tissue

101
Q

Stem Cell Potency

Where can multipotent cells in blood cells?

A

Haematopoetic stem cells in bone marrow are multipotent because this gives rise to the various types of blood cell.

102
Q

Stem Cell Potency

What other cells are mutlipotent?

A

Bone marrow, cord blood, adipose tissue, skin, MSCs

103
Q

Erythrocytes and neutrophils are both present in blood. How is this differentiation?

A

They are both adapted to their specific function

104
Q

Where are all blood cells derived from?

A

Bone marrow

105
Q

How long is the blood cell of a mammalian erythrocyte?

106
Q

The stem cell colonies in bone marrow produce how many erythrocytes to keep up with demand?

A

3 billion per kg of body mass per day

107
Q

How long do neutrophils live for?

108
Q

The stem cell colonies in bone marrow produce how many neutrophils to keep up with demand?

A

1.6 billion per kg per hour

This figure increases during infection

109
Q

Embryonic stem cells are present when?

A

At an early stage of embryo development and are totipotent

110
Q

What must be destroyed and when to get embryonic stem cells?

A

After about seven days, a blastocyst (mass of cells) has formed and cells are now pluripotent

111
Q

Tissue / adult stem cells are present when and where?

A

From birth in bone marrow

112
Q

What potency do adult stem cells have?

A

Multipotent, but there is new evidence that they can be artificially triggered to become pluripotent

113
Q

Where can stem cells be harvested from that’s not bone marrow?

A

Umbilical cord of newborn babjes

114
Q

Advantages of getting stem cells from umbilical cords?

A
  • Plentiful supply of umbilical cords
  • Invasive surgery isn’t needed
115
Q

Where are stem cells present in plants?

A

Meristematic tissue - this is found wherever growth is occurring in plants (roots/shoots)

116
Q

Where is meristematic tissue found that’s not in roots and shoots?

A

Sandwiched between the phloem and xylem issues called the vascular cambium

117
Q

Stem cells transplanted into specific areas have what potential?

A

To treat certain diseases

118
Q

What diseases can stem cells treat in the future?

A

Heart disease
Type 1 diabetes
Parkinson’s disease
Alzheimer’s disease
Macular degeneration
Birth defects
Spinal injuries

119
Q

How are stem cells already used to treat burns?

A

Stem cells grown on biodegradable meshes can produce new skin Whicker than the normal process of taking a graft from another body part

120
Q

How are stem cells used in drug trials?

A

Potential new drugs can be tested on cultures of stem cells before being tested on humans/animals

121
Q

How are stem cells used in developmental biology?

A

The study of the changes that occur as multicellular organisms grow and develop from a single cell (fertilised egg)

122
Q

Where were embryonic stem cells first used?

A

Donated from those left over after fertility treatment

123
Q

What is the UK law most recently on embryonic stem cells?

A

Embryos can be specifically created in a lab as a source of stem cells

124
Q

What are the ethical oppositions against embryonic stem cells?

A
  • religion
  • many people begin life begins at conception, so you’re killing a life
125
Q

What are induced pluripotent stem cells (iPSCs)?

A

Adult age cells that have been genetically modified to act like embryonic stem cells and so are pluripotent

126
Q

What happens to cambium cells that differentiate to form xylem?

A
  • they lose their cytoplasm
  • deposit lignin in their cell walls
  • lose their end cell walls
127
Q

What happens to cambium cells that differentiate to form phloem?

A
  • lose some of their cytoplasm
  • lose organelles
  • develop sieve plates
128
Q

What are haematopoetic stem cells?

A

A multipotent blood stem cell located in bone marrow (in colonies)

129
Q

What can haematopoetic stem cells differentiate into?

A

Several types of blood cell types like lymphocytes, monocytes, neutrophils

130
Q

What can haematopoetic stem cells not differentiate into?

A

Brain cells, bone cells, or other non-blood cell types

131
Q

What are cells with two chromosomes?

132
Q

What are sex cells called?

133
Q

What is a fertilised egg called?

134
Q

Each characteristic of a gene is coded for by what?

A

Two copies of each gene, one from each parent

135
Q

What are homologous chromosomes?

A

Matching sets of chromsomes

136
Q

What is an allele?

A

Different versions of the same gene

137
Q

What qualities do homologous chromosomes have?

A
  • same loci
  • same shape
  • same size
  • same position of centromeres
138
Q

Mitosis VS Meiosis

How many daughter cells?

A

Mitosis = 2
Meiosis = 4

139
Q

Mitosis VS Meiosis

How many divisions?

A

Mitosis = 1 nuclear, 1 cytoplasmic
Meiosis = 2 nuclear, 2 cytoplasmic

140
Q

Mitosis VS Meiosis

Gamete / Somatic (body) cell?

A

Mitosis = somatic
Meiosis = gamete

141
Q

Mitosis VS Meiosis

Does crossing over occur?

A

Mitosis = no
Meiosis = yes

142
Q

Mitosis VS Meiosis

Reason for cell division

A

Mitosis = TOAD
Meiosis = sexual reproduction

143
Q

What do you not get from asexual reproduction?

A

Variation because the offspring are clones of the parent

144
Q

What is a male gametocyte (sperm) called?

A

Spermatocyte

145
Q

What is a female gametocyte (egg) called?

146
Q

Meiosis

What happens in interphase?

A

Same as mitosis with G1, S and G2 phases

147
Q

Meiosis

What happens in Meiosis 1?

A

Reduction division where homologous chromosomes separate into two cells

148
Q

Meiosis

What happens in Meiosis 2?

A

Pairs of chromatids are separated like in mitosis

149
Q

Meiosis

What suggests meiosis evolved from mitosis?

A

First stage as mitosis is the same (interphase)

150
Q

Meiosis

Why is it helpful to have duplicate chromatids?

A

Increases potential for genetic variation

151
Q

Meiosis

What happens in Prophase 1?

A
  • DNA condenses = visible chromosomes
  • nuclear envelope disintegrates
  • nucleolus disappears
  • spindle fibres formation begins
152
Q

Meiosis

Prophase 1

What is a pair of homologous chromosomes called?

A

A bivalent = homologous chromosomes undergo a process called synapsis

153
Q

Meiosis

Prophase 1

What is chiasma (chiasmata; plural)?

A

The point at which the crossing over occurs

154
Q

Meiosis

Prophase 1

What is crossing over?

A

Crossing over of genetic material between non-sister chromatids as they are very close together and become entangled

155
Q

Meiosis

Prophase 1

What does crossing over result in?

A

Recombinant DNA = exchange of genetic material creates new combinations on chromatids

156
Q

Meiosis

Metaphase 1

Where does the bivalent go?

A

Lines up along the equator of the spindle, with spindle fibres attached to the centromeres

157
Q

Meiosis

Metaphase 1

What do the maternal and paternal chromosomes in each pair do?

A

They position themselves independently of the others = independent assortment

158
Q

Meiosis

Metaphase 1

What does independent assortment mean?

A

That the proportion of paternal/maternal chromosomes that end up on each side of the equator is random and due to chance

159
Q

Meiosis

Metaphase 1

What does independent assortment result in?

A

Genetic variation

160
Q

Meiosis

What generally happens Metaphase 1?

A
  • 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
Q

Meiosis

Metaphase 1

What is the equator also called that homologous chromosomes line up along?

A

Metaphase plate

162
Q

Meiosis

What happens in Anaphase 1?

A
  • homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite end of the spindle
  • centromeres do not divide
163
Q

Meiosis

What happens in telophase 1?

A
  • chromosomes arrive at opposite poles
  • spindle fibres break down
  • nuclear envelope reforms
164
Q

Meiosis

What do plant cells sometimes do at the end of Meiosis 1?

A

Skip telophase 1 and go straight into meiosis 2

165
Q

Meiosis

What happens in plant cells during the start of cytokinesis in Meiosis 1?

A

vesicles from the Golgi gather along the equator of the spindle

166
Q

Meiosis

How does a cell surface membrane form in plants in cytokinesis 1?

A
  • 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
Q

Meiosis

How is the cell walls of plant cells created during cytokinesis 1?

A

Layers of cellulose are laid upon the middle lamella to form the walls

168
Q

Meiosis

What doesn’t happen between Meiosis 1 and 2?

A

Interphase so DNA isn’t replicated

169
Q

Meiosis

What happens in Prophase 2?

A
  • nuclear envelope breaks down and chromosomes condense
  • a spindle forms at a right angle to the old one
170
Q

Meiosis

What happens in Meiosis 2?

A

Chromosomes (not in pairs) line up in single file along the equator of the spindle

171
Q

Meiosis

What does not happen in Prophase 2?

A

Crossing over

172
Q

Meiosis

What happens in Anaphase 2?

A
  • centromeres divide and individual chromatids are pulled to opposite piles
  • this creates 4 groups of chromosomes that are haploid
173
Q

Meiosis

What happens in Telophase 2?

A

Nuclear membranes form around each group of chromosomes

174
Q

Meiosis

What happens in cytokinesis 2?

A

Cytoplasm divides as new cell surface membrane are formed creating 4 haploid cells

175
Q

Meiosis

What is the key difference between metaphase 1 and 2?

A

Metaphase 1 = homologous chromosomes pair up at the metaphase plate

Metaphase 2 = single chromosomes line up at the metaphase plate

176
Q

Meiosis

When does independent assortment happen?

A

Metaphase 1 and 2

177
Q

Meiosis

Chromosomal numbers before and after mitosis

A

Before interphase = 46 chromosomes
= 46 chromatids
After interphase = 46 chromosomes
= 92 chromatids

178
Q

Meiosis

Chromosome numbers after meiosis 1 and meiosis 2

A

Meiosis 1 = 23 chromosomes
= 46 chromatids
Meiosis 2 = 23 chromosomes
= 23 chromatids

179
Q

Meiosis

Summarise chromosomal numbers

A

46 —> 23 —> 23

A-level Biology (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions