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OCR A level Biology > 2.1.6 - Cell Division, Cell Diversity and Cellular Organisation > Flashcards

2.1.6 - Cell Division, Cell Diversity and Cellular Organisation Flashcards

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1
Q

What’s in interphase

A

G1
S
G2

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2
Q

G0

A

Cell has left cell cycle:
To differentiate
Apoptosis
Senescence

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3
Q

Senescence

A

Cells no longer divide

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4
Q

Checkpoints in cell cycle

A

At G1

At G2

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5
Q

Why are there checkpoints

A

To prevent uncontrolled division that would lead to tumours

To detect and repair damage to DNA

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6
Q

M phase

A

Checkpoint chemical triggers condensation of chromatin
Cell growth stops
4 stages of mitosis
Cytokinesis then occurs

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7
Q

G1

A

Cells grow
Transcription of genes to make RNA occurs
Synthesis of biological molecules occur e.g. protein synthesis

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8
Q

S phase

A

DNA replicates (doubles)
Each chromosome has two sister chromatids
Once the cell has entered this phase, it is committed to completing the cell cycle

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9
Q

Why does S phase happen very rapidly

A

Exposed DNA base pairs are more susceptible to mutagens so this phase happens quickly to reduce the chances of mutations

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10
Q

G2

A

Cells grow
Chemicals stimulate histones and formation of the spindle
Organelles duplicate

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11
Q

Prophase

A 
Chromosomes condense 
Centrioles duplicate and move to opposite poles 
Mitotic spindle begins to form 
Nuclear envelope breaks down 
Nucleolus no longer visible
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12
Q

Metaphase

A

Chromosomes align at equator and attach by their centromeres
Two sister chromatids of each chromosome are attached to spindle fibres

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13
Q

Anaphase

A

Centromere splits
Sister chromatids separate from each other and are pulled towards opposite poles of the cell due to spindle fibres shortening (now chromosomes)

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14
Q

Telophase

A

Chromosomes decondense
Spindle disappears
Nuclear envelope reforms and a nucleolus reappears

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15
Q

Cytokinesis in an animal cell

A

An actin ring around the middle of the cell pinches inwards, creating an indentation called the cleavage furrow

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16
Q

Cytokinesis in a plant cell

A

The cell plate forms down the middle of the cell, creating a new wall that partitions it in two

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17
Q

Where does mitosis occur in plants

A

Roots

Shoots

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18
Q

Prophase I

A

Starting cell is diploid

Homologous chromosomes pair up and exchange fragments (crossing over of non-sister chromatids)

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19
Q

Metaphase I

A

Homologue pairs line up at the metaphase plate

The orientation of pairs is random

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20
Q

Anaphase I

A

Homologues separate to the opposite ends of the cell

Sister chromatids stay together

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21
Q

Telophase I

A

Newly forming cells at haploid

Each chromosome has 2 non-identical sister chromatids

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22
Q

Prophase II

A

Chromosomes condense

Spindle fibres begin to capture chromosomes

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23
Q

Metaphase II

A

Chromosomes line up individually along the equator

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24
Q

Anaphase II

A

Independent segregation of sister chromatids to opposite ends of the cell

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25
Q

Telophase II

A

New forming gametes are haploid

Each chromosome has just one chromatid

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26
Q

Reasons we get many genetically different gametes

A

Crossing over

Random orientation of homologue pairs

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27
Q

How does crossing over ensure genetically different gametes

A

The points where homologues cross over and exchange genetic material are chosen more or less at random
They will be different in each cell and humans undergo meiosis a lot

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28
Q

How does random orientation of homologue pairs ensure genetically different gametes

A

The random orientation in metaphase I allows for the production of gametes with many different assortments of homologous chromosomes

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29
Q

Why do we need mitosis

A

Growth
Repair
Asexual reproduction

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30
Q

Genetic variation in meiosis

A

Crossing over genetic material (allele reshuffling) in prophase I
Independent assortment of homologous chromosomes in metaphase I
Independent assortment of sister chromatids in metaphase II
Independent segregation of sister chromatids in anaphase II

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31
Q

How does sexual reproduction increase genetic variation

A

It involves the combining of genetic material from 2 individuals
Variation increases species chance of survival due to adaptations

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32
Q

Tissues

A

A group of specialised cells working together to perform a specific function

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33
Q

Organs

A

A group of tissues working together to perform a specific function

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34
Q

Animal tissues

A

Epithelial
Connective
Muscle
Nervous

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35
Q

Plant tissues

A

Epidermal
Vascular
Meristematic

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36
Q

Epithelial tissue

A

This tissue lines free surfaces in the body such as the skin, cavities of the digestive and respiratory system, blood vessels, heart chambers and walls of organs

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37
Q

Characteristics of epithelial tissue

A

Made up almost entirely of cells
Cells are very close to each other
No blood vessels
Squamous epithelium is made of specialised squamous
Ciliated epithelium is made up of ciliated epithelial cells

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38
Q

Squamous epithelium

A

Very flat cells
Only one cell thick
Form lining of lungs and of blood vessels

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39
Q

Ciliated epithelium

A

Cells that have cilia on the surface that move in a rhythmic manner
Lines the trachea

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40
Q

How do epithelium cells recive nutrients

A

Diffusion from tissue fluid in the underlying connective tissue

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41
Q

What does connective tissue consist of

A

A non-living extracellular matrix

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42
Q

What does a non-living extracellular matrix contain

A

Proteins e.g. collagen and elastin

Polysaccharides (hyaluronic acid, which traps water)

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43
Q

What does a non-living extracellular matrix do

A

Separates the living cells within the tissue

Strengthens it

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44
Q

Examples of connective tissues

A 
Blood 
Bone 
Cartilage
Tendons
Skin 
Ligaments
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45
Q

Where is cartilage found

A

In the outer ear, nose and at the edge of and in between bones

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46
Q

What is cartilage composed of

A

Chondrocyte cells embedded in an extracellular matrix that secrete collagen

47
Q

Muscle tissue is well …

A

… vascularised

48
Q

What do muscle cells contain

A

Special organelles called myofilaments made of actin and myosin, these allow the muscle tissue to contract

49
Q

Types of muscle tissue

A

Skeletal
Cardiac
Smooth

50
Q

Skeletal muscle

A

Joined to bones by tendons, causing bones to move

Forms multinucleate fibres containing protein filaments that slide pass each other

51
Q

Cardiac muscles

A

Makes up the walls of the heart, allowing it to pump

Forms cross-bridges to ensure that the muscle contracts in a squeezing action

52
Q

Smooth muscle

A

Lines walls of intestines, blood vessels, uterus and urinary tracts
Propels substances along these tracts

53
Q

What does epidermal tissue consist of

A

Flattened cells that apart from guard cells lack chloroplasts and form a protective covering over leaves, stems and roots

54
Q

What do some epidermal cells have

A

Walls with a waxy substance (cuticle)

Important as reduces water loss - plants in dry areas

55
Q

What does meristematic tissue contain

A

Stem cells

From this all other plant tissues are derived

56
Q

Where is meristematic tissue found

A

Meristems:
At root and shoot tips
In the cambium of vascular bundles

57
Q

Features of meristem cells

A

Have thin walls containing little cellulose
Do not have chloroplasts
Do not have a large vacuole
Divide by mitosis and differentiation into other types of cell

58
Q

What is vascular tissue concerned with

A

Transport

59
Q

Xylem vessels

A

Carry water and minerals from roots to all parts of the plant

60
Q

Phloem sieve tubes

A

Transfer the products of photosynthesis in solution from leaves to parts of the plant that do not photosynthesise, such as roots, flowers and growing shoots
Contains sieve tube elements and companion cells

61
Q

How do xylem derive from cambium

A

Differentiation
Lignin is deposited in cell wall - reinforcement and waterproofing
Kills the cells - non - living xylem cells
Ends of cells break down so xylem forms continuous columns with wide lumens to carry water and dissolved minerals
Lignification is incomplete in some areas -> bordered pits

62
Q

How do phloem derive from cambium cells

A

Differentiation:
Sieve tubes lose most of their organelles and sieve plates develop between them from the numerous sieve pores that develop

Companion cells retain their organelles and continue metabolic functions to provide ATP for the active loading of sugars into the sieve tubes

63
Q

Function of roots

A

Anchorage in soil
Absorption of mineral ions and water
Storage

64
Q

Life processes carried out by the digestive system

A

Nutrition to provide ATP and materials for growth and repair

65
Q

Life processes carried out by the circulatory system

A

Transport to and from cells

66
Q

Life processes carried out by the respiratory system

A

Breathing and gaseous exchange excretion

67
Q

Life processes carried out by the urinary system

A

Excretion and osmoregulation

68
Q

Life processes carried out by the integumentary system

A

Waterproofing
Protection
Temp regulation

(Skin, hair and nails)

69
Q

Life processes carried out by the musculoskeletal system

A

Support
Protection
Movement

70
Q

Life processes carried out by the immune system

A

Protection against pathogens

71
Q

Life processes carried out by the nervous and endocrine systems

A

Communication
Coordination
Control

72
Q

Life processes carried out by the lymphatic system

A

Lymph nodes and vessels transport fluid back to the circulatory system and is also important in resisting infections

73
Q

Why are stem cells able to express all their genes

A

All genes are switched on

74
Q

Potency

A

A cell’s ability to differentiate

75
Q

Totipotent

A

Can differentiate into any type of cell and produce a whole organism (zygote)

76
Q

Pluripotent

A

Can form all tissue types but not produce an organism

77
Q

Multipotent

A

Can become any type of cell within a group of cells e.g. any type of blood cell

78
Q

Sources of stem cells in humans

A

Embryonic stem cells
Umbilical cord blood
Adult stem cells found in bone marrow of flat bones, skin, adipose tissue, brain, blood
iPS (induced pluripotent stem cells)

79
Q

iPS

A

Developed in lab by reprogramming differentiated cell’s to switch on genes and become pluripotent

80
Q

Current uses of stem cells

A

Bone marrow transplants (used to treat sickle-cell anaemia and leukaemia)
Drug research (check toxicity)
Test effectiveness of medicines
Study cell function to find out what can make it fail
Developmental research - studying cells to see how they develop into diff cell types

81
Q

Types of blood cells produced from stem cells

A

Erythrocytes

Neutrophils

82
Q

Haploid

A

Having only one set of chromosomes

83
Q

Homologous

A

Matching chromosomes, containing the same genes at the same places (loci)
May contain different alleles for some of the genes

84
Q

Diploid

A

Having two complete sets of chromosomes (found as pairs)

85
Q

Maternal homologues

A

These chromosomes will have the same genes as the maternal homologue in the chromosome pair

86
Q

Paternal homologues

A

These chromosomes will have the same genes as the paternal homologue in the chromosome pair

87
Q

Non-sister chromatids

A

Replicated of chromosomes, originating from different chromosomes

88
Q

How are palisade cells adapted

A

Long and cylindrical - able to pack several together
Chloroplasts - absorb as much light as possible
Large vacuole - stores nutrients/water, provides structural support, stores waste
Cytoskeleton / motor proteins - moves chloroplasts to reduce CO2 diffusion pathway

89
Q

How are sperm cells adapted

A

Mitochondria - releases energy for movement
Acrosome - digestive enzymes (egg)
Protein fibres in flagellum - enable rapid movement/ strength
Nucleus - contains genetic info (haploid gamete)

90
Q

How are guard cells adapted

A

Thicker inner wall - so cell doesn’t change symmetrically when turgid
Large vacuole - to take up water and expand stoma
Active pump - move water in/out to alter water potential of cell
Stomata - O2 and CO2 can diffuse out

91
Q

How are ciliated epithelial cells adapted

A

Cilia - move mucus

Goblet cells - produce mucus and trap harmful substances

92
Q

How are squamous epithelial cells adapted

A

Flat - cover a large area

Thin - short diffusion pathway

93
Q

How are neutrophils adapted

A

Membrane bound receptors - recognise materials that needs to be destroyed
Well developed cytoskeleton - enable movement
Many mitochondria - release energy needed
Multi lobed nucleus - easy to squeeze through small gaps
Granular cytoplasm - contains lysosomes w/ digestive enzymes to attack pathogens

94
Q

How are erythrocytes adapted

A

No nucleus - more space for haemoglobin
Small and flexible - fit through capillaries
Flattened bioconcave shape - increase SA:V - take in more O2
Well developed cytoskeleton - allows it to change shape

95
Q

How are root hair cells adapted

A

Long extension - increase surface area for diffusion
Active pump - absorb mineral ions and water through active transport
Thin cell wall - short diffusion pathway
Vacuole containing sap - low water potential (sugars and ions) - water can diffuse in

96
Q

How are sieve tube elements and companion cells linked

A

By numerous plasmodesmata

97
Q

Plasmodesmata

A

Connections between cells where the cytoplasm is continuous

98
Q

Homologous pair of chromosomes

A

Chromosomes that contain same alleles
Same length
Centromeres in same position

99
Q

Bivalent

A

Pair of homologous chromosomes

100
Q

G1 checkpoint

A

Checks cell is ready for S phase

101
Q

G2 checkpoint

A

Checks DNA has replicated correctly

102
Q

Do plant cells have centrioles

A

No

103
Q

Centromere

A

Where each chromatid touches (usually in the middle)

104
Q

Why is the second division in meiosis different to mitosis

A

The separating chromatids of a pair aren’t the same

105
Q

Where are erythrocytes and neutrophils produced

A

Stem cells in bone marrow

106
Q

What are spindle fibres made from

A

Proteins

107
Q

In what stage of meiosis are chiasmata formed

A

Prophase I

108
Q

Why is the formation of chiasmata an important feature of meiosis

A

It provides opportunities for new genotypes to arise

109
Q

Telomere

A

A region of repetitive nucleotide sequences at the end of a chromatid

110
Q

How are erythrocytes formed from stem cells

A

Haemoglobin is synthesised

Organelles associated w/ protein synthesis are digested

111
Q

Examples of pluripotent cells

A

Embryonic cells in blastocyst

112
Q

Examples of totipotent cells

A

Stem cells of fertilised eggs

113
Q

Meiosis in plant cells

A

Skip from Anaphase 1 to Prophase 2

114
Q

Muscle tissue

A

Group of cells that can contract together

OCR A level Biology (25 decks)

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