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A-Level OCR Biology > Chapter 6 - Cell Divisions > Flashcards

Chapter 6 - Cell Divisions Flashcards

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1
Q

What are the 3 parts of interphase?

A

G1, S, G2

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2
Q

What happens in G1?

A
  • Organelles replicate

- Cell grows in size

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3
Q

What happens in S?

A
  • DNA is replicated in the nucleus
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4
Q

What happens in G2?

A
  • Energy stores are increased

- Cell continues to grow in size

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5
Q

What is checked at the G1 checkpoint?

A
  • Cell size
  • Nutrients
  • Growth factors
  • DNA damage
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6
Q

What is checked at the G2 checkpoint?

A
  • Cell size
  • DNA replication
  • DNA damage
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7
Q

What is G0?

A

The phase when the cell leaves the cycle (resting state)

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8
Q

What are 3 common reasons why cells enter G0?

A
  • The cell has differentiated
  • The cell is damaged
  • The cell is old
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9
Q

What are senescent cells?

A

When old cells stop dividing and undergo changes

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10
Q

What is cytokineses?

A

Where the cytoplasm divides and two cells are produced

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11
Q

What is the spindle assembly check point?

A

A checkpoint during mitosis where all chromosomes should be attached to spindles and be alligned

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12
Q

What is the spindle assembly check point also known as?

A

The metaphase checkpoint

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13
Q

What is mitosis?

A

Nuclear division

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14
Q

What would the indefinite replication of cells lead to?

A
  • Mutations occur during cell division
  • Increased cell replication = increased chance of mutation
  • Can lead to harmful mutations e.g. tumours/cancer
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15
Q

Why is DNA length give by number of base pairs?

A

Because DNA is double stranded

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16
Q

What does mitosis produce?

A

Two identical daughter cells

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17
Q

How are chromatids produced?

A

When a chromosome is converted into two identical DNA molecules (chromatids)

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18
Q

What is the centromere?

A

The centre point of two chromatids joining to form a chromosome

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19
Q

How is chromatin produced?

A

When chromatids and proteins called histones combine

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20
Q

What are the four stages of mitosis?

A

Prophase, metaphase, anaphase and telophase

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21
Q

What is the acronym to remember the order of mitosis phases?

A

P-MAT

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22
Q

What happens to the nucleolus during prophase?

A

It disappears

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23
Q

What do chromatin fibers do during prophase?

A

They coil and condense to form chromosomes

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24
Q

What do spindle fibres do during prophase?

A

They move chromosomes to the centre of the cell

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25
Q

What has happened by the end of prophase?

A

The nuclear envelope has disappeared

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26
Q

What happens in animal and some plant cells during prophase to do with centrioles?

A

Two centrioles move to opposite poles of the cell

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27
Q

What happens during metaphase?

A

The chromosomes are moved by the spindle fibres to form a line across the centre of the cell, and then are held in position

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28
Q

What is the metaphase plate?

A

The (invisible) line through the centre of the cell, where chromosomes line up (during metaphase)

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29
Q

What happens during anaphase?

A

The centromeres holding the pairs of chromatids together in each chromosome divide
The chromatids are separated and pulled to opposite poles of the cell by the shortening of the spindle fibres

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30
Q

When does cytokinesis begin?

A

During telophase

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31
Q

What happens during telophase?

A

Two new sets of chromosomes assemble at each pole of the cell
The nuclear envelope reforms around these chromosomes
The chromosomes begin to uncoil and the nucleolus is formed
Cytokinesis begins

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32
Q

What happens in cytokinesis in animal cells?

A
  • Cleavage furrow forms around the middle of the cell

- Cytoskeleton pulls cell surface membrane inwards until it is close enough to fuse around the middle, forming two cells

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33
Q

What happens in cytokinesis in plant cells?

A

Vesicles gather along the middle of the cell and fuse with one another and the cell surface membrane, eventually the cell divides, forming two separate cells

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34
Q

What are homologous chromosomes?

A

Homologous chromosomes are chromosome pairs (one from each parent) that are similar (e.g. in length)

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35
Q

Overview of meiosis 1

A

The first division is the reduction division when the pairs of homologous chromosomes are separated into two cells- each will contain 23 chromosomes

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36
Q

What is the name for cells with only 23 chromosomes?

A

Haploid

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37
Q

Overview of meiosis 2

A

Similar to mitosis- the pairs of chromatids present in each cell are separated, forming two more cells (4 total overall)

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38
Q

What is the main thing that occurs in prophase 1 of meiosis?

A

Crossing over, where homologous chromosomes pair up and trade genes, forming bivalents

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39
Q

What is the main thing that occurs in metaphase 1 of meiosis?

A

Homologous pairs together assemble along the metaphase plate equator, contrary to in mitosis where they line up individually

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40
Q

What is independent assortment?

A

Where the orientation and location of each homologous pair on the metaphase plate equator is random and independent of any other homologous pair, meaning there are many different combinations that can occur

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41
Q

What does independent assortment result in?

A

Genetic variation

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42
Q

What are the main difference between anaphase 1 in meiosis and anaphase in mitosis?

A

In anaphase 1, homologous chromosomes are pulled to opposite poles, and chromatids stay joined to each other, whereas in anaphase in mitosis, the individual chromatids are pulled apart

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43
Q

What does diploid mean?

A

2 sets of chromosomes (46)

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44
Q

What happens to the number of chromosomes during prophase?

A

They remain the same, however each DNA molecule (aka chromosome) is converted into two identical chromatids

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45
Q

What happens in telephase 1 of meiosis?

A
  • Nuclear membrane reforms around each group of chromosomes

- Cell undergoes cytokinesis

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46
Q

What happens to the number of chromosomes following meiosis 1?

A

Goes from one diploid cell to two haploid cells

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47
Q

What is meiosis 2 similar to?

A

Mitosis

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48
Q

What are the 4 final products of meoisis?

A

4 non identical haploid daughter cells

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49
Q

What are erythrocytes also known as?

A

Red blood cells

50
Q

Erythrocytes properties (3)

A
  • Flattened biconcave shape
  • No nuclei or many other organelles
  • Flexible
51
Q

Why do erythrocytes have a flattened biconcave shape?

A

Increase surface area to volume ratio - transports oxygen around the body more efficiently

52
Q

Why do erythrocytes have no nuclei or many other organelles?

A

`Increases space available for haemoglobin

53
Q

Why are erythrocytes flexible?

A

Can squeeze through narrow capillaries

54
Q

What are neutrophils?

A

A type of white blood cell

55
Q

Neutrophils properties (3)

A
  • Essential role in immune system
  • Multi-lobed nucleus
  • Granular cytoplasm contain many lysosomes
56
Q

Why do neutrophils have a multi-lobed nucleus?

A

Can squeeze through small gaps to get to the site of infection

57
Q

Why do neutrophils have many lysosomes?

A

Lysosomes contain enzymes used to attack pathogens

58
Q

Sperm cells properties (3.5)

A
  • Function is to deliver genetic information to the female gamete
  • Flagellum/tail and many mitochondria
  • Head of sperm contains digestive enzymes
59
Q

Why do sperm cells have a flagellum/tail?

A

Flagellum makes them capable of movement, and mitochondria provide energy needed to move/swim

60
Q

Why do sperm cells have digestive enzymes in their head?

A

To break down the protective layers of the egg, allows penetration and fertilisation

61
Q

Palisade cells properties (5)

A
  • Present in mesophyll
  • Contain chloroplasts
  • Thin walls
  • Large vacuole
  • Chloroplasts can move within the cytoplasm
62
Q

Why do palisade cells contain chloroplasts?

A

To absorb large amounts of light for photosynthesis

63
Q

Why do palisade cells have thin walls?

A

To increase rate of diffusion of CO2

64
Q

Why do palisade cells have a large vacuole?

A

To maintain turgor pressure

65
Q

Why can chloroplasts within the cytoplasm of palisade cells move?

A

To absorb more light

66
Q

Root hair cells properties (2)

A
  • Present at surfaces of roots near growing tips

- Have long extensions called root hairs

67
Q

Why do root hair cells have root hairs?

A

To increase the surface area to volume ratio of the cell, which maximises the uptake of water and minerals from the soil

68
Q

Guard cells properties

A
  • Pairs of guard cells on the underside surfaces of leaves form small openings
  • Cell wall thicker on one side than the other
  • Change shape depending on water/K ion levels
69
Q

What are the small openings between guard cells known as?

A

Stomata

70
Q

What do guard cells control?

A

The entry of CO2, and the exit of water and oxygen

71
Q

Where are stomata found and why?

A

On the underside of plant leaves, to reduce their exposure to heat and air current

72
Q

How and why do stomata become turgid?

A

When the concentration of K ions within guard cells are high, water diffuses into the cells by osmosis, causing the cells to become turgid and have a large stomatal opening for CO2 to enter

73
Q

How and why do stomata become flaccid?

A

When the concentration of K ions within guard cells are low, water diffuses out of the cells by osmosis, causing the cells to become flaccid and the stomatal opening closes- this is to prevent further loss of water from the plant.
Also stomata close at night, as CO2 is not needed as photosynthesis is not occuring

74
Q

What is the effect of one cell wall being thicker than another in guard cells?

A

The cell does not change shape symmetrically as its volume changes

75
Q

What are tissues?

A

Made up of a collection of differentiated cells that have a specialised function/functions. As a result each tissue is adapted for a particular function

76
Q

What are the four main categories of tissues in animals?

A
  • Nervous tissue- adapted to support the transmission of electrical impulses
  • Epithelial tissue- adapted to cover internal and external body surfaces
  • Muscle tissue- adapted to contract
  • Connective tissue- adapted to either hold tissues together or as a transport medium
77
Q

What is squamous epithelium also known as?

A

Pavement epithelium

78
Q

Where do you find squamous epithelium?

A

Lining of the lungs

79
Q

Why is squamous epithelium very thin?

A

Due to the flat cells that make it up, and because it is just one cell thick

80
Q

What is the function of squamous epithelium?

A

To allow for rapid diffusion

81
Q

What is squamous epithelium made up of?

A

Specialised squamous epithelial cells

82
Q

What is ciliated epithelium made up of?

A

Specialised ciliated epithelial cells

83
Q

What are cilia?

A

Hair like structures found on ciliated epithelial cells, that move in a rhythmic manner, causing (in the respiratory tract) mucus, dust and bacteria to be swept away

84
Q

What do goblet cells do?

A

Release mucus, which traps any unwanted particles, which may be bacteria, from entering the lungs/alveoli

85
Q

What type of tissue is cartilage?

A

Connective tissue

86
Q

Where is cartilage found?

A

Outer ear, nose and ends/between bones

87
Q

What fibres does cartilage contain?

A

Fibres of the proteins elastin and collagen

88
Q

What is cartilage made up of?

A

Chondrocyte cells embedded in an extracellular matrix

89
Q

What is the function of cartilage?

A

Prevents bones rubbing together and causing damage

90
Q

What is the function of muscle?

A

Shortens in length (contracts) to move bones

91
Q

What is skeletal muscle tissue?

A

Muscles attached to the bone

92
Q

What is epidermis?

A
  • Single layer of closely packed cells covering the surface of plants
  • Usually covered by waxy, waterproof cuticle
  • Contain stomata
93
Q

What is vascular tissue in plants?

A

Adapted for transport of water and nutrients

94
Q

What is xylem tissue?

A
  • Vascular tissue

- Responsible for transport of water and minerals throughout plants

95
Q

What is the purpose of lignin?

A

Waterproof material that strengthens the xylem tissue in plants

96
Q

What are vessel elements?

A

Elongated dead cells

97
Q

What is phloem tissue?

A
  • Vascular tissue

- Responsible for transport of organic nutrients from photosynthesis to where it is needed in plants

98
Q

What is xylem tissue made up of?

A

Vessel elements (elongated dead cells)

99
Q

What is phloem tissue made up of?

A

Columns of sieve tube cells separated by sieve plates

100
Q

What is an organ?

A

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

101
Q

Example of organ in plants

A

Leaf- made up of vascular and epidermis tissue- adapted for photosynthesis

102
Q

What are organ systems?

A

Composed of a number of organs working together to carry out a major function

103
Q

The digestive system functions (4)

A
  • Takes in food and breaks down large insoluble molecules into small soluble ones
  • Absorbs nutrients into the body
  • Retains water needed by the body
  • Removes any undigested material from the body
104
Q

The cardiovascular system functions (2)

A
  • Moves blood around the body

- Provides a transport system for substances to be transported around the body (e.g. oxygen)

105
Q

The gaseous exchange system function

A
  • Brings air into the body so oxygen can be extracted and carbon dioxide expelled
106
Q

What stage of meiosis is reduction division?

A

Meiosis 1

107
Q

Do all cells in plants and animals begin differentiated?

A

No, all cells begin undifferentiated

108
Q

What does undifferentiated mean and what are these cells known as?

A

They are not adapted to any particular function, and have the potential to differentiate to become a specialised cell. These cells are called stem cells

109
Q

What is potency?

A

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

110
Q

What are the 3 different types of potency?

A
  • Totipotency
  • Pluripotent
  • Multipotent
111
Q

What are totipotent stem cells?

A

They can differentiate into any type of cell

112
Q

Example of totipotent cell

A

Very early embryonic stem cells

113
Q

What pluripotent stem cells?

A

They can differentiate into any tissue cell type

114
Q

3 sources of stem cells in animals

A
  • Embryos
  • Umbilical cord
  • Bone marrow
115
Q

After how long do embryonic stem cells become pluripotent?

A

7 days

116
Q

What is a blastocyst?

A

The mass of cells that form after 7 days after embryo production, turning the stem cells pluripotent

117
Q

Where are all blood cells derived from?

A

Stem cells in the bone marrow

118
Q

How could stem cells be used to treat heart disease?

A

Muscle tissue in the heart that has been damaged can be replaced and repaired by stem cells

119
Q

How could stem cells be used to treat Parkinson’s disease?

A

Some symptoms are caused by the death of dopamine producing cells- these can be replaced by stem cells

120
Q

3 areas in which stem cells are already being used

A
  • Treatment of burns- stem cells can produce new skin
  • Drug trials- drugs can be tested on cultures of stem cells
  • Developmental biology- can be studied to improve knowledge on how organisms grow
121
Q

Source of stem cells in plants

A

Meristems are pluripotent throughout the life of the plant, and are found in meristematic tissue

A-Level OCR Biology (21 decks)

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