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BIOLOGY A LEVEL > CHAPTER 6 - CELL DIVISION > Flashcards

CHAPTER 6 - CELL DIVISION Flashcards

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1
Q

What is the cell cycle?

A

A highly ordered sequence of events that takes place in a cell, resulting in division of the cell, and formation of two genetically identical daughter cells

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2
Q

What happens in Interphase

A

DNA is replicated and checked for errors

Protein synthesis occurs in the cytoplasm

Mitochondria grow and divide increasing in number

Chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number

The normal metabolic processes of the cell occur

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3
Q

What are the stages in Interphase

A

G1- First growth phase: proteins from which organelles are synthesised are produced and organelles replicate. The Cell increases in size

S - Synthesis phase: DNA is replicated in the nucleus

G2 - Second growth phase: The cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors

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4
Q

What are the two stages to Cell division

A

Mitosis/ Mitotic phase - Nucleus Divides

Cytokinesis - The Cytoplasm divides and two cells are produced

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5
Q

What is G0

A

The name of the phase where the cell leaves the cycle, either temporarily or permanently

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6
Q

What are the reasons for a cell entering the G0 stage

A

Differentiation - A cell that is specialised is no longer able to divide and will not enter the cell cycle again

DNA may be damaged, no longer viable. Most cells can only divide a limited amount of times, then eventually become senescent - higher proportion of cells become senescent with age, leads to cancer and arthritis etc…

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7
Q

How many checkpoints are there in the interphase and mitotic sections?

A

3
G1Checkpoint
G2 Checkpoint
Spindle assembly

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8
Q

What is checked at the G1 Checkpoint?

A

Occurs at end of G1 phase (before S phase)
Checks cell size, nutrients, growth factors and DNA damage

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9
Q

What happens if a cell fails a checkpoint?

A

Sent to G0/ resting state/ permanent cell arrest

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10
Q

What is checked during the G2 checkpoint

A

Happens before mitotic phase
Checks for Cell size, DNA replication and DNA Damage

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11
Q

What is checked at the metaphase checkpoint (Spindle assembly)

A

Chromosome attachment to spindle fibres
Alignment on metaphase plate

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12
Q

ADD FLASHCARD ON CELL-CYCLE REGULATION AND CANCER PG 122

A

innit

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13
Q

Mitosis and cytokinesis, are processes involved in the production of new cells. Explain the difference between mitosis and cytokinesis.

A

Mitosis is the process of replicating and diving the genome
cytokinesis is the physical division of the cell

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14
Q

Explain, with reference to the structure and function of proteins, the importance of G2 Checkpoint.

A

DNA has been checked for errors

change in sequence of bases is a mutation

(leads to) change in amino acid sequence

function of protein dependent on, 3D shape / tertiary structure

tertiary structure dependent on primary structure

primary structure is sequence
of amino acids

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15
Q

Suggest a disadvantage of indefinite cell division

A

Mutations occur during DNA replication

indefinite replication, increases chances of mutation / accumulation of mutations

increased chance of harmful mutation

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16
Q

Telomerases are enzymes that result in the elongation of telomere. They are not usually present in differentiated cells. Describe what the presence of telomerase could cause

A

indefinite replication

cancer / formation of tumour

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17
Q

A typical human cell contains 3x10^9 base pairs of DNA divided into 46 chromosomes. DNA replication in eukaryotic cells takes place at the rate of about 50 base pairs per minute. Calculate the time it would take to replicate a section of DNA of this length, assuming replication started at one end and dint stop until the other end

A

3 × 10^9 / 50

6 × 10^7

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18
Q

Suggest why the length of DNA is usually given by the number of base pairs rather than number of nucleotides

A

DNA is double stranded

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19
Q

The DNA of a eukaryotic cell is usually replicated in eight hours. Explain how this is possible

A

Many origins of replication

Simultaneous replication of different lengths

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20
Q

Suggest why it takes a much shorter time to replicate the genome of a prokaryotic cell

A

(prokaryotic) genome, is shorter / has fewer genes / has no introns

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21
Q

What is asexual reproduction

A

The production of genetically identical offspring from one parent in multicellular organisms including plants, fungi and some animals eg amoeba.

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22
Q

what happens to DNA during interphase

A

Replicated
Turns from a single chromatid per chromosome
to 2 chromatids per chromosome
Held by centromere
(pg 124)

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23
Q

What are the 4 stages of mitosis

A

Prophase, Metaphase, Anaphase, Telophase

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24
Q

What happens during prophase

A

Nucleolus disappears,

nuclear envelope is digested

Chromosomes coil and condense

Centrioles move to poles of cell

Spindle fibres attach to centromeres

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25
Q

What happens during metaphase

A

Spindle fibres move chromosomes to metaphase plate across equator of cell

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26
Q

What happens during anaphase

A

Centromeres pull chromosomes apart, shortening spindle fibres, forming V shapes with chromatids as they are pulled through cytosol

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27
Q

What happens during Telophase

A

Chromatids reached poles, now called chromosomes

New sets of chromosomes assemble

Nuclear envelope reforms

Nucleolus is reformed

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28
Q

What happens during cytokinesis

A

Actual division of cell into 2 separate cells, which began in telophase

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29
Q

What his formed during telophase in animal cells

A

Cleavage furrow, to allow separate fusion of two cell surface membranes

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30
Q

What is formed during telophase in plants

A

Vesicles from Golgi join in centre of cell and form a cell plate

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31
Q

Explain why we normally see chromosome as a double structure containing two chromatids

A

Chromosomes only become visible under the microscope during mitosis/meiosis

DNA needs to replicate for cell division. Chromosomes consist of two sister chromatids, which are identical copies of DNA

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32
Q

Explain why it is essential that DNA replication results in two exact copies of the genetic material

A

So that each daughter cell has identical DNA after mitosis/cell division

and correct number of chromosomes

eg, diploid after mitosis and haploid after meiosis.

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33
Q

Describe the differences between cytokinesis in animal and plant cells and give reasons for these differences

A

Animal cells cleavage furrow forms around middle of cell

Furrow pulls inwards and fuses

plants cells furrow cannot form due to cell wall

vesicle assemble across centre of cell and fuse

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34
Q

How many chromatids would be present in a human cell at prophase and at G1 during interphase

A

Prophase – 92 chromosomes have replicated

G1 – zero replication has not occurred yet

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35
Q

Explain why plant root tips are a good source of cells to examine for mitosis

A

Plant root tips continually grow at regions called meristems

Meristems are a good source of cells for studying mitosis as they are constantly diving

Plant cells are easy to obtain

and prepare for microscopy

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36
Q

What is a gamete

A

A (Haploid) sex cell

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37
Q

What is a zygote?

A

A fertilised egg cell

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38
Q

How many daughter cells does meiosis produce?

A

4 haploid cells - known as reduction division

39
Q

What is an Allele?

A

A version of a gene

Different alleles lead to different characteristics eg. blue eyes, green eyes

40
Q

What will different alleles have the same?

A

Locus (position on a particular chromosome)

41
Q

What are homologous chromosomes

A

A pair of same chromosomes, one from each parent

which have the same genes but can have different alleles of each gene

42
Q

How many stages of meiosis are there

A

2
Meiosis I and Meiosis II

43
Q

What happens in Meiosis I

A

The first division is the reduction division when the pairs of homologous chromosomes are separated into two cells.

Each intermediate cell will only contain one full set of genes instead of two, so the cells are haploid

44
Q

What happens in Meiosis II

A

Second division is similar to mitosis, and the pairs of chromatids present in each daughter cell are separated forming two more cells

Four haploid cells are produced in total
(pg 129)

45
Q

What happens in Prophase I

A

Chromosomes condense, nuclear envelope disintegrates, nucleolus disappears, spindle fibres form, bivalents form as chromosomes pairs (allows for crossing over)

46
Q

What happens in Metaphase I

A

Chromosomes align on equator of cell (metaphase plate)
Any random combination (independent assortment)

47
Q

What happens in Anaphase I

A

Homologous pair of chromosomes are pulled to each pole of the cell, still joined

DNA sections on sister chromatids which became entangled during crossing over break off and rejoin - forming chiasmata

Leads to genetic variation

48
Q

What happens in telophase I

A

Chromosomes assemble at each pole, nuclear membranes reform, chromosomes uncoil.

Cytokinesis then occurs, diploid to haploid complete

49
Q

What happens in Prophase II

A

Chromosomes (2 chromatids) condense
nuclear envelope is digested, spindle fibres form

50
Q

What happens during Metaphase?

A

Individual chromosomes align on metaphase plate

Due to crossing over, chromatids are no longer identical, so more independent assortment

51
Q

What happens in Anaphase II

A

Individual chromosomes are pulled to poles

52
Q

What happens in Telophase II

A

Chromosomes uncoil, Nuclear envelopes and Nucleolus becomes visible,

Cytokinesis occurs
forms 4 genetically different cells due to IA and CO

53
Q

State which division in meiosis is a reduction division

A

Meiosis I is a reduction division as each daughter cell is haploid from a diploid cell

54
Q

Explain why a reduction division is necessary in the production of gametes

A

Gametes are the sex cells and two sex cells (one from each parent) must combine to produce a diploid offspring

therefore gametes must contain only half the number of chromosomes/DNA, i.e., be haploid

55
Q

Explain the meaning of the term homologous chromosomes

A

A pair of same chromosomes, one from each parent

which have the same genes but can have different alleles of each gene

56
Q

Outline how you could observe meiosis in a plant cell

A

Anther(s) from a flower should be used

prepare a squash slide

use stain

observe using microscope

57
Q

Explain how crossing over and independent assortment lead to genetic variation

A

Crossing over –
homologous chromosomes pair up (in prophase), non-sister chromatids entangle (chiasmata)

and exchange genes/ alleles when they pull apart

Produces new combinations of alleles.

Independent assortment – pairs of homologous chromosomes (meiosis I)/chromosomes (meiosis II) line up on the equator and each (pair/chromosome) orientates independently

before being separated to opposite poles of the cell

This produces new combinations of alleles

58
Q

Suggest the importance of the creation of different allele combinations in populations

A

Creating different allele pairs during meiosis is an important source of genetic variation in a population.

Genetic variation is important for the process of natural selection

giving individuals in a population characteristics/traits that might give an advantage

in changing environment

eg. pathogen resistance. If there was no genetic variation in a population, the entire population would be vulnerable and there would be no opportunity for adaptation

59
Q

What are specialised cells?

A

Differentiated cells to carry out a function

60
Q

How are Red Blood Cells specialised to their function?

A

Biconcave shape - increases SA:V (diffusion)

Flexible - can squeeze through narrow capillaries

No Nucleus or many organelles - more oxygen can be transported

61
Q

How are White Blood Cells specialised to their function?

A

Multi-lobed nucleus - Easier of them to squeeze through small gaps to get to the site of infections

Granular Cytoplasm - Contains many lysosomes containing enzymes used to attack pathogens

62
Q

How are Sperm Cells specialised to their function?

A

Contain many mitochondria - lots of energy needed to move

Tail/Flagellum - Ability to move

Acrosome - contains digestive enzymes needed to digest layers around egg cell

63
Q

How are Palisade cells specialised to their function?

A

Contain chloroplasts - needed for photosynthesis

Box shaped - Can be closely packed

Thin walls - increased rate of diffusion

64
Q

How are Root Hair Cells specialised to their function?

A

Long extensions (hairs) - increases SA, maximises uptake of water and minerals from the soil

65
Q

How are Guard Cells specialised to their function?

A

Pairs - Allows for opening of stomata

Thicker cell wall on one side - Shape doesn’t change symmetrically

66
Q

What are the four main categories of tissue

A

Nervous
Epithelial
Muscle
Connective

67
Q

What does nervous tissue do?

A

Support the transmission of electrical impulses

68
Q

What does epithelial tissue do?

A

Cover body surfaces, internal and external

69
Q

What does muscle tissue do?

A

Contract

70
Q

What does Connective tissue do?

A

Hold tissues together and as a transport medium

71
Q

What are the 4 specialised animal tissues?

A

Squamous epithelium
Ciliated epithelium
Cartilage
Muscle

72
Q

What is Squamous epithelium tissue specialised to do?

A

Allows rapid diffusion across a surface

Thin - 1 cell thick

Forms lining of the lungs

73
Q

What is Ciliated epithelium tissue specialised to do?

A

Contain Cilia that move rhythmically and goblet cells

Sweeps away unwanted bacteria and releases mucus to trap them

Lines Trachea to stop bacteria reaching lungs

74
Q

What is Cartilage tissue specialised to do?

A

Contains fibres of elastin and collagen

Prevents bones rubbing together and causing damage

75
Q

What is Muscle tissue specialised to do?

A

Designed to shorten in length

Contains muscle fibres and myofibrils

76
Q

What are the 2 types of specialised Plant tissues?

A

Epidermis and Vascular

77
Q

What is Epidermis tissue specialised to do?

A

Single layer of closely packed cells covering the plant surface

covered by waxy cuticle to reduce transpiration

Contains Somata to allow diffusion

78
Q

What is Xylem tissue specialised to do?

A

Transport of water through plants

Elongated dead cells

Strengthened by Lignin - provides structural support for plants

79
Q

What is Phloem tissue specialised to do?

A

Transport of nutrients - mostly sucrose - from leaves and stems

Composed of sieve tube cells separated by perforated walls called sieve plates

80
Q

What is an organ?

A

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

81
Q

Example of a mammalian Organ and its tissues

A

Heart
Adapted for pumping blood
Muscle and connective tissue

82
Q

Example of a plant organ and its tissues

A

Leaf
Adapted for Photosynthesis
Contains epidermis and vascular tissues

83
Q

What are Organ systems?

A

A number of organs working together eg.
Digestive system
Cardiovascular system
Gaseous Exchange System

84
Q

State two examples of epithelial tissue and describe how each is adapted for its function

A

Squamous
flattened cells provide thin surface
e.g. (alveoli) in lungs diffusion of gases

ciliated (have cilia), for movement, of cell / liquid outside cell
e.g. trachea
movement of mucus

85
Q

The cardiac muscle that makes up most of the heart is a tissue, but the heart itself is an organ. Explain the difference

A

A tissue is a collection of cells that work together

an organ is a collection of tissues that work together

86
Q

Using the digestive system as an example, explain the relationship between organs in an organ system

A

Digestive system is a group of organs working together carry out a function

pancreas produces digestive enzymes

stomach contains acid for digesting food

liver produces bile to aid digestion of fats

small intestine digests and absorbs soluble food

large intestine absorbs water from undigested food, producing faeces

87
Q

What are stem cells?

A

undifferentiated cells which have they ability to change into many cells

88
Q

What happens when a cell differentiates?

A

Enters G0 phase and cannot replicate

89
Q

What are the types of stem cell potency?

A

Totipotent
Pluripotent
Multipotent

90
Q

What is a totipotent stem cell?

A

Differentiate into any type o cell
Found in the first few mitotic cell divisions
Can also differentiate into extra-embryonic tissues like the amnion and umbilicus

91
Q

What is a Pluripotent stem cell

A

The stem cells can form all types of tissue.
present in early embryos

92
Q

What are multipoint stem cells?

A

Cells tray can only form a range of cells within a certain type of tissue
eg. Haematopoetic stem cells in bone marrow make various types of blood cell

93
Q

pg 139 differentiation

A

BIOLOGY A LEVEL (24 decks)

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