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A Level Biology > Component 2 - Cell division > Flashcards

Component 2 - Cell division Flashcards

1
Q

What are the phases during the cell cycle?

A

Interphase - preparation phases for mitosis
Mitosis - cell division

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2
Q

What are the three phases of interphase?

A

G1
S
G2

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3
Q

When does interphase occur?

A

Stage before mitosis

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4
Q

What is the G1 phase?

A

First growth phase: protein synthesis, cytoplasm and number of organelles increase rapidly

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5
Q

What is the S phase?

A

Dna replicates (DNA doubles)

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6
Q

What is the G2 phase?

A

Proteins necessary for cell division are synthesised

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7
Q

What is meant by cell division?

A

Process by which a cell divides into 2 genetically identical daughter cells

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8
Q

Why do cells need to divide?

A

Asexual reproduction
Living things grow by producing more cells
Repair of damaged tissue
To replace old or worn out cells, e.g. RBCs and skin cells

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9
Q

What is DNA’s function and where is it located?

A

Controls all cell activities including cell division
It is located in the nucleus

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10
Q

What is a chromatin?

A

Long and thread-like DNA in a non-dividing cell

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11
Q

What is a chromosome?

A

Doubled, coiled, short DNA in a dividing cell

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12
Q

What 2 parts does DNA consist of?

A

Chromatid and centromere

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13
Q

How does chromatin change into chromosomes?

A

Duplicates itself
Coils up into chromosomes

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14
Q

Describe the structure of a chromosome and what happens to the structure when it undergoes cell division?

A

2 identical “sister” chromatids attached at an area in the middle called a centromere
When cells divide “sister” chromatids separate and 1 goes to each new cell
Each chromatid is an exact copy of the other due to semi conservative theory of replication

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15
Q

What is significant about interphase?

A

The cell spend most of its life cycle in interphase

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16
Q

What is mitosis?

A

Division of the nucleus into 2 nuclei, each with the same number of chromosomes

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17
Q

Where does mitosis occur?

A

In all the somatic cells

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18
Q

Why does mitosis occur in terms of chromosomes?

A

So each new daughter cell has nucleus with a complete set of chromosomes

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19
Q

What are the 4 phases of nuclear division, directed by the cell’s DNA?

A

Prophase
Metaphase (middle)
Anaphase (apart)
Telophase (two)

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20
Q

What occurs during prophase?

A

Chromosomes coil up/condense (shorten and thicken)
Nuclear envelope disappears
Nucleolus disappears
The centrioles move to opposite sides of the nucleus
Spindle fibres form

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21
Q

What does prophase look like under a microscope?

A
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22
Q

What occurs during metaphase?

A

The chromosomes arrange themselves on the equator of the spindle
The centrioles are attached to the centromeres

23
Q

What does metaphase look like under a microscope?

24
Q

What occurs during anaphase?

A

The centromere divides in two
The attached centrioles contract and pull chromatids to opposite poles of the cell, centromere first
Chromatids now called daughter chromosomes

25
What does anaphase look like under a microscope?
26
What occurs during telophase?
The daughter chromosomes reach the poles and uncoil and lengthen Nuclear envelope and nucleolus re-form 2 new nuclei are formed Spindle fibres disintegrate
27
What does telophase look like under a microscope?
28
What is cytokinesis?
The division of the rest of the cell (cytoplasm and organelles) after the nucleus divides
29
How is cytokinesis different in animal and plant cells?
In animal cells the cytoplasm pinches in whereas in plant cells a cell plate forms
30
What happens after mitosis and cytokinesis?
The cell returns to interphase to continue to grow and perform regular cell activities
31
What is cancer?
Uncontrolled cell division , i.e. uncontrolled mitosis
32
How is a tumour formed?
Cancerous cells divide repeatedly
33
What is a tumour?
An irregular mass of cells
34
What does cancerous cells do to the cells/organs of a human?
Prevent them from functioning
35
What is asexual reproduction and what living organisms does it take place in?
Results in complete offspring that are identical to the parent This takes place in yeast and bacteria, certain flowering plants
36
What is the meaning of the term homologous pair of chromosomes?
Consists of one chromosomes from the mother and one from the father Each one pair contains the same genes as the other, but may have a different allele
37
Comparison of mitosis and meiosis
In mitosis one division resulting in two daughter cells whereas in meiosis two division resulting in four daughter cells In mitosis number of chromosomes is unchanged whereas in meiosis number of chromosomes is halved In mitosis daughter cells are genetically identical wheres in meiosis they are genetically different In mitosis homologous chromosomes are not associated in pairs whereas in meiosis they pair up In mitosis crossing over does not occur whereas in meiosis crossing over occurs and chiasmata forms In mitosis there is no variation between individuals wheres in meiosis there is variation
38
What is meant by a diploid?
A cell containing homologous chromosomes (2n)
39
What is meant by a haploid?
A cell containing only one of each chromosome (n)
40
What is a somatic cell?
A cell which contains a diploid number of chromosomes
41
What is a gamete and how are they produced?
A gamete is a haploid sex cell and are produced through meiosis
42
When does meiosis occur?
During sexual reproduction; 1 diploid cell divides to produce 4 haploid cell (gametes)
43
What are the two stages of cell division in meiosis?
Meiosis I and II
44
How is variation achieved in meiosis?
Crossing over Random assortment Production of haploid gametes for random fertilisation
45
What happens during prophase I?
Chromatin condenses, coils and thickens to become visible Chromosomes are now visible as two chromatids Centrioles move to opposite poles of the cell SYNAPSIS: Each homologous pair of chromosomes come together to form a bivalent
46
What occurs during late prophase I and what does it look like?
Crossing over takes place between the non-sister chromatids in the bivalent Each chromatid may break and reconnect to another chromatid The point of crossing over is called a chiasma (chiasmata) This process results in the recombination of maternal and paternal genetic information
47
What occurs during metaphase I and what does it look like?
Spindle fibres attach to the centromere and move the whole chromosome to the equator of the cell The bivalents arrange themselves at the equator of the spindle Homologous chromosomes arrange themselves randomly at the equator of the cell (random assortment) leading to genetic variation
48
What happens during anaphase I and what does it look like?
The spindle fibres attached to the centromere of each homologous chromosome shorten to pull them to opposite poles of the cell Whole chromosomes are pulled (still made of two chromatids)
49
What occurs during telophase I and what does it look like? (Give full detail)
Two new nuclear envelopes reform (animals) Each nucleus now contains half the number of original chromosomes The chromosomes are genetically different from those in the original cell The organelles. cytoplasm and membrane become evenly distributed in two new cells: cytokinesis
50
What happens during prophase II?
Chromatin condenses and chromosomes become visible Centrioles replicate A new spindle forms at right angles to the first Nuclear envelope and nucleolus disappear
51
What occurs during metaphase II?
The spindle fibres align the chromosomes randomly on the equator of the spindle Each chromosome is made up of a pair of chromatids This phase again introduces genetic variation due to random assortment of chromatids at equator
52
What occurs during anaphase II?
The centrioles contract and the centromeres divide Chromatids are pulled to opposite poles of the cell by the attached spindle fibres As soon as they are separated they are called chromosomes
53
What occurs during telophase II?
Chromosomes uncoil: each new chromosome may be genetically different from the original one Nuclear envelope and nucleolus reappear Cytokinesis begins Four haploid cells are produced
54

A Level Biology (9 decks)

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