C2: The cell cycle and cell division

Question 1

Define chromosome

Answer 1

A long, thin structure of DNA and protein (Histones), in the nucleus of eukaryotic cells, carrying genes

Question 2

Define chromatid

Answer 2

One of the two identical copies of a chromosomes, joined at the centromere prior to cell division

Question 3

Define centromere

Answer 3

Specialised region of a chromosome where two chromatids join and to which the microtubules of the spindle fibres attach during metaphase

Question 4

Describe the difference between haploid and diploid

Answer 4

Haploid - having one set of chromosomes

Diploid - Having two sets of complete chromosome

Question 5

Define homologous

Answer 5

Chromosomes that are identical in size shape and they carry the same gene at the same loci, with genes for the same characteristic. One chromosome of each pair comes from each parent.

Question 6

Define ploidy level and state what is meant by Polyploid

Answer 6

Ploidy level - Is the number of complete sets of chromosomes in an organism

Polyploidy - is when organisms have more than two complete sets of chromosomes

Question 7

Name all the stages of the cell cycle

3 points

Answer 7

Interphase
Cell division
Cytokinesis

Question 8

Describe the three stages of interphase

Answer 8

it is a time of high metabolic activity for the cell. interphase has 3 stages:

G1:
there is a replication of organelles
new organelles are made
synthesis of ATP and proteins
Increase in cell size

S
Replication of DNA

G2
Preparation for division
Further Growth occurs
Cell synthesises any other molecules it needs to divide

Question 9

Define mitosis

Answer 9

A type of cell division that produces two daughter cells that have the same number of chromosomes and are genetically identical with each other and the parent cell.

Question 10

Name the four stages of mitosis

Answer 10

Prophase
Metaphase
Anaphase
Telophase

Question 11

Describe prophase

Answer 11

Chromosomes condense and become visible.

Centrioles move to opposite sides of cell in animal cells.

Spindle forms from microtubules.

Nuclear envelope disintegrates and nucleolous disappears

Question 12

Describe Metaphase

Answer 12

Centromeres of chromosomes attach to the spindle fibres and line up on the equator.

Question 13

Describe anaphase

Answer 13

Spindle fibres shorten
Centromere separates and individual chromatids are pulled to the poles centromere first.

Question 14

Describe telophase

Answer 14

The spindle breaks down.

Chromosomes uncoil.

Nuclear envelope reforms.

Question 15

Simply describe cytokenisis

Answer 15

The division of the cytoplasm, to make two new genetically identical cells

Question 16

Describe how mitosis and cytokenisis is diffierent in plant cells and animal cells

Answer 16

Mitosis:

Centrioles are only present in Animal cells

Spindle degenerates at telophase in animals whereas it remains throughout new cell wall formation in plants

Cytokinesis:

Animals’ cytoplasm and membrane divide by cleavage and it develops from the outside inward

Plant cytoplasms, cell wall and membrane divide by the development of cell plate which develops from the centre outwards

Question 17

What is the significance of mitosis as a process

Answer 17

It produces cells which are genetically identical to the parent cell, giving genetic stability. Cell division occurs for a number of reasons, including:

Growth
Repairing damaged cells
Replacement of old, worn-out cells
Asexual reproduction.

Question 18

How is mitosis significant in damage and disease

Answer 18

The length of the cell cycle can be controlled by genes
this allows for the replacement and repair of tissues
but if these genes are damaged or faulty it can lead to unrestricted division leading to cancerous growth

Question 19

Describe two genes involved in cancerous growth

Answer 19

Tumor suppressor gene - prevents the cell cycle from repeating continuously

Oncogenes - a gene with the potential to cause cancer

Question 20

Define meiosis

Answer 20

A two-stage cell division in sexually reproducing organisms that produce four genetically identical haploid daughter cells ( With half the chromosomes of the parent cell)

Question 21

Describe how Prophase I in meiosis differs from prophase in mitosis

Answer 21

Crossing over occurs when the arms of the chromatids cross over at the chiasmata. Here, genetic material can be exchanged between chromatids of homologous chromosomes, therefore increasing the variation in inherited genomes.

Question 22

Define chiasmata

Answer 22

The site at which chromosomes exchange DNA in genetic crossing over.

Question 23

Define Bivalent

Answer 23

The association of the two chromosomes of a homologous pair at prophase I of meiosis (pairs of homologous chromosomes).

Question 24

Describe how Metaphase I in meiosis differs from metaphase in mitosis

Answer 24

Homologous chromosomes arrange themselves in pairs along the equator.

Independent assortment occurs here

Question 25

Define independant assortment

Answer 25

Describes the random way round (toward different poles) maternal and paternal homologous chromosomes line up at the equator during metaphase in meiosis.

Question 26

Describe how anaphase I in meiosis differs from anaphase in mitosis

Answer 26

The chromosome bivalents separate as each chromosome is pulled by its centromere towards the opposite pole.

Question 27

Describe how telophase I in meiosis differs from telophase in mitosis

Answer 27

Nuclear envelopes reform around the chromosomes at the poles.

In meiosis, prophase II occurs after telophase I.

As the chromosome pairs have separated, chromosomes are no longer in pairs and the cells are haploid.

Question 28

Describe meiosis II

Answer 28

It is essentially the same as the processes in mitosis

Question 29

Describe where and how genetic variation takes place in meiosis and mitosis

Answer 29

Mitosis:
Does not occur

Meiosis:
Crossing over in Prophase I
Independent assortment in Metaphase I & II

Question 30

Describe the differences between mitosis and meiosis

8 points

Answer 30

Number of nucleus divisions:
Mitosis - 1 , Meiosis - 2

Number of cells formed
Mitosis - 2 , Meiosis - 4

Ploidy level of parental cells/nuclei
Mitosis: 2(diploid) , Meiosis: 2(diploid)

Ploidy level of daughter cells/nuclei
Mitosis: 2(diploid) , Meiosis: 1(Haploid)

Genetic composition compared to parent cell and each other
Mitosis - Identical , Meiosis - different

Pairing of homologous chromosomes
Mitosis: No , Meiosis: yes to form bivalents

Crossing over
Mitosis: No , Meiosis: yes at chiasmata

Segregation of homologous chromosomes
Mitosis: No , Meiosis: Yes bivalents separate