cell division

Question 1

In order what are the stages of the cell cycle

Answer 1

interphase (G1, S, G2), mitosis then cytokinesis

Question 2

what does the cell cycle do

Answer 2

replaces dead cells and is important in growth

Question 3

what happens in interphase

Answer 3

the period during which cells are not dividing - DNA is replicated

Question 4

what happens in the mitosis phase

Answer 4

the nuclear division of the cell

Question 5

what happens in the cytokinesis phase

Answer 5

Is the splitting of the cell into two daughter cells.
In animals the plasma membrane folds inwards until the two dents meet - forming separate cells
Im plants cellulose builds up at the equator, and a plasma membrane forms in the middle of the end plate - forming separate cells

Question 6

what does mitosis involve

Answer 6

one divisions and creates a diploid cell

Question 7

what does mitosis produce

Answer 7

two genetically identical daughter cells

Question 8

what is the purpose of mitosis

Answer 8

it is used to form somatic cells rather than gametes and is critical for growth and repairs of multicellular organisms.
It is also used for asexual reproduction in unicellular eukaryotes (yeast)

Question 9

what is the stages of mitosis

Answer 9

Prophase
Metaphase
Anaphase
Telophase

Question 10

what happens in prophase

Answer 10

it is the first stage
DNA super coils, condensing to form visible chromosomes.
The nuclear Envelope disintegrates and centrioles divide and move to the poles
Spindle fibres form from the centrioles

Question 11

what happens in Metaphase

Answer 11

Chromosomes line up along the equator of the cell.
The chromosomes are first attached to spindle fibres at their centromere.
The chromosomes are then pulled along by the spindle fibres to the equator of the cell.
This prepares the sister chromatids for separation

Question 12

what happens in Anaphase

Answer 12

The sister chromatids are separated and pulled to opposite poles of the cell.
Chromatids are separated by the spindle fibres and moved to the poles aided by motor proteins.
This requires ATP so mitochondria gather around the spindle fibres.
Each pole of the cell ends up with identical full sets of chromosomes

Question 13

what happens in Telophase

Answer 13

The nucleus reappears and chromosomes decondense.
The spindle fibres begin to disintegrate, and the chromosomes lengthen and uncurl - meaning they can no longer be seen under a microscope.
The nuclear envelope reforms around the chromosomes

Question 14

what is meiosis

Answer 14

It involves two divisions and creates haploid cells such as gametes, Meiosis I it occurs after chromosomes duplication and separates homologous chromosomes into different cells. Meiosis II separates sister chromatids of each chromosome into different cells

Question 15

what is the order of Meiosis

Answer 15

Interphase 
Prophase I
Metaphase I 
Anaphase I
Telophase I
Prophase II 
Metaphase II
Anaphase II 
Telophase II

Question 16

what happens in Prophase I

Answer 16

chromosomes supercoil, nuclear enveloped break down and spindle fibres form.
At the end of prophase I crossing over occurs and DNA is exchanged between chromatids on homologous chromosomes. (this is what makes prophase in Meiosis different to Mitosis)

Question 17

what happens in Metaphase I

Answer 17

Chromosomes attach to spindle fibres by their centromeres and line up along the equator.
The position of each homologous chromosome along the equator determines which daughter cell they are separated into - This is called independent assortment and is a form of random process that introduces variation.

Question 18

what happens in Anaphase I

Answer 18

Each chromosome from the homologous pair is pulled to opposite poles of the cell.

Question 19

what happens in Telophase I

Answer 19

the chromosomes then uncoil, and two nuclei containing each set of chromosomes are temporarily formed

Question 20

what is a difference between Meiosis and Mitosis

Answer 20

mitosis produces diploid cells, where as meiosis produces haploid cells.
Mitosis produces somatic cells Meiosis produces gametes

Question 21

what happens in Prophase II

Answer 21

The DNA supercoils, and the nucleus disintegrates and new spindle fibre is formed

Question 22

what happens in Metaphase II

Answer 22

Chromosomes are lined up at the equator of the cell, and the sister chromatids are not identical due to crossing over

Question 23

what happens in Anaphase II

Answer 23

The genetically different chromatids are separated to opposite poles.
This leads to a second round of independent assortment.

Question 24

what happens in Telophase II

Answer 24

The nuclei reform and the cells each spilt in two by cytokinesis.
This results in four genetically different haploid cells

Question 25

Why does meiosis require 4 stages of cell division

Answer 25

To increase genetic variation, and to produce maximum number of gametes. Also they need to be haploid, so the homologous pairs have to have separate chromosomes to sister chromotids.

Question 26

Where does crossing over take place

Answer 26

In meiosis I and allows alleles to be swapped between homologous chromosomes.

Question 27

How does crossing over take place

Answer 27

The sister chromatids twist around each other during crossing over, and the wrapping causes sections of the chromatid to break off - They are then swapped to the homologous chromosome
Crossed over chromosomes have the same genes but different alleles