1.6 Cell division Flashcards
what is interphase?
longest stage of the eukaryotic cell cycle
cells grow and synthesise new organelles, proteins and DNA in preparation for mitosis
what is mitosis?
form of cell division
produces two genetically identical copies of genes (diploid) daughter cells
why is mitosis important?
important for the growth of tissue and repair and replacement of cells.
name the stages of mitosis
prophase
metaphase
anaphase
telophase
summarise the process of mitosis.
prophase = nuclear envelope breaks down, chromosomes condense, centrioles move to opposite poles of the cell.
metaphase = sister chromosomes line up at the equator, centromeres attach to the spindle fibres
anaphase = sister chromatids separated and pulled apart to the opposite poles
telophase = nuclear envelope reforms, spindle fibres break down, chromosomes uncoil
what are sister chromatids?
a pair of identical chromatids formed by DNA replication, joined by a centromere.
what is cytokinesis?
the division of the cytoplasm at the end of mitosis to produce two new daughter cells.
compare mitosis in plant and animal cells.
Animal cells/Plant cells
occurs in most tissues/ occurs in meristematic cells only
involved centrioles/no centrioles involved
involved micro filaments/ no micro filaments involved
spindle fibres disappear prior to cytokinesis/ some spindle fibres remain during cytokinesis
what may unrestricted mitosis divisions lead to?
cancerous growth
what is meiosis?
form of cell division
produces 4 genetically different daughter cells (gametes) with a haploid number of chromosomes
involves two divisions
what is the significance of meiosis in reproduction?
gametes must be haploid so that when they combine during fertilisation, the full number of chromosomes is present within the resulting zygote. It also creates genetic variation.
what is meiosis one?
first stage of meiosis
homologous chromosomes separated to form two haploid cells
describe what happens during meiosis one.
homologous chromosomes pair for form bivalents
crossing over occurs at chiasmata
cell divides into two; independent segregation of homologous chromosomes, each cell contains either a maternal or paternal copy.
what are homologous chromosomes?
pair of chromosomes with genes at the same locus.
one maternal one paternal.
some alleles may be the same while others are different
define crossing over.
process in meiosis 1
homologous chromosomes pair up, their chromatids wrap around one another and their alleles are exchanged at equivalent portions of chromatids
creates genetic variation
what is independent segregation?
the random separation of homologous chromosomes in meiosis one that produces genetic variation
what is meiosis two?
second stage of meiosis
sister chromatids separated to form four haploid gametes
describe what happens during meiosis two
independent segregation of sister chromatids
each cell divides again, producing four haploid cells
how does meiosis produce genetic variation?
crossing over during meiosis one
independent assortment of homologous chromosomes and sister chromatids
results in new combinations of alleles
Where in plants can cells undergoing mitosis be found?
Meristem tissue at shoot and root tips.
What is the mitotic index?
The ratio of cells undergoing mitosis to the total number of cells in a sample.
Outline the procedure to prepare a root tip slide.
- Warm 1M HCl to 60°C in a water bath.
- Cut a root tip using a scalpel and add to the HCl. Leave for 5 minutes.
- Remove from HCl and wash with cold distilled water.
- Dry and place on a slide. Macerate with needle to spread out the cells.
- Add a few drops of stain to make chromosomes visible.
State the formula for the mitotic index.
Mitotic index =
Number of cells with visible chromosomes / Number of cells in sample
State the hazards and precautions for reagents used in this procedure.
HCl - corrosive, avoid contact with skin, wear eye protection
Toluidine Blue O stain - irritant, avoid contact with skin, wear eye protection
Scalpel - cut away from fingers
Why is the root tip placed in hot HCI?
HCl dissolves the middle lamellae in order to break up the cellulose cell wall. This allows the stain to permeate and the tip to be squashed more easily.
Why are the cells flattened on the slide?
To spread out the cells and reduce the thickness of the layers so that cells can be observed more clearly.
Which cells in an anther undergo meiosis?
Pollen sacs contain pollen mother sacs that divide by meiosis.
State the stages of meiosis.
Prophase, Metaphase, Anaphase,
Telophase one and two
How is the magnification of a drawing calculated?
Calibrate the eyepiece graticule using a stage micrometer.
Use the eyepiece graticule to measure the actual size of the cell.
Use a ruler to measure the size of the cell drawing.
Calculate magnification using magnification = size of image / size of object.
What can be observed in a cell undergoing prophase one and two?
Individual chromosomes visible, nuclear envelope absent.
What can be observed in a cell undergoing metaphase one?
Pairs of chromosomes line up along the the cell equator.
What can be observed in a cell undergoing metaphase two?
Individual chromosomes line up along the equator of the cell.
What can be observed in anaphase one?
Chromosomes (consisting of 2
chromatids each) separated to opposite poles of the cell.
What can be observed in a cell undergoing anaphase two?
Chromosomes (consisting of 1 chromatid each) are separated to opposite poles of the cell.
What is observed in a cell undergoing telophase one and two?
2 groups of chromosomes at opposites poles of the cell, individual chromosomes no longer visible.
