2.5: CELL DIVISION
2.5.1: Cell Cycle: Outline the stages of the cell cycle, including interphase (G1, S, G2), mitosis and
cytokinesis
Cytokinesis starting
*During its life, a cell passes through a well-ordered series of events known as the cell division
cycle.
*The cell division cycle involves three basic stages: interphase, mitosis and cytokinesis.
*Interphase is much longer than mitosis and it begins as soon as a daughter cell is formed. It is
an active period during which: the cell grows; DNA transcription and DNA replication occur; and
biochemical reactions are performed. Interphase is broken up into three stages:
*G1 Stage (first growth stage) The cell performs its normal differentiated
function. Protein synthesis mitochondria replication/ chloroplast replication.
*S Stage DNA replication. At this point the mass of DNA in the cell has doubled.
*G2 Stage (second growth stage) Preparation for cell division
*Mitosis is a continuous process but it is useful to divide it into four stages: prophase,
metaphase, anaphase, and telophase. During mitosis the nucleus divides into two daughter
nuclei each with same the number of chromosomes as the parent nucleus.
*Cytokinesis the cell separates its cytoplasm, organelles and DNA equally and pinching in of the
plasma membrane to divide the cell into two equal daughter cells. Cytokinesis commences
towards the end of mitosis.
2.5.2: STATE: Tumours (cancer) cells are the result of uncontrolled cell
division and these can occur in any organ or tissue
2.5.3: STATE: Interphase is an active period in the life of a cell when many metabolic
reactions occur, including protein synthesis, DNA replication and an increase in the
number of mitochondria and / or chloroplasts
Mitosis is division of the
nucleus in which one parent
nucleus divides into two
daughter nuclei each having
the same number of
chromosomes as the parent
nucleus and genetticaly
identical to the parent
nucleus.
2.5.4 and 2.5.5: Mitosis
Supercoiling of chromosomes
Nuclear membrane breaks down
Spindle microtubles extend from pole to equator
Microtubules attach to centromere
line along equator of cell
Chromosomes
Centromere splits and sister
Chromatids
(now chromosomes) move to opposite poles
Reformation of nuclear membrane around
chromosomes
Chromosomes uncoil
STATE: Growth, embryonic development, tissue repair
and asexual reproduction (of eukaryotic cells) involve
mitosis
IB Question: Describe the events that occur during mitosis. [9]
IB Question: Describe the events that occur during mitosis. [9]
sequence of stages is prophase metaphase anaphase telophase;
chromosomes condense/supercoil/become shorter and fatter in prophase;
spindle microtubules grow (from poles to equator) in prophase/metaphase;
nuclear membrane breaks down in prophase/metaphase;
spindle microtubules attach to the centromeres/chromosomes in metaphase;
chromosomes line up at equator in metaphase;
centromeres divide / (paired) chromatids separate / chromosomes separate into two chromatids
in metaphase/anaphase;
(sister) chromatids/chromosomes pulled to opposite poles in anaphase;
spindle microtubules disappear in telophase;
nuclear membrane reforms around chromosomes/chromatids in telophase;
chromosomes/chromatids decondense in telophase; [9 max]
IB Question: Before cell division in unicellular and multicellular organisms, the nucleus must
divide to produce two genetically identical nuclei. Explain the events that occur in cells that
result in the production of genetically identical nuclei. [8]
IB Question: Before cell division in unicellular and multicellular organisms, the nucleus must
divide to produce two genetically identical nuclei. Explain the events that occur in cells that
result in the production of genetically identical nuclei. [8]
mitosis;
DNA replication;
each chromosome consists of two sister / identical chromatids;
chromosomes condense / supercoiling;
nuclear membrane breaks down;
chromosomes align (at equatorial plate);
spindle fibres / microtubules attach to centromeres of chromosomes on opposite
sides;
centromeres split;
chromatids become chromosomes;
sister / identical chromosomes pulled to opposite poles;
nuclear membranes reform;
events correctly assigned to interphase, prophase, metaphase, anaphase, and
telophase; [8 max]
Mitosis is division of the nucleus in which one parent nucleus divides into two daughter nuclei
each genetically identical as the parent nucleus.
The cell below shows the sequence of events which leads to the production of two genetically
identical nuclei.
Cell is in interphase of the cell cycle. Two pairs of chromosomes
are shown. One pair contains the A gene while the second pair
contains the B gene
During the S-phase of interphase, each chromosome
makes an identical copy of itself. Each chromosome is
composed of two identical sister chromatids
Prophase:
The cell enters the first stage of mitosis called prophase in which
the following events occur:
*Supercoiling of chromosomes
*Nuclear membrane breaks down
*Spindle microtubles extend from pole to equator and
will attach to the centromere of each duplicated chromosome.
Metaphase:
The second stage of mitosis is metaphase. During this
stage the spindle microtubles have aligned the
duplicated chromosomes along the equator of the cell
Anaphase:
During anaphase of mitosis the centromeres
split and the sister chromatids of each
duplicated chromosome are pulled to opposite
poles of the cell
Telophase:
In the final stage of mitosis, telophase, the
following events occur
*Reformation of nuclear membrane around
chromosomes
*Chromosomes uncoil
*cytokinesis also occurs which is division of
the cytoplasm
The end result of mitosis is two daughter nuclei have been produced which are
identical to each other and identical to the parent nucleus.
IB QUESTION: Describe the events that occur in the four phases of mitosis in animals. [6] May 11
TZ2
(a) anaphase [1]
(b) growth (through increasing cell number);
embryonic development;
tissue production/repair;
(asexual) reproduction; [2 max]
(c) uncontrolled mitosis/cell division [1]