Biology Chapter 6: Cell Division
1) Distinguish cytokinesis from karyokinesis.
Cytokinesis Karyokinesis
Cytokinesis is the biological process Karyokinesis is the biological process
involving the division of a cell’s cytoplasm involving the division of a cell’s nucleus
during mitosis or meiosis. during mitosis or meiosis.
2) Describe the events taking place during interphase.
Interphase involves a series of changes during which DNA synthesis occur. In this phase, the
amount of DNA (per cell) experiences growth and DNA replication in an orderly manner.
Interphase is divided into three phases:
i) G1 phase:
It is the stage during which the cell grows and prepares its DNA for replication. In this phase,
the cell is metabolically active.
ii) S phase:
It is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per
cell) doubles, but the chromosome number remains the same.
iii) G2 phase:
In this phase, the cell continues to grow and prepares itself for division. The proteins and
RNA required for mitosis are synthesised during this stage.
3) Why is mitosis called equational division?
Mitosis is the process of cell division wherein the chromosomes replicate and get equally
distributed into two daughter cells. The chromosome number in each daughter cell is equal to
that in the parent cell i.e diploid. Hence, mitosis is known as equational division.
4) Name the stage of cell cycle at which one of the following events occur:
i. Chromosomes are moved to spindle equator = Metaphase
ii. Centromere splits and chromatids separate = Anaphase
iii. Pairing between homologous chromosomes takes place = Prophase I
iv. Crossing over between homologous chromosomes takes place = Prophase I
5) Describe the following:
a) Synapsis
The pairing of homologous chromosomes is called synapsis. This occurs during the second
stage of prophase I.
b) Bivalent
Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed
during the stage of prophase I of meiosis.
c) Chiasmata
Chiasmata is the site where two sister chromatids have crossed over. It represents the site
of cross-over. It is formed during the stage of prophase I of meiosis.
6) How does cytokinesis in plant cells differ from that in animal cells?
Cytokinesis in plant cells Cytokinesis in animal cells
The division of the cytoplasm takes place by The division of the cytoplasm takes place by
cell plate formation. cleavage.
Cell plate formation starts at the centre of Cleavage starts at the periphery and then
the cell and grows outward, toward the moves inward, dividing the cell into two
lateral walls. parts.
7) Distinguish anaphase of mitosis from anaphase 1 of meiosis.
Anaphase of mitosis Anaphase I of meiosis
Anaphase is the stage during which the During anaphase I, the homologous
centromere splits and the chromatids chromosomes separate, while the
separate. The chromosomes move apart, chromatids remain attached at their
toward the opposite poles. These centromere.
chromosomes are genetically identical. Hence, in anaphase I, the chromosomes of
each bivalent pair separate, while the sister
chromatids remain together.
8) List the main differences between mitosis and meiosis.
Mitosis Meiosis
In mitotic division, a single division results Meiotic division involves two successive
in two daughter cells. divisions – meiosis I and meiosis II. These
divisions result in four daughter cells.
Mitosis is known as equational division. Meiosis I is known as reductional division.
This is because the daughter cells have the This is because the chromosome number is
same diploid number of chromosomes as reduced to half.
the parent. Meiosis II is known as equational division.
This is because the sister chromatids
separate and the chromosome number
remains the same.
There is no pairing of chromosomes, During prophase I, pairing of chromosomes
crossing-over, or chiasmata formation (synapsis), crossing-over and chiasmata
during prophase. formation takes place.
Anaphase involves the separation of the During anaphase I, the homologous
chromatids of each chromosome. chromosomes separate, while the
chromatids remain attached at their
centromeres.
During anaphase II, the chromatids separate
as a result of the splitting of the centromere.
Mitosis plays a significant role in the Meiosis brings about variation and
healing, repair, and growth of a cell. maintains the chromosome number from
generation to generation.
9) Can there be DNA replication without cell division?
There can be DNA replication without cell division. During cell division, the parent cell gets
divided into two daughter cells. However, if there is a repeated replication of DNA without
any cell division, then this DNA will keep accumulating inside the cell. This would increase
the volume of the cell nucleus, thereby causing cell expansion. An example of DNA
duplication without cell division is commonly observed in the salivary glands of Drosophila.
The chromosome undergoing repeated DNA duplication is known as polytene chromosome.
10) Analyse the events during every stage of cell cycle and notice how the following
parameters change:
i. Number of chromosomes per cell
During anaphase I of the meiotic cycle, the homologous chromosomes separate and start
moving toward their respective poles. As a result, the bivalents get divided into two sister
chromatids and receive half the chromosomes present in the parent cell. Therefore, the
number of chromosomes reduces in anaphase I.
ii. Amount of DNA content per cell
