1.6 - Cell Divison

Question 1

(a)

Interphase

Answer 1

During most of the cell cycle, the cell
remains in a phase called interphase.
Interphase is a time of high metabolic
activity for the cell. Cells grow and synthesise new organelles, proteins and DNA in preparation for mitosis.

Question 2

(a)

Main stages of mitosis

Answer 2

Prophase
Metaphase
Anaphase
Telophase

Question 3

(a)

Prophase

Answer 3

Nuclear envelope breaks down, chromosomes condense, centrioles move to opposite poles of the cell

Question 4

(a)

Metaphase

Answer 4

Sister chromosomes line up at the equator, centromeres of chromosomes attach to the spindle fibres

Question 5

(a)

Anaphase

Answer 5

Sister chromatids separated and pulled apart to opposite poles

Question 6

(b)

Mitosis

Answer 6

It produces cells which are genetically identical to the parent cell, giving genetic stability.

Question 7

(b)

Cytokinesis

Answer 7

Cytokinesis is the division
of the cytoplasm to create the 2 new
genetically identical cells.

Question 8

(c)

Importance of mitosis

Answer 8

Cell division occurs for a number of reasons, including:
* growth
* repairing damaged cells
* replacement of old, worn-out cells
* asexual reproduction.

Question 9

(d)

Meiosis

Answer 9

It produces cells which are
haploid for sexual reproduction (gametes).

Question 10

(d)

Main stages of meiosis

Answer 10

Prophase I
Metaphase I
Anaphase I
Telophase I

Question 11

(d)

Prophase I

Answer 11

Differs from prophase in mitosis
as chromosomes form bivalents (pairs
of homologous chromosomes).
Arms of the chromatids may
cross over forming chiasmata. Here,
genetic material can be exchanged
between homologous chromosomes,
therefore increasing the variation in
inherited genomes.

Question 12

(d)

Metaphase I

Answer 12

Homologous chromosomes arrange themselves in pairs along the equator. Independent assortment occurs here where the homologous chromosomes from parent 1 and parent 2 arrange themselves randomly along the spindle facing each pole.

Question 13

(d)

Anaphase I

Answer 13

The chromosome bivalents separate as each chromosome is pulled by its
centromere (which does not split)
towards the opposite pole.

Question 14

(d)

Telophase I

Answer 14

Nuclear envelopes reform around the
chromosomes at the poles. As the chromosome pairs have separated, chromosomes are no longer in pairs and the cells are haploid.

Question 15

(d)

Meiosis II

Answer 15

Events occur in each new nucleus in the second phase of meiosis exactly as they do in mitosis. Finally, cytokinesis occurs resulting in 4 genetically varied cells.

Question 16

(e)

Differences between mitosis and meiosis

Answer 16

Mitosis produces genetically identical daughter cells whereas meiosis produces non-identical daughter cells.

Mitosis has 1 number of nuclear divisions in the process whereas meiosis has 2.

Mitosis forms 2 cells whereas meiosis forms 4.

Mitosis doesn’t have pairing of homologous chromosomes whereas meiosis does to form biavalents.

Mitosis doesn’t have crossing over whereas meiosis does for forming chiasmata.

Mitosis does not have degregation of homologous chromosomes whereas meiosis does (bivalents seperate)