Topic 6: Cell Cycle And Division

Question 1

What is mitotic cell division?

Answer 1

Mitotic cell division is a process in which a cell (parent cell) divides to form new cells (daughter cells).

Question 2

Why is cell division important?

Answer 2

It involves the passing on of genetic information from parent cells to daughter cells.
This information determines the structure and functions of the cells and is carried in DNA.

Question 3

What is a centromere?

Answer 3

A centromere is the junction between two sister chromatids of the same chromosome.

Question 4

What are sister chromatids?

Answer 4

When a cell is not dividing, individual chromosomes are not visible. They exist as a mass of long thin fibres called chromatins.
When cell division begins, the chromatin fibres coil up tightly. Each chromosome is seen to consist of two identical chromatids called sister chromatids.

Question 5

What are chromosomes?

Answer 5

Inside the nucleus, DNA and proteins together form structures called chromosomes.

Question 6

What are the properties of chromosomes?

Answer 6

1. They exist in pairs called homologous chromosomes in body cells.
2. One member in a homologous pair comes from the male parent (paternal chromosome), and the other from the mother (maternal chromosome).
3. A body cell that has 2 sets of chromosomes is a diploid, and 1 set of chromosomes a haploid.
4. Number of chromosomes are the same among individuals of the same species but different among different species.

Question 7

What is a cell cycle?

Answer 7

A cell cycle is the sequence of events that takes place in a body from one cell division to the next.

Question 8

Mitotic cell division only occurs in __________.

Answer 8

Body cells

Question 9

Stages of mitotic cell division?

Answer 9

1. Interphase (cell growth)
2. Mitotic cell division:
   Nuclear division:
   a. Prophase
   b. Metaphase
   c. Anaphase
   d. Telophase (Cytoplasmic division)

Question 10

Interphase

The cell is very active and still carries out its functions!

Answer 10

Prepare for cell division
2. 1. Active phase: synthesis of new organelles and proteins
2. DNA replicates.
3. Each chromosome becomes duplicated and consists of 2 identical DNA molecules.
a. Sister chromatids: n to 2n
b. DNA: x to 2x
c. chromosomes: 2n to 2n
4. Cell grows to its maximum size
5. Chromosomes are invisible at this stage.
6. The nuclear membrane or nucleus is present.

Question 11

Properties of mitotic cell division

Answer 11

1. A body cell divides to form two daughter cells.
2. The daughter cell contains the same number and kind of chromosomes as their parent cell. They are genetically identical.
3. Involves both nuclear and cytoplasmic division.

Question 12

Stages of nuclear division

Answer 12

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 13

What is nuclear division?

Answer 13

It is called mitosis. It involves the separation of sister chromatids of each chromosomes and the equal distribution of chromatids between two daughter nuclei.

Question 14

Stages of mitotic cell division

Answer 14

1. Mitosis (nuclear division)
2. Cytoplasmic division

Question 15

Prophase

Answer 15

1. Chromosomes shorten and thicken. They become visible.
2. The nuclear membrane breaks down.

Question 16

Metaphase

Answer 16

1. The chromosomes line up along the equator.
2. Spindle fibres attach to the chromosomes.

Question 17

Anaphase

Answer 17

1. The spindle fibres contract.
2. Sister chromatids separate and move to opposite poles of the cell.
3. The cytoplasm starts to divide.

Question 18

Telophase

Answer 18

1. New nuclear membranes form around each group of chromosomes.
2. The chromosome uncoil to become chromatin again.

Question 19

What is cytoplasmic division?

Answer 19

It is called cytokinesis. The cytoplasm of a parent cell divides into two equal halves, forming two daughter cells.

Question 20

Properties of cytoplasmic division

Answer 20

In animal cells, the cell membrane around the centre of the cell constricts inwards until the cell separates into two.
In plant cells, a cell plate is formed between the two daughter nuclei. It grows outwards from the centre of the cell, dividing the cell into two halves.

Question 21

The importance of mitotic cell division?

Answer 21

1. Growth: provides new cells for growth
2. Repair: provides new cells to replace worn out cells or repair damaged tissues
3. Asexual reproduction: produces offspring genetically identical to their parents e.g. potatoes

Question 22

What is meiotic cell division?

Answer 22

Meiotic cell division occurs only in gamete-producing cells and results in the formation of zygote.

Question 23

Properties of meiotic cell division

Answer 23

Meiotic cell division reduces the chromosome number by half. It gives rise to 4 haploid daughter cells which are genetically different from the parent cell and among themselves.

Question 24

Stages of meiotic cell division

Answer 24

1st meiotic division:
1. Interphase
2. Nuclear division
3. Cytoplasmic division

2nd meiotic division:
1. Interphase (with no DNA replication)
2. Nuclear division
3. Cytoplasmic division

Question 25

Prophase I

Answer 25

1. Chromosomes shorten, thicken and become visible. 2. Members of each homologous pair pair up. 3. The nuclear membrane breaks down.

Question 26

Metaphase I

Answer 26

1. Homologous pairs line up along the equator. 2. Spindle fibres attach to the chromosomes.

Question 27

Anaphase I

Answer 27

1. The spindle fibres contract. 2. The two members of each pair of homologous chromosomes move to opposite sides of the cell. 3. The cytoplasm starts to divide.

Question 28

Telophase I

Answer 28

New nuclear membranes form around each group of chromosomes. | Chromosomes don't uncoil! Haploid cells are already formed!

Question 29

Prophase II

Answer 29

The nuclear membrane breaks down again.

Question 30

Metaphase II

Answer 30

1. Chromosomes line up along the equator. 2. New spindle fibres attach to the chromosomes.

Question 31

Anaphase II

Answer 31

1. The spindle fibres contract. 2. The sister chromatids separate and move to opposite poles of the cells. 3. The cytoplasm starts to divide.

Question 32

Telophase II

Answer 32

1. New nuclear membranes form around each group of chromosomes. 2. The chromosomes uncoil to become chromatin again.

Question 33

The importance of meiotic cell division?

Answer 33

1. Producing haploid gametes 2. Producing genetic variations in gametes

Question 34

Producing haploid gametes

Answer 34

- produces haploid gametes for sexual reproduction - the male and female gamete fuse at fertilisation to form a zygote, the diploid number of chromosome can be restored.

Question 35

Producing genetic variations in gametes

Answer 35

Genetic variations within a species increase the chance of the species to survive when environmental conditions change. Genetic variations are produced by the independent assortment of chromosomes and crossing over during meiotic cell division.

Question 36

Independent assortment of chromosomes

Answer 36

Pairs of homologous chromosomes line up along the equator of the cell. The members of each homologous pair separate independently of the other pairs of the chromosomes.

Question 37

When does the independent assortment of chromosomes occur?

Answer 37

1. in metaphase I, when the pairs of homologous chromosomes are arranged along the equator 2. in metaphase II, the sister chromatids separate to form new combinations

Question 38

Crossing over

Answer 38

It is an exchange of corresponding segments of non-sister chromatids. During prophase I, homologous pair up. Non-sister chromatids wrap around each other, forming a chiasma. At the chiasma, the chromatids break, exchange and rejoin.

Question 39

What is a gene?

Answer 39

A gene is a segment of DNA that contains a feature

Question 40

What is an allele?

Answer 40

A version of a gene.

Question 41

Similarities between Mitotic and Meiotic cell division?

Answer 41

1. DNA is replicated during the first interphase. 2. Both involve nuclear division and cytoplasmic division. 3. Both involvement the movement and distribution of chromosomes among daughter cells.

Question 42

What are the differences in the processes of mitotic and meiotic cell division?

Answer 42

1. Number of cell divisions: meiosis x 2, mitosis x 1. 2. Pairing of homologous chromosomes: only meiosis. 3. Crossing over and independent assortment: only meiosis. 4. Number of cells produced: meiosis x 4, mitosis x 2

Question 43

What are the differences in daughter cells of meiosis and mitosis?

Answer 43

1. Number of cells produced: meiosis x 4, mitosis x 2. 2. Chromosome number: Mitosis same as parent cell, meiosis is half of parent cell. 3. Cell type: body cells vs gametes