CHAPTER 6: CELL DIVISION

Question 1

What is cell division?

Answer 1

1. Cells in our body produce new cells through the cell division

Question 2

Cell division involves two stages, which is?

Answer 2

1. Karyokinesis - involves the division of the nucleus
2. Cytokinesis - involves the division of the cytoplasm

Question 3

The organism’s body cells are divided into?

Answer 3

1. Somatic cells
2. Reproductive cells/ gametes

Question 4

What is somatic cell?

Answer 4

1. Body cells apart from gametes
2. Somatic cells are produced through the mitosis process
3. It contains a diploid number of chromosomes, that is, each cell contains two sets of chromosomes or 2n. In human somatic cells, 2n = 46

Question 5

What is gamete?

Answer 5

1. Gametes are reproductive cells
2. Gametes are produced through the meiosis process
3. It contains a haploid number of chromosomes, that is, each cell contains one set of chromosomes or n. In human gametes, n = 23

Question 6

What is paternal chromosomes?

Answer 6

One set of chromosomes originate from the male parent in diploid cells

Question 7

What is maternal chromosomes?

Answer 7

One set of chromosomes originate from the female parent in diploid cells

Question 8

What is homologous chromosomes?

Answer 8

Both paternal and maternal chromosomes have same structural characteristics. This pair is called homologous chromosomes

Question 9

What is chromatin?

Answer 9

A chromosome that looks like a long thread

Question 10

What is a cell cycle?

Answer 10

The cell cycle refers to the sequence of events that involves DNA multiplication and cell division to produce two daughter cells

Question 11

What are interphase and M phase?

Answer 11

The phases consisted by the cell phase

Question 12

What is Interphase?

Answer 12

The longest phase in the cell cycle

Question 13

Interphase is made of?

Answer 13

G1, S, G2 phase

Question 14

What is G1 phase?

Answer 14

1. Cell grow
2. Cell components such as mitochondrion and endoplasmic reticulum are produced at this stage.
3. Proteins used in the cell cycle are also synthesised during this time
4. At this stage, the nucleus looks big and the chromosomes is in the form of chromatin

Question 15

What is S phase?

Answer 15

1. DNA synthesis occurs in the S phase
2. The DNA in the nucleus is replicated
3. Each chromosome multiplies into two identical chromosomes known as sister chromatids
4. Both chromatids contain the same copy of the DNA molecule.
5. Both chromatids are joined at the centromeres

Question 16

What is G2? phase

Answer 16

1. The cells are continue to grow and remain active metabolically during the G2 phase
2. Cells gather energy and make final arrangements to enter the next stage of cell division
3. After the interphase stage, the cell will enter the M phase

Question 17

What is the M phase?

Answer 17

1. M phase is made up of mitosis and cytokinesis. Mitosis involves prophase, metaphase, anaphase and telophase

Question 18

What is mitosis?

Answer 18

Defined as the division of the nucleus of parent cell into two nuclei

Question 19

What is prophase?

Answer 19

1. In the nucleus, chromatin starts to shorten and thicken to form a chromosome structure that can be seen through a light microscope
2. The chromosome is seen to be made up of two identical threads called sister chromatids
3. Both sister chromatids are joined at the centromere
4. The nucleus membrane disintegrates, the nucleolus disappears, the centriole moves to the opposites poles and spindle fibres start to form

Question 20

What is metaphase?

Answer 20

1. Centrioles are at the opposite poles of the cell
2. The spindle fibres maintain the chromosomes at the equatorial plane
3. The chromosomes become aligned in a single row on the equatorial plane
4. Metaphase ends when the centromere begins to divide

Question 21

What is anaphase?

Answer 21

1. The centromere divides into two and the sister chromatids separate
2. Spindle fibres shorten, contact and the sister chromatids are pulled to the opposite poles of the cell
3. Anaphase ends when the chromatid arrives at the pole of the cells

Question 22

What is telophase?

Answer 22

1. When the chromatids are at the opposite poles, they are now called the daughter chromosome
2. Each pole contains one set of complete and identical chromosomes
3. Chromosomes are re-formed as fine chromatin threads
4. Nucleoli are formed again
5. Spindle fibres disappear
6. A new nucleus membrane is formed
7. The telophase stage is followed by cytokinesis

Question 23

What is cytokinesis?

Answer 23

Cytokinesis is the division of cytoplasm that happens immediately after the nucleus is formed, that is, at the end of telophase

Question 24

What is the differences between mitosis and cytokinesis in animal cells and plant cells? [ Animal Cells ]

Answer 24

1. Cytokinesis occurs in animal cells when the plasma membrane constricts in the middle of the cell between the two nuclei
2. Microfilaments at the point of constriction will contact, causing the cell to constrict until it splits to form two daughter cells

Question 25

What is the differences between mitosis and cytokinesis in animal cells and plant cells? [ Plant Cells ]

Answer 25

1. Cytokinesis in plant cells also begins when the formed vesicles combine to form cell plates at the centre of the cell 2. The cell plates are surrounded by a new plasma membrane and a new cell wall substance is formed among the spaces of the cell plates 3. The cell plates expand outwards until they combine with the plasma membranes 4. At the end of cytokinesis, cellulose fibres are produced by the cells to strengthen the new cell walls 5. Two daughter cells are formed 6. Each cell has a diploid condition

Question 26

What is the necessity of mitosis?

Answer 26

1. For embryo development and organism growth, mitosis ensures that rapid cell growth occurs 2. Through the mitosis process, the lizard is able to grow a new tail [ regeneration ] if the tail breaks 3. Mitosis aids organisms such as hydra to produce new individuals through the information of new buds 4. When the body is injured, mitosis will produce new cells to replace cells that are dead or damaged 5. The culturing technique uses stem cells from animals which are then cultured in laboratories to produce meat 6. Stem cell therapy uses stem cells from bone marrows to treat damage cartilage 7. In agriculture, the technique of culturing plant tissues is used to produce young plants through the fertilisation process

Question 27

What is meiosis?

Answer 27

1.The process of cell division that occurs in reproductive organs to produce gametes that contain half the number of chromosomes [ haploid ] of the parent cells [ diploid ] 2. Occurs in the testis [ male ] and ovary [ female ] for animals and humans

Question 28

What is the need for meiosis?

Answer 28

1. Forms gametes through the process of gametogenesis and ensures that the diploid chromosome number of organisms that carry out sex reproduction is always maintained from one generation to the next 2. Also produces genetic variation in the same species 3. Divided into 2 stages of cell division, that is meiosis 1 and meiosis 2

Question 29

Meiosis 1 comprises of?

Answer 29

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

Question 30

Meiosis 2 comprises of?

Answer 30

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

Question 31

What is prophase 1?

Answer 31

1. Chromatin shortens, thickens and forms visible chromosomes. The pairing of homologous chromosomes [ synapsis ] forms bivalent [ or known as a tetrad, that is four chromatids for each homologous chromosome ] 2. The crossing over process that is an exchange of genetic material between non - identical chromatids takes place. Crossing over produces a combination of genes that are new in chromosomes. The point where the chromatids cross over is called chiasma. At the end of prophase 1, the nucleus membrane and nucleoli will start to disappear. Both centrioles will move towards the opposite pole cells. Spindle fibres are formed among the centrioles

Question 32

What is metaphase 1?

Answer 32

1. The homologous chromosomes are arranged at the equatorial plane 2. One chromosome from each pair of the homologous chromosome is tied to the spindle fibres from one pole cell and its homologous is tied to the spindle fibres from the opposite pole cell 3. The sister chromatids are still tied together because the centromere has not separated

Question 33

Anaphase 1

Answer 33

1. The spindle fibres contract and cause each homologous chromosome to separate from its homologous pair and be pulled to the opposite poles 2. Each chromosome is still made up of a pair of sister chromatids tied to a centromere and move as one unit

Question 34

What is telophase 1?

Answer 34

1. The chromosomes arrive at the opposite pole cells 2. Each polar cell contains a number of haploid chromosomes that are made up of one set of chromosomes only 3. The spindle fibres will then disappear 4. Nucleoli will reappear and the nuclear membrane is formed 5. Telophase 1 is succeeded by the cytokinesis process that produces two daughter cells 6. Both daughter cells produced are in the haploid condition 7. The interphase for meiosis 1 is usually short and the DNA does not replicate

Question 35

What is prophase 2?

Answer 35

1. The nucleoli and the nuclear membrane disappear 2. Each chromosome is made up of sister chromatids that are joined at the centromere 3. The spindle fibres start to form in both daughter cells

Question 36

What is anaphase 2?

Answer 36

1. The sister chromatid centromere starts to separate 2. The sister chromatid pair separates and moves towards the opposite poles led by the centromere 3. Each chromatid at this stage is known as a chromosome

Question 37

What is metaphase 2?

Answer 37

1. Chromosomes are arranged at random on the equatorial plane for each daughter cell 2. Each chromatid is tied to the spindle fibres at the centromere 3. Metaphase 2 ends when the centromere separates

Question 38

What is telophase 2?

Answer 38

1. Chromosomes arrive at the pole of the cell 2. Spindle fibres disappear. The nuclear membrane and the nucleoli are reconstructed 3. The number of chromosome for each daughter cell is half the number of parent chromosomes 4. Telophase 2 ends with the process of cytokinesis that produces four daughter cells that are haploid 5. Each haploid cell contains half the number of parent cell chromosomes. The genetic content is also different from the diploid parent cell. The haploid cells develop into gametes

Question 39

Tumour is divided into two types which are?

Answer 39

1. Benign tumour 2. Malignant tumour

Question 40

What is benign tumour?

Answer 40

Not dangerous and can be removed surgically

Question 41

What is malignant tumour?

Answer 41

1. Also called cancer 2. Caused by several factors such as radiation [ x-ray, gamma rays and ultraviolet rays], chemical substances [ such as tar in tobacco ], carcinogens [ such as formaldehyde and benzene ], genetic factors, and also bacteria and viruses 3. This will cause the cells to divided continuously and develop into a tumour 4. The cancer cells will spread and destroy normal cells around them 5. This condition will affect the functions of the tissues around them 6. Cancer that is not identified at the early stage can cause damage to the organs and finally death

Question 42

Explain the development of breast cancer?

Answer 42

1. The tumour grows from a single cell 2. Cancer cells compete to get nutrients from other tissues around them 3. The cancer cells spread through the lymph vessels and blood vessels to the other parts of the body 4. A new tumour develops on the organs

Question 43

What is the cause of down syndrome?

Answer 43

1. Any abnormality during the division of meiosis 2. The spindle fibres fail to function during anaphase 1 or anaphase 2. 3. As a result, the chromosome fails to separate [ nondisjunction ] 4. Gametes will have an abnormal number of chromosomes [ 22 or 24 chromosomes ] 5. If fertilisation between a normal gamete [ 23 chromosomes ] and abnormal chromosome [ 24 chromosomes ] occurs, the zygote will carry 47 chromosomes which is an abnormal condition

Question 44

What is trisomy 21?

Answer 44

1. An individual with Down syndrome has 47 chromosomes, which is an extra chromosome at the 21th set 2. This syndrome can cause mental retardation, slanted eyes and a slightly protruding tongue