Cell Division

Question 1

What are the types of cell division?

Answer 1

Mitosis and meiosis

Question 2

What is mitosis?

Answer 2

The most common form of cell division that is required for growth and replacement of dead or worn-out cells.

Question 3

What is meiosis?

Answer 3

Only occurs in reproductive cells where the number of chromosomes is halves and is also known as reduction division.

Question 4

What is a diploid number?

Answer 4

The number of chromosomes in a normal body’s cell (2n). For example, 46 in human cells.

Question 5

What is a haploid number?

Answer 5

The number of chromosomes in reproductive cells (n). For example, 23 in human cells.

Question 6

What is a gamete?

Answer 6

A reproductive cell

Question 7

What is a zygote?

Answer 7

The initial cell formed from the union of gametes.

Question 8

What is fertilisation?

Answer 8

The fusion of male and female gametes.

Question 9

What occurs in the process of mitosis?

Answer 9

When a parent cell divides, it produces daughter cells. Mitosis produces two daughter cells that are genetically identical to the parent cells.

Question 10

What are two things that a dividing cell must do during mitosis?

Answer 10

1) Make a copy of each chromosome before the cell divides.

2) Each daughter cell then receives one copy of every chromosome.

Question 11

Interphase (Mitosis)

Answer 11

DNA content of the cell is doubled.

Question 12

Prophase (Mitosis)

Answer 12

Chromosomes shorten and thicken, each has two chromatids joined by a centromere. Nucleolus disappears and the nucleus membrane disintegrates.

Question 13

Metaphase (Mitosis)

Answer 13

Spindle is formed from pole to pole. Chromosomes arrange themselves in the centre.

Question 14

Anaphase (Mitosis)

Answer 14

Spindle fibres shorten and pull the chromatids to opposite poles of the cells.

Question 15

Telophase (Mitosis)

Answer 15

Two nuclei form at the poles. Each has a copy of every chromosome from the parent cell.

Question 16

What is the process of meiosis?

Answer 16

A type of cell division that results in reducing diploid number of chromosomes in half. It is a more complex process than mitosis, involving two cell divisions. Meiosis produces four cells that are not genetically identical.

Question 17

What are two things a dividing cell has to do in meiosis?

Answer 17

1) Must copy each chromosome so that there is enough genetic material to be shared between four daughter cells.
2) Must divide twice so that each cell receives just one chromosome from each homologous pair.

Question 18

Why are only a haploid number of chromosomes in each cell divided by meiosis?

Answer 18

This is so that when male and female gametes fuse together, the resulting cell will contain the full complement of chromosomes, and can then divide and grow into a new individual.

Question 19

State the differences and similarities between mitosis and meiosis.

Answer 19

• in both processes, chromosomes duplicate before division begins.
• in mitosis, the parent cell divides once while in meiosis it divides twice.
• mitosis produces two daughter cells and meiosis produces four.
• mitosis occurs in all cells of the body and meiosis occurs in only reproductive cells (gametes - male and female)
• cells formed by mitosis are diploid and genetically identical, whereas cells formed by meiosis are haploid and produce variations.

Question 20

Give reasons for the variation in sexual reproduction.

Answer 20

One reason is because of the huge variation in sex cells. Another reasons is the random way in which fertilisation takes place. In humans, anyone of the billions of sperms formed could potentially fertilise any one of the thousands of ovum formed. Hence, every individual is likely to be genetically unique.

Question 21

How are identical twins formed?

Answer 21

Identical twins are formed from the same zygote. When the zygote divides by mitosis, two genetically identical cells are formed that separate and each cell then behaves and grows as an individual zygote into an embryo.

Question 22

How are fraternal twins formed?

Answer 22

They are developed from different zygotes, and so are not genetically identical.

Question 23

What is cloning?

Answer 23

A process that produces a genetically identical offspring from part of the parent organism.