Cell division

Question 1

What is interphase?

Answer 1

• Longest stage of the eukaryotic cell cycle.

- Cells grow and synthesise new organelles, proteins and DNA in preparation for mitosis.

Question 2

What is mitosis?

Answer 2

• Form of cell division.

- Produces two genetically identical diploid daughter cells.

Question 3

Why is mitosis important?

Answer 3

Important for the growth of tissue and repair and replacement of cells.

Question 4

Name the stages of mitosis.

Answer 4

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 5

Summarise process of mitosis.

Answer 5

• Prophase = nuclear envelope breaks down, chromosomes condense, centrioles move to opposite poles of the cell.
• Metaphase = sister chromosomes line up at the equator, centromeres attach to the spindle fibres.
• Anaphase = sister chromatids separated and pulled apart to opposite poles.
• Telophase = nuclear envelope reforms, spindle fibres break down, chromosomes uncoil.

Question 6

What are sister chromatids?

Answer 6

A pair of identical chromatids formed by DNA replication, joined by a centromere.

Question 7

What is cytokinesis?

Answer 7

The division of the cytoplasm at the end of mitosis to produce two new daughter cells.

Question 8

Compare mitosis in plant and animal cells.

Answer 8

Animal cells: 
- Occurs in most tissues.
- Before mitosis, cell become rounded.
- Involves centrioles.
- Involves microfilaments.
- Spindle fibres disappear prior to cytokinesis.
Plant cells: 
- Occurs in meristematic cells only.
- Cell does not change shape.
- No centrioles involved.
- No microfilaments involved.
- Some spindle fibres remain during cytokinesis.

Question 9

What may unrestricted mitosis lead to?

Answer 9

Cancerous growths.

Question 10

What is meiosis?

Answer 10

• Form of cell division.
• Produces four genetically different daughter cells (gametes) with a haploid number of chromosomes.
• Involves two divisions.

Question 11

What is the significance of meiosis in reproduction.

Answer 11

Gametes must be haploid so that when they combine during fertilisation, the full number of chromosomes is present within the resulting zygote. It also creates genetic variation.

Question 12

What is meiosis 1?

Answer 12

• First stage of meiosis.

- Homologous chromosomes are separated to form two haploid cells.

Question 13

Describe what happens during meiosis 1.

Answer 13

1. Homologous chromosomes pair to form bivalents.
2. Crossing over occurs at chiasmata.
3. Cell divides into two; independent segregation of homologous chromosomes, each cell contains either a maternal or paternal copy.

Question 14

What are homologous chromosomes?

Answer 14

• Pair of chromosomes with genes at the same locus.
• One maternal and one paternal.
• Some alleles may be the same while others are different.

Question 15

Define crossing over.

Answer 15

• Process in meiosis 1.
• Homologous chromosomes pair up, their chromatids wrap around one another and their alleles are exchanged at equivalent portions of chromatids.
• Creates genetic variation.

Question 16

What is independent segregation?

Answer 16

The random separation of homologous chromosomes in meiosis 1 that produces genetic variation.

Question 17

What is meiosis 2?

Answer 17

• Second stage of meiosis.

- Sister chromatids separated to form four haploid gametes.

Question 18

Describe what happens during meiosis 2.

Answer 18

1. Independent segregation of sister chromatids.

2. Each cell divides again, producing four haploid cells.

Question 19

How does meiosis produce genetic variation?

Answer 19

• Crossing over during meiosis 1.
• Independent assortment of homologous chromosomes and sister chromatids.
  Results in new combinations of alleles.