Chapter 6 - The Cell Cycle + Cell Division

Question 1

What is a Chromosome?

Answer 1

A long, thin structure of DNA and protein, in the nucleus of eukaryotic cells, carrying the genes.

Question 2

What is the difference between Diploid and Haploid?

Answer 2

Diploid - Having 2 complete sets of chromosomes.

Haploid - Having 1 complete set of chromosomes.

Question 3

What is Mitosis?

Answer 3

A type of cell division in which the 2 daughter cells have the same number of chromosomes and are genetically identical to each other and the parent cell.

Question 4

What are the 3 stages in the cell cycle?

Answer 4

• Interphase.
• Mitosis.
• Cytokinesis.

Question 5

What happens in the Interphase stage of the cell cycle?

Answer 5

Its the longest phase. The newly formed cell grows and its organelles replicate, replacing those lost in the previous division. The DNA replicates, proteins are synthesised.

Question 6

What are the 4 stages of Mitosis?

Answer 6

• Prophase.
• Metaphase.
• Anaphase.
• Telophase.

Question 7

What happens in Prophase?

Answer 7

• Chromosomes condense becoming distinguishable as chromatids.
• Centrioles separate and move to opposite poles of the cell. Microtubules form from each centriole making the spindle.
• The nuclear envelope disintegrates and nucleolus disappears.

Question 8

What occurs in Metaphase?

Answer 8

Chromosomes attach to spindle fibres at their centromeres and align on the equator.

Question 9

What happens in Anaphase?

Answer 9

Very rapid stage. The centromere separates and the spindle fibres shorten, pulling the now separated chromatids to the poles, centromere first.

Question 10

What happens in Telophase?

Answer 10

Final stage of mitosis. Chromatids reach the poles of the cell and are referred to as chromosomes. The spindle fibres break down, nuclear envelope re-forms and nucleolus reappears.

Question 11

What is the division of the nucleus by mitosis called?

Answer 11

Cytokinesis.

Question 12

What is mitosis used for?

Answer 12

• Growth.
• Repair tissues.
• Replace dead cells.

Question 13

Where does mitosis occur in plants?

Answer 13

In the root and shoot apex, called meristems.

Question 14

What is an Oncogene?

Answer 14

A gene with the potential to cause cancer.

Question 15

What is Meiosis?

Answer 15

A two-stage cell division in sexually reproducing organisms that produces four genetically distinct daughter cells each with half the number of chromosomes of the parent cell.

Question 16

What are the 2 divisions in Meiosis called and what are the stages within them?

Answer 16

Meiosis I & Meiosis II and they go through the same steps as mitosis E.g. PMAT.

Question 17

How does Prophase I differ to Prophase in Mitosis?

Answer 17

The homologous chromosomes associate in their pairs, the bivalents. The chromatids wrap around each other and partially repel but remain joined at chiasmata. This swapping is called crossing over.

Question 18

What is independent assortment?

Answer 18

Where either of a pair of homologus chromosomes moves to either pole at Anaphase I of meiosis, independently of the chromosomes of other homologus pairs.

Question 19

What happens in Anaphase I and Telophase I?

Answer 19

The chromosomes in each bivalent separate and as the spindle fibres shorten, one of each pair is pulled to one pole. In the majority of cases, the chromosomes stay in their condense form. Then cytokinesis.

Question 20

What happens in Prophase and Metaphase II?

Answer 20

The centrioles separate and organise a new spindle at right angles to the old one. Chromosomes line up on the equator, with each chromosome attached to a spindle fibre by its centromere (Independent assortment).

Question 21

What is the significance of Meiosis and how does it create genetic variation?

Answer 21

• It keeps the chromosome number constant from one generation to the next.
• It generates genetic variation in the gametes through crossing over (Prophase I) and independent assortment (Metaphase I & II).