Cells - Cell Cycle

Question 1

Describe binary fission in bacteria

Answer 1

1. Replication of (circular) DNA;
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);

Question 2

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 2

(During prophase)
1. Chromosomes coil / condense / shorten / thicken / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the
centromere;

(During metaphase)
3. Chromosomes line up on the equator of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;

(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles

(During telophase)
8. Chromatids / chromosomes uncoil / unwind / become longer / thinner

Question 3

What are the three main stages of the cell cycle?

Answer 3

Interphase – The cell grows and DNA is replicated.
Mitosis – The nucleus divides.
Cytokinesis – The cytoplasm divides, forming two daughter cells.

Question 4

What are the three phases of interphase, and what happens in each?

Answer 4

• G1 phase (Gap 1) – Cell growth and synthesis of new proteins/organelles.
• S phase (Synthesis) – DNA replication occurs.
• G2 phase (Gap 2) – Further growth, organelle replication, and preparation for mitosis.

Question 5

Describe what happens during prophase in mitosis.

Answer 5

• Chromosomes condense and become visible.
• The nuclear envelope breaks down.
• Spindle fibers begin to form from centrioles.

Question 6

what happens during metaphase

Answer 6

• Chromosomes line up along the equator of the cell.
• Spindle fibers attach to centromeres of the chromosomes.

Question 7

Explain what happens during anaphase.

Answer 7

Sister chromatids are pulled apart by spindle fibers.
They move towards opposite poles of the cell.

Question 8

What happens in telophase and cytokinesis?

Answer 8

• Chromosomes reach the poles and decondense.
• A new nuclear envelope reforms around each set of chromosomes.
• The cytoplasm divides (cytokinesis), forming two genetically identical daughter cells.

Question 9

What is the role of the spindle fibers in mitosis?

Answer 9

• They attach to the centromeres of chromosomes.
• They help separate sister chromatids by pulling them to opposite poles.

Question 10

How does cancer relate to the cell cycle?

Answer 10

• Cancer occurs due to uncontrolled cell division.
• This is caused by mutations in genes that regulate the cell cycle.
• The uncontrolled division leads to the formation of a tumor.

Question 11

How do drugs used in chemotherapy target the cell cycle?

Answer 11

• Some drugs prevent DNA replication in the S phase, stopping the cell cycle.
• Others disrupt spindle formation in metaphase, preventing mitosis.