AQA A Level Biology: All cells arise from other cells

Question 1

What is the cell cycle?

Answer 1

A sequence of stages that cells go through to grow and divide, consisting of interphase, mitosis, and cytokinesis.

Question 2

What are the three stages of interphase?

Answer 2

1. G1 phase: Cell growth and organelle replication.
   
   2. S phase: DNA replication.
   3. G2 phase: Preparation for mitosis, checking for errors.

Question 3

What happens during mitosis?

Answer 3

A parent cell divides to produce two genetically identical daughter cells.

Question 4

What are the four stages of mitosis?

Answer 4

1. Prophase: Chromosomes condense, nuclear envelope breaks down, spindle forms.
   
   2. Metaphase: Chromosomes line up at the equator, spindle fibers attach to centromeres.
   3. Anaphase: Sister chromatids are pulled to opposite poles.
   4. Telophase: Chromatids uncoil, nuclear envelope reforms.

Question 5

What is cytokinesis?

Answer 5

The division of the cytoplasm to form two separate daughter cells.

Question 6

Why is mitosis important?

Answer 6

• Growth of organisms.
  
  • Repair of damaged tissues.
  • Asexual reproduction in some organisms.

Question 7

How is the cell cycle regulated?

Answer 7

By checkpoints at G1, G2, and metaphase to ensure DNA is replicated correctly and the cell is ready for division.

Question 8

What is cancer?

Answer 8

Uncontrolled cell division caused by mutations in genes controlling the cell cycle.

Question 9

How do cancer treatments work?

Answer 9

• Chemotherapy: Disrupts the cell cycle to stop rapid division.
  
  • Radiation: Damages DNA to trigger apoptosis (cell death).

Question 10

What is binary fission?

Answer 10

The process by which prokaryotic cells divide:
1. Circular DNA replicates.
2. Plasmids replicate.
3. Cell grows, DNA moves to opposite poles.
4. Cytoplasm divides, forming two daughter cells.

Question 11

How do viruses replicate?

Answer 11

1. Attach to host cell using attachment proteins.
   
   2. Inject genetic material into the host.
   3. Host cell replicates viral components.
   4. Viruses assemble and burst out, destroying the host cell.

Question 12

How do mutations in genes cause cancer?

Answer 12

• Mutations in proto-oncogenes → oncogenes → uncontrolled cell division.
  
  • Mutations in tumor suppressor genes prevent regulation of cell division.

Question 13

What is the difference between benign and malignant tumors?

Answer 13

• Benign tumors: Do not invade other tissues, stay in one place.
  
  • Malignant tumors: Invade nearby tissues and spread (metastasis).

Question 14

What are the key differences between mitosis and binary fission?

Answer 14

• Mitosis: Eukaryotic cells, involves chromosomes and spindle fibers.
  
  • Binary fission: Prokaryotic cells, simpler process with no spindle formation.

Question 15

What happens if DNA is not copied accurately during S phase?

Answer 15

Mutations may occur, which can lead to genetic disorders or cancer.

Question 16

What is the role of centrioles in mitosis?

Answer 16

Centrioles help organize the spindle fibers that pull chromatids apart during mitosis.

Question 17

What is the mitotic index and how is it calculated?

Answer 17

Mitotic index= (number of cells in mitosis)/(total number of cells) x 100

Indicates the percentage of cells undergoing mitosis.

Question 18

What happens during metaphase?

Answer 18

Chromosomes line up along the equator, with spindle fibers attaching to the centromeres.

Question 19

What happens during anaphase?

Answer 19

Sister chromatids are pulled apart to opposite poles by the shortening of spindle fibers.

Question 20

What is the purpose of G1 and G2 checkpoints?

Answer 20

• G1 checkpoint: Ensures the cell is ready for DNA replication.
  
  • G2 checkpoint: Ensures DNA has been replicated without errors.

Question 21

What is the role of p53 in the cell cycle?

Answer 21

A tumor suppressor protein that regulates the cell cycle and prevents cancer by triggering apoptosis if errors are detected.