all cells arise from other cells

Question 1

Define the cell cycle

Answer 1

Cycle of division with intermediate growth periods

Question 2

Outline the stages of the cell cycle

Answer 2

1. Interphase
2. Mitosis / meiosis
3. Cytokinesis

Question 3

Explain why the cell cycle doesn’t occur in some cells

Answer 3

After differentiation, some types of cell in multicellular organisms no longer have the ability to divide

Question 4

What is the difference between the cell cycle and mitosis?

Answer 4

Cell cycle includes growth period between divisions, mitosis is only 10% of the cell cycle and refers only to nuclear division

Question 5

Outline what happens during interphase

Answer 5

G1: Cell synthesises proteins for replication and cell size doubles

S: DNA replicates, chromosomes consist of 2 sister chromatids joined at a centromere

G2: the cell continues to elongate and proteins for cell division are made

Question 6

State the purpose of mitosis

Answer 6

1. Growth
2. Cell replacement / tissue repair
3. Asexual reproduction

Question 7

Name the stages of mitosis

Answer 7

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 8

Outline what happens during prophase

Answer 8

1. Chromosomes condense, becoming visible
2. Centrioles move to opposite poles of cells and spindle fibres form
3. Nuclear envelope and nucleolus break down

Question 9

Outline what happens during metaphase

Answer 9

1. Sister chromatids line up at the cell equator, attached to the mitotic spindle by their centromere

Question 10

Outline what happens during anaphase

Answer 10

1. Spindle fibres contract, centromeres divide
2. Sister chromatids separate into 2 chromosomes and are pulled to opposite poles of the cell
3. Spindle fibres break down

Question 11

Outline what happens during telophase

Answer 11

1. Chromosomes decondense, becoming invisible
2. New nuclear envelope forms around each set of chromosomes

Question 12

Why is only the root tip used when calculating a mitotic index?

Answer 12

• Meristematic cells at the root tip are actively undergoing mitosis
• Cells further from the root tip are elongating rather than dividing

Question 13

Suggest how cancer treatments control the rate of cell division

Answer 13

• Disrupt the cell cycle so prevent DNA replication and disrupt spindle formation which inhibits metaphase and anaphase

Question 14

How do prokaryotic cells replicate?

Answer 14

1. The single, circular DNA molecule undergoes DNA replication
2. Any plasmids present undergo DNA replication
3. The parent cell divides into two cells, with the cytoplasm roughly halved between the two daughter cells
4. The two daughter cells each contain a single copy of the circular DNA molecule and a variable number of plasmids

Question 15

What causes cancers and how do they start?

Answer 15

• Caused by uncontrolled cell division which forms a tumour

- Cancers start when a mutation occurs in the genes that control cell division.

Question 16

What are carcinogens?

Answer 16

Any agents that may cause cancer

Question 17

What are the 2 types of tumours

Answer 17

1. Malignant

2. Benign

Question 18

Describe malignant tumours

Answer 18

• Malignant tumour cells can break off the tumour and travel through the blood and/or lymphatic system to form secondary growths in other parts of the body

Question 19

Describe benign tumours

Answer 19

• They don’t spread from their original site, these don’t cause cancer
• They grow until there is no more room

Question 20

How are cancers inherited?

Answer 20

The harmful mutation occurring in the original cell can be passed on to all that cell’s descendants

Question 21

What is an oncogene?

Answer 21

A mutated gene that causes cancer

Question 22

What causes cancers and how do they start?

Answer 22

Cancers are caused by uncontrolled cell division which forms a tumour, cancers start when a mutation occurs in the genes that control cell division.