All cells arise from other cells (mitosis)

Question 1

Explain what happens in each stage of mitosis

Answer 1

1. Prophase= chromosomes condense and become visible. Nuclear membrane breaks down. Centrioles move to opposite poles of the cell. Spindle fibres form
2. Metaphase= spindle fibres attach to centromere. Chromosomes are lined up at the equator of the cell.
3. Anaphase= centromeres divide. Spindle fibres shorten. Sister chromatids separate and are pulled apart to opposite poles of the cell.
4. Telophase= identical chromosomes have reached the poles. Spindle fibres break down. A new nuclear membrane forms around each group of chromosomes. Chromosomes uncondense.

Question 2

State all stages of mitosis

Answer 2

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

Question 3

List the stages by which prokaryotes replicates

Answer 3

1. The circular DNA ans plasmids replicate
2. The copies of circular DNA move to separate poles of the cell
3. The cytoplasm divides to produce 2 daughter cells
4. Each cell contains a single copy of the circular DNA but a variable number of plasmids

Question 4

State the stages of the cell cycle

Answer 4

1. Interphase (longest phase)
2. Mitosis
3. Cytokinesis

Question 5

List the stages by which viruses replicate

Answer 5

1. The virus attachment protein binds to a specific complementary receptor protein on a specific host cell
2. The virus DNA/ RNA is injected into the host cell
3. The host cell uses the viral DNA/ RNA and its own ribosomes and enzymes to synthesise virus proteins.
4. The viral particles are formed and released from the host cell

Question 6

Explain why mitosis is important to organisms

Answer 6

It allows organisms to;
- grow
- repair tissues
- replace cells

Question 7

Describe cell division in a cancer cell

Answer 7

uncontrolled cell division, shorter cell cycle and divide most often

Question 7

Name some targets for treating cancer and where it disrupts in the cell cycle

Answer 7

Many cancer treatments target parts of the cell cycle to prevent the cell from dividing for example these drugs may stop;
- DNA replication (disrupts interphase)
- Spindle formation/ spindle contraction (prevents metaphase/ anaphase)
- Cytokinesis

Question 8

Why do cancer treatments kill more cancer cells than healthy cells?

Answer 8

Tumour cells divide more frequently than normal cells, so the treatments target tumour cells more

Question 9

Why are viruses difficult to treat?

Answer 9

They replicate inside the cells where the drug is unable to bind to them

Question 10

Define homologus chromosome

Answer 10

a pair of chromosomes with the same genes at the same gene loci but can have different alleles

Question 11

Define haploid cell

Answer 11

a cell containing one of each type of chromosome e.g. gamete
Represented by n

Question 12

Define diploid cell

Answer 12

a cell containing two of each type of chromosome e.g. normal body cell
Represented by 2n

Question 13

Describe the events that happen during Interphase

Answer 13

• New organelles are replicated
• DNA replicates
• Increase in protein and ATP sythesis

Question 14

Explain why DNA replication must take place before cell division

Answer 14

DNA replication occurs before mitosis so that each daughter cell receives a full set of genetically identical chromosomes from the parent cells

Question 15

How do you calculate mitotic index?

Answer 15

mitotic index= number of cells undergoing mitosis/ total number of cells

(give as a decimal)

Question 16

What is mitotic index?

Answer 16

The proportion of cells that are undergoing mitosis. The higher the index the faster the tissues growing

Question 17

Name the method prokaryotes use to divide

Answer 17

Binary fission