Cell Division

Question 1

How many chromosomes are in a human cell?

Answer 1

46

Question 2

What are the phases of the cell cycle?

Answer 2

• Interphase
• Mitosis
• Cytokinesis

Question 3

What are the stages in mitosis?

Answer 3

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 4

What are the stages in interphase and what happens at each?

Answer 4

• G1 phase = cell grows
• S phase = DNA synthesis
• G2 phase = Cell gets ready for division, it makes stores of ATP and new organelles

Question 5

What happens in prophase?

Answer 5

• Chromosomes condense and are now visible when stained.
• The chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA molecule) that are joined together at the centromere.
• The nuclear envelope breaks down

Question 6

What happens in metaphase?

Answer 6

• Chromosomes line up at the equator of the spindle
• Spindle fibres reach the chromosomes and attach to the centromeres
• Each sister chromatid is attached to a spindle fibre originating from opposite poles

Question 7

What happens in anaphase?

Answer 7

• The sister chromatids separate at the centromere (the centromere divides in two)
• The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres

Question 8

What happens in telophase?

Answer 8

• Chromosomes arrive at opposite poles and begin to decondense
  -Nuclear envelopes begin to reform
• The spindle fibres break down

Question 9

What is cytokenisis?

Answer 9

The physical separation of the parent cell into two genetically identical daughter cells

Question 10

What is the region of the plant where growth occurs?

Answer 10

Meristems

Question 11

How do you do the identify mitotic stages required practical?

Answer 11

1 - Remove the tips of the roots (about 1cm) and place them in ethanoic alcohol. This helps to prevent mitosis from continuing.
2 - Place the root tips in warm (60oC) dilute hydrochloric acid. This separates the cells
3 -Transfer the root tip to a microscope slide
4 -Using a pipette, add a suitable stain
5 - Place a coverslip on top of the root tip and press down firmly using a paper towel. This spreads out the cells so they are only one layer thick
6 - View the cells under a microscope

Question 12

What are the limitations of the method used in the identify mitotic stages required practical?

Answer 12

• The preparation of tissue for microscope slides can damage cells and alter their appearance
• The size of cells or structures of tissues may appear inconsistent in different specimen slides
• Optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that cannot be seen

Question 13

How do you calculate the mitotic index?

Answer 13

mitotic index = number of cells with visible chromosomes ÷ total number of cells

Question 14

What is cancer?

Answer 14

The rapid and uncontrollable division of cells, forming a tumour, which starts due to changes in the genes that control cell division.

Question 15

What are carcinogens?

Answer 15

Any agents that may cause cancer (e.g. UV light, tar in tobacco smoke and X-rays).

Question 16

What are benign tumours?

Answer 16

Tumours (such as warts) that do not spread from their original site and don’t cause cancer.

Question 17

What is a malignant tumour?

Answer 17

Tumours which spread through the body, invading and destroying other tissues and causes cancer.

Question 18

How do eukaryotic cells divide in the body?

Answer 18

The cell cycle (mitosis)

Question 19

How do prokaryotic cells divide?

Answer 19

• Binary fission

Question 20

What are the stages of binary fission?

Answer 20

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

Question 21

How do viruses replicate?

Answer 21

Viral replication

Question 22

What are the stages of viral replication?

Answer 22

1. Virus attaches to surface of host cell
2. Viral RNA enters host cell
3. Viral RNA is used to make viral DNA by reverse transcriptase
4. Host cell DNA is mixed with viral DNA and it is replicated, more viral particles made
5. Host cell lyses/bursts and releases newly made viruses

Question 23

Why can’t viruses replicate on their own?

Answer 23

They are non-living

Question 24

In prophase of mitosis, the chromosomes become visible. Describe what happens in a) metaphase b) anaphase (4)

Answer 24

a) Chromosomes line up along equator of cell
Chromosome attaches to spindle by centromere
b) Centromere divide
Chromatid pairs split in two and pulled to opposite ends of the cell

Question 25

Describe the appearance and behaviour of chromosomes during mitosis. (5)

Answer 25

(During prophase)
1. Chromosomes coil/condense/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 are pulled to opposite poles of the cell
(During telophase)
8. Chromosomes uncoil