12 Ass 6 cell division pt 2

Question 1

Q21 a Name the stage of mitosis shown in Fig. 2.1.

Answer 1

metaphase

Question 2

Q21 a) ii) Fig. 2.2 shows the cell in Fig. 2.1 at the start of cytokinesis.
Complete Fig. 2.2 to show the daughter chromosomes in each nucleus

Answer 2

On written paper in file

Question 3

State the role of telomeres during DNA replication.

Answer 3

They prevent DNA coding from being lost

Question 4

Multiple myeloma is a type of cancer in the bone marrow where some of the stem
cells start to produce abnormal blood cells.
* One treatment is to collect stem cells from the bone marrow of the person with
multiplemyeloma. Healthy stem cells are isolated and grown in the laboratory.
* Radiation is then used to destroy all stem cells and cancerous cells in the bone
marrow.
* Finally, large numbers of the healthy stem cells grown in the laboratory are
returned to the bone marrow.
Suggest the role of stem cells in this treatment of multiple myeloma. 3

Answer 4

The stem cells are undifferentiated

So after being grown in a lab and dividing, they can differentiate into red blood cells, neutrophils and lymphocytes

because they are multipotent and can then replace the patient’s lost blood cells

Question 5

Q22 a) The group of chromosomes shown in Fig. 6.1 is magnified many times.
The actual width of the human chromosome between A—B is 1400 nm.
Calculate the magnification of the scanning electron micrograph shown in Fig. 6.1.

Answer 5

A=1400nm

I=15cm = 150 000000nm

M = 150000000/1400
M= x107143

Question 6

Q22 b) Draw chromosome C in Fig. 6.1 in the space provided.
Label your drawing to show the structure of the chromosome. 4

Answer 6

On written paper

Question 7

Suggest why the metaphase stage is the best time during a mitotic cell cycle to obtain a
clear image of chromosomes. 2

Answer 7

The chromosomes will line up along the cell equator

so they’ll be easier to see bc they’re grouped together

Question 8

Name the stage of mitosis that immediately follows metaphase.

Answer 8

Anaphase

Question 9

Describe the role of the spindle during anaphase. 2

Answer 9

The spindle fibres shorten from the pole ends

and pull the sister chromatids apart to opposite ends

Question 10

Describe the structure of a monomer of a DNA molecule 4

Answer 10

Made of a nitrogen containing base

base can be thymine, adenine, cytosine and guanine

a deoxyribose sugar

and a phosphate group

Question 11

Telomeres are located at the ends of each chromosome.
Telomeres progressively shorten each time a healthy human cell divides, until the cell is no
longer able to divide.
Stem cells have an enzyme called telomerase that prevents the telomeres from shortening during
the cell cycle.

Suggest why telomerase activity is important in stem cells. 2

Answer 11

It allows stem cells to continue to divide

in order to differentiate into specialised cells for tissue repair

Question 12

Suggest why tumour cells produce high concentrations of telomerase

Answer 12

This allows the tumour to continue to uncontrollably divide

Question 13

Scientists have researched the possibility of treating cancer by inhibiting the action of telomerase.
One method that has been studied involves inserting small, single-stranded DNA into cancer cells.

These sections of DNA have a base sequence that is complementary to a section of the mRNA transcribed from the gene coding for telomerase.

Explain how inserting small, single-stranded DNA could prevent translation of the mRNA that is needed to produce telomerase. 3

Answer 13

DNA binds to the mRNA, forming hydrogen bonds between bases

This stops the mRNA from binding to the ribosome so it can’t move along the mRNA

making the molecule too large to leave the nucleus through nuclear pores

Question 14

24 a)Identify which stage of mitosis is shown in cell E and in cell F 2

Answer 14

E metaphase

F anaphase

Question 15

State the function of microtubules in mitosis. 2

Answer 15

They form spindle fibres

and attach to the centromere to line up chromosomes

Question 16

24 State, with a reason, whether Fig. 1.1 shows a region of animal or plant tissue.

Answer 16

It’s a plant because the cells are all square and uniform

Question 17

What type of bonds hold the two DNA strands together

Answer 17

hydrogen bonds

Question 18

What, does DNA ligase do?

Answer 18

enzyme joins fragments together to form a continuous strand of DNA

Question 19

What does DNA polymerase do?

Answer 19

catalyses complementary DNA nucleotides being added to template strands

Question 20

What are telomeres 2

Answer 20

Regions of repeating nucleotide sequences at the ends of chromosomes

that allow the continued replication of DNA without loss of genes