Cell Division

Question 1

Describe the features of Prophase

Answer 1

Nuclear membrane begins to breakdown;
Centrioles move to poles of the cell;
Chromatin supercoils and condense in chromosomes;

Question 2

Describe the features of Metaphase

Answer 2

Spidle fibres form;
Spindle fibres attach;
To the centromere of chromosomes;
Chromosomes align at the equator;

Question 3

Describe the features of Anaphase

Answer 3

Spindle fibres shorten;
Centromere splits;
Sister chromatids are separated;
Chromatids pulled to opposite poles of the cell;

Question 4

Describe the features of Telophase

Answer 4

Nuclear membrane begins to reform;
Chromosomes unwind;

Question 5

What is a homologous pair of chromosomes?

Answer 5

Two chromosomes that carry the same genes in the same loci / location

Question 6

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

Answer 6

Description; Explanation;
E.g, 1. Examine large number of fields of view / many cells;
2. To ensure representative sample;

OR
3. Repeat count;
4. To ensure figures are correct;

OR

5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting;

Question 7

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how.

Answer 7

1. Homologous chromosomes pair up;
2. maternal and paternal chromosomes are arranged in any order;
3. Independent segregation;
4. Crossing over;
5. (Equal) Portions of chromatids are swapped between chromosomes;
6. Produces new combination of alleles;
7. Chromatids separated at meiosis II/ later;

Question 8

Describe the process of crossing over and explain how it increases genetic diversity

Answer 8

1. Homologous pairs of chromosomes associate / form a bivalent;
2. Chiasma(ta) form;
3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
4. Producing new combinations of alleles;

Question 9

Give two differences between mitosis and meiosis.

Answer 9

Mitosis given first
1. One division, two divisions in meiosis;
2. (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
3. Two cells produced, (usually) four cells produced in meiosis;
4. Diploid to diploid/, diploid to haploid in meiosis;
5. Separation of homologous chromosomes only in meiosis;
6. Crossing over only in meiosis;
7. Independent segregation only in meiosis;

Question 10

Describe binary fission in bacteria.

Answer 10

1. Replication of (circular) DNA;
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);

Question 11

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 11

(During prophase)
1. Chromosomes supercoil / condense / shorten / thicken / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;
(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes uncoil / unwind / become longer / thinner.

Question 12

Describe and explain the processes that occur during meiosis that increase genetic variation.

Answer 12

Homologous chromosomes pair up;
2. Independent segregation;
3. Maternal and paternal chromosomes are re-shuffled in any combination;
4. Crossing over leads to exchange of parts of (non-sister) chromatids / alleles between homologous chromosomes;
5. (Both) create new combinations of alleles;

Question 13

Give two ways in which the arrangement of prokaryotic DNA is different from the arrangement of the human DNA in Figure 1.

Answer 13

(Prokaryotic DNA) is
1. Circular (as opposed to linear);
2. Not associated with proteins/histones ;
3. Only one molecule/piece of DNA
OR
present as plasmids;

Question 14

Homologous chromosomes carry the same genes but they are not genetically identical.Explain why.

Answer 14

(Homologous chromosomes) carry different alleles;
Accept alternative descriptions for ‘alleles’ eg different forms of a gene / different base sequences
Neutral: reference to maternal and paternal chromosomes

Question 15

Other than independent segregation, give one way in which meiosis allows the production of genetically different cells.

Answer 15

Crossing over / alleles exchanged between chromosomes or chromatids / chiasmata formation / genetic recombination;

Question 16

Mitosis is important in the life of an organism. Give three reasons why.

Answer 16

Growth / increase in cell number;
Ignore growth of cells
2. Replace cells / repair tissue / organs / body;
Ignore repair cells
Reject bacteria
3. Genetically identical cells;
‘Produces 2 genetically identical cells’ does not reach MP1 as well as MP3
4. Asexual reproduction / cloning;

Question 17

Explain why the biologist chose to examine 200 cells.

Answer 17

(Ensures) representative (sample);

Question 18

Suggest why the development of a monopolar mitotic spindle would prevent successful mitosis. (3)

Answer 18

No separation of chromatids/chromosomes/centromeres;
Accept anaphase prevented
Accept nondisjunction
Reject homologous pairs
2. Chromatids/chromosomes all go to one pole/end/sides of cell/not pulled to opposite poles;
3. Doubles chromosome number in cell/one daughter cell gets no chromosomes or chromatids;

Question 19

What is the evidence that cell is in anaphase?

Answer 19

Chromosomes / chromatids moved apart;

Question 20

The offspring produced from farmed trout are sterile. Suggest and explain why.

Answer 20

Too many/extra set/three copies of chromosomes;
Accept 1 paternal, 2 maternal
2. (Homologous) chromosomes do not pair

Question 21

Explain why all the cells of the body will have this mutation.
(disease where there is an extra chromosome) (not directly on the spec but could come up as A02) Patau syndrome

Answer 21

Mutation / extra chromosome in gamete / egg / sperm (that formed zygote);

2. All cells derived (from a single cell / zygote) by mitosis;

OR

3. All cells derived from a single cell / zygote by mitosis;
4. Mitosis produces genetically identical cells / a clone;

Mark points 1 and 2 OR 3 and 4

4. Accept: have same DNA / same alleles

Question 22

Describe how the change in chromosome number in Patau syndrome was produced.
(disease where there is an extra chromosome) (not directly on the spec but could come up as A02) Patau syndrome

Answer 22

In meiosis;

2. Homologous chromosomes / sister chromatids do not separate;

Question 23

Suggest how the flow of some of the blood between the aorta and pulmonary artery could cause children to die in the first 12 months. (3)

Answer 23

(Some) oxygenated blood (from the aorta) flows into pulmonary artery;
OR
Less oxygenated blood flows out through aorta;
OR
Lower blood pressure in aorta;
2. Less oxygen delivered to cells / tissues / organs / named organ / via named blood vessel;
3. So less / not enough oxygen for aerobic respiration (in cell / tissue / organ);
4. Tissue / organ doesn’t grow / develop properly (causing death);
OR
Tissue dies / organ stops working (causing death);

Question 24

Suggest and explain how two environmental variables could be changed
to increase the growth rate of these cells.

Answer 24

Increased (concentration of) glucose;
2. Increased respiration;
3. Increased (concentration of) oxygen;
4. Increased respiration;
5. Increased temperature;
6. Increased enzyme activity;
7. Increased (concentration of) phosphate;
8. Increased ATP/DNA/RNA;
9. Increased (concentration of) nucleotides;
10. Increased DNA synthesis;

Question 25

A microbiologist investigated the ability of different plant oils to kill the bacterium
Listeria monocytogenes. She cultured the bacteria on agar plates. She obtained
the bacteria from a broth culture.
(b)
Describe two aseptic techniques she would have used when transferring a
sample of broth culture on to an agar plate.
Explain why each was important.

Answer 25

Keep lid on Petri dish
OR
Open lid of Petri dish as little as possible.
To prevent unwanted bacteria contaminating the dish.
OR
L. monocytogenes may be dangerous / may get out.
Wear gloves
OR
Wear mask
OR
Wash hands;
To prevent contamination from bacteria on hands / mouth
OR
Prevent spread of bacteria outside the lab;
Use sterile pipette
OR
Flame the loop
OR
Flame the neck of the container of the culture;

To maintain a pure culture of bacteria

Question 26

A student investigated mitosis in the tissue from an onion root tip.
(a)
The student prepared a temporary mount of the onion tissue on a glass
slide. She covered the tissue with a cover slip. She was then given the
following instruction.
“Push down hard on the cover slip, but do not push the cover slip
sideways.”
Explain why she was given this instruction. 2

Answer 26

push hard – spread / squash tissue;
Not push sideways – avoid rolling cells together / breaking
chromosomes

Question 27

the student counted the number of cells she observed in each stage of
mitosis.
Of the 200 cells she counted, only six were in anaphase.
One cell cycle of onion root tissue takes 16 hours. Calculate how many
minutes these cells spend in anaphase.
Show your working.

Answer 27

6/200 x 960 = 28.8/29

Question 28

suggest why preventing the formation of spindle fibres (lines 2–3) stopped
the cell cycle.
2
b)
Suggest and explain why ABZ could be used as a treatment for cancer
even though it affects some healthy cells 1

Answer 28

thromosomes/centromeres cannot attach (to spindle)

Chromosomes cannot line up (on spindle);
(So, no) metaphase;

chromatids cannot separate (on spindle) so no anaphase

b)cancer cells divide more/uncontrollably/rapiy
OR
Healthy cells divide less/slowly;