2.2.1- MITOSIS

Question 1

Q1.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 1

1. Push hard – spread / squash tissue;
2. Not push sideways – avoid rolling cells together / breaking
   chromosomes.
   Neutral – to see cells clearly

Question 2

The image below shows one cell the student saw in the onion tissue.

The student concluded that the cell in the image above was in the anaphase stage
of mitosis.
Was she correct? Give two reasons for your answer. (2)

Answer 2

1. Chromosomes / chromatids are (in two groups) at poles of spindle / at
   ends of spindle;
   Do not accept ‘ends of cell’
2. V-shape shows that (sister) chromatids have been pulled apart at their
   centromeres / that centromeres of (sister) chromatids have been pulled
   apart.

Question 3

Q2.The figure below shows some cells from an onion root tip at different stages of the cell cycle.

Place stages A to E in the correct order. Start with stage D. (1)

Answer 3

(D)CBEA.

Question 4

To obtain these images, the onion root tip was cut off, stained and put on a
microscope slide. A cover slip was placed on top. The root tip was then firmly
squashed and viewed under an optical microscope.
(b) Complete the table below to give one reason why each of these steps was
necessary.

1. Taking cells from thr root tip
2. Firmly squashing the root tip

(2)

Answer 4

Region where
mitosis / cell division
occurs;

To allow light
through /

Question 5

The figure below shows how the amount of DNA per cell changed during interphase
and meiosis in an animal.

Explain how the behaviour of chromosomes causes these changes in the amount of
DNA per cell between F and G. (3)

Answer 5

(Increase)
1. Chromosomes / DNA replicates;
(First decrease)
2. Homologous chromosomes separate;
(Second decrease)
3. Sister chromatids separate

Question 6

What would happen to the amount of DNA per cell at fertilisation of cell G? (1)

Answer 6

DNA would) double / go to 2 (arbitrary units)

Question 7

Q3.Metastatic melanoma (MM) is a type of skin cancer. It is caused by a faulty receptor protein
in cell-surface membranes. There have been no very effective treatments for this cancer.
Dacarbazine is a drug that has been used to treat MM because it appears to increase
survival time for some people with MM.
Doctors investigated the use of a new drug, called ipilimumab, to treat MM. They
compared the median survival time (ST) for two groups of patients treated for MM:
• a control group of patients who had been treated with dacarbazine
• a group of patients who had been treated with dacarbazine and ipilimumab.
The ST is how long a patient lives after diagnosis.
The doctors also recorded the percentage of patients showing a significant reduction in
tumours with each treatment.
The total number of patients in the investigation was 502.
The table below shows the doctors’ results.

The doctors compared median survival times for patients in each group.
How would you find the median survival time for a group of patients? (2)

Answer 7

1. Rank all STs in ascending order;
2. Find value with same number (of people) above and below.
   Accept find middle value

Question 8

b) In many trials of new drugs, a control group of patients is given a placebo that does
not contain any drug.
The control group in this investigation had been treated with dacarbazine.
Suggest why they had not been given a placebo. (1)

Answer 8

Not ethical to fail to treat cancer.

Question 9

c) A journalist who read this investigation concluded that ipilimumab improved the
treatment of MM.
Do the data in the table support this conclusion? Give reasons for your answer. (4)

Answer 9

Yes since with ipilimumab:

1. Median ST increased by 2.1 months;
2. Percentage of patients showing reduction in tumours increased from
3. 3% to 15.2%;

No because:
3. No standard errors shown / no (Student) t- test / no statistical test carried
out;
4. (So) not able to tell if differences are (statistically) significant / due to
chance (alone);
5. Improvement might only be evident in some patients / no improvement in
some patients;
6. Quality of (extra) time alive not reported;
If answers relate only to ‘Yes’ or ߢNo’, award 2 marks max
4

Question 10

MM is caused by a faulty receptor protein in cell-surface membranes.
Cells in MM tumours can be destroyed by the immune system.
Suggest why they can be destroyed by the immune system

(3).

Answer 10

1. Faulty protein recognised as an antigen / as a ‘foreign’ protein;
2. T cells will bind to faulty protein / to (this) ‘foreign’ protein;
3. (Sensitised) T cells will stimulate clonal selection of B cells;
4. (Resulting in) release of antibodies against faulty protein.

Question 11

Q4.In many parts of the world, crops have to be watered to grow enough food but fresh water is
often in short supply.
Barley is a plant that grows a leafy shoot and then produces seed that is harvested for
food.
Scientists investigated whether barley could be grown successfully using fresh water
mixed with seawater. This would reduce the use of fresh water. However, seawater
contains dissolved sodium chloride (salt).
The scientists grew barley in plots of equal size in the same large field. Each plot received
one of four treatments.
A No watering.
B Watering with fresh water during growth and seed production.
C Watering with a 1:1 mix of fresh water and seawater during growth and
seed production.
D Watering with fresh water during growth and with a 1:1 mix of fresh water and
seawater during seed production.
At the end of the investigation, the scientists measured the concentration of salt in the soil
in each plot and the yield of barley seed harvested from each plot.
The scientists’ results are shown in the table below.

Watering treatment was the independent variable in this investigation.
Explain what is meant by the independent variable. (1)

Answer 11

Variable that is changed;

Reject ‘the variable that changes’

Question 12

The same variety of barley was used in all the plots. Why was this important? (2)

Answer 12

1. Idea of a confounding variable;
2. (So) genetically similar;
3. Do not accept ‘genetically identical / same DNA’.
4. (So) have similar salt tolerance / response to salt water / response to
   watering treatment;
5. (So) have similar yield / mass of seeds;
   Do not accept ‘amount / number of seeds’ or ‘growth rate’

Question 13

When barley plants are growing, the number of cells increases.
Name the process that increases the number of cells. (1)

Answer 13

Mitosis;

Question 14

What do the data in the table above show about the effect of watering barley with a
mixture of fresh water and seawate
r (2)

Answer 14

1. Irrigation with sea water / C / D increased yield compared with no
   irrigation / A;
   For ‘yield’ accept ‘mass of seed’ throughout.
2. Yield was lower when irrigated with sea water / C / D compared with
   fresh water / B;
   Only penalise once for use of ‘amount / number of seeds’.
3. Yield was lower when watered with sea water throughout growth and
   seed formation / C than when watered with sea water just at seed
   formation / D;
   Accept use of figures from table.
   ’It’ refers to watering with seawater / mixture

Question 15

(e) The scientists suggested that watering barley with diluted seawater might not be
sustainable if repeated every year.
Do these data support this suggestion? (3)

Answer 15

1. Irrigation with sea water / C / D increases concentration of salt in soil;
   Ignore reference to standard deviation / quality of the data.
2. Lower water potential in the soil linked to reduced uptake of water;
3. Salt concentration in the soil might / might not increase in the future;
   Mark point 3 includes the principle for mark point 1 so mp3
   gains 2 marks (for mp1 and mp3)
4. Might decrease plant growth / yield in the future;
5. Less food / fewer seeds for future planting;
   Mp 3 and 4. Allow ‘further’ for the idea of ‘in the future’.
   3 m

Question 16

Figure 1 shows all the chromosomes present in one human cell during mitosis. A
scientist stained and photographed the chromosomes. In Figure 2, the scientist has
arranged the images of these chromosomes in homologous pairs.

0 1 . 1 Give two pieces of evidence from Figure 1 that this cell was undergoing mitosis.
Explain your answers.(2)

Answer 16

1. The (individual) chromosomes are
   visible because they have condensed;
2. (Each) chromosome is made up of two
   chromatids because DNA has
   replicated;
3. The chromosomes are not arranged in
   homologous pairs, which they would be
   if it was meiosis;

Question 17

0 1 box . 2 Tick ( ) one box that gives the name of the stage of mitosis shown in Figure 1.
[1 mark]

Answer 17

Prophase

Question 18

1.3 When preparing the cells for observation the scientist placed them in a solution that
had a slightly higher (less negative) water potential than the cytoplasm. This did not
cause the cells to burst but moved the chromosomes further apart in order to reduce
the overlapping of the chromosomes when observed with an optical microscope.
Suggest how this procedure moved the chromosomes apart.
[2 marks]

Answer 18

1. Water moves into the cells/cytoplasm by
   osmosis;
2. Cell/cytoplasm gets bigger;
3. Reject water moving into
   chromosomes/nucleus.

2. Accept idea of
cell/cytoplasm has greater
volume/swells/expands.
2. Ignore references to
pressure changes, turgidity and
chromosomes being more
dilute.
2. Ignore references to
changing water/fluid contents
of the cell.
2. Allow ECF for ‘nucleus
expands’ but not for
‘chromosomes expan
d’.

01.3 was based on a similar principle, but using a different method. It required standard
knowledge of osmosis, but the novel context threw many students. The majority could state that
the water would move into the cells by osmosis, but then often referenced increased pressure,
rather than the idea of the volume of the cells increasing. Some complex, incorrect answers were
seen in which students attempted to describe changes in polar interactions between the
chromosomes and water, and how these would chang

Question 19

0 1 box . 4 The dark stain used on the chromosomes binds more to some areas of the
chromosomes than others, giving the chromosomes a striped appearance.
Suggest one way the structure of the chromosome could differ along its length to
result in the stain binding more in some areas.
[1 mark]

Answer 19

Differences in base sequences
OR
Differences in histones/interaction with
histones
OR
Differences in condensation/(super)coiling;

Answer must be in context of
differences in arrangement of
chromosomes not just related
to the properties of the stain.
Accept spec section 8 ideas
e.g. different
methylation/acetylation
Accept different genes
Reject different alleles

Question 01.4 tested Assessment Objective 2 (application of knowledge) and there were several
parts of the specification from which students could select material to support their answer. 42.2% did this successfully; those who did not often did not describe sufficiently how a feature would be
different along the length of the chromosome to result in the striped appearance. For example,
mentioning “histones” or “bases” alone was not creditworthy

Question 20

0 1 . 5 In Figure 2 the chromosomes are arranged in homologous pairs.
What is a homologous pair of chromosomes?
[1 mark]

Answer 20

(Two chromosomes that) carry the same
genes;

In question 01.5, only 36.9% of students could define the term ‘homologous chromosome’. It is
likely that more students could have written about independent segregation or crossing over of
homologous chromosomes, but this question revealed that they did not fully understand this
biological term. Many students only referred to the origin of the chromosomes as paternal and
materna

Question 21

0 1 . 6 Give two ways in which the arrangement of prokaryotic DNA is different from the
arrangement of the human DNA in Figure 1.
[2 marks]

Answer 21

(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 22

0 4 . 1 Bacteria are often used in industry as a source of enzymes. One reason is
because bacteria divide rapidly, producing a large number of them in a short time.
Describe how bacteria divide.
[2 marks]

Answer 22

1. Binary fission;
2. Replication of (circular) DNA;
3. Division of cytoplasm to produce 2 daughter
   cells;
4. Each with single copy of (circular) DNA;

Question 23

1 0 . 2- P7 Figure 6 shows an image from an optical microscope of meiosis occurring in a
flower bud of a flowering plant. W and Z are undergoing meiosis.
Figure 6
Explain the appearance of W and Z.
[4 marks]

Answer 23

1. W has 4 cells/nuclei since it is at the (end of) 2
   nd
   division (of meiosis);
2. Z has 2 cells/nuclei since it is at the (end of) 1
   st
   division (of meiosis);
3. W shows haploid cells/cells containing n
   chromosomes;
4. (Cells in) W contain half the (mass of) DNA of
   (Cells in) Z;
   OR
   (between Z and W) chromatids have separated;
   OR
   In Z homologous chromosomes have separated;

Question 24

Describe how presentation of a virus antigen leads to the secretion of an antibody
against this virus antigen.
[3 marks]

Answer 24

1. Helper T cell/TH cell binds to the antigen (on
   the antigen-presenting cell/phagocyte);
2. This helper T/TH cell stimulates a specific B
   cell;
3. B cell clones
   OR
   B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;

Question 25

Q2. (a) The photographs show two stages in mitosis of a plant cell.

A B

Name stages A and B. In each case describe what is happening to the chromosomes.

STAGE A (2)

STAGE B(2)

Answer 25

(a) (i) prophase;

chromosomes thickening / becoming visible;

(ii) anaphase;
chromatids / chromosomes moving to opposite poles /
ends of spindles;

Question 26

Describe two events during interphase which prepare a cell for mitosis. (2)

Answer 26

DNA replication;
synthesis or proteins / build-up of energy stores / growth /
increase in cytoplasm;
replication of organelles / named example;

Question 27

Describe what happens in

i) metaphase (2

Answer 27

(a) (i) Spindle formed / chromosome / centromere / chromatids

attaches to spindle;
Chromosomes / chromatids line up / move to middle / equator
(of cell);
Do not award second mark for answers referring to
chromosomes ‘pairing up’.
Ignore reference to homologous chromosomes unless context
suggests pairing which negates second mark.
Neutral: Details on nuclear membrane.
Accept: Diagram for second marking point.

Question 28

Describe what happens in anaphase (2)

Answer 28

Chromosome / centromere splits / chromatids / ‘chromosomes’ separate /
pulled apart;
To (opposite) sides / poles / centrioles (of cell);

Reject: Homologous chromosomes separate for first marking
point.
Accept: Diagram for second marking point.
Chromatids / ‘chromosomes’ move to poles / sides / centrioles =
2 marks.

Question 29

Cells lining the human intestine complete the cell cycle in a short time. Explain
the advantage of these cells completing the cell cycle in a short time. (1)

Answer 29

(i) Form / replace cells quickly / rapidly / divide / multiply / replicate rapidly;

Neutral: Repair cells.
Answers must convey idea of ‘speed’.

Question 30

Mikanolide is a drug that inhibits the enzyme DNA polymerase.

Explain why this drug
may be effective against some types of cancer. (2)

Answer 30

Prevents / slows DNA replication / doubling / prevents / slows mitosis;
New strand not formed / nucleotides (of new strand) not joined
together / sugar-phosphate bonds not formed;

First marking point must be in context of DNA replication not cell
replication.
Do not negate first marking point if role of DNA polymerase is
described incorrectly e.g. Reject: ‘joins bases / strands
together’.
Role of DNA polymerase must be correct for last marking point.

Question 31

A student investigated the stages of mitosis in a garlic root. The root tip was placed on a
microscope slide with a stain. A cover slip was placed on top and the root tip was firmly
squashed.
(a) Explain why
(i) a root tip was used; (1)

Answer 31

(i) where mitosis / division / growing / occurs

reject growing cells

Question 32

A student investigated the stages of mitosis in a garlic root. The root tip was placed on a
microscope slide with a stain. A cover slip was placed on top and the root tip was firmly
squashed.
(a) Explain why (ii) a stain was used; (1)

Answer 32

(ii) to distinguish chromosomes / chromosomes not visible

without stain;

Question 33

A student investigated the stages of mitosis in a garlic root. The root tip was placed on a
microscope slide with a stain. A cover slip was placed on top and the root tip was firmly
squashed.

(iii) the root tip was firmly squashed. (1)

Answer 33

(iii) the root tip was firmly squashed.

Question 34

describe the structure of the HIV (4)

Answer 34

Reverse transcriptatse
Capsid
Envelope
attachment proteins

Question 35

The offspring produced from farmed trout are sterile. Suggest why (2)

Answer 35

cannot form homologous pairs

too many chromosomes

Question 36

Suggest and explain why ABZ could be used as a treatment for cancer even though it affects some healthy cells. (1)

Answer 36

• cancer cells divide more rapidly

Question 37

What can you conclude about the effect of ABZ on tumour cells? (4)

ABZ stopped mitosis by preventing the formation of spindle fibres, and it also affected some healthy cells.

Mitosis is controlled. Cyclin B is a protein in the nucleus. It regulates mitosis timing. M starts when CB conc rises sharply and ends when it falls. ABZ increased, and maintained, a high concentration of cyclin B in stomach tumour cells.

Programmed cell death = apoptosis. Two nuclear proteins, Bcl-2 and Bax control apoptosis. Apop is prevented when the Bcl-2 and Bax ratio is high, and is promoted when the ratio is low. The scientists found that ABZ decreased conc of Bcl-2 and increased Bax in stomach tumour cells

Answer 37

• ABZ maintains Cyclin B
• so mitosis starts but does not end, so no tumour growth
• ABZ lowers ratio of Bcl-2 to Bax
• so apoptosis occurs and no tumour growth

Question 38

Evaluate the suggestion that ABZ could be used for the successful treatment of stomach cancer. (3)

Answer 38

SUPPORT:
- stops mitosis so no tumour growth

AGAINST

• healthy cells damaged
• these results are from laboratory tests, not clinical trials involving pople

Question 39

A trout body cell has 80 chromosomes

Farmed female trout are treated so they produce diploid egg cells

7.5- The offspring produced from farmed trout are sterile. Suggest and explain why [2 Marks]

Answer 39

Because there are too many chromosomes

Cannot form homologous pairs

Question 40

During Interphase in eukaryotic cells, DNA replication takes place

Explain why one strand of DNA replicates continuously, whereas the opposite strand replicates discontinuously [5 Marks]

Answer 40

DNA polymerase only/ works/ replicates to 5’ to 3’ direction

Two strands are anti-parralel/ in opposite orientation to eachother

DNA polymerase is very specific ( to its binding site)

On one strand , DNA polymerase can work straight from the replication fork

whereas, on the other hand , a replication fork has to open downstream and DNA polymerase replicates backwards

Question 41

Some cell biologists believe that use of the term cell division should be discontunued and replaced with cell multiplication

Evaluate this claim using your own knowledge of the cell cycle [4 Marks]

Answer 41

• Observed cell diving into two/ cytokinesis / tow daughter cells arising from one cell
• The cell appeared dormant for much of the time before and after division

Cell multiplaicaion

The number of cells doubles

The amount of DNA goes from 2n to 2x2n/ chromosomes are not halved as cell splits

Daughter cells contain the same number of chromosomes as original cell

Tissues/ organs/ organisms grow so more cells are necessarlity made

Question 42

Identify which tissue sample A or B was taken from the root tip. Use info in table 1 to explain [2 Marks]

Answer 42

B - Lower % of cells in interphase

Therefore more of the cells are in division stages