Jan 2013 Unit 2

Question 1

An arteriole is described as an organ. Explain why.

Answer 1

made up of more thatn one type of tissue

Question 2

An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow
to capillaries.

Answer 2

1. (Muscle) contracts;

2. (Arteriole) narrows

Question 3

A capillary has a thin wall. This leads to rapid exchange of substances between the
blood and tissue fluid. Explain why

Answer 3

Short diffusion distance

Question 4

Blood flow in capillaries is slow. Give the advantage of this.

Answer 4

(More) time for exchange/diffusion

Question 5

Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a
swollen abdomen due to a build up of tissue fluid.
Explain why a lack of protein in the blood causes a build up of tissue fluid.

Answer 5

1. Water potential (in capillary) not as
low/is higher/less negative / water
potential gradient is reduced;
2. Less/no water removed (into capillary);
3. By osmosis (into capillary)

Question 6

They found that hybrid DNA from a leopard and a
cheetah separated into single strands at a higher temperature than hybrid DNA from a
leopard and a puma.
These results suggest that leopards are more closely related to cheetahs than to
pumas. Explain why.

Answer 6

1. More hydrogen bonds (form);

2. Similar DNA sequence

Question 7

Use this information to explain what is meant by a genetic bottleneck.

Answer 7

1.Drop in population / many killed / only
single female left;
2. Idea of reduced/low genetic
variation/diversity / reduction in
(variety of) alleles / smaller gene poo

Question 8

The fertility of cheetahs is low. The proportion of abnormal sperm cells produced is
higher in cheetahs than in other members of the family Felidae. Suggest an
explanation for this.

Answer 8

Inbreeding / closely related cheetahs
breed;
4. High chance of inheriting allele / high
frequency of allele

Question 9

What is intraspecific variation?

Answer 9

Variation within a species

Question 10

Explain why both types of twin were used in this investigation.

Answer 10

1. Identical twins show genetic influence
/ differences between them show
environmental influence;
2. Non-identical twins (also) show an
environmental/non-genetic influence

Question 11

What do these data suggest about the relative effects of genetic and environmental
factors on the development of schizophrenia?

Answer 11

Genes play a greater role

Question 12

Suggest two factors that the scientists should have taken into account when selecting
the twins to be used in this study

Answer 12

1. Age;
2. Family/medical history (of mental
   illness)

Question 13

Describe how the students would have returned the air bubble to the start of the capillary tube in this investigation.

Answer 13

Open/use tap

Question 14

Give two precautions the students should have taken when setting up the potometer to
obtain reliable measurements of water uptake by the plant shoot.

Answer 14

1. Seal joints / ensure airtight / ensure watertight;
2. Cut shoot under water
   Ensure no air bubbles are present

Question 15

A potometer measures the rate of water uptake rather than the rate of transpiration.
Give two reasons why the potometer does not truly measure the rate of transpiration.

Answer 15

1. Water used for support/turgidity;

2. Water used in photosynthesis;

Question 16

Explain the relationship between the number of leaves removed from the plant shoot
and the mean rate of water uptake.

Answer 16

Less surface area;
Fewer stomata;
Less transpiration

Question 17

Mycolic acids are substances that form part of the cell wall of the bacterium that
causes tuberculosis. Mycolic acids are made from fatty acids. Isoniazid is an antibiotic
that is used to treat tuberculosis. The diagram shows how this antibiotic inhibits the
production of mycolic acids in this bacterium.

Answer 17

1. Cell wall not formed / production inhibited;
2. Lower water potential in bacterium;
3. Water enters and causes
   lysis/expansion

Question 18

Human cells also produce fatty acids. Isoniazid does not affect the production of these
fatty acids.
Use information in the diagram to suggest one reason why isoniazid does not affect
the production of fatty acids in human cells.

Answer 18

human cells have a different enzyme

Question 19

A mutation in the gene coding for enzyme B could lead to the production of a
non-functional enzyme. Explain how.

Answer 19

1. Change in base sequence (of DNA/gene);
2. Change in amino acid sequence /
   primary structure (of enzyme);
3. Change in hydrogen/ionic/ disulphide
   bonds

Question 20

Using isoniazid to treat diseases caused by other species of bacteria could increase
the chance of the bacterium that causes tuberculosis becoming resistant to isoniazid.
Use your knowledge of gene transmission to explain how.

Answer 20

1. Resistance gene/allele;
2. On plasmid;
3. (Spread by) horizontal transmission;

Question 21

Suggest one ethical argument for maintaining biodiversity.

Answer 21

Prevent extinction

Question 22

Suggest one economic argument for maintaining biodiversity

Answer 22

tourism

Question 23

Explain the relationship between the percentage of original forest area remaining and
the percentage of bird species that have become extinct.

Answer 23

1. Fewer plant species / decrease in
plant diversity;
2. Fewer habitats/nesting sites;
3. Fewer niches;
4. Fewer food sources/varieties;

Question 24

The ecologists noted that the species of birds surviving on the coldest islands had a
larger body size than those surviving on warmer islands.
Explain how a larger body size is an adaptation to a colder climate.

Answer 24

1. (Larger birds have) a low(er) SA:VOL;
2. (So) less heat loss / more heat
   retained;

Question 25

Describe how DNA is replicated.

Answer 25

1. Strands separate / H-bonds break;
2. DNA helicase (involved);
3. Both strands/each strand act(s) as (a)
   template(s);
4. (Free) nucleotides attach;
5. Complementary/specific base pairing /
   AT and GC;
6. DNA polymerase joins nucleotides (on
   new strand);
7. H-bonds reform;
8. Semi-conservative replication / new
   DNA molecules contain one old strand
   and one new strand

Question 26

Explain how the doctor could have recognised which cells were in interphase when
looking at the tissue samples.

Answer 26

1. No visible chromosomes/chromatids;

2. Visible nucleus

Question 27

Which tissue sample, C or D, was taken from a cancerous tumour?
Use information in the table to explain your answer.

Answer 27

1. Lower % (of cells) in interphase /
 higher % (of cells) in mitosis/named
 stage of mitosis;
2. (So) more cells dividing / cells are
 dividing quicker;

Question 28

Describe one way the scientists could have allocated the patients to each group.

Answer 28

Random;

number generator

Question 29

What do the standard deviation bars suggest about the difference in the mean increase
in FEV1 between Group 1 and the other groups? Explain your answer.

Answer 29

1. (Differences) are real/significant/not
   due to chance;
2. (As) bars/SDs do not overlap;

Question 30

What do the data suggest about the ‘placebo effect’ in this investigation? Explain your
answer.

Answer 30

1. No/slight (placebo) effect;

2. Group 2 and 3 results are similar

Question 31

On each occasion that a patient’s FEV1 was measured, a doctor repeated the
measurement several times. Explain why

Answer 31

1. (Allows) anomalies to be identified
2. (Makes) average/mean (more)
   reliable;

Question 32

Suggest why all the patients were allowed to continue with their normal asthma
treatment in this investigation.

Answer 32

1. Unethical/unfair not to treat patients;
2. Dangerous / could cause an asthma
   attack

Question 33

Suggest why the patients were told to stop their normal asthma treatment 24 hours before their FEV1 measurements were taken.

Answer 33

1. Ensures normal treatment does not
affect results / improvements are only
due to the spray;
2. (As) normal treatment is short-lived/
effective for less than 24 hours/ (24h)
is long enough for normal treatment to
wear off;

Question 34

The scientists concluded that the data obtained for the Improvement Scores were less
reliable than the data obtained measuring FEV1. Suggest why they concluded this.

Answer 34

1. (Improvement scores) are qualitative /
subjective/rely on own judgement/
different patients may assess
symptoms differently;
2. Some patients may
lie/exaggerate/want to please doctors;

Question 35

Group 3 reported the lowest mean Improvement Score. Suggest one explanation for
this.

Answer 35

1. Not blind / patients knew they were not
   receiving treatment/ patients did not
   receive treatment;
2. (So) more likely to underestimate/give
   lower scores / did not expect to
   improve / less improvement