Jun 2013 Unit 2

Question 1

Describe the role of centromeres in mitosis.

Answer 1

1. Holds chromatids together;

2. Attaches (chromatids) to spindle

Question 2

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

Answer 2

carry different alleles

Question 3

The appearance of each chromosome in Figure 2 is different from those shown in
Figure 1. Explain why

Answer 3

Chromatids have separated

Question 4

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

Answer 4

Crossing over of alleles

Question 5

Explain how these results suggest that animal A is the most closely related to humans

Answer 5

1. (Only) one amino acid different /
least differences / similar amino
acid sequence / similar primary
structure;
2. (So) similar DNA sequence

Question 6

A student who looked at these results concluded that animals B and C are more
closely related to each other than to any of the other animals.
Suggest one reason why this might not be a valid conclusion.

Answer 6

1. Compared with humans / not

compared with each other;

Question 7

Cytochrome c is more useful than haemoglobin for studying how closely related
different organisms are. Suggest one reason why

Answer 7

1. All organisms respire/have

cytochrome c

Question 8

DNA helicase is important in DNA replication. Explain why

Answer 8

1. Separates/unwinds/unzips strands/helix / breaks H-bonds;

2. (So) nucleotides can attac

Question 9

Cytarabine has a greater effect on cancer cells than on healthy cells. Explain why

Answer 9

(Cancer cells/DNA) divide

Question 10

Give one way in which antibiotics can prevent the growth of bacteria.

Answer 10

Prevent cell wall formation / cause (cell)
lysis / inhibit ribosomes / inhibit protein
synthesis / prevent DNA replication / affect
function of cell membrane;

Question 11

Describe how bacteria can become resistant to antibiotics by vertical gene transmission.

Answer 11

cell division/

Question 12

The doctors used samples of this bacterium taken from many patients in the hospital.
Explain why this was important.

Answer 12

different types of bacteria

Question 13

Do these data support the conclusion that hypochlorite was the most effective at killing
this bacterium? Explain your answer.

Answer 13

(Yes)
1. Largest clear zone/diameter/mean (so
more bacteria killed);
(No)
2. Standard deviations of chlorhexidene
overlap/share values;
3. (Overlap means difference) is not
significant / is due to chance

Question 14

Doctors in a different hospital repeated this investigation. They found that hypochlorite
had little effect on samples of P. aeruginosa they obtained. Suggest how this different
result may have arisen.

Answer 14

1. Mutation (in bacterium);

2. Gene/allele for resistance;

Question 15

The oxygen dissociation curve of the fetus is to the left of that for its mother. Explain
the advantage of this for the fetus.

Answer 15

1. Higher affinity / loads more oxygen;
2. At low/same/high partial pressure/pO2;
3. Oxygen moves from mother/to fetus;

Question 16

After birth, fetal haemoglobin is replaced with adult haemoglobin. Use the graph to
suggest the advantage of this to the baby

Answer 16

1. Low affinity / oxygen dissociates;
2. (Oxygen) to respiring
   tissues/muscles/cells;

Question 17

Hereditary persistence of fetal haemoglobin (HPFH) is a condition in which production of fetal haemoglobin continues into adulthood. Adult haemoglobin is also produced.
People with HPFH do not usually show symptoms. Suggest why

Answer 17

enough adult hb is also produced oxygen released

Question 18

Use the information provided and your knowledge of the founder effect to explain why
Ellis-van Creveld syndrome occurs at a higher frequency in the Amish population than
in people in America who are not Amish.

Answer 18

1. Population formed by a small
number of founders/people /30
people;
2. (Founders show) less genetic
diversity / small(er) gene pool /
less variety of alleles;
3. Individuals breed within group /
do not breed with outsiders;
4. High(er) chance of inheriting
allele (than in non-Amish
population)

Question 19

The faulty allele that causes Ellis-van Creveld syndrome is the result of a mutation of a
gene called EVC. This mutation leads to the production of a protein that has one
amino acid missing.
Suggest how a mutation can lead to the production of a protein that has one amino
acid missing.

Answer 19

1. Change in tertiary structure/
   active site;
2. (So) faulty/non-functional protein
   /enzyme

Question 20

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves.

Answer 20

2. Active transport by endodermis;
3. (Of) ions/salts into xylem;
4. Lower water potential in xylem /
   water enters xylem by osmosis
   /down a water potential gradient;
   (Xylem to leaf)
5. Evaporation / transpiration (from
   leaves);
6. (Creates) cohesion / tension /
   H-bonding between water
   molecules / negative pressure;
7. Adhesion / water molecules bind
   to xylem;
8. (Creates continuous) water
   column;

Question 21

Suggest how a mutation can lead to the production of a protein that has one amino
acid missing.

Answer 21

loss of 3 bases

Question 22

Abdominal pumping increases the efficiency of gas exchange between the tracheoles
and muscle tissue of the insect. Explain why

Answer 22

1. More air/oxygen enters /
   air/oxygen enters quickly/quicker;
2. (So) maintains/greater diffusion
   or concentration gradient;

Question 23

Explain how their small size enables gas exchange to be efficient without the need for
abdominal pumping.

Answer 23

short(er) diffusion distance

Question 24

The insect opens its spiracles at a lower frequency in very dry conditions.
Suggest one advantage of this.

Answer 24

to prevent water loss

Question 25

The ends of tracheoles connect directly with the insect’s muscle tissue and are filled
with water. When flying, water is absorbed into the muscle tissue. Removal of water
from the tracheoles increases the rate of diffusion of oxygen between the tracheoles
and muscle tissue. Suggest one reason why

Answer 25

Gases move/diffuse faster in air than through water

Question 26

Apart from the size of the female, suggest two factors that should have been kept
constant in order to obtain reliable results.

Answer 26

concentration of skin lipid

same speices

Question 27

The male snakes used for each trial were selected at random. Explain why this was
important.

Answer 27

To avoid bias;

Question 28

The scientists used different male snakes in each trial. Suggest why.

Answer 28

1. To avoid change in (courtship)
 behaviour (due to past
 experience);
2. To observe a
 typical/general/representative
 (response)

Question 29

What should the scientists have placed in the cage as a control, to show that males
were responding to lipids from females?

Answer 29

Filter paper without (skin) lipids

Question 30

The scientists concluded that male snakes showed more courtship behaviour towards
long female snakes and to lipids from the skins of long females.
Explain one other conclusion that can be made from the data.

Answer 30

1. Similar response to lipids and
   (whole) snakes;
2. (So males are) responding to
   lipids

Question 31

Suggest two advantages of male snakes courting with longer females.

Answer 31

(Parent/offspring)
1. Produce more/larger offspring/eggs;
2. Better predators / fitter / more
successful at gaining food / less
likely to be eaten / more able to
protect offspring/eggs;

Question 32

Use Figure 3 and Figure 4 to suggest why male garter snakes show greater courtship
behaviour to longer female snakes.

Answer 32

1. (Males) respond to/sense
   (unsaturated) fatty acids;
2. (Long females) produce/have
   more fatty acids / positive
   correlation

Question 33

Describe how Figure 4 could be used to predict the percentage of unsaturated fatty
acids produced by female garter snakes of body length greater than 75 cm.

Answer 33

1. Draw a line of best fit;

2. Extrapolation / extend line;

Question 34

The females of other species of snake secrete lipids on their skin. These lipids also
contain unsaturated fatty acids. Male garter snakes do not show courtship behaviour
towards these females. Suggest why

Answer 34

produce different fatty acids;