2011 Unit 2 Jan

Question 1

Hydrogen bonds are important in cellulose molecules. Explain why

Answer 1

• Forms cross links between chains/forms microfibrils;
• Providing strength/rigidity (to cellulose/cell wall);
• Hydrogen bonds strong in large numbers

Question 2

A starch molecule has a spiral shape. Explain why this shape is important to its
function in cells.

Answer 2

• Compact/occupies small space/tightly packed;

Question 3

The total number of bases in the DNA of the α-polypeptide gene is more than 423.
Give two reasons why there are more than 423 bases.

Answer 3

• Stop/start sequences;
• Non coding DNA (in the gene)/introns
• Two chains/a non-coding strand/complementary base
pairs;
• Addition of base by mutation;

Question 4

The haemoglobin in one organism may have a different chemical structure from the
haemoglobin in another organism. Describe how

Answer 4

• Different primary structure

Question 5

Use the graph to explain why llamas are better adapted to live in high mountains than
horses

Answer 5

• Low partial pressure of oxygen;
• In lungs;
• (Llama) haemoglobin able to load more
oxygen/
• Higher affinity for oxygen

Question 6

Explain what is meant by a phylogenetic relationship.

Answer 6

• Shows evolutionary relationship;

Question 7

They made samples of hybrid DNA using a gene that was found in all three species.
Explain why it was important that they made samples of hybrid DNA from the same
gene.

Answer 7

• Base sequence will be similar
• These bases will bind together/hydrogen
bonds/complementary pairs;

Question 8

Explain what caused the DNA to separate at a higher temperature.

Answer 8

• Relationship is closer/more complementary
bases
• More hydrogen bonds
• More hydrogen bonds

Question 9

What information is required to calculate an index of diversity for a particular community?

Answer 9

•Number of a/each (species)

Question 10

Farmers clear tropical forest and grow crops instead. Explain how this causes the
diversity of insects in the area to decrease.

Answer 10

• Lower diversity of plants/ few species of plants/
• Few sources/types of food
• Few habitats
• Aspect of agriculture (killing insects)

Question 11

The points on the graph have been joined with straight lines rather than with a smooth
curve. Explain why they have been joined with straight lines.

Answer 11

• Cannot predict/ do not know intermediate values

Question 12

It would have been useful to have had a control ditch in this investigation. Explain why

Answer 12

• To see what would happen

Question 13

The gene that codes for this enzyme may be passed from one species of bacteria to
another species. Describe how.

Answer 13

• Horizontal (gene) transmission

* (Gene passed by) conjugation

Question 14

Use your knowledge of enzyme action to explain why the different sort of penicillin is effective in treating the infection

Answer 14

Shape
• Active site has specific shape/different penicillin has different shape/
Binding
• Not complementary
to active site/does not form E-S complex;
Consequence
• (Different) penicillin not broken down

Question 15

Suggest how adding antibiotics to the food of the cattle increased profit for the farmers.

Answer 15

• Suggest how adding antibiotics to the food of the cattle increased profit for the farmers.
• Reduces spread of infection;
• Faster growth/more productive animals

Question 16

Use your knowledge of selection to explain why adding antibiotics was banned.

Answer 16

• Resistant bacteria more likely to survive;
• Increase in numbers
• May infect humans

Question 17

Suggest an explanation for the difference in transpiration rate between
conditions A and B.
A Still air 15oC 1.2 trans rate
B Moving air 15oC 1.7 trans rate

Answer 17

• Removes water vapour/moisture/saturated air
• Increases water potential gradient/more
diffusion/more evaporation;

Question 18

Suggest an explanation for the difference in transpiration rate between conditions A and C
A Still air 15oC 1.2.trans rate
C Still air 25oC 2.3trans rate

Answer 18

• Increases kinetic energy;
• Water molecules move faster
• Increases diffusion/evaporation;

Question 19

Describe the relationship between the rate of water movement through the xylem and
the light intensity

Answer 19

• Positive correlation/as light intensity increases so does

rate of water movement

Question 20

Explain the change in the rate of water movement through the xylem between
06.00 and 12.00 hours.

Answer 20

• Stomata open;
• Photosynthesis increases/transpiration increases;
• More water pulled up;
• Cohesion between water molecules/by cohesion
tension;

Question 21

Arteries and arterioles take blood away from the heart.
Explain how the structures of the walls of arteries and arterioles are related to their
functions

Answer 21

Elastic tissue
• Elastic tissue stretches under pressure/when heart
beats;
• Recoils/springs back
• Evens out pressure/flow;
Muscle
• Muscle contracts;
• Reduces diameter of lumen/
• Changes flow/pressure;
Epithelium
• Epithelium smooth
• Reduces friction

Question 22

Explain how standard deviations of these

mean values would help you to interpret the data in Figure 2.

Answer 22

• Standard deviation gives a measure of
spread/variation
• More standard deviations overlap, the less likely it is
that differences are real

Question 23

Describe how the biologists should carry out these breeding experiments.

Answer 23

• Cross shrimps from two sites/watch courtship
• Breed young together
•
•

Question 24

The results of breeding experiments would help the biologists to decide whether the
shrimps were the same species. Explain how

Answer 24

• If same species the shrimps would breed,

producing fertile young/courtship species specific