Exam Questions

Question 1

Describe how comparisons of biological molecules in

these two species could be used to find out if they are closely related.

Answer 1

Compare DNA & Sequence of bases/nucleotides.
Separate DNA strands by breaking hydrogen bonds.
Mix DNA/strands (of different species).
Temperature/heat required to separate (hybrid) strands indicates relationship.

Inject (seahorse) protein/serum into animal;
Obtain antibodies/serum;
Add protein/serum/plasma from other (seahorse) species;
Amount of precipitate indicates relationship;

Question 2

Describe how haemoglobin loads and unloads oxygen in the body.

Answer 2

Loading/association of oxygen at high p.O2.
In lungs haemoglobin is almost fully saturated and
therefore has a high affinity for oxygen.
Unloads/dissociates oxygen at low p.O2
Unloading linked to higher carbon dioxide concentration

Question 3

Describe the processes that lead to a reduction in the

genetic diversity of populations of organisms.

Answer 3

Reduced variety/number of different alleles and reduced gene pool
Founder effect- A few individuals from a population become isolated/form colonies.
Genetic bottlenecks- fall in size of population
Selective breeding- using organisms with particular alleles and phenotypes.

Question 4

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 4

Elastic tissue
1 Elastic tissue stretches under pressure/when heart
beats
2 Recoils/springs back;
3 Evens out pressure/flow;

Muscle
4 Muscle contracts;
5 Reduces diameter of lumen/vasoconstriction/constricts
vessel;
6 Changes flow/pressure

Epithelium
7 Epithelium smooth;
8 Reduces friction/blood clots/less resistance;

Question 5

In humans, substances move out of the capillaries to form tissue fluid. Describe how
this tissue fluid is returned to the circulatory system.

Answer 5

1. Hydrostatic pressure lower in
capillary and higher in tissue fluid.
2. Water (returns).
3. By osmosis
4. Water potential lower in capillary and
higher in tissues 
5. Due to protein in blood.
6. Returns via lymph
system

Question 6

Describe how gene transmission and selection have increased the difficulty of treating bacterial infections with antibiotics.

Answer 6

1. Antibiotic resistant gene
2. Vertical gene transmission
3. Resistant bacteria survive and
   reproduce and population of resistant
   bacteria increases.
4. Increase in frequency of
   resistant gene in future
   generations.
5. Horizontal (gene) transmission;
6. Can occur between
   bacteria of different species;

Question 7

Scientists can use protein structure to investigate the evolutionary relationships
between different species. Explain why

Answer 7

1. Amino acid sequences
2. Closer, the closer the relationship
3. Protein structure related to
   DNA base/triplet sequence

Question 8

Root pressure moves water through the xylem. Describe what causes root pressure.

Answer 8

1. Active transport by endodermis;
2. ions/salts into xylem;
3. Lowers water potential (in xylem);
4. (Water enters) by osmosis;

Question 9

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside
the leaf.

Answer 9

1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;

Question 10

Describe how DNA is replicated.

Answer 10

Strands separate as H-bonds break
Free nucleotides attach
Complementary/specific base pairing (AT and GC)
DNA polymerase joins nucleotides
H-bonds reform;
Semi-conservative replication / new
DNA molecules contain one old strand
and one new strand