January 2010 Biology unit 2

Question 1

Ponds provide a very stable environment for aquatic organisms.
Three properties of water that contribute to this stability are as follows:
• the density of water decreases as the temperature falls below 4 °C so ice floats on the
top of the pond
• it acts as a solvent for ions such as nitrates (NO3
–)
• a large quantity of energy is required to raise the temperature of water by 1 °C.

Explain how these three properties help organisms survive in the pond.

Answer 1

ice floats
(ice less dense because) molecules spread out ;
molecules form, crystal structure / lattice / AW ;
ice forms insulating layer / clearly described ;
water (below ice), does not freeze / still liquid /
remains water / kept at higher temperature ;
organisms do not freeze ;
animals / organisms, can still, swim / move ;
allows, currents / nutrients, to circulate ;
solubility
ions / named ion, polar / charged ;
ions /named ion, attracted to / bind to / interact with, water;
(named) organisms / plants / animals,
uptake / AW, minerals / named mineral / nutrients ;
correct use of named, mineral / nutrient, in organism ;

temperature stability
many / stable, (hydrogen) bonds between molecules ;
at lot of energy to, force apart molecules / break bonds ;
high (specific) heat capacity ;
temperature does not change much /
small variation in temperature ;
effect of temperature on , enzymes / metabolic rate ;
gases remain soluble ;
Award once in any section
hydrogen bonds ;

Question 2

Suggest three reasons why a hospital might use a multodisc to select the most suitable antibiotic for treating a patient. (3)

Answer 2

1 cheap / AW ;
2 (test is) quick to carry out /
(deals with several antibiotics) at same time / AW ;
3 (idea of) allowing early treatment of patient ;
4 (idea of) compares antibiotics under same conditions ;
5 (correct antibiotic first time)
to prevent antibiotic resistance developing ;

Question 3

Drugs, such as antibiotics, are often first discovered in the natural environment.

Explain why it may become increasingly difficult to discover new drugs in the future. (2)

Answer 3

(new) drugs come from (named) organisms ;
biodiversity is reducing ;
habitats / named habitat, destroyed / lost ;
reason for habitat destruction ;

Guidance 
ACCEPT plants / animals / fungi / species / etc.
ACCEPT deforestation / natural environment lost
e.g. global warming
 logging
 fuel
 crops
 construction / industrialisation
mining
 fishing
 pollution
 tourism

Question 4

The primary structure of a protein consists of a chain of amino acids.

Describe how a second amino acid would bond to cysteine in forming the primary structure of a protein.

Answer 4

1 peptide bond ;
2 between, amine / J group (of one amino acid) and
carboxyl / L group (of another) ;
3 H (from amine group ) combines with OH (from carboxyl
group) ;
4 condensation reaction
OR
water, lost / eliminated / produced / created / AW ;
5 covalent ;

Question 5

Each amino acid has a different R group.

Describe how these R groups can interact to determine the tertiary structure of a protein. (4)

Answer 5

1 some R groups, attract / repel ;
2 disulfide, bridges / bond ;
3 between, cysteine / SH / S (atoms) ;
4 hydrogen / H, bonds ;
5 ionic bonds between, oppositely charged / + and -, R groups ;
6 hydrophilic R groups, on outside of molecule / in contact with
water (molecules) ;
7 hydrophobic R groups,
on inside of molecule / shielded from water (molecules)

Question 6

Complete the table below to give three differences between the structure of glycogen and collagen

Answer 6

glycogen collagen
1 carbohydrate / polysaccharide protein / polypeptide ;
2 (alpha) glucose (units) amino acid (units) ;
3 identical units different amino acid units ;
4 glycosidic, bonds links peptide, bonds / links ;
5 branched unbranched / linear ;
6 non-helical helical ;
7 one chain (per molecule) three chains (per molecule) ;
8 no cross links cross links (between chains) ;
9 contains C H O contains C H O N

Question 7

Collagen is found in the ligaments which hold bones together at joints.
State two properties of collagen that make it suitable for this purpose.

Answer 7

high tensile) strength / strong ;
does not stretch / is not elastic ;
insoluble ;
flexible ;

Question 8

State the components of a DNA nucleotide (3)

Answer 8

deoxyribose (sugar) ;
phosphate (group) ;
(nitrogenous / purine or pyrimidine) base /
one correctly named base ;

Question 9

Describe how the structure of RNA differs from that of DNA.

2

Answer 9

has ribose ;
uracil / U, instead of, thymine / T ;
single stranded ;
3 forms / AW ;

Question 10

Before a cell divides, the DNA needs to be accurately replicated.

Describe how a DNA molecule is replicated.

Answer 10

untwist / unwind ;
unzip / described ;
H bond breaks ;
both strands act as template ;
(aligning of) free (DNA) nucleotides ;
complementary, base / nucleotide, pairing ;
C to G and T to A / purine to pyrimidine ;
hydrogen bonds reform ;
sugar-phosphate back bone forms ;
(using) covalent / phosphodiester, bond ;
semi-conservative replication ;
DNA polymerase ;
AVP ;

Question 11

State what a gene codes for

Answer 11

polypeptide / protein / primary structure /

a sequence of amino acids ;

Question 12

Suggest how changing the sequence of DNA nucleotides could affect the final product the DNA codes for (2)

Answer 12

different, sequence of amino acids / primary structure / AW ;
different protein / protein folds up differently /
different tertiary structure ;
(product) no longer functions / different function ;

Question 13

Define the terms

1. Habitat

2. Biodiversity

Answer 13

Habitat: the e place where, an organism / organisms /
a population / a community, lives ;

Biodiversity:

2 variety of life / the range of living organisms found / AW ;
3 variety / range, of, habitats / ecosystems ;
4 number of different species ;
5 variety / genetic diversity, within species ;

Question 14

In this study, a student placed his quadrat on areas he considered to have the most biodiversity.

Explain what is wrong with this technique. (2)

Answer 14

not random / should have been random ;
unrepresentative / skewed / biased, results ;
creates an over-estimate of diversity ;
may miss some (dominant) species /
does not cover full range of species ;

Question 15

The student was asked to calculate the biodiversity using Simpson’s Index of Diversity.

Suggest what additional data he would need to collect in order to calculate Simpson’s index of Diversity in this habitat. (2)

Answer 15

record / identify / list / AW, all species / (all) other plants ;
(count / estimate) numbers of individuals within each species /

Question 16

The student calculated Simpson’s Index as 0.2. This is a low value.

State the significance of this low value for this habitat. (1

Answer 16

not stable / at risk / low ability to withstand change / AW ;
more likely to lose species ;