Unity and diversityIB Biology SL: Topic test

20 questions, 54 marks

IB Biology SL

Unity and diversity topic test

Total 54 marks

Name

Class

Date

1
A textile scientist compares two fabric strips, both 20 cm long and 2 cm wide, hung vertically with their lower 1 cm dipped in a dish of water dyed with blue food colouring. Strip X is woven from cotton, a natural fibre made of cellulose with many exposed hydroxyl (–OH) groups. Strip Y is woven from polypropylene, a synthetic fibre made of long hydrocarbon chains with no polar groups. After 10 minutes, the dye has risen 14 cm up strip X but only 0.3 cm up strip Y.
(a)
Which property of water, combined with the surface chemistry of the cellulose fibres, best explains the rapid rise of dye up strip X?
[1 mark]
ABuoyancy of water pushing dye molecules upward because they are less dense than water
BAdhesion of water to the polar cellulose surface combined with cohesion between water molecules
CHigh specific heat capacity of water slowing evaporation from the fibre surface
DLow viscosity of water allowing it to flow downward under gravity
(b)
Which feature of polypropylene explains why the dye barely rises up strip Y?
[1 mark]
APolypropylene chains are non-polar and hydrophobic, so water does not adhere to them
BPolypropylene has a higher density than cotton, so water cannot rise within it
CPolypropylene conducts heat well, so the water evaporates before it can rise
DPolypropylene fibres are woven more tightly than cotton, leaving no spaces for water
(c)
Explain, in terms of hydrogen bonding, why cohesion between water molecules is needed for capillary action to continue after the first layer of water molecules has adhered to the cellulose surface.
[2 marks]
Total for question 1: 4 marks
2
A laboratory technician is given two unlabelled tubes, each containing a purified nucleic acid extracted from cell-free virus particles. Chemical analysis of tube 1 shows the sugar deoxyribose and the bases adenine, thymine, guanine and cytosine, with adenine present at 30% and thymine also at 30% of the total bases. Chemical analysis of tube 2 shows the sugar ribose and the bases adenine, uracil, guanine and cytosine, with adenine present at 25% and uracil at 34% of the total bases.
(a)
Which nucleic acid is contained in tube 1?
[1 mark]
ASingle-stranded RNA
BSingle-stranded DNA
CDouble-stranded DNA
DDouble-stranded RNA
(b)
Which statement about tube 2 is best supported by the data?
[1 mark]
AThe nucleic acid is single-stranded, because adenine and uracil are not present in equal amounts
BThe nucleic acid is double-stranded, because adenine and uracil are not present in equal amounts
CThe nucleic acid is single-stranded RNA, because thymine is present in an amount equal to adenine
DThe nucleic acid is double-stranded DNA, because ribose is one of its four bases
(c)
State two structural differences between the nucleic acid in tube 1 and the nucleic acid in tube 2, other than the difference in strand number.
[2 marks]
Total for question 2: 4 marks
3
A microbiologist compares two cell types viewed by electron microscopy. Cell P is roughly 2 μm long, contains a single loop of naked DNA in a nucleoid region, ribosomes about 20 nm in diameter, and a cell wall, but no membrane-bound organelles. Cell Q is roughly 30 μm across, contains DNA enclosed within a double membrane with pores, mitochondria, an extensive network of membranous tubules and flattened sacs, and ribosomes about 25 nm in diameter, some of which are attached to the membranous tubules.
(a)
Identify cell P and cell Q, and outline two structural differences between them shown by the description (other than size).
[3 marks]
(b)
State the type of ribosome (70S or 80S) present in cell P and in cell Q, referring to the measurements given, and outline the function of each of the two membrane-bound organelles named in the description of cell Q.
[4 marks]
Total for question 3: 7 marks
4
A dam built across a river 200 years ago has divided a single population of a freshwater fish species into an upstream population and a downstream population, with no interbreeding since the dam was built. Researchers have found that the two populations now differ consistently in body shape, colouration and the temperature at which males begin courtship displays. When individuals from the two populations are brought together in a laboratory aquarium, courtship displays rarely lead to mating, and on the few occasions mating is observed, no fertile offspring are produced.
(a)
Using the biological species concept, evaluate whether the upstream and downstream populations should now be classified as separate species, and explain the role reproductive isolation has played in producing the differences between them.
[6 marks]
(b)
Explain why the splitting of the original fish population by the dam is an example of speciation rather than simply variation within one species, and discuss one difficulty that could arise in deciding exactly when the two populations became separate species.
[6 marks]
Total for question 4: 12 marks
5
A student extracts genome-size data (in millions of base pairs, Mbp) from an online database for four organisms: a bacterium, 4 Mbp; a unicellular yeast (a fungus), 12 Mbp; a fruit fly, 180 Mbp; and a salamander, 30,000 Mbp. The student also records that the fruit fly is diploid with 8 chromosomes per body cell and the salamander is diploid with 24 chromosomes per body cell.
(a)
Which statement is best supported by these data?
[1 mark]
AGenome size generally increases from prokaryotes to more structurally complex eukaryotes, but is not a precise measure of complexity
BGenome size is directly proportional to chromosome number across all four organisms
CAll eukaryote genomes are larger than all prokaryote genomes by exactly the same factor
DThe salamander must be the most complex organism because it has the largest genome
(b)
Which statement about chromosome number, based on general principles illustrated by the data, is correct?
[1 mark]
AAn odd chromosome number in a body cell is expected in a diploid organism
BA diploid organism is expected to have an even number of chromosomes in its body cells
CChromosome number is always proportional to genome size in base pairs
DAll organisms, regardless of ploidy, must have the same chromosome number
(c)
Using the data, compare the genome size of the bacterium with that of the salamander, and suggest one reason genome size is not always a reliable indicator of the number of genes an organism has.
[2 marks]
Total for question 5: 4 marks
6
A conservation organisation is deciding how to allocate limited funding between two threatened species. Species M is a small, brightly coloured songbird that is popular with the public, found only on one island, and is estimated to have diverged from its nearest living relative around 2 million years ago. Species N is a drab-coloured, burrowing rodent found across a wide but shrinking range on the mainland, and is estimated to have diverged from its nearest living relative around 40 million years ago, having no other close living relatives.
(a)
Which term describes a conservation approach based on protecting both species within areas of their natural range, alongside law enforcement and habitat management?
[1 mark]
AEx situ conservation
BGerm plasm storage
CCaptive breeding in a zoo
DIn situ conservation
(b)
Under the EDGE of Existence approach to conservation prioritisation, which species would be given higher priority, and why?
[1 mark]
ASpecies M, because it is more visually appealing to the public
BSpecies M, because island species always have higher genetic diversity
CSpecies N, because it is evolutionarily more distinct, having no close living relatives
DSpecies N, because it has a wider geographical range
(c)
State two different approaches to conservation, other than in situ conservation, that could be used to help protect species M or species N.
[2 marks]
Total for question 6: 4 marks
7
A ringed seal (Pusa hispida) hauls out of Arctic water at −5 °C air temperature onto sea ice, having spent the previous hour diving in water at 0 °C. A researcher lists physical properties of water and air, both close to 0 °C: density: water 1000 kg m⁻³, air 1.3 kg m⁻³. Viscosity: water 1.8 mPa s, air 0.017 mPa s. Thermal conductivity: water 0.56 W m⁻¹ K⁻¹, air 0.024 W m⁻¹ K⁻¹.
(a)
Calculate how many times more viscous water is than air at these temperatures, and use this value to explain one way in which the ringed seal's body shape is adapted to reduce the energetic cost of swimming.
[3 marks]
(b)
Using the thermal conductivity values, explain why the seal loses heat faster in water than in air at the same temperature, and describe one adaptation that reduces this heat loss.
[4 marks]
Total for question 7: 7 marks
8
Researchers compare short DNA sequences that code for part of a highly conserved protein in a bacterium, a fungus, a plant and a human. Despite the four organisms having diverged from a common ancestor a very long time ago, the DNA sequences are similar enough that the same amino acid sequence is produced in each organism when the gene is expressed by that organism's own cellular machinery. In a separate experiment, a gene from a jellyfish that produces a fluorescent protein is inserted into bacterial cells, which then produce the same functional fluorescent protein.
(a)
Explain what these observations suggest about the genetic code, and discuss how this supports the idea of universal common ancestry.
[6 marks]
(b)
Explain how the ability of bacterial cells (which lack a nucleus and endoplasmic reticulum) to correctly translate a gene from a eukaryotic jellyfish cell illustrates a structural feature shared by prokaryotic and eukaryotic cells, and outline one structural difference between the two cell types that is not challenged by this observation.
[6 marks]
Total for question 8: 12 marks

End of questions