HL Paper 2
The Chinese soft-shelled turtle, Pelodiscus sinensis, lives in salt water marshes. The turtle can live under water and out of water.
These turtles have fully developed lungs and kidneys, however, many microvilli have been discovered in the mouth of P. sinensis. A study was undertaken to test the hypothesis that oxygen uptake and urea excretion can simultaneously occur in the mouth.
Initial experiments involved collecting nitrogen excretion data from P. sinensis. The turtle urinates both in water and out of water. When in water it allows waste products to be washed out of its mouth. When out of water it regularly dips its head into shallow water to wash its mouth. The table shows the mean rates of ammonia and urea excretion from the mouth and kidney over six days.
It was noted that during long periods out of water, turtles rhythmically moved their mouths to take in water from a shallow source and then discharge it. Changes in the dissolved oxygen and the quantity of accumulated urea in the rinse water discharged by the turtles were monitored over time as shown in this graph.
In order to test whether a urea transporter was present in the mouth tissues of the turtles, phloretin (a known inhibitor of membrane proteins that transport urea) was added to the water in which a further set of turtles submerged their heads. The results of that treatment are shown.
Further research was conducted to determine where mRNA expression of a urea transporter gene might be occurring in P. sinensis. Gel electrophoresis was used to analyse different tissue samples for mRNA activity.
Expression of the urea transporter gene by cells in the turtle’s mouth was assessed by measuring mRNA activity. Turtles were kept out of water for 24 hours and then injected with either a salt solution that matched the salt concentration of the turtle, dissolved ammonia or urea, followed by another 24 hours out of water.
Deduce whether the excretion of ammonia or urea changes more when a turtle emerges from water.
Compare and contrast the changes in urea excretion in the mouth with the changes in urea excretion in the kidney when a turtle emerges from the water.
Describe the trends shown by the graph for dissolved oxygen in water discharged from the mouth.
Suggest reasons for these trends in dissolved oxygen.
Deduce with a reason whether a urea transporter is present in the mouth of P. sinensis.
Outline the additional evidence provided by the gel electrophoresis results shown above.
Identify which of these turtle groups represent the control, giving a reason for your answer.
Suggest a reason for the greater expression of the gene for the urea transporter after an injection with dissolved ammonia than an injection of urea.
The salt marshes where these turtles live periodically dry up to small pools. Discuss the problems that this will cause for nitrogen excretion in the turtles and how their behaviour might overcome the problems.
Isolated communities in rural Finland, Hungary and some of the Scottish islands have a high incidence of red-green colour blindness. Describe the inheritance of red-green colour blindness.
Outline the causes of variation in one example of continuous variation in humans.
Explain how evolution occurs and which factors can cause the process to be rapid.
A broad bean is the seed of a species, Vicia faba, in the Fabaceae, a family of flowering plants. This family contains many species that are used as sources of food.
On the diagram, label the testa and the radicle.
An experiment was done to test the hypothesis that temperature affects the rate of germination of the broad bean. Outline two factors apart from temperature that should be controlled in this experiment.
State the genus of the broad bean.
Broad beans are rich in starch and cellulose. Compare and contrast the structure of starch and cellulose.
Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.
The land snail Cepaea nemoralis is very common in North America and in Europe.
The base colour of its shell varies between brown, pink and yellow, and also in its intensity. Some shells are unbanded, but most show one to five bands of different width on top of the shell base colour.
The genes coding for the shell base colour and the presence of banding have linked loci. Allele C causes a dark pink shell and is dominant to allele c, which codes for a dark yellow shell. Allele B codes for the absence of bands and is dominant to allele b, which codes for the presence of bands.
C. nemoralis is a mollusc. Identify two external features that distinguish this snail from an arthropod.
State the major chemical component of the shell in molluscs.
Distinguish between sex-linked genes and genes with linked loci.
Outline how it can be shown that the genes for shell base colour (Cc) and presence or absence of bands (Bb) are linked.
Boreal forests stretch across Canada, Russia and Scandinavia. This northern ecosystem accounts for 29 % of the world’s forest areas. The long, cold winters favour tall evergreen trees with either needles or scale-like leaves. These trees are wind-pollinated and their seeds are not enclosed in a fruit. The photograph shows a typical boreal forest in winter.
Identify the dominant plant phylum in the boreal forest.
In some areas there are gaps in the boreal forest where trees fail to grow and peat tends to accumulate. Suggest reasons for this.
An increase in global temperatures poses a critical threat to boreal forests. Explain the consequences of climate change to this northern ecosystem.
Suggest one advantage for the evergreen trees of the boreal forest being pollinated by wind.
Discuss the advantages of the production of seeds enclosed in fruit.
The boreal forests are situated close to the north pole and even in summer the intensity of sunlight is lower than at the equator. Sketch a graph showing the effect of light on the rate of photosynthesis, labelling the axes.
In some boreal species, Rubisco is down-regulated during the winter months. Describe the role of Rubisco in photosynthesis.
The black-legged tick (Ixodes scapularis) is an arthropod which sucks blood from humans and other mammals. It is encountered mainly in wooded and semi-wooded areas. Some ticks can be infected by the bacterium Borrelia burgdorferi. When a tick bites a human, the bacterium is often introduced, causing Lyme disease. Lyme disease is a public health problem in North America and, if left untreated, can cause important neurological impairment. The diagram represents the two-year life cycle of a tick.
[Source: Cary Institute of Ecosystem Studies / Leslie Tumblety]
Scientists fear that global warming will change the distribution range of ticks.
The graphs show the developmental stages of ticks throughout seasons in a densely human-populated area of south-eastern Canada, surrounded by woods (circled on the map). Values are already established for 2000 and are predicted for 2080.
[Source: reprinted from International Journal for Parasitology, 36(1), N.H. Ogden, A. Maarouf, I.K. Barker, M. Bigras-Poulin,
L.R. Lindsay, M.G. Morshed, C.J. O’Callaghan, F. Ramay, D. Waltner-Toews, D.F. Charron, Climate change
and the potential for range expansion of the Lyme disease vector Ixodes scapularis in Canada,
63–70, Copyright (2006), with permission from Elsevier]
White-footed mice (Peromyscus leucopus) in eastern North America’s wooded areas often host B. burgdorferi bacteria. To determine whether bacterial transmission from mice to tick nymphs could be prevented, mice were vaccinated with antigens from Lyme disease-causing B. burgdorferi. Scientists captured wild mice at two different sites in the woods once a month, over 4 months. Each time, they measured the levels of antibodies to B. burgdorferi present in the captured and re-captured mice, inoculated all of them, and released them into the woods. The control group was not vaccinated with B. burgdorferi antigen.
[Source: Copyright (2004) National Academy of Sciences, U.S.A. An ecological approach to preventing human infection:
Vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle, Jean I. Tsao, J. Timothy Wootton, Jonas Bunikis,
Maria Gabriela Luna, Durland Fish, Alan G. Barbour, Proceedings of the National Academy of Sciences
Dec 2004, 101 (52) 18159–18164; DOI: 10.1073/pnas.0405763102]
The summer after vaccination, the prevalence of B. burgdorferi infection in tick nymphs collected on mice from the two sites was measured.
[Source: Copyright (2004) National Academy of Sciences, U.S.A. An ecological approach to preventing human infection:
Vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle, Jean I. Tsao, J. Timothy Wootton, Jonas Bunikis,
Maria Gabriela Luna, Durland Fish, Alan G. Barbour, Proceedings of the National Academy of Sciences
Dec 2004, 101 (52) 18159–18164; DOI: 10.1073/pnas.0405763102]
State the domain into which ticks are classified.
Using information from the text, identify one possible simple treatment for Lyme disease.
Identify the month when small birds had the greatest chance of being infected by B. burgdorferi bacteria in the year 2000 and the month when they would be most likely to become infected according to the 2080 predictions.
2000:
2080:
Using the life cycle diagram and the graph for the year 2000, analyse the distribution of adult ticks throughout the different seasons.
Evaluate the effect of the change in distribution of the different life stages of ticks on the spread of Lyme disease in south-eastern Canada.
State the reason for performing the experiment in the months of May to August.
Suggest possible reasons for the observed pattern of presence of antibodies in vaccinated mice.
Analyse the data on the state of infection of tick nymphs with B. burgdorferi in control and vaccinated mice.
Using all the data, discuss whether inoculating mice with the antigen to B. burgdorferi could be an effective method of controlling the spread of Lyme disease.
Variation in genetically inherited characteristics is the basis for evolution.
Outline the inheritance of blood types in the ABO blood system in humans.
Explain how genetic variation between the individuals in a species can be generated.
Outline the use of analogous and homologous traits in natural classification.
The images show parts of plants belonging to two different phyla.
State the phylum of plant X and of plant Y.
X:
Y:
Some plant families, such as the figwort family, have been reclassified on the basis of evidence from cladistics. Explain the methods that have been used recently to reclassify groups of plants.
Successful sexual reproduction in flowering plants depends on several essential processes. Outline the role of pollination and seed dispersal.
Pollination:
Seed dispersal:
Describe what is shown in a cladogram.
Outline how variation in organisms of the same species could lead to natural selection.
Outline the roles of helicase and ligase in DNA replication.
Explain how natural selection can lead to speciation.
Outline the features of ecosystems that make them sustainable.
The biological insights of Mendel and Darwin in the 19th century remain important to this day.
Discuss the role of genes and chromosomes in determining individual and shared character features of the members of a species.
Outline the process of speciation.
Describe, using one example, how homologous structures provide evidence for evolution.
Cell biologists play an important role in research into disease, fertility, evolution and many other areas of science.
Describe the origin of eukaryotic cells according to the endosymbiotic theory.
Cell biologists play an important role in research into disease, fertility, evolution and many
other areas of science.
Compare and contrast the processes of spermatogenesis and oogenesis.
Cell biologists play an important role in research into disease, fertility, evolution and many
other areas of science.
Outline the evidence for evolution provided by selective breeding.
The image shows a food web.
Using the food web, identify a detritivore.
Using the food web, identify a saprotroph.
State the name of the domain to which birds, such as the Elf owl, belong.
Outline the energy flow through this food web.
State two features that are found only in mammals.
Birds, bats and humans are all vertebrates with pentadactyl limbs. Birds and bats use their forelimbs to fly whereas humans can use them to lift and manipulate objects. Outline how the bird, bat and human forelimb can be used to illustrate the concept of homologous structures.
List two causes of variation within a gene pool.
Describe how variation contributes to evolution by natural selection.
Outline what is required for speciation to occur.