SL Paper 2
Native oyster populations are decreasing where rivers meet the ocean along the northwest coast of North America. These oyster populations are being attacked by a gastropod.
It is known that oysters and gastropods have hard parts composed of calcium carbonate and that ocean acidification is increasing. Studies were carried out using juvenile oysters and gastropods to investigate the effects of acidification on the decrease in the population of oysters.
The first step was to raise oysters in two different mesocosms. One had seawater at a normal concentration of CO2 and the other had sea water with a high concentration of CO2. Gastropods were raised in two further mesocosms with normal and high CO2 concentrations respectively.
A juvenile gastropod will attack a juvenile oyster by using its tongue-like structure (radula) to drill a hole through the oyster shell. Once the hole has been drilled, the gastropod sucks out the soft flesh. Researchers investigated the shell thickness at the site of the drill hole in relation to the size of the oyster. The results are seen in this graph.
Equal numbers of oysters raised in seawater with a normal CO2 concentration and in seawater with a high CO2 concentration were then presented together to the gastropod predators in seawater with a normal CO2 concentration. The same numbers of oysters from the two groups were also presented together to the gastropods in seawater with a high CO2 concentration. The bar charts show how many of the oysters were drilled by the gastropods and the mean size of drilled oysters.
Outline how acidified sea water could affect the shells of the oyster.
Outline the trends shown in the data in the graph.
Estimate how much smaller drilled oysters raised in seawater at a high CO2 concentration were than drilled oysters raised in seawater at a normal CO2 concentration.
Deduce from the data in the bar charts which factors were and were not correlated significantly with the number of oysters drilled by the gastropods.
Suggest reasons for the differences in the numbers of oysters drilled, as shown in the bar charts.
The radula in a gastropod is hard but not made of calcium carbonate. Outline how this statement is supported by the drilling success of the gastropods in seawater with normal or high CO2 concentrations.
Using all the data, evaluate how CO2 concentrations affect the development of oysters and their predation by gastropods.
The following cladogram shows three possible evolutionary routes for the turtle (Turtles 1, Turtles 2 and Turtles 3). The taxa in italics are extinct.
State the organism most closely related to the lizards.
Based on the taxa shown, deduce a difficulty in gathering data to study turtle ancestry.
Molecular evidence is often used to construct a cladogram. Describe one type of molecular-based evidence to identify members of a clade.
Suggest one type of additional evidence that could provide strong support for Turtles 3 as the evolutionary route for turtles rather than Turtles 1 or Turtles 2.
Taxonomists aim to place species into genera, families and higher taxa according to their evolutionary origins. This is known as natural classification.
Explain the usefulness of natural classification in biodiversity research.
State one reason that viruses are not classified as living organisms.
State the plant phylum which is characterised by the absence of vascular tissue.
C. nemoralis (pictured below) is a mollusc. Identify two external features that distinguish this snail from an arthropod.
Outline the role of plant pigments in the process of photosynthesis.
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.
In the early 1950s, scientists studied the proportion of colours and banding of C. nemoralis in woods and fields near Oxford, UK, which differed in the type of plants and background colour. Each data point on the graph represents the percentage of yellow base colour shells and unbanded shells in a sample from either one type of wood or field, although other snail colours were present.
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 population of C. nemoralis has been studied for many years in open fields in a similar area. In the graph, each data point represents the percentage of adults of a given base colour plotted against the percentage of juveniles of the same base colour collected each year.
Determine the maximum percentage of yellow base colour shells found in woods.
Suggest either one possible advantage or one disadvantage of having a banded shell, stating whether it is an advantage or disadvantage.
Using the data in the graph, distinguish between the distribution of C. nemoralis shells in woods and fields.
Deduce from the data in the graph which shell base colours are on average most and least frequent among adult snails.
Most frequent:
Least frequent:
Discuss whether there is evidence in the data that colour plays a role in the survival of the snails.
Using the theory of natural selection, explain the differences shown in the graph between the three colours of snail.
The diagram shows a leaf from Dryopteris arguta.
[https://commons.wikimedia.org/wiki/File:E20161208-0001%E2%80%94Dryopteris_arguta_(Reverse)%E2%80%94RPBG_(30698925004).jpg, E20161208-0001—Dryopteris arguta (Reverse)—RPBG Source: https://www.flickr.com/photos/john_d_rusk/30698925004/ Author: John Rusk from Berkeley, CA, United States of America, licensed under Creative Commons licence: https://creativecommons.org/licenses/by/4.0/legalcode]
State the phylum of this plant.
State two characteristics of plants from the phylum you stated in (a)(i).
Outline why the number of trophic levels is limited in a food chain.
Sketch the complementary strand to complete the section of a DNA diagram.
Define mutation.
Explain how evolution by natural selection depends on mutations.
Compare and contrast the mode of nutrition of detritivores and saprotrophs.
The image shows an example of a soil food web.
[Source: Anon., n.d. The Soil Food Web. [image online] Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/
photogallery/soils/health/biology/gallery/?cid=1788&position=Promo [Accessed 11 March 2020].]
Draw a food chain from this food web, showing at least three organisms.
Explain the reasons for food chains rarely containing more than four or five trophic levels.
The amount of food passing into food chains can be affected by the rate of photosynthesis. Explain the effect of one limiting factor on photosynthesis.
All of the leaves in the image are from Solanum, a wild genus of tomato.
[Source: Courtesy: National Science Foundation, Credit Leonie Moyle.]
State one cause of variation in a plant such as the tomato.
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.
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.
The table gives common names and binomial names for some mammals.
State one feature that characterizes these species as mammals.
Identify the two species most closely related.
1.
2.
Identify two species from the list that are classified in different genera.
1.
2.
Draw a labelled diagram to show the structure of a single nucleotide of RNA.
Distinguish between the processes of meiosis and mitosis.
Explain the development of antibiotic resistance in terms of natural selection.
The images show parts of plants belonging to two different phyla.
State the phylum of plant X and of plant Y.
X:
Y:
Explain one cause of mutation.
Outline the types of evidence that can be used to place a species in a particular clade.
The cladogram includes four marsupial (non-placental mammal) families.
[Source: Koala image: Quartl, https://commons.wikimedia.org/wiki/Phascolarctos_cinereus#/media/
File:Friendly_Female_Koala.JPG; Wombat image: JJ Harrison, https://en.wikipedia.org/wiki/Wombat#/
media/File:Vombatus_ursinus_-Maria_Island_National_Park.jpg; Marsupial lion: Nobu Tamura,
https://en.wikipedia.org/wiki/Marsupial_lion#/media/File:Thylacoleo_BW.jpg;
Diprotodontoidea image: Anne Musser]
Deduce the family that is most closely related to the Diprotodontoidea.
The image shows the wings of an insect, bird and bat.
[Source: [insect wing] Halvard Hatlen https://upload.wikimedia.org/wikipedia/commons/0/0f/Dip-trichoceridae-wing.png. [bird wing] University of Maryland, Department of Geology. [bat wing] University of Maryland, Department of Geology.]
Based on their structure, the insect and bat wings are analogous. Outline what is meant by an analogous trait.
The bird and bat wings share homologous bone structures whereas the insect wing does not. Outline the conclusion that can be drawn about the evolution of these wings, based on homologous structures.
Explain how cladistics can be used to investigate evolutionary relationships.
Cladistics and other evolutionary evidence suggest that mammals and birds have a more recent common ancestor than mammals and amphibians. Draw a cladogram to show the relationships between mammals, birds and amphibians.
Mutations are the ultimate source of genetic variation and are essential to evolution.
Lice are wingless insects that belong to the phylum arthropoda.
State one type of environmental factor that may increase the mutation rate of a gene.
Identify one type of gene mutation.
State two characteristics that identify lice as members of the arthropoda.
1.
2.
Some lice live in human hair and feed on blood. Shampoos that kill lice have been available for many years but some lice are now resistant to those shampoos. Two possible hypotheses are:
Discuss which hypothesis is a better explanation of the theory of evolution by natural selection.
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.
The human hand is an example of adaptive radiation. Outline adaptive radiation.
Explain how the human body defends itself against pathogens.
The growing human population has an increasing demand for energy derived from crop plants. At the same time, increasing droughts that are part of climate change make it difficult to grow crops in some parts of the world.
Outline energy flow through a community in a natural ecosystem.
Explain how natural selection can cause traits such as drought resistance to develop in wild plants.
Suggest possible benefits and risks of using genetic modification to develop varieties of crop plant with traits such as drought resistance.
Living organisms have been placed in three domains: archaea, eubacteria and eukaryote. Distinguish archaea from eubacteria.
List two types of evidence used to determine which species belong in the same clade.
The photomicrograph below shows the protozoan Paramecium caudatum.
[Source: Deuterostome, CC BY-SA 3.0
https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons.]
State the genus of this organism.
State the domain in which it is classified.
Outline the method of nutrition carried out by P. caudatum.
Outline one aspect of how P. caudatum carries out homeostasis.
Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
Outline the structures in M. tuberculosis that are not present in a human cell.
Explain the production of antibodies when a patient is infected with the TB bacterium.
Describe the risk to the human population of indiscriminate use of antibiotics.
Outline the stages in the production of mRNA by transcription.
Describe the functions of proteins in cell membranes.
Explain how natural selection can lead to speciation.
Three-toed sloths (Bradypus variegatus) are placental mammals that live in trees in Central and South America. They eat leaves and fruit and get almost all their water from succulent plants.
[Source: Adapted from Laube, S., 2003. Three-toed-sloth (Bradypus variegatus), Lake Gatun, Republic of Panama. [image online] Available at: https://meta.wikimedia.org/wiki/User:Bradipus#/media/File:Bradypus.jpg]
Three-toed sloths change their body posture in response to the temperature of their environment (ambient temperature). Researchers assessed posture on a scale from 1 to 6, with 1 being when the sloth was curled into a tight ball and 6 when it had all limbs spread. The percentage of time the sloths were observed in each position was recorded at ambient temperatures from 22 °C to 34 °C. The researchers also measured the body temperature of the sloths over the same range of ambient temperatures.
[Source: Adapted from Cliffe, R.N., Scantlebury, D.M., Kennedy, S.J., Avey-Arroyo, J., Mindich, D. and Wilson, R.P., 2018. The metabolic response of the Bradypus sloth to temperature. PeerJ, [e-journal] 6: e5600. http://dx.doi.org/10.7717/peerj.5600. Licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/.]
The daily food intake of three-toed sloths and daily ambient temperatures were monitored over a 160-day period from February to early July. The graphs show the mean results.
[Source: Cliffe et al. (2015), Sloths like it hot: ambient temperature modulates food intake in the brown-throated sloth (Bradypus variegatus). PeerJ 3:e875; DOI 10.7717/peerj.875 Licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/.]
State the relationship between sloth body temperature and ambient temperature.
Explain how this relationship differs from that in humans.
Describe the trend in body posture as ambient temperature rises from 22 to 34 °C.
Suggest reasons for this trend.
The mean daily food intake fluctuated from day to day. State the month that contains the day on which the mean intake of food was highest.
Outline the relationship between ambient daily temperature and food intake in March.
Suggest, with a reason, how the activity of the sloth varies with ambient temperature.
State one feature of the sloth that would indicate it is a mammal.
Organisms have evolved a great diversity of cell types.
Describe the endosymbiotic theory.
Explain the need for halving the chromosome number during a sexual life cycle and how this is done.
Outline the binomial system of classification.
Although simple in structure, bacteria as a group show a wide range of diversity.
Outline the roles bacteria play in the carbon cycle.
Describe the evolution of antibiotic resistance in bacteria.
Explain the process of genetically modifying bacteria.