17.3. Evolution
A subsection of Biology, 9700, through 17. Selection and evolution
Listing 10 of 28 questions
Spea multiplicata is one of several species of American spadefoot toad. Young spadefoot toads are called tadpoles and live in water in ponds. S. multiplicata tadpoles show three different phenotypes due to genetic variation. The three phenotypes are: detritus feeder, intermediate and carnivore. Detritus feeders are small, and carnivores are large. Intermediates vary in size between the two extremes. A detritus feeder and a carnivore are shown in . carnivore detritus feeder fairy shrimp Detritus feeders: • eat detritus (small pieces of dead organic matter) and algae (photosynthetic protoctists) • have smooth mouthparts, small jaw muscles and long intestines. Intermediates: • can eat all available food (detritus, algae and fairy shrimps) • have teeth‑like mouthparts, medium‑sized jaw muscles and medium‑sized intestines. Carnivores: • eat fairy shrimps and other small animals • have teeth‑like mouthparts, large jaw muscles and short intestines. Scientists counted the number of each type of tadpole in two different ponds: pond 1 and pond 2. In pond 1, the scientists observed: • a high density of tadpoles • a low abundance of food • that most of the tadpoles they counted were either detritus feeders or carnivores, with very few intermediates present. Describe and suggest explanations for the type of natural selection that appears to be acting in pond 1. In pond 2, the scientists observed: • a low density of tadpoles • sufficient food availability for all tadpoles • that most of the tadpoles they counted were intermediates, with fewer detritus feeders or carnivores. Describe and suggest explanations for the type of natural selection that appears to be acting in pond 2. The intestine length of S. multiplicata tadpoles shows continuous variation. Sketch a curve on to show how intestine length varies in the tadpole population in pond 2. length of intestine number of tadpoles A student suggested that the variation in S. multiplicata tadpoles could lead to sympatric speciation in some populations. Outline the features of sympatric speciation. shows the evolutionary relationships between three species of American spadefoot toad. Spea multiplicata Spea hammondii Spea bombifrons time / millions of years ago Explain how analysis of DNA allowed the evolutionary relationships shown in to be determined.
9700_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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Russian scientists have discovered the fruits of a flowering plant, Silene stenophylla, in the food store in a burrow of a ground squirrel in frozen sediments in Siberia. Dating techniques suggest that the fruits were stored by the ground squirrel about 32 000 years ago, shortly before the ground became permanently frozen. Tissue samples were taken from the fruits and grown in a nutrient culture medium. After treatment with plant hormones to stimulate the growth of roots and shoots, 36 complete plants were produced. These ‘regenerated’ plants, which looked identical to one another, flowered and after cross-pollination, produced seeds that were able to germinate. Explain why cross-pollination produces more genetic variation among the offspring than self-pollination. The flowers of modern-day S. stenophylla look similar, but not identical, to the flowers of the ‘regenerated’ plants. Outline how DNA sequencing could be used to compare the DNA of modern-day and ‘regenerated’ S. stenophylla. Suggest a simple experiment, using plants of modern-day and ‘regenerated’ S. stenophylla to find out whether, after 32 000 years, they are still the same species.
9700_s14_qp_41
THEORY
2014
Paper 4, Variant 1
View
Russian scientists have discovered the fruits of a flowering plant, Silene stenophylla, in the food store in a burrow of a ground squirrel in frozen sediments in Siberia. Dating techniques suggest that the fruits were stored by the ground squirrel about 32 000 years ago, shortly before the ground became permanently frozen. Tissue samples were taken from the fruits and grown in a nutrient culture medium. After treatment with plant hormones to stimulate the growth of roots and shoots, 36 complete plants were produced. These ‘regenerated’ plants, which looked identical to one another, flowered and after cross-pollination, produced seeds that were able to germinate. Explain why cross-pollination produces more genetic variation among the offspring than self-pollination. The flowers of modern-day S. stenophylla look similar, but not identical, to the flowers of the ‘regenerated’ plants. Outline how DNA sequencing could be used to compare the DNA of modern-day and ‘regenerated’ S. stenophylla. Suggest a simple experiment, using plants of modern-day and ‘regenerated’ S. stenophylla to find out whether, after 32 000 years, they are still the same species.
9700_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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Bison are a type of large wild cattle. Ancestors of modern bison appeared in Asia 2.5 million years ago. This ancestral bison species increased its range into Europe and North America. While the ancestral species is now extinct, its descendants include Bison bonasus, the European bison, and Bison bison, the American bison. shows an American bison. After the end of the last ice age, populations of the ancestral bison were separated by sea and by forests that were not suitable as habitats. The separation resulted in the evolution of the European bison and the American bison. Explain how this separation resulted in the evolution of the two bison species. Table 5.1 compares features of European bison and American bison. Table 5.1 feature European bison, B. bonasus American bison, B. bison type of food grass and higher vegetation such as leaves of bushes and trees grass and low vegetation height / m 2.1 2.0 maximum mass / kg Assess the relative importance of natural selection and genetic drift in producing the different heights and masses of the two species of bison. The European bison has a nuclear genome that is very similar to that of the American bison. The European bison has a mitochondrial genome that is more similar to that of wild cattle of the genus Bos than to the American bison. Discuss what this implies about the evolutionary history of the European bison. Outline how practical techniques could be used to test the hypothesis that farmed cattle are closely related to European bison.
9700_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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The puma, Puma concolor, lives in North and South America. shows a puma. Fig 5.2 shows the distribution of the puma species. puma distribution Florida Texas A B Members of different subspecies belong to the same species but have some morphological differences and are found in different geographical locations. In the past the puma has been divided into 32 subspecies. The subspecies of puma varied in body size, coat colour and behaviour to adapt each population to its environment. Explain how the different subspecies of puma evolved. In 2016, genetic analysis concluded that there are only two genetically distinct subspecies of puma, one in North and Central America and one in South America. Outline how practical techniques could be used to conduct a genetic analysis of the puma species. shows the location of an isolated puma population in Florida. In 1990, the size of this population was very small, with fewer than 30 individuals. Three phenotypic features that vary in pumas are the shape of the tail, the pattern of hair growth on the back and the position of the testes in male pumas. Variant forms of these phenotypic features that are normally rare occur at a high frequency in the small Florida population. These variant forms are: • bent tail • abnormal pattern of hair growth on the back • testes remain in abdomen in some male pumas. Predict, with reasons, whether these phenotypic features show a continuous or a discontinuous pattern of variation. Explain how the small size of the Florida population resulted in a high frequency of these normally rare variant forms. In 1995, eight puma females from Texas were introduced to Florida to increase the breeding success and future size of the puma population in Florida. In the next 20 years the population grew substantially. Suggest why the introduced females were taken from Texas and not from points A or B on .
9700_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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DNA barcoding is used in species identification. To create a DNA barcode, a specific region of DNA is sequenced so that it can be compared to an online database of reference DNA. One region of DNA that is commonly used is 648 base pairs long within a mitochondrial gene, coding for the enzyme cytochrome c oxidase I. The solitary sandpiper, Tringa solitaria, is a migratory bird. DNA barcoding has shown that approximately 2.5 million years ago T. solitaria evolved into two subspecies, Tringa solitaria solitaria and Tringa solitaria cinnamomea. A subspecies is a genetically distinct population of a species that has some phenotypic differences but is not yet reproductively isolated. T. s. solitaria breed in eastern North America whereas T. s. cinnamomea breed in western North America. Suggest and explain how the two subspecies T. s. solitaria and T. s. cinnamomea could have evolved from the original T. solitaria population. shows an American oystercatcher, Haematopus palliatus. The black oystercatcher, Haematopus bachmani, has all black feathers. DNA barcoding analysis suggests that the American oystercatcher and the black oystercatcher are not separate species. Suggest how DNA barcoding evidence could indicate that the American oystercatcher and black oystercatcher are not separate species. Customs officers at airports can use a hand-held DNA barcoding device to identify biological specimens entering or leaving a country. Suggest how this helps protect endangered species.
9700_w20_qp_41
THEORY
2020
Paper 4, Variant 1
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DNA barcoding is used in species identification. To create a DNA barcode, a specific region of DNA is sequenced so that it can be compared to an online database of reference DNA. One region of DNA that is commonly used is 648 base pairs long within a mitochondrial gene, coding for the enzyme cytochrome c oxidase I. The solitary sandpiper, Tringa solitaria, is a migratory bird. DNA barcoding has shown that approximately 2.5 million years ago T. solitaria evolved into two subspecies, Tringa solitaria solitaria and Tringa solitaria cinnamomea. A subspecies is a genetically distinct population of a species that has some phenotypic differences but is not yet reproductively isolated. T. s. solitaria breed in eastern North America whereas T. s. cinnamomea breed in western North America. Suggest and explain how the two subspecies T. s. solitaria and T. s. cinnamomea could have evolved from the original T. solitaria population. shows an American oystercatcher, Haematopus palliatus. The black oystercatcher, Haematopus bachmani, has all black feathers. DNA barcoding analysis suggests that the American oystercatcher and the black oystercatcher are not separate species. Suggest how DNA barcoding evidence could indicate that the American oystercatcher and black oystercatcher are not separate species. Customs officers at airports can use a hand-held DNA barcoding device to identify biological specimens entering or leaving a country. Suggest how this helps protect endangered species.
9700_w20_qp_43
THEORY
2020
Paper 4, Variant 3
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Questions Discovered
28