18.1. Classification
A subsection of Biology, 9700, through 18. Classification, biodiversity and conservation
Listing 10 of 21 questions
Spartina alterniflora is a grass that grows in salt marshes. It spreads by means of seeds and by underground stems. On its native east coast of North America it prevents salt marshes from being eroded by the sea and provides a food source for a large number of different species of animals. Some time after its introduction to the west coast of North America in 1973, S. alterniflora hybridised with Californian cord grass, S. foliosa. The hybrid now outcompetes the native species. The hybrid differs from its parent species in a number of ways: • it is taller • it produces very large numbers of pollen grains which are dispersed by wind to the other species, producing yet more hybrid plants • it produces larger numbers of seeds capable of germination • it can self-pollinate. State the structural features that are characteristic of a wind-pollinated flower and explain how each feature contributes to successful pollination. Suggest how self-pollination could help the population of hybrid plants to increase. Suggest why the hybrid plant is not considered to be a new species of Spartina.
9700_s15_qp_42
THEORY
2015
Paper 4, Variant 2
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In 2014, scientists published a phylogenetic tree diagram showing how and when different groups of insects developed from ancestral groups. To construct the diagram, the scientists compared nucleotide and amino acid sequence data for 1478 genes from each of 103 different insect species. The 103 species represented all 32 orders of the class Insecta. The data were used to arrange the species in related groups according to their degree of molecular similarity and to track how sequences changed over time. Outline three ways in which the members of a species are similar. Organisms are classified in a hierarchical system of taxonomic units. Name the domain and kingdom to which insects belong. domain kingdom Explain why a phylogenetic tree diagram is useful for classifying insect species. For this study, new software for processing large quantities of data was developed. Calculate the total number of sequences that were compared, considering both the nucleotide and amino acid sequences for each gene. Explain why this study needs to make use of bioinformatic techniques.
9700_s21_qp_41
THEORY
2021
Paper 4, Variant 1
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Fruit flies of the genus Bactrocera are pests that damage fruit crops. Table 3.1 gives the names and geographical ranges of Bactrocera fruit flies that were classified as four separate species. Table 3.1 name geographical range B. dorsalis China, India, Thailand B. invadens Africa, India B. papayae Indonesia, Malaysia B. philippinensis Philippine Islands, Borneo In 2014, the classification of these flies was changed. All four species were recognised as belonging to a single species, B. dorsalis. Suggest reasons why the four species were originally classified as separate species. Some students decided to investigate whether the flies were members of one species or four separate species. Suggest a simple investigation that the students could carry out. Female B. dorsalis lay their eggs in different types of fruits, such as avocados, bananas, mangos and papayas. The eggs hatch into larvae that eat the fruit. The actions of the female flies and larvae allow microorganisms to enter the fruit. The microorganisms feed by secreting extracellular enzymes, causing the fruit to rot. Name two kingdoms that include organisms that could spoil fruit by secreting extracellular enzymes. Before the four Bactrocera species were reclassified as a single species in 2014, some governments in Asia banned fruit imports from African countries to avoid introducing B. invadens as an alien species. Explain why the introduction of alien species should be avoided. Suggest how reclassifying B. invadens as B. dorsalis will benefit fruit‑producing countries in Africa.
9700_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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The Hawaiian archipelago is a group of volcanic islands in the Pacific ocean. shows the relative locations of five of these islands. O’ahu Lana’i Moloka’i Maui Hawai’i Table 4.1 shows the size and age of these five islands and the total number of Mecyclothorax ground beetle species and their species density, on each island. Data for the island of Maui is shown as two distinct regions, West and Haleakalã. This is because they formed at different times from two separate volcanoes. Table 4.1 island area / km2 age of island / million years total number of Mecyclothorax species species density / number of species per km2 Hawai’i 10 433 0.4 0.003 Lãna’i 1.3 0.008 Maui (West) 1.3 0.061 Maui (Haleakalã) 1.1 0.081 Moloka’i 1.9 – 1.8 0.064 O’ahu 3.7 – 2.6 shows a ground beetle of the genus Mecyclothorax. All the beetle species of this genus on the Hawaiian archipelago form a monophyletic group, descended from one original colonising species that reached Maui from Australia. Complete Table 4.1 by calculating the density of Mecyclothorax beetle species on the island of O’ahu. Use Table 4.1 to explain why the island of Hawai’i has the lowest density of Mecyclothorax beetle species. Use and Table 4.1 to suggest why O’ahu has a lower number of Mecyclothorax beetle species than Moloka’i. The rate of speciation of Mecyclothorax beetles on the slopes of the volcano Haleakalã, on Maui, is the highest recorded for any genus or location on earth. The volcano last erupted 400 years ago. This produced lava flows which cut through ancient forest and vegetation, dividing it into many separate microhabitats. Explain how the large number of Mecyclothorax beetle species on Haleakalã developed.
9700_w18_qp_41
THEORY
2018
Paper 4, Variant 1
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Questions Discovered
21