19.2. Food chains and food webs
A subsection of Biology, 0610, through 19. Organisms and their environment
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Moose, Alces americanus, shown in , are large herbivores that primarily live in northern parts of North America. They have a varied diet that includes young shoots of willow trees and aquatic plants. Isle Royale is a large island in Lake Superior in the United States where there is a population of moose that has been studied by ecologists for a long time. The animals’ only predator is the wolf. The island has a population of wolves that has changed in numbers over the years. Draw a food chain for the organisms in the passages above. Complete Table 6.1 by stating the name and identifying the trophic level of each organism in the food chain. Table 6.1 name of organism trophic level State two factors that influence the numbers of a top predator, such as wolves. In the 1970s, the American ecologist Paul Colinvaux investigated the energy flow between moose and wolves. His results are summarised in Table 6.2. Table 6.2 energy input or output or energy flow energy / MJ consumed by moose 4 320 000 respiration of moose 380 000 consumed by wolves 56 000 respiration of wolves 53 000 Calculate the percentage of the energy obtained by the moose that is consumed by the wolves. Show your working. % Explain why the number of wolves on Isle Royale has never risen above 50 while the highest number of moose recorded is 2450.
0610_s15_qp_31
THEORY
2015
Paper 3, Variant 1
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Adaptive features are defined as the inherited features of an organism that increase its fitness. State what is meant by fitness in this context. Rodents are the most common mammals in many hot deserts. shows the lesser Egyptian jerboa, Jaculus jaculus, which lives in North Africa and the Middle East in areas that have high daytime temperatures and very little rainfall. Like many desert-living mammals, jerboas are active at night. Suggest two features of J. jaculus that adapt it to each of the following challenges of living in desert ecosystems: very high daytime temperatures very little or no light at night A scientist studied communities in different parts of a desert and estimated the biomass of the organisms in each area. He divided the organisms into four groups according to their roles in the food web as shown in Table 2.1. Detritivores are animals that eat dead organisms or parts of organisms. Table 2.1 groups of organisms in the food web biomass / g per m2 producers herbivores detritivores carnivores Some of these results are shown as a pyramid of biomass in . herbivores and detritivores producers Use the information in Table 2.1 to complete the pyramid of biomass in . The scientist observed the detritivores and decided to include them with herbivores in this pyramid of biomass. Suggest what the scientist discovered about the detritivores that made him make this decision. Explain why there are rarely more than four or five trophic levels in ecosystems. Explain the advantages of presenting information about food webs as a pyramid of biomass and not as a pyramid of numbers.
0610_s18_qp_41
THEORY
2018
Paper 4, Variant 1
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