20. Human influences on ecosystems
A section of Biology, 0610
Listing 10 of 393 questions
For Examiner's Use Sewage disposal involves the removal of human waste in pipes from houses to sewage treatment works. is a diagram that shows how sewage is treated. collection and pumping primary sedimentation screening grit removal aeration and digestion final sedimentation disinfection grit to landfill effluent solids to anaerobic digester oxygen solids to anaerobic digester chlorine recycled microorganisms river For Examiner's Use During stage 5 microorganisms break down organic matter consisting of cellulose, starch, protein and lipid . The microorganisms multiply during this stage and are recycled. Complete by writing in the boxes the names of the enzymes used to catalyse the reactions shown. The first box has been completed for you. cellulose cellobiose glucose cellulase starch maltose glucose protein amino acids lipid fatty acids and glycerol For Examiner's Use State why it is important that sewage is treated. At stage 5 in , oxygen and microorganisms are added. Explain why oxygen is bubbled through the tank at this stage. Suggest and explain the advantage of recycling microorganisms from stage 6 to stage 5 as shown in . 0610/32/O/N/11 For Examiner's Use Explain why chlorine is added at stage 7.
0610_w11_qp_32
THEORY
2011
Paper 3, Variant 2
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When a mass of still air becomes trapped over a city, pollutants build up in the air next to the ground. Name two chemical pollutants that might build up over a busy city centre. Vehicles such as cars burn fossil fuels. Explain why vehicles may be banned from the city if pollution becomes severe. For Examiner's Use If air pollution is very severe, warnings may be given not to take young babies into the city centre and for any people with heart and respiratory problems to stay inside. Suggest two reasons for this advice.
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THEORY
2013
Paper 2, Variant 2
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For Examiner's Use Molluscs are important animals in many aquatic and terrestrial ecosystems. shows four species of mollusc that live in the sea. common octopus Octopus vulgaris common whelk Buccinum undatum edible mussel Mytilus edulis stout razor clam Tagelus plebeius not to scale State two features shown by all mollusc species. State two features, visible in , in which the octopus differs from the other three molluscs. For Examiner's Use The edible mussel, Mytilus edulis, is attached to rocks that are exposed to the air at low tide. Use to suggest how an edible mussel is adapted to attach to rocks and survive when exposed to the air. The zebra mussel, Dreissena polymorpha, is a freshwater mussel that originates from rivers in southern Russia. The mussel was introduced into the Great Lakes of North America and has increased in huge numbers with serious effects on the food webs of the lakes. Explain why an introduced species, such as the zebra mussel, can have serious effects on the populations of the species that are already living in the area. For Examiner's Use The freshwater mussel, Pletholophus swinhoei, was used in a project to monitor water pollution by chemical waste in northern Vietnam. This was done by regularly counting the number of mussels in the river. Suggest the advantages of using freshwater mussels to monitor the pollution of water instead of carrying out chemical analysis of the water. Non-biodegradable plastics are a serious problem in many aquatic ecosystems. Explain the harm that non-biodegradable plastics may cause to organisms in aquatic ecosystems.
0610_w13_qp_32
THEORY
2013
Paper 3, Variant 2
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Some pollutants are not broken down easily and remain in the environment for a long time. These are described as persistent pollutants. PCBs are a waste material from the manufacturing of electrical insulation. PCBs are one of the most persistent pollutants in the environment. Between 1947 and 1976, factories dumped large quantities of PCBs into the Hudson River in the USA. Studies measured the concentrations of PCBs in the tissues of organisms in a food chain in the sea near the Hudson River, as shown in . 11 400 – 17 300 concentrations of PCBs in arbitrary units 6 – 45 1.56 0.85 porpoise herring zooplankton phytoplankton not to scale Describe the results shown in . Suggest an explanation for the different concentrations of PCBs in the organisms of the food chain. PCBs are toxic to many organisms because they bind to a protein molecule known as AHR. The Atlantic tomcod, Microgadus tomcod, is a fish that lives in the Hudson River and other rivers nearby. 90% of the tomcod population in the Hudson River is resistant to the effects of PCBs. This is because these fish have a different type of AHR compared with other tomcod populations. Suggest how this resistance came about. Scientists predict that the proportion of fish resistant to PCBs will decrease if the concentration of PCBs in the river decreases. Suggest reasons why the proportion of fish with the altered AHR protein might decrease. Describe the problems caused by non-biodegradable plastics in the environment.
0610_w14_qp_32
THEORY
2014
Paper 3, Variant 2
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Some students studied water pollution in a stream near their school. They took samples of water at six sampling points along the stream and carried out a chemical analysis on the water samples. They also counted the numbers of five different invertebrates at the same sampling points. The students used a four point scale to record the numbers they found in each sample. Their results are shown in Table 6.1. Table 6.1 sampling points chemical analysis types of invertebrates nitrate concentration oxygen concentration rat-tailed maggot mayfly nymph stonefly nymph tubifex worm water louse low high + +++ + + + high very low ++ – – +++ ++ high very low ++ – – +++ ++ very high very low ++ + – +++ ++ very high low + ++ – ++ ++ low high + +++ + + + key – none + 1 to 10 ++ 11 to 100 +++ too many to count Using only the information from Table 6.1, state the invertebrates that survive in polluted water state the invertebrate that is most sensitive to a decrease in the oxygen concentration of the water. The students noticed there were many algae and aquatic plants growing in the stream at sampling points 4 and 5. Use the results in Table 6.1 to explain why there are many algae and aquatic plants growing in these parts of the stream. The students decided there were advantages in sampling invertebrates to assess the level of pollution in the stream, compared with carrying out a chemical analysis of the water. Suggest the advantages of carrying out a survey of invertebrates when studying the pollution of freshwater ecosystems, such as streams and rivers. The students found that the stream was polluted by sewage from a nearby house. Outline how sewage should be treated before entering a stream. The stream contained many plastic items that had been thrown away. Most of the plastic was non-biodegradable. Describe the likely environmental problems caused by non-biodegradable plastics in streams and rivers.
0610_w15_qp_32
THEORY
2015
Paper 3, Variant 2
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Questions Discovered
393