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IM 11 Environmental Science MATSEC Examinations Board Marking Scheme IM 11 Environmental Science Main Session 2019 Marking Scheme (Main Session 2019): IM Environmental Science Marking schemes published by the MATSEC Examination Board are not intended to be standalone documents. They are an essential resource for markers who are subsequently monitored through a verification process to ensure consistent and accurate application of the marking scheme. In the case of marking schemes that include model solutions or answers, it should be noted that these are not intended to be exhaustive. Variations and alternatives may also be acceptable. Examiners must consider all answers on their merits, and will have consulted with the MATSEC Examinations Board when in doubt. Page 1 of 10 Marking Scheme (Main Session 2019): IM Environmental Science Question Marking scheme and suggested answers Marks Section A 1. a Any THREE from the following or suitable alternative: 3 Lowering of water table / Reduced surface water supplies / Land subsidence / Water quality concerns / Salt water contamination b Reverse osmosis; is the process in which seawater is pushed through an ultra-fine semi- 1, 2 permeable membrane. Only the water molecules can pass through the membrane, while salt and other chemicals cannot. c Any THREE from the following or suitable alternative: 3 Installing low flow shower heads / Turning off the tap while brushing your teeth or shaving / Placing water bottles in flushing tank / Buy washing appliances which are more water and energy efficient / Washing appliances are run only when they are full Total: 9 marks 2. a Insolation is the amount of incoming solar radiation that reaches the Earth’s surface. 1 b At the equator (A) the sun’s rays strike the Earth perpendicular to the ground and so 2 insolation is at a maximum. At higher altitudes (B) the rays are slanted /at an angle and the insolation is diffused / spread out. c (i) Troposphere; Stratosphere; Mesosphere; Thermosphere; Exosphere 5 (ii) decreases; increases; increases 3 Total: 11 marks 1 3. a Salinisation: As the salinity of soil increases plants start to die out leading to a lack of surface cover and therefore increase the vulnerability of soils to erosion. Gullying: Occurs where surface water flow has become trapped in a small concentrated 1 stream and begins to erode deep channels on the ground surface. Overgrazing: Too much grazing by animals on too little land will not give grasses time 1 to re-establish themselves and soil becomes barren. Up and down ploughing: Occurs when farmers plough up and down hills. Rainfall will 1 then flow easily down the furrows and removes top soil. b Any ONE from the following or suitable alternative: Soil conservation techniques: Multicropping / contour farming / reduce ploughing / 1 terracing / wind breakers. Biological pest control: use of organism to eliminate/reduce pests / introducing the 1 ladybird to kill aphids / wasps to kill butterfly caterpillars. Reduction of arable land degradation: reduce the use of pesticides / reduce the use of 1 artificial fertilizers / use organic farming. Total: 7 marks Page 2 of 10 Marking Scheme (Main Session 2019): IM Environmental Science 4. Denitrification; Catalytic Converter; Disinfection; Composting; Biomagnification; 10 Incineration; Neutralisation; Desulfurisation; Bioaccumulation; Carbon Footprint (1 mark each) Total: 10 marks 5. a DO NOT assign any marks if no reason is given TRUE - Reason: O3 (ozone or trioxygen) and O2 (dioxygen) are allotropes of the same 1, 1 element. Although each ozone molecule is made up of three atoms of oxygen, it reacts very differently from atmospheric oxygen (dioxygen). b FALSE - Reason: Ozone-depleting substances (ODS) are halogen-containing compounds 1, 1 (e.g. CFCs and halons) which are unreactive in the lower atmosphere but break down and release halogen atoms (free radicals) which react and destroy ozone in the upper atmosphere. c TRUE - Reason: Ozone is mostly found in the stratosphere, contained in the ‘ozone 1, 1 layer’. It shields life on earth from harmful UV radiation from the sun. d FALSE - Reason: Oxygen molecules require solar UV radiation to be broken apart and 1, 1 produce highly reactive oxygen atom which then combine with other O2 molecules to produce ozone, O3. Hence conversion of O2 to O3 would not occur (or slows down significantly) in the absence of light. e FALSE - Reason: Ozone is produced by photochemical reactions involving gaseous 1, 1 hydrocarbons and nitrogen oxides (NOx), as well as ozone itself. Main source is fossil fuel combustion. f FALSE - Reason: Stratospheric ozone is considered as ‘good’ as it absorbs UV-B 1, 1 radiation from the sun which can otherwise increase incidence of skin cancers, etc. g FALSE - Reason: Tropospheric ozone is regarded as ‘bad’ as it is produced by pollution 1, 1 and is harmful to organisms as it reacts strongly and destroys or alters biological tissue, affects crop yields and forest grown and causes a number of health disorders. It is also a GHG. h TRUE - Reason: They decompose in the upper atmosphere, releasing chlorine free 1, 1 radicals which react with ozone catalysing its breakdown, hence depleting it. Total: 16 marks 6. a Mutualism: Biological interaction between two species from which both organisms 1, 1 benefit. Example: The partnership between nitrogen-fixing bacteria and leguminous plants. (accept any valid example) b Amensalism: Biological interaction between two organisms of two different species in 1, 1 which one is harmed or killed and the other is unaffected. Example: When growing Acacia plants secrete substances that inhibit the growth of or kill outright nearby plants. (accept any valid example) Page 3 of 10 Marking Scheme (Main Session 2019): IM Environmental Science c Parasitism: Biological interaction between two organisms of two different species in 1, 1 which the parasite harms the host. Example: tapeworm living in the intestine of a human. (accept any valid example) d Commensalism: Biological interaction in which one organism benefits and the other is 1, 1 unaffected. Example: Remora fish attaches itself to a shark and is carried around without the need to swim. The shark is not effected. (accept any valid example) Total: 8 marks 7. a A group/number of organisms belonging to the same species; and inhabiting the same 2 area that can reproduce and produce fertile offspring. Accept any other definition as long as it refers to NUMBER and SAME/ ONE species. b 1994 – 2004 1 c A low environmental resistance implies that the impact of environmental factors (such 2 as drought, mineral deficiencies, and competition) on the survival of an organism is low and hence the organism can thrive. d There are no limiting factors: many resources are available and predators and disease 1 are few. Organisms show maximum biotic potential/ A high reproductive rate exceeding birth 1 rate exceeds death rate low. e Irruptive growth is a growth pattern that happens over a timeframe, within a 2 population, characterised by sudden population explosions (when resources are 2 abundant and they overshoot the carrying capacity) and then sudden crashes (when resources are depleted, giving time for the environment to recover). f There was a decrease in predators that hunt and kill these lizards. 1 Accept any other valid answer. g Accept any food web that shows the following features: 4 (½ mark for each correctly placed organism) (1mark for the correct arrow direction) h Energy stored in the body tissue is lost as heat. As food moves up a trophic level some 3 of the body tissue is not eaten (e.g. bones, horns). About 10% of the energy originally available is transferred from each trophic level to the next Total: 19 marks Page 4 of 10 Marking Scheme (Main Session 2019): IM Environmental Science Section B 1. a Accept any other correct reason as long as ALL the 4 sources are mentioned. When burnt all three fossil fuels (coal, oil and gas) release poisonous gases into the air; gases that contribute towards the greenhouse effect which causes global warming; 3 increase particulates in the air which reduces visibility and the increases the incidence of respiratory ailments. Coal mining creates a negative visual impact on the environment (like gaping holes or 2 barren land); and the loss of soil and biodiversity. 1 Oil spillages can cause serious environmental problems and the death of wildlife. Disposal and storage of nuclear waste is very costly. The leakage of radioactive waste 2 can cause cancer, abnormal growth, and even immediate death. b Any THREE from the following or suitable alternative: Wind: Kinetic energy in the wind is converted to mechanical power in the turbines. A 6 generator converts this mechanical power into electricity. (2 marks Wave: Wave energy is converted to kinetic energy in turbines placed around the coast. for each The waves come in and provide the up and down motion which is used to drive the source) generator. Tides: Tidal barrages are dams built across river estuaries with turbines in them. As the tide comes in, it fills up the estuary. The water is allowed to return back through the turbines at a controlled speed. Solar: The sun’s energy is used either directly as thermal energy (heat) or through the use of photovoltaic cells in solar panels and transparent photovoltaic glass to generate electricity. Water: Hydroelectric power requires the flooding of a valley by building a dam. Rainwater is collected behind the dam and allowed to pass through turbines which generate electricity. Biomass: Biomass is organic material that comes from plants and animals. A biomass- fired power plant produces electricity and heat by burning biomass in a boiler. The boiler heats up the water to steam which turns the turbines. Geothermal: Geothermal energy is the heat generated from the Earth’s interior. Water is pumped down to hot rocks inside the earth and it returns as steam which drives the generator.
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