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.

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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

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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)

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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 ) 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

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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.

c Advantages (Accept any valid alternative): Renewable sources of energy will not run out. 3 They are a clean source of energy having low or zero carbon and greenhouse emission. The source of energy is free. Disadvantages (Accept any valid alternative):

Most require large areas of either land or water to be effective. They often have a visual impact on the natural beauty of the countryside or coastline. 3 Most renewables do not provide a constant supply of energy because they are affected by the weather, time of day, etc. Total: 20 marks

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Marking Scheme (Main Session 2019): IM Environmental Science

2. a Any illustration containing the following or other 2 relevant information: (½ mark Accept any valid alternative feature as long as the each candidates give at least ONE feature for each layer. label) The inner layers are composed mostly of iron and

nickel. The inner and outer cores are denser and at much 4 greater pressure than the outer layers. The inner core has a temperature hotter than the surface of the Sun. The mantle is mostly solid but at certain depths it can flow and behaves like a liquid (magma). It is mainly composed of silicon, oxygen, magnesium, iron and aluminium. The crust is the Earth’s surface. A solid thin layer divided into the continental crust and the oceanic crust. It contains of a variety of rocks: igneous rocks, sedimentary rocks, and metamorphic rocks b Plate tectonics is the theory that Earth's outer shell is divided into several plates that 3 glide over the mantle. The plates act like a hard and rigid shell compared to Earth's fluid mantle. The plates are driven by convection currents within the upper mantle. c Accept any diagrams similar to the one below that show the three kinds of plate tectonic 2 boundaries: A. Divergent; B. Convergent; C. Conservative plate boundaries. (1 mark for correct label) (1 mark for correct direction of arrows)

A. Divergent boundaries (Constructive boundary): where two plates are moving apart. The space created can fill with new crustal material sourced from molten magma that

forms below.

On land: divergent boundaries within continents initially produce rifts, which produce 3 rift valleys and eventually open up and become ocean basins.

Under the sea: the most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges. B. Convergent boundaries (Destructive boundary): where two plates are colliding / moving towards each other. Subduction zones occur when the denser plate is subducted underneath the less dense plate. The plate being forced under is eventually melted and destroyed. 3 Where oceanic crust meets ocean crust, island arcs and oceanic trenches occur and submarine volcanoes form.

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Marking Scheme (Main Session 2019): IM Environmental Science

Where oceanic crust meets continental crust, the denser oceanic plate is subducted, often forming a mountain range on the continent. Where continental crust meets continental crust, both continental crusts are too light to subduct so a continent-continent collision occurs, creating especially large mountain

ranges.

C. Conservative boundaries (Transform boundaries) – where plates slide past each

other. The relative motion of the plates is horizontal. They can occur underwater or on land, and crust is neither destroyed nor created. Because of friction, the plates cannot simply glide past each other. So, stress builds up 3 in both plates and when it exceeds the threshold of the rocks, the energy is suddenly released causing earthquakes. Total: 20 marks 3. a Sewage treatment is a process that ensures the removal of contaminants (e.g. organic 3 matter, phosphates, nitrates, solids, etc.) from wastewater and household sewage water to produce an environmentally safe effluent and a solid waste (sludge) suitable for disposal or re-use (e.g. for agricultural purposes or as a fuel source). b First class water: is water fit for human consumption and hence free from pathogens 1 and other organic and inorganic pollutants. Second class water: is non-potable water of lower quality than first class water that can 1 be used for toilets, for other domestic uses and for irrigation purposes. c Any THREE from: organic wastes, suspended solids, bacteria (or microorganisms), 3 nitrates, phosphates, heavy metals. d Sewage has a high BOD because it contains a high amount of organic matter which is 3 degraded by microorganisms (mainly by aerobic bacteria) which consume a lot of oxygen. e Primary Treatment (Physical) – consists of removing floating and suspended solids by 3 mechanical means. They settle out at the base of a primary settlement tank. The sludge is continuously removed by anaerobic process which reduces drastically the total mass

compared to the original volume entering the system.

Secondary Treatment (Biological) – involves the biological degradation of organic 3 material by microorganisms under aerobic conditions, in which waste is aerated to supply oxygen for microbial growth. The degraded material settles out in secondary settling tanks and is afterwards removed by sedimentation. The clarified waste water may be discharged in outfalls to rivers, lakes or oceans, or passed on for tertiary treatment.

Tertiary Treatment (Chemical) – aims to purify wastewater further and recycle it for 3 irrigation. Methods involved in the final stage of sewage water treatment include chemical precipitation and filtration, adsorption, chemical oxidation, desalination and oxidation ponds. Disinfection may also be applied to removal pathogens. This is done by treating it with chlorine, UV or ozone. The recycled wastewater can be used for irrigation and industry. It can also serve as an indirect source for drinking water. Total: 20 marks Page 7 of 10

Marking Scheme (Main Session 2019): IM Environmental Science

4. a Volatile Organic Compounds (VOCs): Any organic compound that participates in 5 atmospheric photochemical reactions, having a low boiling point. E.g. petrol, industrial solvents (such as benzene, toluene, xylene, dry cleaning agents). Particulate Matter (PM): Fine solid or liquid particles that pollute the air and are added to the atmosphere by natural and man-made processes. E.g. dust, smoke, soot, pollen and soil particles.

b Hazardous Waste: This is the waste that poses a risk to human health and / or the 5 environment and needs to be handled and disposed of carefully. E.g. oil-based paints, car batteries, weed killers, bleach, waste from electrical / electronic devices. Inert Waste: This is a waste that is neither chemically nor biologically reactive and will not decompose in nature. E.g. sand, concrete, construction waste.

c Eutrophication: The slow aging process during which a body of water (e.g. lake or 5 estuary or bay) becomes enriched with nutrients which induce excessive growth of plants and algae, which may result in algal bloom and oxygen depletion. Biodegradation: The breakdown of organic matter by enzymes produced by microorganisms such as bacteria and fungi. Biodegradation is a natural process and may occur aerobically (in the presence of oxygen) and anaerobically (in the absence of oxygen).

d Industrial Smog: The result of smoke particles from industrial plumes mixing with fog 5 producing a yellow-brown haze. Occurs when smoke and SO2 emissions from coal burning combine with fog under the right conditions such as when pollutants are trapped by temperature inversion. Photochemical Smog: This originates from combustion of fossil fuels (e.g. petrol) by

motor vehicles and industry which release primary pollutants e.g. VOCs and NOx which react in the presence of sunlight in a series of photochemical reactions resulting in

secondary pollutants e.g. O3, PAN, aldehydes. It is a common problem in major cities with a lot of traffic and industrial activity. Total: 20 marks

5. a Pyramid of Numbers shows the number of organisms in each trophic level in an 1 without any consideration for their size. Usually the producers are more in number than any other trophic level but an 1 inverted pyramid of numbers can also be found. Pyramid of Biomass shows amount of organic matter in organisms at each trophic 1 level in a particular ecosystem. Biomass pyramids are always largest at the base, and decreasing in amount as it goes 1 through the apex.

b Density Independent Factors limit population size regardless of the population density. 1 These include physical (abiotic) factors such as weather and seasonal cycles and natural 1 disasters. Density Dependent Factors become more effective as the population density 1 decreases.

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Marking Scheme (Main Session 2019): IM Environmental Science

These are usually biological (biotic) factors such as , competition, disease and 1 stress. c Crude Birth Rate refers to the rate at which new individuals are added to a population 1 by reproduction. It is expressed as the number of live births per 1000 individuals of a population per 1 year (Accept equation).

Assign only ½ mark if answer is: Fecundity and fertility rate effect CBR.

Crude Death Rate refers to the rate at which new individuals are lost from a population 1 as they die or get killed.

Expressed as the number of deaths per 1000 individuals of a population per year 1 Assign only ½ mark if answer is: Infant and child mortality affect CDR. d Resilience is the capacity of an ecosystem to maintain its fundamental structure, 1, 1 processes and functioning; when subjected to stress, disturbance or invaders. Resistance refers to the biotic and abiotic factors and ecological processes in an 1, 1 ecosystem; that resist and limit the population growth of an invading species. e Accept any TWO points as long as the biomes are well compared. Tundra: Has the arctic climate, which is cold and then hot during summer. 2 Precipitation is generally less than 50-60 cm, but in low lying areas soils may remain saturated with water during most of the growing season. The soil is nutrient poor. Some distance below the surface, the ground is permanently frozen (permafrost). Plants are low, ground hugging forms. Lichens, mosses coniferous and other shrubby growths, and herbs with brilliantly coloured flowers, are characteristic of the habitat.

Animals of this biome are well protected by fur or layers of blubber. White is protective colouration in a snowy environment and also minimizes heat loss by radiation.

Extremities of animals are small to reduce heat loss.

Temperate: These biomes are exposed to warm and cold air masses, causing them to have four seasons: winter, spring, summer and fall. The average yearly temperature is 2 about 10 °C. Precipitation is about 75 cm - 150 cm spread fairly evenly throughout the year Soils are mull soils, which have a high level of organic matter especially close to the surface that is well mixed with mineral matter. Plants include lichens, moss, ferns, wildflowers and other small plants on the forest floor. Shrubs fill the middle level and hardwood trees like maple, oak, birch, make up the upper level. Most deciduous trees shed their leaves. This biome contains very few mammals, because there is no complex series of layers and the vegetation is seasonal. During autumn, the animals of this biome feed on and lay in stores for the winter and then they enter hibernation.

Total: 20 marks

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Marking Scheme (Main Session 2019): IM Environmental Science

6. a The practice of renewing and restoring degraded, damaged, or destroyed 1, 1 and habitats in the environment; by active human intervention and action

b Accept any TWO of the following: Disruption of biological communities/food webs by hunting. 2, 2 Removal of top predators and keystone species. Chemical pollution by excess nutrients and contaminants. Deterioration of habitat – logging/ deforestation/ clearing land for agriculture.

c The steps in enabling recovery of any degraded ecosystem include: 1. remove or reduce current impacts so that actions used will have the most effect. 1 2. the area needs to be physical and chemically rectified. 1 3. identification of a keystone species. 1 4. restoring such species not only adds structure to habitat but also allows the 1 ecosystem to start refunctioning. (i) Accept any process that directly involves accelerating the process d Regeneration of species 2 Reforestation

Direct seedling

Enrichment planting/ planting mature plants Introduction of native species (ii) Accept any process that allows natural succession to occur after removing the source of disturbance Abandoning farms 2 Reducing logging Reducing livestock grazing Reduce non-native species

e Reclamation: is the returning of lands disturbed from e.g. mining, transportation or 2 logging back into their natural habitat to restore disturbed land back to an ecologically stable condition. Land reclamation might involve razing a strip mall/ planting crops/

Decontamination: is the process of removal of contaminants such as harmful micro- 2 organisms or pollutants (hazardous materials, chemicals, radioactive substances) from

the environment. Removal of environmental pollutants can be done by metabolic processes and organisms that degrade the environmental pollutants. This can also involve a physical clean-up of the environmental pollution. Bioremediation: involves using naturally occurring or deliberately introduced microorganisms to consume and break down environmental pollutants used during the 2 agricultural procedures. Examples include Remove any / Identify

keystone species and reintroduce it/ Permanent vegetation cover is set to stabilize the

soils and slow-down erosion/ Afforestation and reforestation with tree and plant species/ Stimulate groundwater recharge/ Conservation status - protection and management measures /Crop production and grazing banned. Total: 20 marks

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