environmental science - draft paper may 2000 · harvested at different times. this method also...

MARKING SCHEME

IM ENVIRONMENTAL SCIENCE

FIRST SESSION 2018

MARKING SCHEME: IM ENVIRONMENTAL SCIENCE (FIRST SESSION 2018)

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Section A

Qn No.

Suggested Answer Marks

1 Geothermal energy

Hydroelectric

Biofuel

Wind turbines

Photovoltaic cell

Passive solar energy

Biomass

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(1 mark per term)

Total: 7 marks

2 a. It is the cycling of carbon in different forms/compounds between and within the lithosphere, hydrosphere, atmosphere and biosphere.

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b. (i) Plants take up carbon dioxide via photosynthesis and incorporate it into themselves and eventually into consumers.

(ii) The hydrosphere is a carbon dioxide sink. When the water bodies get warmer less gas is dissolved in it, thus carbon dioxide is released into the atmosphere.

(iii) Aquatic organisms die and are deposited on the seabed. Sedimentary rocks are formed by lithification as the remains become part of the oceanic crust and end up in the subduction zone.

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c. Use of fossil fuels realising huge amounts of carbon dioxide to the atmosphere leading to greenhouse effect and global warming.

Deforestation and logging which decrease the potential of carbon dioxide consumers, thus creating air pollution.

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Total: 10 marks

3 a. Hadley cells, Ferrel cells and Polar cells are circulation cells. These cells transport heat towards the poles. Thus, the excess heat from the tropics is redistributed in these cycles through the atmosphere

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b. Deeper water bodies are characterised by the presence of a warmer upper layer that is mixed by the wind and a colder deep layer that is not mixed. The two layers are separated by a distinctive temperature transition zone called the thermocline.

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c. Decreased solubility of oxygen at high temperature fish suffocating / dying. As temperature rises, biochemical reactions in certain

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organisms are affected and these may die immediately. As temperature rises, spawning, fertilisation and fertility of fish eggs is accelerated leading to food shortage.

d. Temperature inversion occurs when a layer of warmer air is trapped between two layers of colder air. The presence of hills, mountains or valleys prevent the horizontal movement of air. The flow of cold air from the hills / mountains into cities creates a cool lower layer. In the absence of wind, pollutants can collect over a city without being dispersed. So warm air on top stays over a mass of cool polluted air near the surface of earth. The mass of warm air acts as a lid trapping polluted air close to the ground.

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Total: 12 marks

4 a. Hazardous: waste that is dangerous or particularly harmful to our health and the environment.

Example (one from the following or suitable alternative): corrosive or flammable waste, radioactive waste, hospital waste, industrial waste.

Non-Hazardous: waste that is ‘inert’ or significantly less harmful to human health and the environment.

Example (one from the following or suitable alternative): food waste, packaging waste, construction waste, glass, plastics, insoluble solid waste.

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b. Biodegradable: plastic that can be broken down (digested) into harmless products by the action of water, light and microorganisms.

Example (one from the following or suitable alternative): plastic from cornstarch, biopolymers, biomass.

Non-Biodegradable: plastic that cannot decompose by microorganisms.

Example (one from the following or suitable alternative): polythene, polypropylene, polystyrene, PVC (i.e. petroleum based polymers).

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c. Greenhouse Gas: one which traps outgoing solar radiation that is reflected by the earth’s surface, leading to an increase in the average temperature of the earth (global warming).

Example (one from the following or suitable alternative): carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), water (H2O), sulfur hexafluoride (SF6).

Ozone-Depleting: gases that react and have an impact on the level of ozone in the stratosphere (ozone layer) which protects life on earth by absorbing harmful UV radiation. Example (one from the following or suitable alternative): CFCs, HCFCs, CCl4, halons (organohalogen compounds containing Br and F and one or two C atoms), bromomethane CH3Br.

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Total: 12 marks

5 a. Platinum or palladium or rhodium (accept ‘heavy metal’). 1

b. The catalyst speeds up chemical reactions which convert toxic pollutants to safe products.

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c. Any TWO from: nitrogen monoxide, nitrogen dioxide, nitrous oxide, carbon monoxide, unburned hydrocarbon CxHy

. 2

d. Any TWO from: nitrogen, carbon dioxide, water. 2

e. (i) nitrous acid or nitric acid. (Do not accept sulfurous or sulfuric acid.)

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(ii) 2CO + 2NO 2CO2 + N2 or

4CO + 2NO2 4CO2 + N2 or

CxHy + NO CO2 + H2O + N2

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Total: 12 marks

6 a. False. Species diversity is the number of species within a community/area or Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species.

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b. True. 1

c. False. An ectone is a transition area between two biomes. It is where two communities meet and integrate

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d. False. Intraspecific competition occurs between members of the same species

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e. True 1

Total: 8 marks

7 a. The change from high birth rates and high death rates to low birth rates and low death rates. Occurs when a country develops from a pre-industrial system to an industrialized and economic system.

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b. Line A: Death Rate

Line B: Birth Rate

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c. Birth rates were high: Family planning and contraception were virtually non-existent/ birth rates were limited only by the ability of women to bear children.

Death rates were high: famine, diseases, lack of clean water, poor health care and war.

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d. (Any one from the following. Accept any other relevant answer)

Urbanisation

Compulsory education increases the cost of children and increases the need to educate them to take up a respected position in society

Increasing female literacy and employment lowers the need of childbearing and motherhood as measures of the status of women.

Improvements in contraceptive techniques.

An increased age for the first marriage results in women having children at a later age.

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e. The death rate is lower than the birth rate.

Therefore there is still an overall increase in population.

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f. Countries have higher death rates than birth rates. 1

Total: 10 marks

8 a. Ecological niche is the role and position a species has in its

environment or

How a species meets its needs for food and shelter, how it survives,

reproduces and interacts with its surroundings.

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b. A fundamental niche is the largest range of environmental conditions

in which each of the species survives.

Ducks can inhabit Zones 1 and 2.

The realized niche is narrower range of environmental conditions

where a species actually lives following competition, predation and

limited resources.

Ducks eventually shift to Zone 1 when in competition with Avocets.

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c. Advantage: (Any one from the following)


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Specialist species typically experience less competition.

Specialist species have less niche overlap.

Disadvantage: (Any one from the following)

A specialist species can thrive only in a narrow range of

environmental conditions or has a limited diet.

They are more likely to suffer from habitat loss/ have higher risks

of extinction.

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Total: 9 marks

Section B

Qn No.

Suggested Answer Marks

1 a. All forms of farming have major impacts on biodiversity as existing habitats and ecological niches are destroyed, while new homogenized habitats and niches are created. (Any 3 from the following)

Monocropping replaces formerly diverse habitats with a single plant species and brings about the loss of native varieties of crop.

Clearing of land destroys habitats which tends to speed up the extinction of species living in those habitats. It also leads to habitat fragmentation, isolating organisms and makes it harder for them to find food and to mate.

Use of pesticides kills organisms indiscriminately. This disrupts ecosystems at various stages. Their impact is further increased when they end up in water courses through leaching.

Genetically modified crops may lead to gene contamination of non-GMOs. GMOs have features which provide them with “unfair” advantages over other species, thus interfering with niches and processes within the ecosystem.

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(2 marks per impact)

b. (i) Soil conservation techniques

Contour farming is the planting of crops in rows around a hill rather than up and down. This creates hundreds of ridges or dams that slow down water flow and increase infiltration thus reducing erosion.

Terracing involves the shaping of the land to create level steps (terraces) that hold soil and water. Locally rubble walls are used to prevent the loss of soil from terraced fields. Terracing makes it possible to farm steep hills.

Windbreakers protect fields from winds. They are created by planting strong wind resistant trees or prickly pears around field margins.

Multi-cropping (Polyculture) involves growing different crops together in the same space during the same season. This reduces erosion by maintaining fertility and increasing soil cover, since different plants have different nutritional requirements and are harvested at different times. This method also enhances biodiversity.

Alternation of land use involves crop rotation where different crops are grown one after the other. Crop rotation maintains soil fertility since different crops have different nutritional requirements. The use of legumes is very useful in crop rotation as legumes host

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(1 mark per technique; maximum 4

marks )


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nitrogen-fixing bacteria in their roots.

Reduced tillage is important since ploughing can cause soil erosion. This occurs as ploughing can degrade the structure of the soil making it easier for the upper layer of soil to become displaced through wind and rain.

(ii) Biological pest control

Repeated use of pesticides causes resistant pests. Exposure to pesticides is also harmful to humans.

Multi-cropping and crop rotation discourage the spread of pests and enable the use of less pesticides than mono-culture.

Encouraging natural predators such as lizards and birds by creating habitats for such predators – hedges, trees, rubble walls etc. can help control pests.

Biological pest control does away with the use of toxic chemicals and introducing natural pest controls such as wasps, ladybirds or pathogens (bacteria, viruses or fungi) that kill off pests in a safer way. If non-native biological controls are going to be introduced studies and risk assessments must be done. There are cases when an introduced species had serious impacts on the ecosystems and native species.

(iii) Reduction in the use of chemical fertilisers

Maintaining soil fertility using natural fertilizers rather than chemicals can reduce pollution.

Organic farming is a sustainable agricultural method of providing a variety of food. No chemical fertilizers are used, and soil fertility is maintained through the careful use of manure, compost and crop rotation.

Natural fertilizers improve soil structure, is cost effective and nutrients are delivered gradually due to slow breakdown.

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Total: 20 marks

2 a. Weather refers to the conditions of the atmosphere at any given place and time. This includes the short-term changes in temperature, pressure, humidity, cloud cover, wind direction and speed in the troposphere.

Climate is the average weather conditions, like general patterns of atmospheric conditions, seasonal variations and weather extremes in a region over a period of thirty years or more.

Malta’s climate: Malta has mild winters and warm to hot summers. Rain occurs mainly in winter, with summer being generally dry.

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b. The coastal zone is the relatively warm, nutrient rich, shallow water that extends from the high tide mark on land to the continental shelf. It contains 90% of all marine life and is the site of most commercial marine fisheries.

The open sea starts at the sharp increase in water depth at the edge of the continental shelf. It has 3 different regions: (i) Photic zone: where photosynthesis occurs; (ii) Bathyal zone: filtered sunlight penetrates up to 600m. It is inhabited by detritus feeding fish and invertebrates; and (iii) Abyssal zone: no light percolates and has near

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freezing temperatures and extremely high pressures. Most fish in this region have bioluminescent organs.

c. Perched aquifers can form due to the impermeable nature of the Blue Clay lying beneath a permeable layer of Upper Coralline Limestone. The Blue Clay layer acts as an aquiclude and thus water is stored within the fissures and fractures found within this zone.

The mean sea level aquifer has formed as the Lower Coralline Limestone is in lateral and vertical contact with sea water. Due to the differences in density between the fresh rainwater and the saline sea water, fresh water being much less dense than saline sea water, the former floats above in the shape of a lens that thins out at the coast

In Malta two different types of groundwater bodies form - the Perched Aquifers, are limited to the north-western extent of the island, and the Mean Sea Level Aquifer, is in the southern and central parts of Malta and western part of Gozo.

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d. Reverse osmosis is a filtration method that removes ions/ molecules/ salt from seawater by applying pressure / energy to the solution on one side of a semipermeable membrane thus providing pure water.

Water harvesting means capturing rain where it falls or capturing the run off. This also involves taking measures to keep that water clean by not allowing polluting activities to take place in the catchment. Thus, instead of runoff being left to cause soil erosion, it is harvested and utilized. In the semi-arid drought-prone areas where it is already practised, water harvesting is a directly productive form of soil and water conservation.

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Total: 20 marks

3 a. Ozone, O3, is an allotrope of ozone consisting of molecules made up of 3 atoms of oxygen.

X` is a product of photochemical reactions among substances produced by burning coal, petrol and other fuels, and other substances derived from solvents, paints and industrial chemicals and toilet preparations.

Stratospheric ozone occurs naturally (in part of the upper atmosphere) and shields the earth against harmful rays from the sun, particularly ultraviolet B radiation.

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b. Point source pollution results when the contaminants come from a single location e.g. release of gases in air by chimneys or the release of waste oil and other chemicals into a stream / river / sea / lake (i.e. water body).

Non-point source pollution results when contaminants are introduced (diffused) into the environment over a very large widespread area. Such source cannot be traced to a single point of origin e.g. emissions from cares and transport vehicles, burning of sulfur-containing fuels (resulting in acid rain), surface run-off, drainage, seepage, atmospheric deposition (resulting in pollution of water bodies).

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c. The greenhouse effect is the trapping of heat under the atmosphere resulting from the presence of greenhouse gases (e.g. CH4, CO2, CFCs, NOx, O3, H2O, etc.) which radiate sufficient heat energy to support life on earth.

The enhanced greenhouse effect occurs when excessive heat is trapped on earth as a result of the rapid increase in concentration of GHGs in the atmosphere. Increased emissions of GHGs is believed to

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cause global warming (increase in average temperature of the earth’s troposphere) and climate change (severe changes in weather patterns.)

d. Hydrocarbons are compounds containing only H and C atoms. They are emitted into the air by natural sources (e.g. trees) and by human intervention (e.g. combustion of fossil fuels, use of solvents, etc.). They are a major contributor to the formation of smog.

Chlorofluorocarbons, CFCs, are compounds containing the elements, Cl, F, and C, which were till recently used in great quantities by the industry (refrigeration, airconditioning, aerosols, etc). They are emitted in the atmosphere (greenhouse gases) and are involved in reactions leading to ozone depletion in the stratosphere.

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e. Industrial smog results from smoke particles from industrial plumes mixing with fog. It forms when smoke (fine particulate matter), soot, sulfur emissions mainly from coal burning, combine with fog (dispersed water droplets) under the right conditions such as the occurrence of a temperature inversion created during the day (which traps pollutants near the surface of the earth) leading to the formation of sulfuric acid. Such smog concentrations in urban areas but is now absent in developed countries due to installation of filters.

Photochemical smog results from burning of other fossil fuels such as petrol and diesel by motor vehicles and industry which release primary pollutants e.g. VOCs and NOx which react in the presence of UV light producing secondary pollutants such as ozone, PANs (peroxyacetylnitrates), aldehydes, ketones, peroxides and NO2. Such smog produces a brown haze due to the presence of the brown gas NO2 and is found in cities as well as areas exposed to lots of sunlight.

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Total: 20 marks

4. a. Diagram of a Sanitary Landfill

Basic features:

Consists of a large pit in the ground, with a thick lining of plastic covered by a compacted clay liner.

Bottom of pit is covered by a liner that helps preventing liquid waste (leachate) from leaking through, to prevent it from reaching groundwater and contaminating the water supply.

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Leachate (liquid waste) that is collected is pumped up to the surface for treatment.

Refuse is added to the landfill in the form of organised layers (alternating layers of waste with layers of soil) to eliminated any unpleasant odours and to speed up decomposition of organic matter.

Gas produced (mainly CH4) during anaerobic decomposition of waste, is collected, pumped up and used to generate electricity.

When landfill is completely full, it is further sealed by a layer of compacted clay and covered by plants and trees, only when land is considered safe for recreational use.

Improvements of Sanitary Landfill over Open Dump (Any two)

Organised way for disposal of waste.

Regulated by authorities.

Less hazardous to the environment.

Carefully monitored to prevent the release of unpleasant odours, pests and pollution.

Involves collection and treatment of leachate.

Gas collected is used to produce energy.

Makes better use of land.

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b. Basic principles of Incineration Incineration is a high temperature (thermal) treatment (temp 700 oC) process involving combustion of organic substances contained in solid waste. Waste storage and feed preparation. Combustion in a furnace producing hot gases and a bottom ash

residue for disposal. (The ash is mostly made up of inorganic constituents of waste and may take the form of solid lumps or particulates carried by flue gas.)

Heat generated by incineration can be used to generate electricity. This is called Incineration with Energy Recovery (which is one of the waste-to-energy technologies).

Treatment of the cooled gas to remove air pollutants and disposal of residuals.

Dispersion of the treated gas to the atmosphere through an induced draft fan and chimney stack.

Advantages of Incineration (Any two) Considerably reduced bulk of solid waste. Ash produced is of uniform composition. Incineration of plastics releases a lot of energy, which covers part of

the energy requirements to run the plant. Better waste management. Reduces space required by landfills (less dependence on landfills). Removal of harmful components (hazardous material) in solid

waste. Savings on transportation of waste. Groundwater remains uncontaminated (no leaks of toxic substances

to water sources).

Disadvantages of Incineration (Any two) Increased emissions of CO2 (greenhouse gas). Releases NOx to atmosphere contributing to photochemical smog

and acid rain. Releases also other harmful pollutants e.g. CO, HCl, HCN, heavy

metals, fly ash. High temperature would help in synthesizing highly toxic substances

(e.g. dioxins and dibenzofurans). High cost to install incineration plant and high running costs.

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Discourages efforts for recycling and waste reduction.

c. Benefits of Composting (Any three) Reduces space required for landfills: Composting diverts food and

organic waste from landfill and uses it to make nutrient rich soil. Creates rich soil: Composting creates soli that helps retain

nutrients, moisture and air; increases drought resistance (and reduces need to add water, fertilisers and pesticides).

Suppresses plant diseases and pests: Soil treated with compost produces plants with fewer pest problems as it provides nutrients and microflora to prevent disease.

Saves water: Compost can act as a natural evaporation barrier for gardens, helping soil to retain water and reducing the need for irrigation.

Saves money: By reducing the need to apply soil conditioners and fertilisers and by reducing the bulk of domestic and commercial waste to be collected and taken to the landfill or for other means of disposal.

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Total: 20 marks

5. a. Curve having the following characteristics

The exponential growth model states that population growth starts off slow and suddenly increases in an exponential form due to a high reproductive rate / birth rate exceeds death rate. For exponential growth, environmental resistance must be low. Many resources have to be available / the population has to have no limiting factors

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(1 mark for correct

labelling of axis)

(1 mark for proper line)

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b. (i) the Neolithic period: the Agricultural Revolution:

The cultivation of crops and the domestication of certain animals (sheep and goats) provided a more abundant and reliable food supply. or

People made stronger weapons and tools. Besides farmers, people could now engage on other tasks and defend their settlements.

(ii) the Industrial Period: Populations moved from country to urban centres/ technological and scientific developments and factory working. Wages rose / Economic prosperity/ More Marriages and birth rate explosion.

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c. Grazing (Any 3 from the following or any other valid reason)

Reduction of primary producer biomass, effects other organisms in the food chains and disrupts food webs.

The species composition of a plant community through herbivores selecting or avoiding specific plants provides selective grazing changing plant species composition.

The disturbances in plant species present opens up niches for invasion. Pulling plants from roots causing soil erosion – by wind and water.

Trampling compacts soils, which damages plant roots. These changes may prevent plants from acquiring sufficient resources for vigorous growth.

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Over-fishing (Any 3 from the following or any other valid reason)

Fish and other aquatic species are a finite resource in our oceans. Over-fishing means we face the threat of depleting the supply of edible sea creatures.

Overfishing, typically, leads to a decline in the population of productive fish, which results in lesser stocking of the fish.

Organisms caught at sea may include endangered or protected species.

Overfishing can have an adverse effect on marine biodiversity and completely disrupt the food chain.

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d. Conservation areas include Reserves or National Parks that face threats to their biodiversity and are internationally recognised by various national governments and the United Nations.

Legislative tools are the laws that these governing bodies issue to protect these areas of significance and instruct how lands should be set aside and managed.

(Any 3 from the following or any other valid reason)

Areas are free from land pollution which endangers communities.

With less disturbances/ more protection, the area is allowed to become a breeding ground for the specific biodiversity in that ecosystem.

Allows preservation and enhancement of the endangered area and its wildlife.

Permission even to visit or work in a conservation area ensures minimum disruption to the ecosystem.

Payment to visit such areas ensure an income which aids in the maintenance of the conservation area and its biodiversity.

Control over building in green areas ensures that area with endangered biodiversity is not exploited.

Reduced permitted development rights and stricter control systems and fines decrease vandalism in these areas and ensure that biodiversity is protected.

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Total: 8 marks

6 a. Resilience is the capacity of an ecosystem to maintain its fundamental structure, processes and functioning when subjected to stress, disturbance or invaders.

Resistance refers to the biotic and abiotic factors and ecological processes in an ecosystem that resist and limit the population growth of an invading species.

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b. Allogenic succession is succession driven by the abiotic components of an ecosystem. Abiotic components include temperature, water, rock formation, etc.

Autogenic succession is driven by the biotic components of the ecosystem. The biotic components include predators, disease causing organisms, parasites etc.

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c. (Main points to be included or any other valid reason)

Grazer food chain: Energy for this food chain starts with the sun. Grazer food chains start with green plants which are producers.

These are grazed upon by herbivores.

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Herbivores are eaten by carnivores.

This food chain fixes inorganic nutrients.

Adds energy to the ecosystem.

Correct Example provided

Decomposer food chain: starts with dead organic matter.

Energy comes from these remains

Energy is eventually lost (mostly as heat).

Dead organic matter is decomposed by sub-soil organisms: detrivores and decomposers.

This food chain helps in fixing inorganic nutrients

Correct Example provided

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Total: 20 marks

environmental science - draft paper may 2000 · harvested at different times. this method also...

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