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GCSE · Biology

B7b Biodiversity, Cycles and Human Impact

AQA 8464 · Calculator allowed · about 110 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Biodiversity Under Pressure

Original text written for Revision Library.

Biodiversity, the variety of species and the genes within them found in an ecosystem, both depends on and helps to maintain stable natural cycles such as the carbon and water cycles. As the human population grows and standards of living rise, increasing amounts of land are used for building, farming, quarrying and waste disposal, leaving less space for other organisms. One example is the loss of peat bogs: these waterlogged habitats take thousands of years to form, store large amounts of carbon, and support specialised plants and animals, yet many have been drained and dug up so the peat can be sold as garden compost. Similar pressures, including large-scale deforestation, pollution of land, air and water, and the effects of global warming, are reducing biodiversity in ecosystems around the world. Conservation organisations use a range of strategies, from captive breeding programmes to the protection and restoration of habitats, to try to maintain and increase biodiversity. This worksheet covers the carbon and water cycles, the effects of waste, land use, deforestation and global warming on biodiversity, the required practical investigating the effect of temperature on the rate of decomposition, and strategies used to conserve biodiversity.

Biodiversity describes the range of living things found on Earth or within an ecosystem.

(a)Define the term 'biodiversity'.(1)

(b)Give two reasons why maintaining a high level of biodiversity is important.(2)

(Total for Question 1 is 3 marks)

An increasing human population, and a rising standard of living, mean that more resources are used and more waste is produced.

(a)Explain why an increasing human population and a rising standard of living have led to an increase in the amount of household, industrial and agricultural waste produced.(2)

(b)Explain how waste materials can reduce biodiversity if they are not handled correctly.(3)

(Total for Question 2 is 5 marks)

Land is a limited resource, and how it is used affects the organisms that can live on it.

(a)State three ways in which land is used by humans that can reduce the amount of land available for other organisms.(3)

(b)Using the information above about peat bogs, give one reason why draining and digging up peat bogs for use in garden compost reduces biodiversity.(1)

(Total for Question 3 is 4 marks)

Using the information above, a peat bog originally covered an area of 850 hectares. Over the last 10 years, 289 hectares of the bog have been drained and dug up for use in garden compost.

(a)Calculate the percentage of the peat bog that has been lost over the last 10 years.(2)

(b)The area lost continues to fall at the same percentage rate (of whatever area remains) for a further 10 years. Calculate the area of peat bog, in hectares, that would remain after this further 10 years. Give your answer to the nearest hectare.(3)

(Total for Question 4 is 5 marks)

Carbon is constantly cycled between the atmosphere, living organisms and the environment.

Figure (to be drawn): A simplified carbon cycle diagram with four labelled boxes: 'Atmosphere (carbon dioxide)', 'Green plants and algae', 'Animals', and 'Dead organisms and waste material'. Arrow X runs from 'Atmosphere (carbon dioxide)' to 'Green plants and algae'. Arrow Y runs from 'Green plants and algae' back to 'Atmosphere (carbon dioxide)'. Further unlabelled arrows connect 'Green plants and algae' to 'Animals' (feeding), 'Green plants and algae' and 'Animals' both to 'Dead organisms and waste material' (death), and 'Dead organisms and waste material' back to 'Atmosphere (carbon dioxide)' (decomposition).

(a)In a simplified carbon cycle diagram, arrow X points from 'Atmosphere (carbon dioxide)' to 'Green plants and algae', and arrow Y points from 'Green plants and algae' back to 'Atmosphere (carbon dioxide)'. Name the processes represented by arrow X and arrow Y.(2)

(b)Write the balanced symbol equation for photosynthesis, including state symbols.(2)

(c)Explain how decomposition of dead organisms and waste material returns carbon to the atmosphere.(2)

(Total for Question 5 is 6 marks)

The water cycle provides a continuous supply of fresh water to ecosystems.

(a)Describe the processes of evaporation and condensation in the water cycle, and how they lead to precipitation (rain).(3)

(b)Explain why the water cycle is important for the survival of plants and animals in an ecosystem.(1)

(c)Higher Tier only. One method of producing fresh water in areas with limited rainfall is desalination of seawater. Suggest one reason why desalination is not widely used to provide fresh water on a large scale.(1)

(Total for Question 6 is 5 marks)

Large areas of tropical rainforest are cleared each year, a process called deforestation.

(a)Give two reasons why large-scale deforestation takes place in tropical regions.(2)

(b)Explain two ways in which deforestation contributes to an increase in atmospheric carbon dioxide concentration.(2)

(c)Explain why deforestation can lead to a reduction in biodiversity in the affected region.(2)

(Total for Question 7 is 6 marks)

An area of tropical rainforest covered 4200000 hectares in 2005. By 2025, the area of rainforest remaining had reduced to 3150000 hectares.

(a)Calculate the percentage decrease in forest area between 2005 and 2025.(3)

(b)Calculate the mean rate of forest loss, in hectares per year, over this 20-year period.(2)

(Total for Question 8 is 5 marks)

Human activities have increased the concentration of greenhouse gases, such as carbon dioxide and methane, in the atmosphere. The table below shows the mean global temperature anomaly (the difference from a long-term average) recorded in a simplified dataset used for this question.

Decade	Temperature anomaly (degrees C)
1980s	0.18
1990s	0.32
2000s	0.52
2010s	0.82

(a)Describe the trend shown by the data in the table.(1)

(b)Calculate the mean rate of increase in temperature anomaly per decade between the 1980s and the 2010s. Give your answer to 2 decimal places.(3)

(c)Describe two biological consequences of continued global warming for ecosystems. Use a named example to support each one.(3)

(Total for Question 9 is 7 marks)

Required practical: a student investigated the effect of temperature on the rate of decomposition, using lipase enzyme to model the breakdown of a lipid. Full-fat milk powder solution (a source of lipid), sodium carbonate solution (an alkali) and a few drops of phenolphthalein indicator (pink in alkaline conditions) were mixed in a test tube. The tube was placed in a water bath at a chosen temperature. Lipase solution was then added, the tube was mixed, and a stop clock was started immediately. As the lipase broke down the lipid into fatty acids, the pH inside the tube fell, and the indicator changed from pink to colourless. The time taken for this colour change was recorded. This was repeated three times at each of five temperatures, keeping the volumes and concentrations of milk powder solution, sodium carbonate solution, indicator and lipase the same each time.
The results are shown in the table below.

Temperature (degrees C)	Repeat 1 (s)	Repeat 2 (s)	Repeat 3 (s)	Mean time (s)
20	330	327	336	331
30	180	174	183	179
40	93	90	87	(to be calculated)
50	128	205	132	(to be calculated)
60	240	249	246	245

Rate of reaction can be calculated using: rate = 1000 / mean time (arbitrary units).

(a)State the independent variable in this investigation.(1)

(b)State one variable that must be controlled in this investigation. Explain why it must be controlled, and what would happen to the validity of the results if it were not.(3)

(c)Calculate the rate of reaction at 40 degrees C, using the mean time from the table. Give your answer to 3 significant figures.(2)

(d)Identify the anomalous result in the table and suggest one possible cause for it.(2)

(e)Describe the pattern shown by the rate of reaction as temperature increases from 20 to 60 degrees C, and explain this pattern in terms of enzyme action.(4)

(f)Evaluate the method used to determine when the colour change had occurred, and suggest one improvement that would make the results more precise.(3)

(g)Explain why this experiment can be used as a model for the process of decomposition, and suggest one way in which it differs from decomposition occurring naturally in the environment.(3)

(Total for Question 10 is 18 marks)

Conservation organisations use a range of methods to try to maintain and increase biodiversity.

(a)State two methods used to help maintain biodiversity.(2)

(b)Choose one method from part (a) and explain how it helps to increase biodiversity.(2)

(Total for Question 11 is 4 marks)

Fertiliser and sewage that enter rivers and lakes can pollute the water and harm aquatic organisms.

(a)Name two substances that can be washed from farmland into rivers and lakes, causing water pollution.(2)

(b)Describe how excess fertiliser entering a lake can lead to the death of fish and other aquatic organisms.(4)

(Total for Question 12 is 6 marks)

Plastic waste that enters rivers and oceans can cause serious harm to wildlife.

(a)Describe two ways in which plastic waste entering rivers and oceans can harm wildlife.(2)

(b)Microplastics (tiny plastic fragments) are increasingly detected in marine food chains. Explain how microplastics could become more concentrated in organisms at higher trophic levels.(3)

(Total for Question 13 is 5 marks)

A conservation charity is working in an upland region of the UK where large areas of native woodland were cleared over the last century for sheep farming. The charity has introduced three measures: a captive breeding and release programme for red squirrels, the planting of new native broadleaf woodland on former grazing land, and the creation of unplanted buffer strips along the rivers that run through the farmland.
Evaluate how effective these three measures are likely to be in maintaining and increasing biodiversity in this region.

(Total for Question 14 is 6 marks)

A national park covers an area of 3.6 x 10⁵ hectares. (1 hectare = 0.01 km², i.e. 100 hectares = 1 km^2.)

(a)Calculate the area of the national park in km^2. Give your answer in standard form.(3)

(b)A survey estimates that 15% of the park's area has been converted to farmland since 1990. Calculate the area, in hectares, that has been converted.(2)

(Total for Question 15 is 5 marks)

A population of an endangered woodland bird was estimated at 2400 breeding pairs in 2005. By 2025, numbers had fallen to 1560 breeding pairs due to habitat loss.

(a)Calculate the percentage decrease in the number of breeding pairs between 2005 and 2025.(2)

(b)A conservation programme aims to increase the population back to 70% of its 2005 level within 10 years. Calculate the target number of breeding pairs.(2)

(Total for Question 16 is 4 marks)

Higher Tier only. Desalination is the process of removing dissolved salts from seawater to produce fresh water.

(a)Name one method that can be used to desalinate seawater.(1)

(b)Explain why desalination is not yet used as the main source of fresh water in most countries, even though seawater is widely available.(3)

(Total for Question 17 is 4 marks)

Governments and individuals can take action to reduce the negative effects of waste on biodiversity.

(a)Explain how increasing the proportion of household waste that is recycled, rather than sent to landfill, could help to maintain biodiversity.(3)

(b)Government policy can also encourage biodiversity by paying farmers to leave unplanted strips of land at the edges of their fields (field margins). Suggest how this policy could increase biodiversity on farmland.(2)

(Total for Question 18 is 5 marks)

Carbon dioxide and methane released by respiration, decomposition and combustion are part of the carbon cycle.

(a)The equation below shows aerobic respiration but is not balanced. Balance the equation and add the correct state symbols.
C6H12O6 + O2 -> CO2 + H2O(2)

(b)Methane gas produced by decomposing organic waste in landfill sites is sometimes collected and burned rather than being released directly into the atmosphere. The equation below shows the combustion of methane but is not balanced. Balance the equation and add the correct state symbols.
CH4 + O2 -> CO2 + H2O(2)

(c)Using the equations above, explain why both the natural decomposition of waste in landfill sites and the combustion of fossil fuels contribute to rising atmospheric carbon dioxide concentrations.(2)

(Total for Question 19 is 6 marks)

The table below shows simplified data collected over 20 years in a fictional tropical region called Karinda, used to model the relationship between forest loss, atmospheric carbon dioxide concentration and biodiversity.

Year	Forest cover remaining (%)	Atmospheric CO2 concentration (ppm)	Biodiversity index (arbitrary units, higher = more biodiverse)
2000	78	370	8.2
2010	61	390	6.5
2020	44	412	4.9

(a)Describe the relationship shown between forest cover and the biodiversity index over the period 2000 to 2020.(2)

(b)A student claims that this data proves that the loss of forest cover directly causes the fall in the biodiversity index. Evaluate this claim.(3)

(c)Suggest one reason why increasing atmospheric carbon dioxide concentration could contribute to further loss of biodiversity in this region.(2)

(Total for Question 20 is 7 marks)

Mark scheme · B7b Biodiversity, Cycles and Human Impact

Question 1

(a) B1 the variety of different species (and the genetic variation within those species) living in an area/ecosystem (oe)
(a) Answer: The variety of different species, and the genetic variation within them, living in an area or ecosystem.
(b) B1 a high biodiversity helps to keep ecosystems stable, since many different species (rather than just one) carry out important processes such as food production, decomposition and the recycling of nutrients (oe)
(b) B1 a wide range of species provides a large gene pool, which could be a source of new medicines, food crops or other resources in the future (oe)
(b) Answer: A high biodiversity keeps ecosystems stable, since important processes such as decomposition and nutrient recycling do not depend on just one species, and it provides a wide gene pool that could be a source of new medicines, food crops or other resources in the future.

Question 2

(a) B1 more people means more products (e.g. food, packaging, goods) are made and consumed, using more resources and producing more waste (oe)
(a) B1 a rising standard of living means people buy and use more goods (e.g. electronics, packaging), which also increases the amount of waste produced (oe)
(a) Answer: More people consuming more products means more resources are used and more waste is produced, and a rising standard of living means people buy and use even more goods, further increasing the amount of waste generated.
(b) B1 if waste is not disposed of correctly (e.g. sent to unmanaged landfill), it can pollute land, water or air (oe)
(b) B1 for example, chemicals from landfill sites can leach into the soil and groundwater, or waste gases can pollute the atmosphere (oe)
(b) B1 this pollution can kill organisms directly, or damage the habitats and food sources they depend on, reducing the number and variety of species that can survive in the affected area
(b) Answer: If waste is not disposed of correctly it can pollute land, water and air, for example by chemicals leaching from landfill into soil and groundwater; this pollution can kill organisms directly, or damage the habitats and food sources they rely on, reducing the number and variety of species able to survive there.

Question 3

(a) B1 building (housing, roads or other construction)
(a) B1 quarrying (extracting stone or minerals)
(a) B1 farming (growing crops or grazing livestock) or dumping/landfill of waste (accept either)
(a) Answer: Any three of: building (housing and roads), quarrying, farming (crops or livestock), and dumping or landfill of waste.
(b) B1 draining/removing the peat destroys the waterlogged habitat that many specialised plants and animals depend on, so those species lose their habitat and can no longer survive there (oe)
(b) Answer: It destroys the waterlogged peat bog habitat that many specialised plants and animals depend on, so those species lose their habitat and are lost from the area.

Question 4

(a) M1 (289 / 850) x 100
(a) A1 34% cao
(a) Answer: 34%.
(b) M1 area remaining after year 10 = 850 - 289 = 561 hectares
(b) M1 loss over the next 10 years = candidate's percentage from part (a) applied to 561, e.g. 0.34 x 561 (= 190.74); allow ecf from part (a)
(b) A1 370 hectares (awrt 370), allow ecf from part (a)
(b) Answer: Approximately 370 hectares.

Question 5

(a) B1 X: photosynthesis
(a) B1 Y: respiration
(a) Answer: X is photosynthesis; Y is respiration.
(b) M1 correct formulae: CO2, H2O, C6H12O6, O2, with correct balancing numbers (6CO2 + 6H2O -> C6H12O6 + 6O2)
(b) A1 all correct state symbols included: 6CO2(g) + 6H2O(l) -> C6H12O6(aq) + 6O2(g) (light energy required)
(b) Answer: 6CO2(g) + 6H2O(l) -> C6H12O6(aq) + 6O2(g), using light energy.
(c) B1 decomposers (bacteria and fungi) break down/digest the complex carbon compounds in dead organisms and waste material (oe)
(c) B1 the decomposers respire (aerobically) as they do this, releasing carbon dioxide into the atmosphere as a waste product
(c) Answer: Decomposers such as bacteria and fungi break down the carbon compounds in dead organisms and waste material, and release carbon dioxide into the atmosphere as they respire.

Question 6

(a) B1 energy from the Sun causes water to evaporate from oceans, lakes and rivers, turning liquid water into water vapour
(a) B1 the water vapour rises and cools, condensing into tiny droplets of water that form clouds
(a) B1 the water droplets in clouds combine/grow until they are heavy enough to fall as precipitation (rain, sleet or snow)
(a) Answer: Energy from the Sun evaporates water from oceans, lakes and rivers into water vapour; this vapour rises, cools and condenses into tiny droplets that form clouds, and these droplets combine until they are heavy enough to fall as precipitation.
(b) B1 it provides a continuous/renewable supply of fresh water that organisms need for essential processes such as drinking, photosynthesis or transporting substances (oe)
(b) Answer: It provides a continuous, renewable supply of fresh water that plants and animals need for essential processes such as drinking, photosynthesis and transporting substances around their bodies.
(c) B1 it requires a large amount of energy (e.g. to evaporate/distil water, or to generate the pressure needed for reverse osmosis), which makes it very expensive to carry out on a large scale (oe)
(c) Answer: Desalination requires a large amount of energy, which makes it expensive to carry out on a large scale.

Question 7

(a) B1 to clear land for cattle grazing or growing crops (e.g. rice), to meet the increasing global demand for food (oe)
(a) B1 to grow crops that are used to produce biofuels (oe)
(a) Answer: To clear land for cattle grazing or growing food crops such as rice, to meet increasing global demand for food, and to grow crops used to produce biofuels.
(b) B1 fewer trees means less photosynthesis, so less carbon dioxide is removed from the atmosphere (oe)
(b) B1 burning the cleared trees releases the carbon stored in the wood directly into the atmosphere as carbon dioxide (oe)
(b) Answer: There are fewer trees to remove carbon dioxide from the atmosphere by photosynthesis, and burning the cleared trees releases the carbon they had stored directly into the atmosphere as carbon dioxide.
(c) B1 deforestation destroys habitats that many species depend on for shelter, food or breeding sites, so organisms may die or be forced to migrate (oe)
(c) B1 species with a very narrow niche may become extinct if their only habitat is destroyed, reducing the variety of species (and genes) in the area (oe)
(c) Answer: Deforestation destroys habitats that many species rely on for shelter, food and breeding, forcing organisms to migrate or die; species with a narrow niche may become extinct if their only habitat is destroyed, reducing the variety of species in the region.

Question 8

(a) M1 decrease = 4200000 - 3150000 (= 1050000)
(a) M1 (1050000 / 4200000) x 100
(a) A1 25% cao
(a) Answer: 25%.
(b) M1 1050000 / 20
(b) A1 52500 hectares per year cao
(b) Answer: 52500 hectares per year.

Question 9

(a) B1 the mean global temperature anomaly has increased every decade from the 1980s to the 2010s (oe)
(a) Answer: The mean global temperature anomaly has risen in every decade shown, from 0.18 degrees C in the 1980s to 0.82 degrees C in the 2010s.
(b) M1 total increase = 0.82 - 0.18 (= 0.64)
(b) M1 0.64 / 3 (three decade-intervals between the 1980s and the 2010s)
(b) A1 0.21 degrees C per decade, awrt
(b) Answer: Approximately 0.21 degrees C per decade.
(c) B1 rising sea levels can destroy low-lying coastal habitats, e.g. mangrove swamps or salt marshes, reducing the area of habitat available for the species that depend on them
(c) B1 changes in the timing of migration or breeding, e.g. some migratory birds such as swallows arriving in the UK earlier in spring as temperatures rise, which can create a mismatch with the timing of their food supply
(c) B1 changes in the distribution of species, e.g. some UK butterfly species extending their range further north as average temperatures increase
(c) Answer: Any two of: rising sea levels destroying low-lying coastal habitats such as mangrove swamps, changes in migration timing such as swallows arriving earlier in spring (which can mismatch with food availability), and changes in species distribution such as some UK butterflies extending their range further north.

Question 10

(a) B1 temperature (of the water bath)
(a) Answer: Temperature.
(b) B1 any one suitable control variable, e.g. the volume/concentration of milk powder solution, sodium carbonate solution, indicator, or lipase used
(b) B1 controlling it ensures that temperature is the only variable that could affect the rate of reaction between the tubes (oe)
(b) B1 if it were not controlled, any difference in the time taken could be caused by this other variable rather than by temperature, so it would not be a valid (fair) test and no valid conclusion about the effect of temperature could be drawn
(b) Answer: The volume and concentration of lipase solution added (or an equivalent variable such as the milk powder solution, sodium carbonate solution or indicator) must be kept the same in every tube, so that temperature is the only variable that could affect the rate; if it were not controlled, any difference in results could be due to this other variable rather than temperature, making the test invalid.
(c) M1 mean time at 40 C = (93+90+87)/3 = 90 s; rate = 1000/90
(c) A1 11.1 (arbitrary units), awrt
(c) Answer: 11.1 (arbitrary units).
(d) B1 the repeat 2 reading of 205 s at 50 degrees C is anomalous, as it does not fit the pattern of the other two repeats at that temperature (128 s and 132 s)
(d) B1 any suitable cause, e.g. the tube may not have reached the stated temperature before timing started, there may have been a delay in adding the lipase or starting the stop clock, or the student may have misjudged the colour change end point
(d) Answer: The 205 s reading (repeat 2 at 50 degrees C) is anomalous, since it is much higher than the other two repeats (128 s and 132 s) at that temperature; a possible cause is a delay in adding the lipase or starting the stop clock, or the tube not having reached 50 degrees C before timing began.
(e) B1 the rate of reaction increases as temperature rises from 20 to 40 degrees C
(e) B1 the rate then decreases as temperature rises further, to 50 and 60 degrees C
(e) B1 up to 40 degrees C, increasing temperature gives the enzyme and substrate more kinetic energy, increasing the frequency of successful collisions between the enzyme's active site and the substrate, so more enzyme-substrate complexes form per second
(e) B1 above the optimum temperature (40 degrees C), the enzyme begins to denature: the shape of its active site changes so it is no longer complementary to the substrate, so fewer enzyme-substrate complexes can form and the rate decreases
(e) Answer: The rate of reaction rises as temperature increases from 20 to 40 degrees C, because more kinetic energy leads to more frequent successful collisions between the enzyme's active site and its substrate; above 40 degrees C the rate falls, because the enzyme starts to denature, changing the shape of its active site so it no longer fits the substrate as well.
(f) B1 judging by eye exactly when the solution becomes colourless is subjective, so different people (or the same person on different occasions) could record slightly different times, reducing precision (oe)
(f) B1 a colorimeter could be used to measure the light transmission/absorbance of the solution at set time intervals, giving an objective, quantitative measurement of the colour change
(f) B1 this would allow a more precise determination of the exact point at which the colour changes, improving the precision/reliability of the calculated rate
(f) Answer: Judging the colour change by eye is subjective and can vary between observers, reducing precision; using a colorimeter to measure light transmission or absorbance at set time intervals would give an objective, quantitative measurement of the colour change, improving the precision of the results.
(g) B1 the lipase breaking down lipid into fatty acids represents the type of chemical breakdown carried out by decomposer microorganisms during natural decomposition (oe)
(g) B1 the pH/colour change models the production of acidic products as complex organic matter is broken down
(g) B1 however, this experiment uses only one enzyme, one substrate and one controlled temperature at a time, whereas natural decomposition involves many species of decomposer microorganisms and enzymes acting on a range of substrates (proteins, carbohydrates and lipids) under conditions (temperature, moisture, oxygen) that are not controlled
(g) Answer: The breakdown of lipid by lipase, and the resulting pH change, models the type of chemical breakdown and acidic products produced during natural decomposition; however, the experiment uses only one enzyme and substrate at a controlled temperature, whereas natural decomposition involves many species of decomposer microorganisms acting on a range of substrates under uncontrolled environmental conditions.

Question 11

(a) B1 any one of: breeding programmes for endangered species; protection and regeneration of rare habitats; reducing deforestation and monoculture farming; reintroducing hedgerows/field margins; creating buffer zones around rivers, lakes and wetlands
(a) B1 a second, different method from the list above
(a) Answer: Any two of: breeding programmes for endangered species, protection and regeneration of rare habitats, reducing deforestation and monoculture farming, reintroducing hedgerows and field margins, and creating buffer zones around rivers, lakes and wetlands.
(b) B1 correct identification of a method given in part (a)
(b) B1 a valid explanation linked to that method, e.g. buffer zones reduce fertiliser and pesticide runoff into rivers, protecting aquatic and bankside species; or hedgerows provide habitat and food for insects, birds and small mammals that would otherwise be lost from intensively farmed land
(b) Answer: For example, creating buffer zones (unplanted strips) along rivers reduces the amount of fertiliser and pesticide runoff entering the water, protecting aquatic and bankside species and helping to maintain a wider range of organisms in that habitat.

Question 12

(a) B1 fertiliser (containing nitrates and/or phosphates)
(a) B1 sewage or animal slurry (accept pesticide)
(a) Answer: Fertiliser (containing nitrates and phosphates) and sewage or animal slurry (pesticide is also accepted).
(b) B1 fertiliser increases the concentration of nutrients (e.g. nitrate) in the water
(b) B1 this causes algae and other aquatic plants near the surface to grow rapidly (an algal bloom), which blocks light from reaching plants below the surface, so they cannot photosynthesise and die
(b) B1 decomposer microorganisms break down the dead plant/algal material; their population increases and they use up dissolved oxygen in the water through respiration
(b) B1 oxygen levels fall too low for fish and other aquatic animals to survive, so they die
(b) Answer: Excess fertiliser raises nutrient levels in the water, causing an algal bloom that blocks light from reaching plants below the surface, which die and are broken down by decomposers; the rapidly increasing decomposer population uses up dissolved oxygen through respiration, and oxygen levels fall too low for fish and other aquatic animals to survive.

Question 13

(a) B1 animals may mistake plastic for food and eat it, which can cause blockages, starvation or injury (oe)
(a) B1 animals may become entangled in plastic debris, causing injury, restricted movement, or drowning (oe)
(a) Answer: Animals may mistake plastic for food and eat it, causing blockages or starvation, or they may become entangled in plastic debris, causing injury or drowning.
(b) B1 microplastics ingested by small organisms (e.g. plankton) are not broken down or excreted, so they build up in the organism's body (oe)
(b) B1 when a predator eats many of these prey organisms, the plastic from all of them accumulates in the predator's body
(b) B1 this process repeats up the food chain, so organisms at higher trophic levels (e.g. large fish or seabirds) can build up much higher concentrations of microplastics than organisms lower down the chain
(b) Answer: Microplastics eaten by small organisms such as plankton are not broken down or excreted, so they accumulate in the body; when predators eat many of these prey organisms, the plastic builds up further, and this repeats up the food chain so that organisms at higher trophic levels can accumulate much higher concentrations than those lower down.

Question 14

Level 1 (1-2): Basic statements are made about the measures, with limited or no linkage to biodiversity. The answer may only describe the measures rather than evaluate them, and shows little or no logical structure.
Level 2 (3-4): A clear explanation is given of how at least two of the measures could increase biodiversity, with some judgement about their effectiveness. The discussion may be one-sided or lack detail on limitations. The answer shows some structure.
Level 3 (5-6): A detailed and logically structured evaluation of all three measures is given, explaining how each could increase biodiversity and discussing relevant limitations (e.g. cost, timescale, genetic diversity, land use conflict), leading to a supported overall judgement.
Indicative content:
- Captive breeding and release programme: can increase the population size and help preserve the genetic diversity of red squirrels, a declining native species.
- Limitation: captive-bred populations may have low genetic diversity if founded from few individuals, and reintroduced animals may still be at risk from competition with grey squirrels or disease (e.g. squirrelpox) unless grey squirrel numbers are also controlled.
- New native woodland planting: provides new habitat and food sources for woodland species (plants, insects, birds, mammals), increasing the area and connectivity of habitat over time.
- Limitation: newly planted woodland can take many years or decades to mature into a habitat that supports the full range of species found in ancient woodland, so benefits to biodiversity will be gradual rather than immediate.
- River buffer strips: reduce the amount of fertiliser, pesticide and soil runoff entering the river, improving water quality and helping to protect aquatic and bankside species (e.g. invertebrates, fish, water voles); the strips also provide habitat and movement corridors for other wildlife.
- Limitation: buffer strips only protect a narrow area, take land out of agricultural use, and may face resistance from farmers who lose grazing or growing land.
- Overall judgement: using several complementary measures together is likely to be more effective at increasing biodiversity than relying on any single measure alone, but success depends on long-term maintenance, funding and cooperation from local landowners.

Question 15

(a) M1 3.6 x 10⁵ x 0.01
(a) M1 = 3.6 x 10³ (km²), correct manipulation of the power of ten
(a) A1 3.6 x 10³ km² (3600 km²) cao
(a) Answer: 3.6 x 10³ km² (3600 km²).
(b) M1 0.15 x 360000
(b) A1 54000 hectares cao
(b) Answer: 54000 hectares.

Question 16

(a) M1 decrease = 2400 - 1560 (= 840); (840/2400) x 100
(a) A1 35% cao
(a) Answer: 35%.
(b) M1 0.7 x 2400
(b) A1 1680 breeding pairs cao
(b) Answer: 1680 breeding pairs.

Question 17

(a) B1 distillation (evaporation and condensation) or reverse osmosis (forcing water through a partially permeable membrane under pressure)
(a) Answer: Distillation, or reverse osmosis.
(b) B1 desalination requires large amounts of energy, e.g. to evaporate water in distillation or to generate the high pressure needed for reverse osmosis, making it expensive to carry out on a large scale (oe)
(b) B1 if the energy used comes from burning fossil fuels, this also increases carbon dioxide emissions, contributing further to global warming (oe)
(b) B1 the plants and infrastructure needed are costly to build and maintain, and are usually only practical in coastal areas (oe)
(b) Answer: Desalination requires large amounts of energy for distillation or reverse osmosis, making it expensive; if that energy comes from fossil fuels it also increases carbon dioxide emissions, and the plants and infrastructure needed are costly to build and are usually only practical near the coast.

Question 18

(a) B1 recycling reduces the amount of raw material (e.g. wood, metal ore, crude oil) that needs to be extracted from the environment, so less land needs to be cleared or mined, protecting habitats (oe)
(a) B1 recycling reduces the amount of waste sent to landfill, so less land is needed for landfill sites (oe)
(a) B1 less landfill also reduces the risk of pollutants leaching into soil or water and harming organisms (oe)
(a) Answer: Recycling reduces the amount of raw material that needs to be extracted from the environment, so less land is cleared or mined; it also reduces the amount of waste sent to landfill, meaning less land is needed for landfill sites and less risk of pollutants leaching out and harming organisms.
(b) B1 unplanted field margins can provide habitat, food or shelter for species (e.g. wildflowers, insects, small mammals, birds) that would not be present in intensively farmed (monoculture) land (oe)
(b) B1 field margins can act as corridors connecting isolated habitats, allowing species to move between areas (oe)
(b) Answer: Unplanted field margins provide habitat, food and shelter for species such as wildflowers, insects, small mammals and birds that would not survive in intensively farmed land, and can act as corridors connecting isolated habitats, allowing species to move between them.

Question 19

(a) M1 correct balancing numbers: C6H12O6 + 6O2 -> 6CO2 + 6H2O
(a) A1 all correct state symbols added: C6H12O6(aq) + 6O2(g) -> 6CO2(g) + 6H2O(l)
(a) Answer: C6H12O6(aq) + 6O2(g) -> 6CO2(g) + 6H2O(l).
(b) M1 correct balancing numbers: CH4 + 2O2 -> CO2 + 2H2O
(b) A1 all correct state symbols added: CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)
(b) Answer: CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g).
(c) B1 both processes release carbon dioxide (decomposition also releases methane, another greenhouse gas) directly into the atmosphere (oe)
(c) B1 because these processes occur on a very large scale worldwide, releasing carbon that would otherwise stay locked away (in fossil fuels) or only be released slowly, they add carbon dioxide faster than it can be removed by processes such as photosynthesis, increasing the overall atmospheric concentration
(c) Answer: Both processes release carbon dioxide (and decomposition also releases methane) directly into the atmosphere; because they happen on a very large scale worldwide, they add carbon dioxide faster than photosynthesis and other processes can remove it, so the overall atmospheric concentration rises.

Question 20

(a) B1 as forest cover decreased (from 78% to 44%), the biodiversity index also decreased (from 8.2 to 4.9), using values from the table
(a) B1 the two variables show a positive correlation: as one decreases, so does the other (oe)
(a) Answer: As forest cover fell from 78% to 44% between 2000 and 2020, the biodiversity index also fell, from 8.2 to 4.9; the two variables show a positive correlation, decreasing together over the period.
(b) B1 the data show a correlation (both variables change together), but this does not necessarily mean that forest loss directly causes the fall in biodiversity (oe)
(b) B1 other factors occurring over the same period could also contribute to the fall in biodiversity, e.g. hunting, disease, or the rising carbon dioxide concentration itself affecting the local climate (oe)
(b) B1 however, there are known biological mechanisms linking forest loss directly to biodiversity loss (e.g. loss of habitat and food sources for species that depend on the forest), so a causal link is plausible and consistent with the data, even though correlation alone cannot prove it (oe)
(b) Answer: The data show a correlation between falling forest cover and falling biodiversity, but correlation alone does not prove causation; other factors occurring over the same period, such as hunting or the rising carbon dioxide concentration itself, could also be involved. However, since habitat loss is a well-understood mechanism linking deforestation to biodiversity loss, a causal link is plausible and consistent with the data.
(c) B1 rising carbon dioxide is linked to global warming, which can alter local temperature and rainfall patterns (oe)
(c) B1 if conditions shift beyond the range resident species can tolerate faster than they can adapt or migrate, this can cause further population decline or local extinction, e.g. more frequent drought stressing the remaining forest, making it more vulnerable to fire and further reducing habitat (oe)
(c) Answer: Rising carbon dioxide is linked to global warming, which can change local temperature and rainfall patterns; if conditions shift faster than species can tolerate, adapt to or migrate from, this can cause further population decline, for example through more frequent drought increasing the risk of fire and further reducing the remaining forest habitat.

Biodiversity, Cycles and Human Impact - Worksheets, Questions and Revision