▶️ Answer/Explanation
(a)
(i)
Pangolins are heterotrophic because they feed on other organisms (such as ants and termites) and do not photosynthesize or produce their own food.
(ii)
To determine the trophic level of pangolins:
a. Information is needed on the prey they consume, such as ants or termites (e.g., from stomach content analysis).
b. The trophic level of the prey must be known (e.g., ants and termites are usually primary consumers).
c. Trophic level refers to the position an organism occupies in a food chain or web.
(b)
Evidence for evolution from the limbs of mammals includes:
a. The presence of a pentadactyl limb structure (five-digit pattern in limbs).
b. This structure is homologous with the limbs of other vertebrates, even if their function is different.
c. This similarity provides evidence of common ancestry.
d. The structure has undergone adaptation to suit different ecological niches, such as digging (pangolins), flying (bats), or swimming (whales).
(c)
(i)
Three genera of pangolins are recognized, based on the branches shown in the cladogram.
(ii)
Times since divergence are estimated by:
Counting base or amino acid sequence differences in DNA or proteins.
These molecular differences act as a molecular clock, with more differences indicating longer times since divergence.
Markscheme:
(a)
(i) Heterotrophic because it feeds on/eats other organisms (ants/termites) / does not photosynthesize/produce its own food.
(ii)
a. Knowledge of its prey (ants/termites) or stomach contents;
b. The trophic level of its prey (ants/termites);
c. Trophic level is the position an organism occupies in a food chain/web.
(b)
a. Pentadactyl limb structure;
b. Homologous with limbs of other vertebrates;
c. Evidence of common ancestry;
d. Adaptation to ecological niches.
(c)
(i) Three genera.
(ii) Estimated by counting base/amino acid sequence differences in DNA/proteins.
▶️ Answer/Explanation
a. DDT is a pesticide (specifically an insecticide) that was widely used to kill insects such as mosquitoes and lice.
b. One benefit of DDT use was the reduction of disease vectors, especially mosquitoes that carry malaria.
c. As a result, areas that used DDT experienced a decrease in malaria rates and other insect-borne diseases such as typhus.
d. However, DDT has serious environmental consequences, particularly due to biomagnification—the process where concentrations of a substance increase at each level of a food chain.
e. This leads to negative health effects in top predators (such as eagles or ospreys), which accumulate the highest concentrations of DDT.
f. In birds of prey, DDT causes thinner eggshells, leading to reduced reproductive success because eggs are more likely to break before hatching.
Markscheme:
a. DDT is a pesticide/insecticide
b. reduction in disease vectors
OR
reduction in mosquitos carrying malaria
c. leading to a reduction in disease/malaria rates
Accept other diseases such as typhus carried by lice.
d. biomagnification in food chains
e. negative impact on health of top predators / example of top predator
f. thin egg shells
OR
reduced reproductive success in birds of prey
▶️ Answer/Explanation
(a) i. The type of growth of the reindeer population up to 1940 is exponential growth.
(a) ii. One possible cause for the decrease in the number of reindeer after 1940 could be:
- Lack of food due to overgrazing by the large population,
- Disease spreading in the dense population,
- Hunting by humans,
- Increased predation if predators were introduced or grew in number.
(b) Biogeographic factors that increase the effectiveness of nature reserves include:
- Large area: Supports a greater variety of habitats, longer food chains, and larger populations.
- Low edge effect: Circular or compact reserves minimize the disturbed perimeter, reducing negative impacts like predation and human interference.
- Intact, unbroken areas: Preserve continuous habitats with less human disturbance.
- Corridors connecting fragmented areas: Enable species migration and movement.
- Proximity of fragmented areas: Promotes animal movement and genetic exchange, reducing inbreeding and maintaining biodiversity.
Markscheme:
a.i. exponential «population growth»
a.ii. lack of food / disease / hunting / increase of predators
b.
a. large area can support greater range of habitats / longer food chains / higher population numbers
b. low edge effect with circular reserves OR reduced edge effect minimises area that is disturbed/competition
c. intact / unbroken areas represent less disturbance on habitats
d. fragmented areas linked by corridors
e. (proximity of fragmented areas) allows for animal movement / genetic exchange
▶️ Answer/Explanation
(a) The interactions between crabs and seagrass are:
- Indirect (as crabs do not feed on seagrass directly),
- Negative effect (as indicated by the minus sign in the diagram),
- Top-down effect (crabs affect organisms lower in the trophic levels that influence seagrass).
(b) The sea otter indirectly has a positive effect on seagrass:
- Sea otters feed on crabs, which in turn feed on isopods.
- Fewer crabs mean more isopods.
- Isopods feed on algae growing on seagrass, so more isopods reduce algae.
- Less algae means less competition for seagrass, leading to healthier/more abundant seagrass.
(c) Nutrients can have both positive and negative bottom-up effects on seagrass:
- Positive effect: Nutrients enhance plant growth by increasing availability of essential resources, leading to increased seagrass growth and abundance.
- Negative effect: Too many nutrients can lead to algal blooms, which:
- Increase competition for light and space,
- May cause eutrophication,
- Lead to decomposition of dead algae, reducing oxygen and harming seagrass.
Markscheme:
a.
• Indirect
• Negative effect
• Top-down
b.
• Sea otters have a positive (indirect) effect as they feed on crabs that feed on isopods that feed on algae
• Fewer crabs means more isopods so less algae
• Less algae means more seagrass
OR
• Less competition between algae and seagrass
c.
• The positive (bottom-up) effect is due to availability of nutrients
• Nutrients increase abundance/plant growth rates
• The negative (bottom-up) effect as excess of nutrients causes a bloom in algae growth/eutrophication/competition
• Limited nutrients have negative effect on seagrass growth
• Excess algae cause seagrass to die/decompose/replenish nutrients
Do not accept answers referring to top down effects.
▶️ Answer/Explanation
Answer: Anti-poaching restrictions within a nature reserve
Explanation:
• An example of an active management strategy in in situ conservation is the use of anti-poaching restrictions.
• This strategy involves patrolling the reserve to enforce laws that prevent illegal hunting, thereby protecting endangered species in their natural environment.
Markscheme:
a. name of strategy \(\checkmark\)
b. detail of the strategy \(\checkmark\)
Example:
a. anti-poaching restrictions within a nature reserve
b. patrolling of the reserve to enforce restrictions
Accept only the first stated strategy if several are listed.
The outline must match the strategy.
▶️ Answer/Explanation
(a) The trophic level of the sea urchin is Herbivore / Primary consumer
(Since it feeds on seagrass, which is a producer.)
(b) Compare and contrast the community structure within and outside the marine protected area:
Compare:
- All three species (sea bream, sea urchin, algae) are present in both areas
- Sea urchin population is higher than sea bream population in both areas
Contrast:
- Sea urchin numbers are much higher outside the protected area (690 vs 70)
- Sea bream numbers are much lower outside the protected area (3 vs 30)
- % algae cover is lower outside the protected area (15% vs 47%)
- Community evenness is lower outside the protected area due to sea urchin dominance
(c) In this food chain, a keystone species is:
- A species that has a disproportionate effect on the structure and functioning of the community
- Sea bream acts as a keystone species: its removal through fishing leads to:
- An increase in sea urchins
- Which causes a decline in algae and seagrass due to overgrazing
Thus, the presence of sea bream helps maintain ecological balance in the food chain.
Markscheme:
a. herbivore/primary consumer \(\checkmark\)
Do not accept second trophic level
b. compare:
a. all three species present in both
OR
richness is the same \(\checkmark\)
b. sea urchin numbers highest in both
OR
sea bream density less than sea urchin density in both \(\checkmark\) Allow converse answer
c. all species numbers are affected by fishing \(\checkmark\)
contrast:
d. sea urchin population is greater outside the marine protected area \(\sqrt{ }\)
e. reduction in sea bream/sea grass percent cover outside the marine protected area \(\checkmark\)
f. less species evenness outside the marine protected area \(\checkmark\)
c. a. keystone species have a disproportionate effect on the biological community \(\checkmark\)
b. removal of the sea bream «due to fishing» \(\checkmark\)
c. results in more sea urchins \(\checkmark\)
d. which significantly reduce the producers/seagrass \(\checkmark\)
Do not accept first trophic level for mpd
▶️ Answer/Explanation
(a) 6.5 m
At 6.5 meters depth, the greatest species richness is observed because three coral species (Orbicella annularis, Agaricia tenuifolia, and Porites divaricata) are present, which is more than at any other depth.
(b)
There is a symbiotic (mutualistic) relationship between Zooxanthellae and reef-building corals.
• Zooxanthellae live inside coral tissues, providing the coral with energy by performing photosynthesis.
• In return, the coral provides the Zooxanthellae with shelter and access to sunlight needed for photosynthesis.
(c)
Depth acts as a limiting factor because at greater depths, light levels are lower and temperatures are cooler, which reduces photosynthesis by Zooxanthellae.
Since corals depend on this photosynthesis for energy, low light and temperature limit coral growth and survival.
Markscheme:
a \(6.5 \mathrm{~m}\)
Unit required
b
a. a symbiotic/mutualistic relationship;
b. Zooxanthellae obtain shelter/habitat/exposure to light;
c. coral obtains energy/food through photosynthesis of the Zooxanthellae;
c low light levels/lower temperatures cannot support growth/metabolism.
Requires the explanation for the mark
▶️ Answer/Explanation
Effects of a forest fire on an ecosystem
Changes in numbers of species
Forest fires can cause a significant decrease in populations of plants and animals due to direct destruction or loss of resources.Habitat alteration
Fires can destroy vegetation and change the physical environment, leading to loss or modification of habitats that species depend on.Disruption of biogeochemical processes
Forest fires can alter nutrient cycles by burning organic matter, which affects soil fertility and slows down processes like decomposition and nutrient recycling.
Markscheme:
Possible impacts (choose any three):
- Changes in numbers of species \( \checkmark \)
- Changes in types of species \( \checkmark \)
- Impacts on food chains/webs \( \checkmark \)
- Altered food production/availability \( \checkmark \)
- Habitat/ecosystem alteration \( \checkmark \)
- Disruption of biochemical processes (e.g., photosynthesis/respiration/decomposition) \( \checkmark \)
- Disruption of biogeochemical processes (e.g., erosion/nutrient cycles) \( \checkmark \)
Notes:
- The environmental disturbance must be named (e.g., fire, farming, construction, extreme weather, introduction of an alien species).
- Award [2 max] if the disturbance is not named.
- Explanations are not required for marks.
▶️ Answer/Explanation
Competitive exclusion occurs when two species with similar ecological niches occupy the same habitat and compete for limited resources such as food, space, or light. This competition causes an increase in competition intensity, which reduces the availability of resources for both species. As a result, one species—usually the weaker competitor—experiences a decline in population and may be completely excluded from that habitat over time.
In the case of an invasive species, such as the grey squirrel introduced into the UK, it often lacks natural predators in the new environment, giving it an advantage over native species. The endemic species, like the red squirrel, typically cannot compete effectively for resources, leading to its population decline or local extinction. This example clearly illustrates how competitive exclusion leads to shifts in species distribution and biodiversity loss.
Markscheme:
a) When two species with similar niches occupy the same habitat \( \checkmark \)
b) The competition increases OR reduction in resources \( \checkmark \)
c) The population of one species will die/be excluded \( \checkmark \)
d) An invasive species often lacks predators \( \checkmark \)
e) The endemic species is usually the one that cannot compete \( \checkmark \)
f) Example: grey squirrel / Japanese knotweed / cane toad \( \checkmark \)
[Maximum 3 marks if the invasive species is not named.]
Note: Do not accept humans as an example.
▶️ Answer/Explanation
a.
- As the world population increases, rock phosphate production also increases, showing a positive correlation.
- However, after around 1985, rock phosphate production levels off and does not continue to rise, even though the world population continues to grow.
b.
- Phosphate can be lost through leaching.
- It can also be lost through soil erosion or run-off.
- Additionally, phosphate is removed when crops are harvested from the land.
c.
- Phosphorus (from rock phosphate) is an important component of fertilizers, which help increase agricultural productivity.
- A decrease or leveling off in phosphate production could result in less fertilizer availability.
- This could reduce agricultural output, potentially leading to less food available for the growing population.
Markscheme:
a. Relationship between rock phosphate production and world population:
As population increases, so does phosphate production (positive correlation). ✓
Since 1985, phosphate production has not risen while population has continued to increase. ✓
b. Phosphate loss from agricultural land:
Leaching/soil erosion, run-off, or removal by the harvesting of agricultural crops. ✓
c. Effects of phosphate production changes after 1985 on food supplies:
Phosphorus is important as a fertilizer. ✓
A drop in phosphate could lead to less agricultural output. ✓
This could mean less food available for the increasing population. ✓
▶️ Answer/Explanation
a.i.
- Overall, the grey squirrel distribution has increased significantly between 1945 and 2010.
- In 1945, the grey squirrel was present in limited areas (mainly scattered patches).
- By 2010, grey squirrels were found throughout almost the entire region shown, including areas where they were previously absent.
- The grey squirrel has expanded its range, nearly eliminating the red squirrel in many areas.
a.ii. Possible reasons for the grey squirrel’s increased distribution include:
- Disease resistance – Grey squirrels might be resistant to diseases that affect red squirrels.
- High reproductive rate – Faster reproduction enables quicker population growth.
b.
- Competitive exclusion states that two species with similar ecological niches cannot coexist indefinitely in the same habitat.
- One species will have a competitive advantage that allows it to outcompete the other.
- This results in the displacement or local extinction of the weaker competitor.
- In this case, grey squirrels have outcompeted red squirrels, replacing them in their habitat and niche.
- Consequently, the niches of the two squirrels may become narrower or one species is eliminated from the area.
Markscheme:
a.i.
a. Overall, the grey squirrel distribution has increased (while the red squirrel decreased) \(\checkmark\)
b. In 2010, the grey squirrel was found in areas where it was previously absent \(\checkmark\)
c. Grey squirrels have dominated, nearly eliminating red squirrels \(\checkmark\)
a.ii.
Possible reasons (any two):
1. No natural predators \(\checkmark\)
2. Ample food supply/habitat availability \(\checkmark\)
3. Few competitors \(\checkmark\)
4. Disease resistance \(\checkmark\)
5. High reproductive rate \(\checkmark\)
6. No physical barriers to prevent grey squirrel spread \(\checkmark\)
b.
Competitive exclusion explanation:
a. Two species with similar niches cannot coexist indefinitely \(\checkmark\)
b. One species will always have a competitive advantage \(\checkmark\)
c. Leads to displacement/extinction of the weaker competitor \(\checkmark\)
d. Grey squirrels have replaced red squirrels in their niches \(\checkmark\)
e. Niches may become narrower for one/both species \(\checkmark\)
▶️ Answer/Explanation
a.i. Marmots born in captivity experienced higher levels of predation compared to those born in the wild.
a.ii.
• Marmots born in the wild have more experience with or better recognition of predators, making them better at avoiding them.
• Wild-born marmots benefit from parental protection or teaching, which helps them learn how to respond to threats.
• Natural selection favors marmots born in the wild, so those more vulnerable to predation are less likely to survive, resulting in a population better adapted to predator avoidance.
b.
Ex situ conservation involves protecting endangered species outside their natural habitats, such as in zoos, captive breeding centers, or botanical gardens.
In situ conservation refers to the protection and management of species within their natural habitats or ecosystems, allowing them to live and reproduce in the environment where they evolved.
Markscheme:
a.i. predation was greater in those born in captivity \( \checkmark \)
a.ii.
a. the marmots have experience with/recognize predators \( \checkmark \)
b. parents shield them from predators
OR
parents teach them about predators \( \checkmark \)
c. those born in the wild are favoured in natural selection \( \checkmark \)
b. ex situ is in artificial environment, in situ is in natural environment \( \checkmark \)
Accept examples as long as it is clear one is natural and one artificial
▶️ Answer/Explanation
a. The arrows in the Gersmehl diagram represent the flow of nutrients between the three main nutrient stores: biomass, litter, and soil. They show how nutrients move and cycle through the ecosystem.
b. In a tropical rainforest compared to the taiga:
- The litter store would be smaller, so the litter circle would be relatively smaller because litter decomposes quickly.
- Warmer temperatures and higher rainfall promote faster decomposition, so the arrow from litter to soil would be thicker, indicating more rapid nutrient transfer.
- There are more decomposers (saprophytes) in tropical rainforests, which speeds up the breakdown of litter.
- More nutrients are stored in living plants, so the biomass circle would be larger in the tropical rainforest than in the taiga.
Markscheme:
a. nutrient flow \( \sqrt{} \)
b.
a. the circle would be «relatively» smaller OR litter layer is less \( \checkmark \)
b. warmer weather favours the decomposition of litter/results in thicker arrow between litter and soil \( \checkmark \)
c. more rainfall favours the decomposition of litter/results in thicker arrow between litter and soil \( \checkmark \)
d. greater number of saprophytes/decomposers in rain forest \( \checkmark \)
e. nutrients would be stored in biomass/biomass circle would be larger \( \checkmark \)
▶️ Answer/Explanation
- Seaweed near the estuary and Arklow town contains a higher concentration of copper because of pollution from human activities or natural sources.
- Birds living in the area often feed on fish, shellfish, or invertebrates that consume or live among this contaminated seaweed.
- Copper is a heavy metal that accumulates in the bodies of organisms because it is absorbed faster than it can be excreted or broken down; this process is called bioaccumulation.
- As smaller organisms with copper are eaten by larger animals, the copper concentration increases at each step of the food chain; this is known as biomagnification.
- Birds, being at a higher trophic level, receive the highest copper concentrations, which can lead to toxic effects such as damage to their nervous system, reproductive failure, and weakened immune response.
- Over time, these toxic effects can reduce bird populations by lowering survival rates and breeding success.
Markscheme:
• Seaweed close to the estuary/town has a higher concentration of copper \(\checkmark\)
• Birds feed on fish/seaweed that have accumulated copper \(\checkmark\)
• Copper accumulates in tissues of organisms/bioaccumulation \(\checkmark\)
• Copper accumulates at a rate faster than that at which it is lost by excretion \(\checkmark\)
• Copper concentration increases as trophic level increases \(\checkmark\)
• Biomagnification occurs \(\checkmark\)
▶️ Answer/Explanation
a.
- A transect was laid vertically from the low tide mark to the upper shore (0 to 2.25 m).
- Quadrats were placed at regular height intervals along the transect.
- The number of barnacles per species within each quadrat was counted and recorded.
- Density per 100 cm² was calculated and plotted for each species at each height.
b.
- Chthamalus montagui (CM):
- Found mostly at higher shore levels (around 1.45 m to 2.25 m).
- Narrow vertical distribution and lower density.
- Semibalanus balanoides (SB):
- Found over a wider vertical range (approximately 0.25 m to 2.05 m).
- Densest in the mid to lower intertidal zone (peak density near 1.05 m).
- Much higher density compared to CM.
c.
- Elminius modestus (EM) occurs across almost the entire vertical range (approx. 0.25 m to 2.05 m).
- It overlaps with both native species: the upper shore with CM and lower shore with SB.
- Its wide vertical distribution suggests a broad ecological tolerance.
- High density in overlapping zones may indicate it outcompetes native species.
- The overlap and spread suggest it disrupts established niches—common behavior in invasive species.
d.
- Tidal exposure (duration of submersion/emersion).
- Other acceptable answers: temperature, salinity, wave action, pH, light, or substrate type.
e.
- Barnacles require clean, oxygenated water and stable conditions.
- Their presence and abundance reflect environmental health.
- A decrease in barnacle numbers or species diversity may indicate pollution.
- Long-term monitoring can reveal trends and detect ecological degradation.
- Used in biotic indices to assess water quality.
Markscheme:
a. Data collection method:
A transect was laid across the area to be studied.
Barnacles were counted/recorded per species in quadrats at regular intervals.
b. Distribution of species:
Both C. montagui and S. balanoides are present throughout the range.
C. montagui has fewer individuals and mostly occupies the upper shore/intertidal zone.
S. balanoides is most abundant in the low tide area.
c. Evidence for invasive nature of E. modestus:
Native species (CM and SB) have distinct, non-overlapping niches.
E. modestus overlaps with both native species, suggesting competition.
E. modestus has a wide niche/higher tolerance, covering the entire intertidal range.
d. Possible abiotic factors (choose one):
Exposure/tides/waves
Temperature
Substrate/surface for attachment
Salinity
Light availability
pH levels
e. Use as indicator species:
Barnacles require specific environmental conditions and are sensitive to changes.
Population changes can indicate environmental quality over time.
Can be used to calculate biotic indices (e.g., high index = clean environment; low index = pollution).
▶️ Answer/Explanation
a.
Two abiotic factors that increase in the fragmented forest compared to the center of the core forest are light penetration and wind exposure. This is because the smaller fragments have more exposed edges, allowing more sunlight and wind to reach the forest floor.
b.
When a forest becomes fragmented, biodiversity often decreases overall because smaller and isolated areas support fewer species. Edge areas may have more diversity, but this is usually due to new or invasive species entering, which can outcompete native ones. Also, native animals may struggle to move between fragments, leading to local extinctions and a faster turnover in species compared to the stable core forest.
Markscheme:
a.
a. light «penetration» \(\checkmark\)
b. temperature \(\checkmark\)
c. wind \(\checkmark\)
d. fires \(\checkmark\)
Allow any two but mark only the first two if more are given in a list.
b.
a. reduction in diversity in fragmented forest as a whole \(\checkmark\)
b. greater diversity towards the edge \(\checkmark\)
c. new species appear/immigration of new/alien/invasive species \(\checkmark\)
d. local species decrease/emigrate
OR
unable to move between fragments \(\checkmark\)
e. faster species turnover than core forest \(\checkmark\)
▶️ Answer/Explanation
- The food conversion ratio (FCR) is the amount of animal feed needed to produce a certain amount of product, such as meat, milk, or eggs.
- A lower FCR means animals convert feed into food products more efficiently, resulting in more food available for human consumption from less feed.
- Different livestock species have different FCRs; some animals, like chickens or fish, are generally more efficient than others, like cattle or sheep.
- A higher FCR means more feed is required to produce the same amount of food, which reduces the overall amount of food available for humans because more crops must be grown for animal feed instead of direct human consumption.
- The amount of biomass lost as heat, waste, or maintenance during digestion affects the FCR and overall efficiency.
- Choosing animal feeds that improve FCR can increase the efficiency of livestock production, making food production more sustainable and freeing up more crops for human consumption.
Markscheme:
a. «food conversion ratio is» mass of animal food required to produce a certain product «in livestock» \(\checkmark\)
b. product may be consumable meat / milk / eggs \(\checkmark\)
c. some dietary choices are more sustainable than others
OR
maximum production of human food for little animal feed is desired \(\checkmark\)
d. some animals are more efficient at converting feed into useful product than others. \(\checkmark\)
e. amount of biomass lost affects this ratio \(\checkmark\)
f. some animal feeds will be better for producing useable products than others \(\checkmark\)
Accept examples for any of these marking points.
▶️ Answer/Explanation
a.i.
The temperature range is calculated by subtracting the minimum temperature from the maximum temperature. From the climograph:
Maximum temperature ≈ 29°C
Minimum temperature ≈ 25°C
Range = 29°C – 25°C = 4°C
a.ii.
There is a clear relationship between maximum temperature and rainfall:
• The maximum temperature occurs just before or at the start of the rainy season.
• As rainfall begins to increase, the maximum temperature starts to decrease.
This indicates a negative correlation: when rainfall rises, temperature falls.
a.iii.
The pattern of rainfall is:
• Rainfall is concentrated mainly between April and November.
• The heaviest rainfall occurs in June to August, which corresponds to the monsoon period.
• From December to March, rainfall is very low or almost absent.
b.
Deciduous trees like teak shed their leaves during the dry season (January–February).
This happens to reduce water loss by transpiration, helping the tree survive the period when rainfall is scarce and water availability is low.
c.
The Gersmehl diagram for a tropical rainforest shows:
• Most nutrients are stored in the biomass (living plants) rather than in litter or soil.
• There is a high flow of nutrients from soil to biomass, shown by thick arrows, indicating rapid nutrient uptake by plants.
• The flow of nutrients from litter to outside the ecosystem is low, meaning few nutrients are lost from the system.
• Nutrient cycling is fast and efficient due to warm, moist conditions that promote rapid decomposition and uptake.
• Overall, the diagram models how nutrients are stored and transferred between biomass, litter, and soil in the ecosystem
Markscheme:
a.i \(4\,^{\circ}\mathrm{C}\)
Accept answers between 3 to \(5\,^{\circ}\mathrm{C}\)
a.ii Maximum temperature occurs just when rainfall begins/at the onset of the rainy season/monsoon
OR
Negative relationship (as maximum temperature drops, rainfall increases)
a.iii Rainfall concentrated between April to December/peaks in June-August (followed by months with little/no rainfall)
b
a. Dry season/Jan/Feb
b. (Drop leaves) to prevent water loss/transpiration (since no rainfall for almost four months)
c
a. Statement correctly explaining the quantity of nutrients in identified circle/circles
e.g., most nutrients are stored in biomass/equal quantities of nutrients stored in soil and litter.
b. Statement correctly explaining high nutrient flow/transfer of any thick/large arrow
e.g., high transfer rate of nutrients from soil to biomass.
c. Statement correctly explaining low nutrient flow/transfer of any thin arrow
e.g., low transfer rate of nutrients from litter to the outside/another ecosystem.
d. Any statement correctly comparing nutrient storage/flow rates
e.g., higher nutrient transfer between soil and biomass than between biomass and litter.
e. A Gersmehl diagram models (interrelationships between) nutrient stores and flows in an ecosystem
▶️ Answer/Explanation
An example of captive breeding and reintroduction is the Giant Panda (Ailuropoda melanoleuca).
- Reason for endangerment: Habitat loss due to deforestation and fragmentation in China.
- Location of breeding: Captive breeding programs mainly in zoos and specialized breeding centers in China.
- Program execution: Giant pandas are bred and raised in captivity under controlled conditions. Once healthy and capable of survival, they are monitored carefully during reintroduction into protected natural reserves in China.
- Success rate: The program has seen successful reproduction in captivity and increasing numbers of pandas surviving in the wild, contributing to a gradual recovery of the species.
Markscheme:
Required components (example: Giant Panda):
- Name of organism: Scientific or common name (e.g., Ailuropoda melanoleuca / Giant Panda) \( \sqrt{ } \)
- Reason for endangerment: Loss of habitat, hunting, etc. \( \sqrt{ } \)
- Location of breeding: Zoos (ex situ), China (in situ), etc. \( \sqrt{ } \)
- Program execution: Bred/raised in captivity, monitored reintroduction \( \checkmark \)
- Success rate: Reproduction in captivity, survival in wild \( \checkmark \)
Notes:
- To award [3], the name of the organism must be provided.
- Other valid examples include California Condor, Black-footed Ferret, or Arabian Oryx.
▶️ Answer/Explanation
a.
- As light intensity changes, the percentage cover of blackberries changes accordingly.
- Blackberry cover is highest at intermediate light levels (around 700–900 lux).
- There is little or no blackberry growth at very low light (<200 lux) or very high light (>1200 lux) intensities.
The distribution forms a bell-shaped curve, showing that blackberries prefer a moderate range of light and are limited outside this range.
b.
- Energy flows through ecosystems: it enters as light energy, is transferred through trophic levels, and is eventually lost as heat to the surroundings. Energy is not recycled.
- Matter (e.g., nutrients, elements) is recycled within the ecosystem through decomposition and nutrient cycling and does not leave the closed system.
c.
Advantages:
- Show quantitative values of energy transferred at each trophic level.
- Clearly illustrate energy loss between trophic levels (e.g., due to respiration, heat).
- Allow comparisons of energy flow efficiency between different ecosystems or over time.
Disadvantages:
- Difficult and time-consuming to measure accurately; often require destructive sampling.
- May oversimplify complex food webs, especially where omnivory occurs.
- Represent a static snapshot and may not reflect seasonal or temporal changes.
Markscheme:
a. Outline how these results indicate that blackberry distribution is limited by light intensity:
i. As light level changes, so does the percentage cover of blackberry \( \checkmark \)
ii. Distribution is higher at intermediate/moderate light intensities \( \checkmark \) (Accept appropriate numerical values)
iii. Little growth at low light intensities OR little growth at high light intensities \( \checkmark \)
iv. Distribution is bell-shaped \( \checkmark \)
b. Distinguish between the transfer of matter and energy in closed ecosystems:
Only energy can be lost/gained/exchanged/transferred with the exterior OR only matter is constant/recycled \( \sqrt{ } \)
c. Discuss the advantages and disadvantages of pyramids of energy:
Advantages:
i. Can show the energy loss/transfer between trophic levels \( \checkmark \)
ii. Permits a quantitative comparison between ecosystems \( \checkmark \)
iii. Shows change over time \( \sqrt{ } \)
Disadvantages:
iv. Are difficult to produce accurately \( \checkmark \)
v. Require destructive methods to obtain the data \( \checkmark \)
vi. Do not show all the interactions/food chains between different members of the community \( \checkmark \)
vii. Cannot represent organisms that feed at different trophic levels \( \checkmark \)
(Award [3 max] if only one side of the argument is given.)
▶️ Answer/Explanation
a.
- Radioactive Caesium isotopes (Cs-134, Cs-137) were released into the ocean after the Fukushima accident in 2011.
- These isotopes entered seawater near Japan.
- Phytoplankton absorbed the radioactive Caesium from the water.
- Some Caesium entered fish directly through their gills.
- Small fish ate the contaminated phytoplankton, acquiring the radioisotopes.
- Larger fish, including bluefin tuna, ate these smaller contaminated fish.
- Caesium is not easily removed from organisms and accumulates in their tissues (bioaccumulation).
- Radioactive Caesium concentrations increase at each level of the food chain (biomagnification).
- Top predators like bluefin tuna have higher levels of Caesium due to this process.
b.
- Indicator species reflect the health of an environment by their presence, absence, or population size.
- They respond to environmental changes such as pollution, temperature, or oxygen levels.
- Scientists use data on these species to calculate a biotic index, measuring ecosystem health.
- Monitoring indicator species over time helps track environmental changes and trends.
- Early detection of changes can lead to conservation actions or pollution control.
- Example: Tubifex worms indicate polluted water with low oxygen levels.
Markscheme:
a. Accumulation of Caesium radioisotopes in fish tissues:
- Radioisotopes entered the sea/water in Japan. ✓
- Taken up by producers/phytoplankton or enter fish gills. ✓
- Producers eaten by consumers/fish. ✓
- Radioisotopes passed up the food chain OR contaminated fish eaten by tuna. ✓
- Radioisotopes are not easily excreted. ✓
- Bioaccumulation/biomagnification occurs at each trophic level. ✓
b. Use of indicator species:
- Presence/absence indicates environmental conditions. ✓
- Environmental changes affect these species. ✓
- Numbers of indicator species can calculate a biotic index. ✓
- Changes are monitored over time. ✓
- Changes can prompt environmental protection measures. ✓
- Example: Tubifex worms indicate sediment pollution. ✓
▶️ Answer/Explanation
a.
- Environmental disturbances cause changes in biodiversity.
- They can increase or decrease species richness (number of species).
- Disturbances can affect species evenness (how evenly individuals are distributed among species).
- Overall, disturbances alter the variety and balance of species in an ecosystem.
b.i.
Cane toads in Australia
b.ii.
- Alien species compete with native/endemic species for food, water, and habitat.
- They may cause extinction or reduce the population of native species.
- Alien species often lack natural predators, which allows them to multiply quickly.
- Their presence disrupts existing food chains and ecological balance.
Markscheme:
Answers:
a.
Changes/increases/decreases in species richness/biodiversity/evenness \(\checkmark\)
b.i.
Example: Cane toads in Australia \(\checkmark\)
(Accept specific species names but not general groups like “toads”)
b.ii.
a. Competition with native species for resources \(\checkmark\)
b. May cause extinction/reduction of native species \(\checkmark\)
c. Often lack natural predators, allowing population growth \(\checkmark\)
d. Disrupts food chains/ecological balance \(\checkmark\)
(Any two points required for full marks)
▶️ Answer/Explanation
a.
- Keystone species have a large effect on the ecosystem, often much bigger than their numbers suggest.
- They influence the balance and structure of populations in the community.
- If keystone species disappear, many other species that depend on them may also disappear.
- Protecting them helps maintain the survival of many other species and the overall ecosystem health.
b.
| Aspect | Fundamental Niche | Realized Niche |
|---|---|---|
| Definition | The potential role or habitat a species could occupy | The actual role or habitat a species does occupy |
| Based on | Species’ adaptations and needs | Limited by competition, predation, and other factors |
| Size | Usually larger | Usually smaller |
| Both | Describe the habitat, role, or relationship of a species | Describe the habitat, role, or relationship of a species |
Markscheme:
a.
• a large effect on the ecosystem/community structure/environment «relative to abundance»
OR
• influence the balance of other populations in the ecosystem
OR
• other species in the habitat would also disappear
OR
• many other species dependent on them for survival \(\sqrt{ }\)
b.
a. both describe the habitat/role/relationship occupied by a species \(\checkmark\)
b. the fundamental niche is the potential role of a species in its ecosystem and realized niche is the actual role
OR
the fundamental niche depends on the adaptations of a species whereas the realized niche is limited by competition/predation
OR
realized niche is (usually) smaller than fundamental niche \(\checkmark\)
▶️ Answer/Explanation
a.
- A higher FCR means more animal feed is needed to produce 1 kg of edible meat, so it is less sustainable.
- Salmon with an FCR of 1.2 is more sustainable than chicken with an FCR of 2.2.
- A salmon-based diet causes lower energy losses compared to chicken.
- Salmon farming produces less waste than chicken farming, making it more environmentally friendly.
b.
Advantages:
- Food webs summarize all possible food chains in a community, showing feeding relationships clearly.
- They give a realistic picture of the complexity of interactions between species.
Limitations:
- Some ecosystems are so complex that food webs become difficult to draw or understand.
- Food webs only show qualitative information and do not provide data on energy quantities or population sizes.
- They often exclude decomposers (saprotrophs) and abiotic factors that also affect ecosystems.
c.
- Keystone species have a disproportionately large effect on their environment compared to their population size.
- They help maintain balance in the ecosystem by regulating population sizes of other species.
- Losing a keystone species causes a domino effect, where many other species decline or disappear.
- This loss disrupts the food web and leads to a decrease in biodiversity.
d.
- A niche is the role or functional position of an organism in its environment.
- It includes the organism’s habitat, feeding behavior, and interactions with other species.
- No two species can occupy exactly the same niche in the same environment (competitive exclusion).
- A niche can be either fundamental (potential role) or realized (actual role limited by competition).
Markscheme:
a.
a. higher FCR implies less sustainability \( \checkmark \) Do not accept efficiency instead of sustainability.
b. salmon based diet is more sustainable/chicken is less \( \checkmark \)
c. salmon diet would have lower energy losses/chicken diet higher energy losses \( \checkmark \)
d. salmon diet will produce less waste/chicken more \( \checkmark \)
b. Advantages:
a. food webs summarize all possible food chains «in the community» \( \checkmark \) OWTTE
b. realistic representation \( \checkmark \)
Limitations:
c. some communities/ecosystems are too complex to represent \( \sqrt{} \)
d. only shows qualitative information/not quantitative data OR saprotrophs/abiotic factors not taken into account \( \checkmark \)
Needs one advantage and one limitation to obtain [2]. Do not accept mentions of trophic levels.
c.
a. «research demonstrates that keystone species» have a «disproportionately» large effect on their environment relative to abundance OR «keystone species» maintain a balance in the «stable» numbers of each species within a community OR «keystone species» have a large impact in preserving and stabilizing the biodiversity by preventing overpopulation/monopoly/out competition \( \checkmark \)
b. a keystone species’ disappearance would start a domino effect/other species in the habitat would also disappear OR their loss leads to an imbalance in the food web OR their loss leads to a decrease in biodiversity \( \checkmark \)
Do not accept protecting keystone species prevents disappearance of other species since it repeats the question.
d.
a. the role of an organism in its environment OR functional position of an organism in its environment \( \checkmark \)
b. includes «spatial» habitat AND feeding activities AND interactions with other species in the community \( \checkmark \) All required.
c. no two species can occupy the same niche \( \checkmark \)
d. a niche can be fundamental or realized \( \checkmark \) OWTTE
▶️ Answer/Explanation
a.
- Both baleen whales and sea turtles have documented cases of entanglement and ingestion of marine debris.
- Sea turtles have a similar percentage of species affected by both entanglement and ingestion, while baleen whales show a much higher percentage affected by entanglement than ingestion.
- A greater proportion of sea turtle species are affected by both threats compared to baleen whales.
- There are more species of baleen whales (10) than sea turtles (7), although this is not the key point—focus is on proportions/percentages.
b.
- Plastics break down into microplastics, which can be ingested by small organisms at the base of the food chain.
- As predators eat prey containing microplastics, these particles accumulate in higher concentrations at each trophic level—a process known as biomagnification.
- For example, sea turtles ingest plastic directly, and predators that consume these turtles could accumulate even more toxins from plastics over time.
c.
- Indicator species reflect the quality or health of an environment by their presence or absence.
- Environmental changes—such as pollution—can reduce their numbers or cause them to disappear.
- The abundance or diversity of these species can be used to calculate a biotic index, which quantifies ecosystem health.
- Monitoring these changes over time helps track trends and inform conservation actions.
- For example, the presence of Tubifex worms indicates high levels of organic pollution in sediments.
Markscheme:
a.
• Both show cases of entanglement/ingestion \(\checkmark\)
• Sea turtles have similar number of species affected by entanglement/ingestion while baleen whales have more species affected by entanglement than ingestion \(\checkmark\)
OR
• Higher percentage of sea turtle species affected by entanglement/ingestion than baleen whales \(\checkmark\)
OR
• Higher number of species of baleen whales than species of sea turtles \(\checkmark\)
Do not accept answers quoting numerical values only.
b.
• Plastic broken down into microplastics to be able to enter the food chain \(\checkmark\)
• Plastic/microplastics become more concentrated at each trophic level \(\checkmark\)
Accept descriptions of biomagnification involving any of the species in the table.
c.
• Presence/absence indicate environmental conditions \(\checkmark\) Accept named environmental condition/pollution.
• Changes in the environment affect these species \(\checkmark\) Number of species or type of species.
• Relative numbers of individuals/indicator species can be used to calculate a biotic index \(\checkmark\)
• Changes monitored over time \(\checkmark\) Accept example of time frame.
• Changes can lead to measures to protect the environment \(\checkmark\)
• Example of an indicator species AND what it indicates (e.g., Tubifex for sediment pollution) \(\checkmark\) Award marks for a species, not a group.
▶️ Answer/Explanation
a.
- Keystone species have a disproportionately large effect on the ecosystem compared to their numbers.
- They help maintain the balance of populations in the ecosystem.
- Many other species depend on keystone species for survival.
- If keystone species disappear, it could cause the loss of other species in that habitat, reducing biodiversity.
b.
- Both fundamental and realized niches describe the role, position, and habitat a species occupies within an ecosystem.
- The fundamental niche represents the full range of environmental conditions and resources a species can potentially use, based on its physiological and behavioral adaptations, without considering competition or other biological interactions.
- The realized niche is the actual role and habitat the species occupies in the presence of other species, including factors like competition, predation, and other limiting factors.
- The realized niche is typically smaller than the fundamental niche because competition and predation restrict the areas or resources a species can actually use.
- The fundamental niche is more of a theoretical or ideal niche, while the realized niche reflects the species’ true ecological role in nature.
- Understanding these niches helps explain species distribution, coexistence, and biodiversity within ecosystems.
Markscheme:
a. Protection of keystone species helps preserve biodiversity because:
- They have a disproportionately large effect on ecosystem structure relative to their abundance
- They influence the balance of other populations in the ecosystem
- Many other species depend on them for survival
- Their disappearance could lead to the loss of other species in the habitat
b. Comparison of fundamental and realized niches:
| Similarity | Differences |
|---|---|
| Both describe the habitat/role/relationship occupied by a species |
|
▶️ Answer/Explanation
a.
- A higher FCR means more feed is needed to produce 1 kg of edible meat, so it is less sustainable.
- Salmon’s FCR is 1.2, meaning it needs less feed and is more sustainable compared to chicken’s FCR of 2.2.
- A salmon-based diet results in lower energy losses during feed conversion, making it more efficient.
- Chicken requires more feed, leading to higher energy losses and more waste production, reducing sustainability.
b.
Advantages:
- Food webs show all possible feeding relationships and interactions between species in a community, providing a more complete picture than single food chains.
- They give a realistic representation of how energy and nutrients flow through ecosystems.
Limitations:
- In very complex ecosystems, food webs can be too complicated to accurately represent all interactions.
- Food webs usually show qualitative relationships only (who eats whom) and do not provide quantitative data like energy amounts transferred.
- They often ignore saprotrophs (decomposers) and abiotic factors, which also play important roles in ecosystems.
c.
- Keystone species have a disproportionately large effect on the ecosystem relative to their population size.
- They help maintain balance by controlling populations of other species and preventing any one species from dominating.
- Many species depend on them for survival, so their presence supports overall biodiversity.
- Removing a keystone species can cause a domino effect, leading to loss of other species and an imbalance in the ecosystem.
d.
- A niche is the role or functional position of an organism in its environment.
- It includes where the organism lives (spatial habitat), what it eats (feeding activities), and how it interacts with other species.
- No two species can occupy exactly the same niche in the same ecosystem at the same time (competitive exclusion principle).
- A niche can be fundamental (the full potential role without competition) or realized (the actual role considering competition and other factors).
Markscheme:
a.
a. higher FCR implies less sustainability \(\checkmark\) Do not accept efficiency instead of sustainability.
b. salmon based diet is more sustainable/chicken is less \(\checkmark\)
c. salmon diet would have lower energy losses/chicken diet higher energy losses \(\checkmark\)
d. salmon diet will produce less waste/chicken more \(\checkmark\)
b.
Advantages:
a. food webs summarize all possible food chains «in the community» \(\checkmark\) OWTTE
b. realistic representation \(\checkmark\)
Limitations:
c. some communities/ecosystems are too complex to represent \(\sqrt{ }\)
d. only shows qualitative information/not quantitative data
OR
saprotrophs/abiotic factors not taken into account \(\sqrt{ }\)
Needs one advantage and one limitation to obtain [2].
Do not accept mentions of trophic levels.
c.
a. «research demonstrates that keystone species» have a «disproportionately» large effect on their environment relative to abundance
OR
«keystone species» maintain a balance in the «stable» numbers of each species within a community
OR
«keystone species» have a large impact in preserving and stabilizing the biodiversity by preventing overpopulation/monopoly/out competition \(\checkmark\)
b. a keystone species’ disappearance would start a domino effect/other species in the habitat would also disappear
OR
their loss leads to an imbalance in the food web
OR
their loss leads to a decrease in biodiversity \(\checkmark\)
Do not accept protecting keystone species prevents disappearance of other species since it repeats the question.
d.
a. the role of an organism in its environment
OR
functional position of an organism in its environment \(\checkmark\)
b. includes «spatial» habitat AND feeding activities AND interactions with other species in the community \(\checkmark\) All required.
c. no two species can occupy the same niche \(\checkmark\)
d. a niche can be fundamental or realized \(\checkmark\) OWTTE