4.7 Ecology — coverage pack

Answer

• Any two from light, space, water and mineral ions from the soil.

Method: Choose two distinct plant requirements that can be limited within a habitat; acceptable examples are light, space, water and soil mineral ions.

Answer

• Less pollination could reduce the plant's reproduction.
• The plant population could fall.
• Other organisms that depend on the plant for food or shelter could also decline.

Method: Follow the interdependence chain from fewer insects to reduced pollination, then to fewer plants and finally to other species that rely on those plants.

Answer

• The two seed-eating species are most likely to compete strongly.
• They require the same food and nesting space.
• The better competitor may reduce the population of the other species.
• If numbers become too low for successful breeding, the weaker competitor could disappear locally and alter the community.

Method: Compare the overlap in limited resources. The first pair shares both food and nesting sites, so competition is strongest; sustained competitive disadvantage can reduce breeding numbers and change community composition.

Answer

• Any two from moisture, pH and mineral content.

Method: Select non-living soil conditions rather than living influences such as herbivores or pathogens.

Answer

• Oxygen availability is an abiotic factor.
• Fish need oxygen for aerobic respiration.
• Less oxygen reduces respiration or survival, so fish numbers fall.

Method: Link the measured change to the biological need for oxygen, then connect reduced aerobic respiration with death and lower abundance.

Answer

• Light intensity is likely to be lower beneath the dense trees.
• The trees shade the ground plants.
• Lower light intensity reduces the rate of photosynthesis.
• Less glucose is made for growth and reproduction, so the plant is less abundant.

Method: Rule out the stated similar variables, identify light as the remaining relevant abiotic factor, and trace its effect through photosynthesis to population abundance.

Answer

• Any two from food availability, new predators, new pathogens and competition from another species.

Method: Choose living influences or interactions, not non-living conditions such as temperature or soil pH.

Answer

• More lizards are killed, so their population may decrease.
• With fewer lizards surviving to reproduce, fewer offspring may be produced.
• The population could become too small for individuals to find mates and breed successfully.

Method: Use the direct effect of predation and then a reproductive consequence to explain why the fall may continue.

Answer

• The pathogen is a biotic factor that reduces species A.
• The two species compete for the same food.
• Fewer individuals of A leave more food available for B.
• Reduced competition allows more individuals of B to survive or reproduce, so B increases.

Method: Identify both living interactions, then connect pathogen-driven loss of A to reduced interspecific competition and increased resources for B.

Answer

• Structural.
• Behavioural.
• Functional.

Method: Recall the three categories used to classify physical features, actions and internal processes.

Answer

• Resting underground is a behavioural adaptation.
• It reduces exposure to high daytime temperatures and therefore reduces overheating or water loss.
• Producing concentrated urine is a functional adaptation.
• It reduces water loss in urine, conserving water in dry conditions.

Method: Classify the action as behavioural and the internal water-conservation process as functional, then link each one to hot, dry conditions.

Answer

• It lives in conditions of extreme temperature and pressure.
• An organism adapted to extreme conditions is an extremophile.
• The observation shows that the bacterium can survive there but gives no structural details.
• Further information or comparison would be needed to identify which feature provides the advantage.

Method: Apply the definition of an extremophile, then distinguish evidence of survival from evidence about the category or mechanism of an adaptation.

Answer

• Grass is the producer.
• Rabbit is the primary consumer.

Method: The producer makes biomass by photosynthesis, and the organism that eats it is the primary consumer.

Answer

• $4$ plants per quadrat.

Method: Add the counts and divide by the number of quadrats: $(3+5+4+2+6)/5=20/5=4$ plants per quadrat.

Answer

• Lay a tape measure in a straight line away from the hedge to form a transect.
• Place equal quadrats at regular distances along the transect.
• Count the target plants in each quadrat using the same method each time.
• Repeat with further transects or quadrats to improve reliability.
• Calculate mean abundance at each distance and plot abundance against distance using suitable scales.

Method: Use systematic sampling along the changing factor, control the quadrat method, repeat the samples, then calculate means and graph the two variables.

Answer

• Photosynthesis.

Method: Plants use atmospheric carbon dioxide to make glucose during photosynthesis.

Answer

• They break down dead organisms and waste materials.
• Their respiration returns carbon to the atmosphere as carbon dioxide.
• Decomposition releases mineral ions into the soil for uptake by plants.

Method: Connect microbial decomposition with one gaseous return pathway for carbon and one return pathway for mineral ions.

Answer

• Reduced precipitation lowers the fresh water available to plants.
• Plant growth or photosynthesis falls and some plants die.
• Less carbon dioxide is removed by photosynthesis and less biomass is available to consumers.
• Decomposers break down the dead plant material.
• Respiration by organisms, including decomposers, returns carbon dioxide to the atmosphere.

Method: Trace water shortage through plant survival and photosynthesis, then trace carbon through reduced feeding material, decomposition and respiration.

Answer

• Temperature.
• Water availability.
• Oxygen availability.

Method: Recall the three conditions that directly control decomposer activity in this specification point.

Answer

• $0.30\,\mathrm{pH\ units\ h^{-1}}$.

Method: The pH decrease is $6.8-5.6=1.2$. Divide by time: $1.2/4=0.30\,\mathrm{pH\ units\ h^{-1}}$.

Answer

• Warm conditions increase decomposer enzyme activity up to a suitable temperature.
• Moist conditions provide water needed by microorganisms.
• Turning introduces oxygen for aerobic respiration.
• The cold, dry, compacted heap provides less favourable conditions and less oxygen.
• Aerobic composting produces compost that can act as a natural fertiliser.
• Anaerobic decay produces methane that can be used as a fuel.

Method: Compare all three controlling conditions, then distinguish the useful compost product from methane made under anaerobic conditions.

Answer

• Any two from temperature, water availability and atmospheric gas composition.

Method: Select two of the three environmental changes named in the specification.

Answer

• Northern locations may become warm enough for the plant to survive.
• The plant may grow or reproduce successfully in areas that were previously too cold.
• Some southern locations may become less suitable if temperatures exceed the plant's tolerated conditions.

Method: Relate geographic distribution to the range of temperatures in which the species can survive and reproduce, considering both newly suitable and less suitable areas.

Answer

• Drainage is a plausible cause because reduced water can alter the wetland habitat or food supply.
• The timing is consistent with the decline but does not prove causation.
• The new predator is an alternative biotic explanation for increased bird deaths.
• Data from comparable undrained sites or from years before and after drainage would strengthen the conclusion.
• The evidence given is insufficient to attribute the decline only to drainage.

Method: Use the proposed environmental mechanism, test the strength of the correlation, consider the competing predator explanation, request comparative evidence and then give a qualified judgement.

Answer

• The variety of different species of organisms on Earth or within an ecosystem.

Method: Include both variety and species; abundance alone does not define biodiversity.

Answer

• There are more possible sources of food or shelter.
• A species is less likely to depend entirely on one other species.
• If one species declines, alternatives can reduce the effect on the rest of the ecosystem.

Method: Link greater variety to reduced dependence, then explain why loss of one species causes less disruption.

Answer

• Habitat X has the greater biodiversity because it has a greater variety of species.
• Biodiversity concerns the number or variety of different species, not just total abundance.
• A large number of individuals could all belong to only a few species.
• Therefore Y's larger total population does not show greater biodiversity.

Method: Use species variety as the deciding measure and distinguish it explicitly from the total number of organisms.

Answer

• Water: sewage, fertiliser or toxic chemicals.
• Air: smoke or acidic gases.

Method: Provide one example matched to each environmental compartment.

Answer

• More people require more resources.
• A higher standard of living tends to increase resource consumption.
• More consumption produces more waste, which causes pollution if it is not handled properly.

Method: Build the causal sequence from population and consumption through waste quantity to pollution risk.

Answer

• Biodiversity includes the variety of species in the river ecosystem.
• Toxic waste may kill plants or animals, reducing the number of species downstream.
• The downstream fall is consistent with pollution causing the reduction.
• Other downstream differences or measurements before discharge would need checking before concluding that the factory alone caused it.

Method: Connect pollution to species loss and the definition of biodiversity, then distinguish supporting association from proof of a single cause.

Answer

• Any two from building, quarrying, farming and dumping waste.

Method: Select two listed activities that replace or damage habitats.

Answer

• Peat removal destroys or reduces the bog habitat.
• Plant, animal and microorganism species may be lost, reducing biodiversity.
• Exposed peat may decay or be burned.
• This releases carbon dioxide into the atmosphere and contributes to global warming.

Method: Develop one chain through habitat loss and biodiversity and a second through peat carbon release and atmospheric change.

Answer

• Growing crops may increase food production.
• Selling peat compost may provide an inexpensive product or economic benefit.
• Drainage and peat removal destroy habitat and reduce biodiversity.
• Decay or burning of peat releases carbon dioxide, contributing to global warming.
• The decision should weigh these benefits against long-term habitat and climate costs; protecting the peatland is preferable where sustainable alternatives exist.

Method: Give relevant benefits, explain both specified environmental costs, and finish with a conditional judgement supported by that balance.

Answer

• Any two from land for cattle, rice fields and crops for biofuels.

Method: Recall two of the agricultural uses listed for cleared tropical land.

Answer

• Clearing removes or changes habitats.
• Organisms lose food, shelter or breeding sites.
• Populations may fall and species may disappear locally, reducing the variety of species.

Method: Trace the effect from land clearance through loss of habitat resources to fewer species in the ecosystem.

Answer

• Biofuel crops remove carbon dioxide while photosynthesising.
• However, removing mature forest reduces the amount of photosynthesis by existing trees.
• Burning or decay of cleared trees can release carbon dioxide.
• Forest clearance also damages habitats and biodiversity.
• Therefore the claim is not always valid; the outcome depends on carbon uptake and emissions across the whole land-use change.

Method: Consider the proposed carbon benefit, counter it with reduced forest uptake and carbon release, add the ecological consequence, and reject the absolute word always.

Answer

• Carbon dioxide.
• Methane.

Method: Recall the two increasing gases named in this ecology specification point.

Answer

• Examples include changed species distributions, changed migration patterns, disruption of food chains, altered breeding times, habitat loss or reduced biodiversity.
• Credit any three distinct biological consequences.

Method: Give consequences for living organisms or ecosystems rather than restating a physical temperature rise.

Answer

• One regional prediction concerns a limited part of a complex system.
• Some uncertainty or incomplete evidence is expected in detailed predictions.
• Scientific consensus is based on systematic reviews of thousands of peer-reviewed publications, not one prediction.
• Therefore uncertainty in that example does not justify rejecting the wider consensus.

Method: Separate uncertainty in a specific forecast from the much broader evidence base used to establish scientific consensus, then judge the claim.

Answer

• Any two from breeding programmes, habitat protection or regeneration, field margins or hedgerows, reduced deforestation or carbon dioxide emissions, and recycling instead of landfill.

Method: Select two distinct conservation measures named in the specification.

Answer

• They provide additional habitats or shelter.
• They provide food or breeding sites for more organisms.
• More species can survive alongside the crop, increasing or maintaining species variety.

Method: Connect the physical habitat added at field edges to resources for organisms and then to the number of species supported.

Answer

• Protection conserves a rare habitat and the species living there.
• It may prevent population declines and maintain ecosystem stability.
• Development may provide employment or other economic benefits.
• Development could destroy habitat and reduce biodiversity.
• More evidence about ecological importance, development scale and alternatives is needed; protection is favoured if irreversible species loss is likely.

Method: Balance the biodiversity benefits against the stated economic pressure, identify missing decision evidence and give a supported conditional judgement.

Answer

• Trophic level $3$, the secondary consumer.

Method: Count from the producer at level $1$: snail is level $2$ and fish is level $3$.

Answer

• It secretes digestive enzymes into the environment.
• The enzymes break large molecules in the dead material into small soluble molecules.
• The soluble molecules diffuse into the microorganism.

Method: Describe external digestion in order: enzyme secretion, extracellular breakdown and absorption of soluble products by diffusion.

Answer

• Leaves are producers at trophic level $1$.
• Caterpillars are primary consumers at level $2$.
• When the bird eats caterpillars it acts as a secondary consumer at level $3$.
• When it eats spiders that consumed caterpillars, it acts as a tertiary consumer at level $4$.

Method: Construct each feeding route separately and count trophic positions from the producer; an omnivorous diet can place the same species at different levels.

Answer

• Trophic level $1$, the producers.

Method: Pyramids begin with the producer biomass that supports the consumer levels above.

Answer

• Place the producer bar at the bottom, primary consumer above it and secondary consumer at the top.
• Use one consistent horizontal scale for all bars.
• Draw widths proportional to $800:160:40$, equivalent to $20:4:1$.
• Centre the bars and label each trophic level or biomass value.

Method: Order bars by feeding level, simplify the biomass ratio to $20:4:1$, and use that same scale for all centred widths.

Answer

• Equal-width bars are inaccurate because the biomass values are different.
• The $600\,\mathrm{g}$ producer bar should be widest and at the bottom.
• The $90\,\mathrm{g}$ consumer bar should be narrower, with the $15\,\mathrm{g}$ bar narrowest and highest.
• All widths should use the same proportional scale, with a ratio of $40:6:1$.

Method: Check order and proportionality. Dividing all values by $15$ gives $40:6:1$, which supplies a consistent relative width for the corrected bars.

Answer

• Approximately $10\%$.

Method: Recall the approximate biomass-transfer value specified between adjacent trophic levels.

Answer

• $7.5\%$.

Method: Efficiency $=(18/240)\times100=7.5\%$.

Answer

• Only a small proportion of insect biomass is transferred to the birds.
• Not all insect material is eaten or absorbed, and some is egested.
• Absorbed material is used in respiration, releasing carbon dioxide and water.
• Material is also lost in urine as water and urea.
• Less biomass is therefore available at the higher trophic level, so fewer birds can be supported.

Method: Identify the incomplete transfer, account for digestive and metabolic losses, and connect the lower available biomass with the smaller supported population.

Answer

• Having enough food to feed a population.

Method: State the specification definition in terms of sufficiency for the population.

Answer

• The pathogen damages or kills crop plants.
• Failed rains reduce water available for crop growth.
• Both factors reduce crop yield or food production.
• Less food is available relative to the population's needs, reducing food security.

Method: Explain the separate effects of the biotic and environmental threats, then combine them through reduced yield and food availability.

Answer

• Higher total food production could improve supply.
• Faster population growth may reduce the amount of food available per person.
• Higher fertiliser costs increase agricultural input costs and may restrict future production.
• Total production alone is insufficient; food per person, affordability and distribution are also relevant.
• Food security may have worsened despite the production increase, but more data are needed for a firm conclusion.

Method: Balance supply growth against demand and input costs, identify the missing per-person and access evidence, and give a qualified conclusion.

Answer

• Limit the animals' movement.
• Control the surrounding temperature.

Method: Recall the two specified methods that reduce energy expenditure or heat transfer.

Answer

• Less movement means less energy is transferred by muscle activity.
• A controlled temperature reduces energy used to maintain body temperature.
• Less glucose is used in respiration for these activities.
• More of the food intake can be converted into animal biomass or growth.

Method: For each technique, identify the avoided energy loss and then connect the saved chemical energy with greater biomass gain.

Answer

• Restricted movement and temperature control reduce energy losses.
• High-protein food can increase growth.
• More biomass or food can therefore be produced efficiently.
• Restricting natural movement may cause animal-welfare or ethical concerns.
• Whether the method is acceptable depends on the balance between increased production and welfare safeguards.

Method: Explain the biological efficiency benefits, identify the specified ethical objection and finish with a balanced judgement.

Answer

• Fishing quotas.
• Control of fishing-net mesh size.

Method: Recall the two fishery-management methods named in the specification.

Answer

• Smaller or younger fish can escape through the net.
• More fish survive until reproductive age.
• They can breed and replace fish removed from the stock.

Method: Trace the conservation effect from size-selective escape to survival, reproduction and stock replacement.

Answer

• Larger meshes allow more small fish to escape and reach breeding age.
• This can increase reproduction and stock recovery.
• However, unrestricted catches may still remove too many larger breeding fish.
• A quota can limit total removal and leave enough adults to breed.
• Mesh control alone may not be sufficient; both stock data and limits on total catch may be needed.

Method: Credit the benefit of size selection, identify the remaining risk to breeding adults, explain the role of quotas and give a qualified judgement.

Answer

• Fusarium.
• Aerobic conditions, with oxygen supplied.

Method: Recall the named microorganism and that it is cultured aerobically on glucose syrup.

Answer

• The fungus Fusarium is cultured.
• It is supplied with glucose syrup as a food source.
• It is grown in aerobic conditions.
• The fungal biomass is harvested and purified to make protein-rich food.

Method: Give the named organism, substrate, oxygen condition and recovery steps in the production sequence.

Answer

• Genetically modified bacteria can produce large quantities of human insulin.
• The insulin is harvested and purified for treating people with diabetes.
• Genetically modified crops can increase food yield or nutritional value.
• Golden rice is an example of a crop with improved nutritional value.
• These methods can increase supplies of useful products or nutritious food as demand rises.

Method: Use one medical microorganism example and one food-crop example, stating the useful product or improvement and linking both to increased demand.