Ecology

What are the levels of organisation in an ecosystem?

Individual organism -> population (all members of one species in a habitat) -> community (all populations in a habitat) -> ecosystem (the community interacting with its non-living environment). A habitat is where an organism lives.

What is competition, and what do plants and animals compete for?

Competition occurs when organisms need the same limited resources, within or between species. Plants compete for light, space, water and mineral ions; animals compete for food, mates and territory.

What is interdependence, and why can removing a species affect a whole community?

Species depend on each other for food, shelter, pollination and seed dispersal. Removing one species changes these relationships and can alter many other populations.

What is a stable community?

A community where species and environmental factors are in balance, so population sizes remain fairly constant overall, although they can fluctuate.

What are the main abiotic factors affecting communities?

Non-living factors: light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels for plants, and oxygen levels for aquatic animals.

How do light intensity, temperature and carbon dioxide affect plants?

Light and carbon dioxide can limit photosynthesis, reducing growth and food for consumers. Temperature affects enzyme activity: low temperatures slow reactions, while very high temperatures can denature enzymes.

How do moisture, soil pH and mineral content affect plant distribution?

Water is needed for photosynthesis and maintaining turgor. Mineral ions are needed for healthy growth. Soil pH affects mineral availability; different species thrive under different conditions.

How do wind and oxygen levels affect organisms?

Wind can increase transpiration and water loss, and influence seed dispersal. Low dissolved oxygen limits aerobic respiration in aquatic animals, reducing their survival and abundance.

What are the main biotic factors affecting communities?

Living factors: food availability, new predators, new pathogens and competition from other species.

How can changes in biotic factors affect population sizes?

More food can increase survival and reproduction. New predators or pathogens can reduce populations. A better competitor can reduce another species until too few remain to breed successfully.

How should you explain a population change shown in ecological data?

Identify the trend and use values as evidence, then link the factor to survival or reproduction. Consider effects on other species through interdependence; correlation alone does not prove causation.

What are structural, behavioural and functional adaptations?

Structural: physical features, such as thick fur or camouflage. Behavioural: actions, such as migration or being active at night. Functional: internal processes, such as producing concentrated urine to conserve water.

How are animals adapted to cold environments?

Thick fur and fat provide insulation. A small surface-area-to-volume ratio, often from a large body and small ears, reduces heat loss.

How are animals adapted to hot, dry environments?

Large ears can increase heat loss; nocturnal activity and shade reduce overheating. Producing concentrated urine and little sweat conserves water.

How are desert plants adapted to conserve and obtain water?

A thick waxy cuticle and reduced leaves/spines reduce water loss. Water-storage tissues store water; extensive shallow roots absorb rain quickly, while deep roots reach underground water.

What are extremophiles? Give an example.

Organisms adapted to extreme temperature, pressure or salt concentration, such as bacteria living around deep-sea vents.

What is a producer, and why do food chains begin with one?

A photosynthetic organism, usually a green plant or alga. It makes glucose using light energy, then builds other biological molecules and biomass that support consumers.

What do food-chain arrows and consumer names mean?

Arrows point from the organism eaten to the eater, showing transfer of biomass and energy. Primary consumers eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers.

What are predators and prey, and why do their populations cycle?

Predators kill and eat prey. More prey supports more predators; increased predation reduces prey; less food then reduces predators, allowing prey to recover. Predator peaks usually follow prey peaks.

How do you interpret a food web when one population changes?

Identify what eats the species and what it eats. Predict effects on food supply, predation and competition, recognising that alternative food sources can change the outcome.

How are mean, median and mode calculated?

Mean = sum of values / number of values. Median = middle value after ordering; average the two middle values if needed. Mode = most frequent value.

How should ecological data be plotted and interpreted?

Choose an appropriate graph, label axes with quantities and units, and use sensible even scales. State trends using data, recognise anomalies and avoid assuming a relationship proves causation.

Why must materials be recycled in ecosystems?

Materials are finite and are recycled between living organisms and the non-living environment, providing building blocks for future organisms. Energy flows through ecosystems rather than being recycled.

How does carbon enter and move through a food chain?

Plants and algae absorb atmospheric carbon dioxide during photosynthesis and use its carbon to make biological molecules. Feeding transfers these carbon compounds to consumers.

How is carbon returned to the atmosphere?

Plants, animals and microorganisms release carbon dioxide in respiration. Decomposers respire while breaking down dead organisms and waste. Burning wood and fossil fuels also releases carbon dioxide.

How do microorganisms recycle materials?

They break down dead organisms and waste, returning mineral ions to the soil for plant uptake and carbon dioxide to the atmosphere through respiration.

What are the main stages of the water cycle?

Solar energy drives evaporation from water surfaces; plants release water vapour by transpiration. Vapour cools and condenses into clouds; precipitation returns water to land. Runoff and groundwater eventually return it to seas.

Why is the water cycle important to living organisms?

It supplies fresh water to land organisms. Water is needed for reactions including photosynthesis, for transport and as a solvent in cells.

What is decomposition, and which conditions affect its rate?

The breakdown of dead biological material and waste by decomposers. Temperature, water availability and oxygen availability affect the rate.

How does temperature affect decomposition?

Warming increases enzyme-controlled reaction rates up to an optimum. Low temperatures slow decay; very high temperatures denature enzymes and may kill decomposers, slowing or stopping decay.

How do water and oxygen availability affect decomposition?

Moist conditions support microbial activity. Oxygen allows aerobic respiration, generally promoting rapid decay. Waterlogged conditions can restrict oxygen and slow aerobic decay.

How is compost produced and why is it useful?

Waste plant material decays under warm, moist, well-aerated conditions. Turning supplies oxygen; microbial respiration releases heat. Compost adds organic matter and mineral nutrients to soil as a natural fertiliser.

What is anaerobic decay and how is it used in biogas generators?

Decay without oxygen can produce methane. A biogas generator allows microorganisms to break down organic waste anaerobically; the methane-rich gas can be burned as fuel.

How do you calculate a rate of decay?

Rate = amount of material broken down / time, with suitable units. For the same fixed amount of change, relative rate can be compared using 1 / time; a shorter time means a faster rate.

Which environmental changes affect species distribution?

Changes in temperature, water availability and atmospheric gas composition. They may be seasonal, geographical or caused by human activity.

How can environmental changes alter species distribution?

Species survive and reproduce only under suitable conditions. Warming can shift ranges towards cooler areas; water shortages can cause migration or population decline; pollutants can exclude sensitive species.

How should you evaluate evidence about environmental change and distribution?

Compare distributions and environmental data using values. Explain a biological mechanism, consider other changing factors and limitations, and distinguish observed evidence from predictions.

What is biodiversity, and how does it support ecosystem stability?

The variety of different species on Earth or in an ecosystem. Greater biodiversity reduces dependence on any one species for food, shelter and maintenance of the physical environment.

Why is maintaining biodiversity important for humans?

Humans rely on ecosystems for food, materials, potential medicines and services such as pollination and recycling materials. Losing species can disrupt these services.

Why are resource use and waste production increasing?

Rapid human population growth and higher living standards increase demand for resources and produce more waste. Poor handling of waste and chemicals causes pollution.

What are the main sources of water, air and land pollution?

Water: sewage, fertiliser and toxic chemicals. Air: smoke and acidic gases. Land: landfill and toxic chemicals. Pollution can kill organisms and reduce biodiversity.

How can fertiliser runoff and sewage harm aquatic life?

Nutrients can cause excessive algal growth, reducing light for plants. Microorganisms decomposing dead material use oxygen in respiration, lowering dissolved oxygen and killing aquatic animals. Sewage also provides material for microbial growth.

How does human land use reduce biodiversity?

Building, quarrying, farming and dumping waste destroy or fragment habitats, leaving less space and fewer resources for other species.

What is peat and why are peatlands important?

Peat forms from partly decomposed plant material in waterlogged, oxygen-poor conditions. Peatlands provide specialised habitats and store carbon; peat forms very slowly.

Why does destroying peatlands harm biodiversity and increase carbon dioxide?

Extracting peat for compost or draining land destroys habitats. Exposing peat to oxygen increases decay; decay and burning release stored carbon as carbon dioxide.

What is the conflict over using peat compost?

Peat can provide cheap compost for growing crops, but extraction destroys habitats and releases carbon dioxide. Peat-free compost helps conserve peatlands while still supporting food production.

Why are tropical forests cleared on a large scale?

To provide land for cattle, rice fields and crops grown for biofuels, as well as other human land uses.

How does deforestation affect biodiversity and atmospheric carbon dioxide?

It destroys habitats and reduces biodiversity. Burning and decay release carbon dioxide, while fewer trees means less carbon dioxide removed by photosynthesis.

How should the consequences of deforestation be evaluated?

Balance benefits such as food, fuel, jobs and income against habitat loss, reduced biodiversity and increased carbon dioxide. Consider sustainable alternatives and long-term effects.

How do carbon dioxide and methane contribute to global warming?

They are greenhouse gases. They absorb outgoing infrared radiation and re-emit it, reducing energy loss to space. Increasing their concentrations strengthens the greenhouse effect and raises average global temperature.

What are major human sources of carbon dioxide and methane?

Carbon dioxide: burning fossil fuels, deforestation and peat destruction. Methane: livestock, rice cultivation and anaerobic decay of organic waste.

What are biological consequences of global warming?

Changing temperature and rainfall alter habitats, migration, breeding and species distribution. Melting ice and rising sea levels remove habitats. Species unable to move or adapt may become extinct, reducing biodiversity.

Why is climate change evidence strong while exact impacts can remain uncertain?

Scientific consensus is based on systematic reviews of thousands of peer-reviewed studies. Exact local effects remain uncertain because climate and ecosystems are complex and future emissions are not fully known.

How do breeding programmes and habitat protection maintain biodiversity?

Breeding programmes increase endangered populations and may allow reintroduction. Protecting and regenerating rare habitats preserves resources and conditions needed by many species.

Why are hedgerows and field margins reintroduced around monocultures?

A monoculture grows one crop and supports relatively few species. Hedgerows and field margins provide varied habitats, food, shelter and connections between habitats.

How do reducing deforestation, reducing emissions and recycling protect biodiversity?

Less deforestation preserves habitats; lower carbon dioxide emissions limit climate change. Recycling reduces resource extraction, pollution and land needed for landfill.

What conflicting pressures affect conservation decisions?

Food production, housing, jobs and profits may compete with habitat protection. Evaluate costs, effectiveness, effects on local people and long-term biodiversity rather than considering only one benefit.

What are the four main trophic levels?

Level 1: producers, such as plants and algae. Level 2: primary consumers, usually herbivores. Level 3: secondary consumers that eat herbivores. Level 4: tertiary consumers that eat other carnivores.

What is an apex predator?

A carnivore at the top of a food chain with no predators. Its trophic level depends on the particular food chain.

How do decomposers digest dead plant and animal matter?

They secrete enzymes into their surroundings for extracellular digestion. The enzymes break large molecules into small soluble molecules, which diffuse into the microorganisms.

What is biomass and what does a pyramid of biomass show?

Biomass is the mass of living biological material, usually measured as dry mass to exclude variable water content. The pyramid shows relative biomass at each trophic level, with producers at the bottom.

How do you construct an accurate pyramid of biomass?

Use equal-height, centred bars whose widths are proportional to biomass on one consistent scale. Place trophic level 1 at the bottom and label levels and biomass units.

How much incident light energy do producers transfer for photosynthesis?

Approximately 1%. Not all light reaches or is absorbed by photosynthetic parts, and some conditions limit photosynthesis.

What proportion of biomass is typically transferred to the next trophic level?

Approximately 10%, so biomass generally decreases up a food chain. The exact proportion varies between organisms and ecosystems.

Why is biomass lost between trophic levels?

Some organisms or parts are not eaten. Some ingested material is not absorbed and is egested as faeces. Absorbed substances are lost as carbon dioxide and water in respiration, and water and urea in urine.

Why does respiration reduce biomass available to the next trophic level?

Glucose is broken down in respiration, releasing carbon dioxide and water rather than being retained as new biomass. Energy is transferred to the surroundings as heat.

How do you calculate biomass-transfer efficiency?

Efficiency (%) = biomass transferred to the next trophic level / biomass available at the previous level x 100. Use the same mass units; as a fraction, omit x 100.

What is the efficiency if 60 kg of biomass is transferred from a level with 800 kg?

60 / 800 x 100 = 7.5%. To predict biomass from an efficiency, multiply the starting biomass by efficiency / 100.

Why are food chains usually short and higher trophic levels less populated?

Repeated biomass losses leave less food and energy for higher levels, so fewer organisms can usually be supported. Organism size also affects numbers, so biomass does not directly equal population size.

What is food security, and why must food production be sustainable?

Food security means having enough food to feed a population. Sustainable production meets present needs without preventing future generations from meeting theirs.

What six factors threaten food security?

Increasing birth rates; changing diets in developed countries; new pests and pathogens; environmental changes such as failed rains; the cost of agricultural inputs; and conflicts affecting food or water supplies.

How do population growth and changing diets threaten food security?

More people need more food. Demand for resource-intensive foods can increase, and scarce food may be transported worldwide, reducing its availability elsewhere.

How do pests, climate, input costs and conflict threaten food security?

Pests and pathogens reduce crop or livestock yields. Drought and other environmental changes cause crop failure. Expensive seeds, fuel, fertiliser and equipment limit production. Conflict disrupts farming and food or water distribution.

How can population and food-production data be used to assess food security?

Compare available food with population size, calculate food per person and examine trends. Rising total production may still mean less food per person if population grows faster; distribution also matters.

How can intensive livestock farming improve food-production efficiency?

Limit movement to reduce energy used in muscle activity and control temperature to reduce energy needed to maintain body temperature. More of the food can then contribute to growth.

Why are some livestock fed high-protein food?

Protein supplies amino acids for making new proteins, supporting growth and increasing biomass production.

What are the advantages and disadvantages of intensive farming?

It can produce more food efficiently at lower cost. Restricted space and movement raise animal-welfare concerns; crowding can spread infection, and farming can cause pollution. Efficiency must be weighed against ethical and environmental costs.

Why must fishing be managed sustainably?

Overfishing removes fish faster than stocks recover. Enough fish must remain to breed and replace those caught, preventing local disappearance and maintaining future supplies.

How do mesh-size controls and fishing quotas conserve fish stocks?

Larger net mesh lets small, young fish escape, grow and reproduce. Quotas limit the amount caught in a set period or area, leaving enough fish for breeding and recovery.

How is mycoprotein produced?

The fungus Fusarium is grown on glucose syrup in aerobic conditions. Its biomass is harvested and purified to make a protein-rich food suitable for vegetarians.

How can mycoprotein help food security?

Large quantities of protein-rich food can be produced without raising livestock, potentially reducing land demand and pressure on animal food supplies.

How is human insulin produced using biotechnology?

Bacteria are genetically modified to contain the human insulin gene. They are cultured, then the insulin they produce is harvested and purified for treating people with diabetes.

How can GM crops improve food security? Include golden rice.

GM crops can have higher yields or resistance to pests, disease or environmental stresses. Nutritionally improved crops can reduce deficiencies; golden rice produces beta-carotene, which the body converts into vitamin A.

How should proposed biotechnology solutions be evaluated?

Use evidence to compare yield, nutritional benefits, costs and accessibility with possible environmental effects and uncertainties. Benefits depend on the particular crop or method, not simply whether it uses biotechnology.