Ecology

What are the levels of organisation in an ecosystem?

Individual organism - population - community - ecosystem.

What is a population?

All organisms of one species living in a habitat.

What is a community?

Populations of different species living and interacting in a habitat.

What is an ecosystem?

Interaction of a community of organisms with the non-living parts of their environment.

What is interdependence?

Species depend on each other for food, shelter, pollination, seed dispersal etc. Removing one species can affect the whole community.

What is a stable community?

Species + environmental factors are in balance - population sizes remain fairly constant.

What do plants compete for?

Light, space, water + mineral ions.

What do animals compete for?

Food, mates + territory.

What is an abiotic factor?

Non-living factor affecting a community.

Which abiotic factors can affect communities?

Light intensity, temperature, moisture, soil pH/minerals, wind, CO2 for plants + oxygen for aquatic animals.

What is a biotic factor?

Living factor affecting a community.

Which biotic factors can affect communities?

Food availability, new predators, new pathogens + one species outcompeting another.

What is an adaptation?

Feature that helps an organism survive and reproduce in its environment.

What are the three types of adaptation?

Structural - physical feature. Behavioural - way organism acts. Functional - internal process.

What is an extremophile?

Organism adapted to extreme conditions e.g. high temperature, pressure or salt concentration.

What is an example of an extremophile?

Bacteria living around deep-sea vents.

What is a producer?

Organism that synthesises its own food/biomass - usually plant or alga using photosynthesis.

Where does every food chain begin?

Producer.

What is a primary consumer?

Organism that eats a producer.

What is a secondary consumer?

Organism that eats a primary consumer.

What is a tertiary consumer?

Organism that eats a secondary consumer.

What is a predator and prey?

Predator - kills/eats another animal. Prey - animal eaten by predator.

What happens to predator and prey populations in a stable community?

Rise and fall in cycles - changes in prey population are followed by changes in predator population.

What is abundance?

Number of organisms of a species in a habitat.

What is distribution?

Where organisms of a species are found within a habitat.

Why do ecologists use quadrats?

Estimate abundance/distribution of organisms without counting the entire habitat.

How should quadrats be placed when estimating population size?

Randomly - reduces sampling bias.

How do you estimate population size using quadrats?

Population estimate = mean number per quadrat x total habitat area / quadrat area.

What is a transect used for?

Investigate how distribution of organisms changes across an environmental gradient.

What is a belt transect?

Quadrats placed at regular intervals along a transect line - abundance recorded at each position.

What are mean, median and mode?

Mean - total / number. Median - middle value. Mode - most frequent value.

RP9 - How do you investigate population size using quadrats?

Randomly place quadrats - count species - repeat many times - calculate mean - estimate population for whole area.

RP9 - How can random quadrat coordinates be generated?

Use random numbers for coordinates - prevents researcher choosing sampling locations.

RP9 - How do you investigate effect of an environmental factor on species distribution?

Lay transect along gradient - place quadrats at regular intervals - measure abundance + environmental factor - compare results.

RP9 - Why use many quadrats?

Larger sample is more representative - reduces effect of anomalies - improves reliability.

What should be controlled in a quadrat investigation?

Quadrat size, sampling/counting method + relevant variables except factor investigated.

What happens to materials in ecosystems?

Continuously recycled between biotic living components + abiotic non-living environment.

Why must materials be recycled?

Provides building blocks needed by future organisms.

What are the main processes in the carbon cycle?

Photosynthesis removes CO2 - feeding transfers carbon - respiration + decomposition return CO2 - combustion also releases CO2.

How does photosynthesis affect the carbon cycle?

Plants/algae take CO2 from atmosphere - carbon becomes part of biomass.

How does respiration affect the carbon cycle?

Plants, animals + microorganisms release CO2 into atmosphere.

How do decomposers contribute to the carbon cycle?

Break down dead organisms/waste - respire - release CO2.

What are the main processes in the water cycle?

Evaporation - condensation - precipitation - water returns to land/seas - cycle repeats.

Why is the water cycle important?

Continuously provides fresh water for organisms on land.

What role do microorganisms have in recycling materials?

Decompose dead material/waste - return CO2 to atmosphere + mineral ions to soil.

Which factors affect the rate of decomposition?

Temperature, water availability + oxygen availability.

How does temperature affect decomposition?

Warmer conditions increase microorganism/enzyme activity to optimum - very high temperatures reduce rate by denaturing enzymes/killing microorganisms.

Why is water needed for decomposition?

Decomposers require water for chemical reactions/growth - dry conditions slow decay.

Why does oxygen increase decomposition rate?

Allows aerobic respiration - transfers more energy for decomposer growth/activity.

How do gardeners increase decomposition in compost?

Provide warm, moist + oxygenated conditions for decomposers.

Why is compost useful?

Decay returns mineral ions - compost acts as natural fertiliser.

What happens during anaerobic decay?

Microorganisms decompose material without oxygen - methane can be produced.

What is biogas?

Mixture containing methane produced by anaerobic decay - methane can be used as fuel.

How do you calculate rate of decay?

Rate = change / time.

RP10 - How do you investigate effect of temperature on milk decay?

Add lipase to milk/indicator mixture - place at different temperatures - measure time or pH change as milk decays - keep other variables constant.

RP10 - Why does pH change as milk decays?

Microorganisms break down substances and produce acidic products - pH decreases.

RP10 - What is the independent variable?

Temperature.

RP10 - What should be controlled?

Volume/type of milk, starting pH, microorganism amount + investigation time/method.

How can environmental change alter species distribution?

Changes conditions - species may move, increase, decrease or disappear from an area. (HT)

Which environmental changes can affect species distribution?

Temperature, water availability + atmospheric gas composition. (HT)

What can cause environmental changes?

Seasonal change, geographic differences + human activity. (HT)

What is biodiversity?

Variety of different species on Earth or within an ecosystem.

Why is high biodiversity important?

Increases ecosystem stability - reduces dependence on individual species + supports human survival.

How can increasing human population affect biodiversity?

More resources used + more waste produced - increases habitat destruction and pollution.

How does water pollution occur?

Sewage, fertilisers + toxic chemicals enter water - can kill organisms and reduce biodiversity.

How does air pollution occur?

Smoke + acidic gases can damage organisms/habitats and reduce biodiversity.

How does land pollution occur?

Landfill + toxic chemicals damage habitats and organisms.

How does human land use reduce biodiversity?

Building, quarrying, farming + waste dumping reduce habitat available to organisms.

Why does destruction of peat bogs reduce biodiversity?

Destroys habitat for plants, animals + microorganisms.

How does peat destruction contribute to global warming?

Decay/burning of peat releases stored carbon as CO2.

Why are tropical forests being deforested?

Land for cattle/rice fields + crops for biofuels.

How can deforestation reduce biodiversity?

Destroys habitats - populations fall/species may become extinct.

How can deforestation contribute to global warming?

Less photosynthesis removes CO2 + burning/decay of trees releases CO2.

Which gases are increasing and contributing to global warming?

Carbon dioxide + methane.

What are possible biological consequences of global warming?

Changes in species distribution, migration, breeding patterns + loss of habitats/biodiversity.

What supports the scientific consensus on global warming?

Systematic reviews of thousands of peer-reviewed scientific publications.

Why can predictions about climate change contain uncertainty?

Climate is complex - many interacting variables + future conditions cannot be known exactly.

How can endangered species be protected?

Captive breeding programmes + reintroduction into habitats.

How can habitats be protected to maintain biodiversity?

Protect/regenerate rare habitats + restore field margins and hedgerows.

Why are field margins and hedgerows important?

Provide habitats/food for many species in areas dominated by single crops.

How can reducing deforestation help biodiversity?

Preserves habitats + reduces CO2 emissions.

How does recycling help biodiversity?

Reduces resource extraction, waste + landfill.

Why can maintaining biodiversity involve conflicting pressures?

Conservation may conflict with food production, housing, industry, jobs + economic development.

What is a trophic level?

Position of an organism in a food chain.

What is trophic level 1?

Producers - plants/algae make their own food.

What is trophic level 2?

Primary consumers - herbivores eating producers.

What is trophic level 3?

Secondary consumers - carnivores eating herbivores.

What is trophic level 4?

Tertiary consumers - carnivores eating other carnivores.

What is an apex predator?

Carnivore with no predators.

How do decomposers digest dead material?

Secrete enzymes outside their cells - digest material into small soluble molecules - molecules diffuse into microorganism.

What is a pyramid of biomass?

Diagram showing relative biomass at each trophic level - producer at bottom.

How should a pyramid of biomass be drawn?

Bar width proportional to biomass at each trophic level - trophic level 1 at bottom.

Approximately how much incident light energy do producers transfer into biomass?

About 1%.

Approximately how much biomass is transferred to the next trophic level?

About 10%.

Why is biomass lost between trophic levels?

Not all material eaten/absorbed + biomass lost in faeces, urine and respiration.

How does egestion reduce biomass transfer?

Undigested material leaves as faeces - not absorbed into consumer biomass.

How does respiration reduce biomass transfer?

Glucose used in respiration - products such as CO2 + water leave organism rather than becoming biomass.

How do excretory products reduce biomass transfer?

Materials such as urea + water leave body instead of being passed to next trophic level.

How do you calculate efficiency of biomass transfer?

Efficiency = biomass transferred to next level / biomass available at previous level x 100.

Why are there fewer organisms at higher trophic levels?

Only about 10% biomass transferred at each level - less biomass/energy available to support organisms.