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ESS Topic 2
2026 Syllabus Topic 2
| Question | Answer |
|---|---|
| Name the ecological system composed of individuals, populations, communities, ecosystems. | The Biosphere |
| Define Species | a group of organisms that can interbreed and produce fertile offspring. |
| Describe a benefit of classifying organisms | It allows for efficient identification and prediction of characteristics. |
| Describe binomial nomenclature | The first name is the genus, the second name is the species; he genus name is given an initial capital letter. The species name is lower case; both genus and species should be either italicized or underlined. |
| Describe tools used in taxonomy | dichotomous keys, comparison of specimens with reference to collections by taxonomists, and deoxyribonucleic acid (DNA) surveys. |
| Define Population | a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding. |
| Describe the two categories of factors that determine the distribution of a population | Abiotic and Biotic |
| Describe Biotic Factors | the living components of an ecosystem |
| Describe Abiotic Factors | non-living physical factors that may influence organisms. |
| List abiotic factors that affect species distributions in ecosystem | Temperature, sunlight, pH, salinity, dissolved oxygen and soil texture are examples |
| List biotic factors that affect species distributions in ecosystem | herbivory, predation, parasitism, mutualism, disease and competition, with ecological, behavioural and evolutionary consequences. |
| Define Carrying Capacity | the maximum size of a population determined by competition for limited resources. |
| Describe how population size can be regulated | by density-dependent factors and negative feedback mechanisms. |
| Describe how density-dependent factors regulate population | regulate the population around the carrying capacity. In addition to competition for limited resources, include the increased risk of predation and the transfer of pathogens in dense populations. |
| Describe population growth - J curves | If there are no limiting factors, population growth follows a J-curve (exponential growth). This can lead to a 'boom and bust' curve. |
| Describe S curve population growth | Density-dependent limiting factors start to operate, the curve becomes S-shaped. The limiting factors can also be referred to as 'environmental resistance'. |
| Describe why human carrying capacity is hard to estimate | Humans have eliminated natural predators, technological advances, and degraded the environment. human populations are less limited due to mobility of resources. rapidly changing human habitat |
| Identify the types of sampling used to estimate population abundance | Can be estimated using random sampling, systematic sampling or transect sampling. |
| Describe the sampling used to estimate population size for non-mobile organisms | Random quadrat sampling. Can include Percentage cover, Percentage frequency to give an estimate of abundance but not actual population size. |
| Describe the index used to estimate population size for mobile organisms | Capture–mark–release–recapture and the Lincoln index |
| Define a community | a collection of interacting populations within the ecosystem. |
| Define a habitat | the location in which a community, species, population or organism lives. |
| Which type of system is an ecosystem? | open systems in which both energy and matter can enter and exit. |
| Why are ecosystems considered sustainable? | Sustainability is a natural property of ecosystems. Inputs are balanced by outputs in a steady-state ecosystem. |
| Describe how human activity can impact ecosystem sustainability | Human activity can lead to tipping points. Tipping points lead to the collapse of the original ecosystem and development of a new equilibrium. For example, deforestation of the Amazon rainforest reduces generation of water vapour through transpiration, |
| Define a keystone species | Species with a disproportionate impact on community structure and the risk of ecosystem collapse if they are removed. e.g. purple sea stars controlling mussel populations on the North Pacific coast that would otherwise overwhelm the ecosystem; |
| Identify the planetary boundary model factor of biosphere integrity and its impact on sustainability | Disturbance of ecosystems due to human activity has led to loss of biosphere integrity. Extinction rates provide evidence that the planetary boundary for biosphere integrity has been crossed. |
| Describe ways in which loss of biosphere integrity can be reversed | protecting the integrity of ecosystems. Protecting ecosystems ensures the preservation of the niche requirements essential for the ongoing survival of a species. e.g. reforestation, |
| Why are keystone species important for sustainability | There is a disproportionate impact on community structure of keystone species and the risk of ecosystem collapse if they are removed. |
| Describe the importance of energy and matter on the sustainability of ecosystems | Ecosystems are open systems in which energy and matter are exchanged. Ecosystems are sustained by supplies of energy and matter. |
| State the first law of thermodynamics in terms of ecosystems | as energy flows through ecosystems, it can be transformed from one form to another but cannot be created or destroyed. |
| Name two processes that transfer matter and energy in ecosystems | photosynthesis and cellular respiration |
| Explain the process of photosynthesis | the conversion of light energy to chemical energy in the form of glucose, some of which can be stored as biomass by autotrophs. |
| Name the first trophic level of a food chain | Producers. They are typically plants, algae and photosynthetic bacteria that produce their own food using photosynthesis. |
| Describe cellular respiration | The process releases energy from glucose by converting it into a chemical form that can easily be used in carrying out active processes within living cells. |
| Why is cellular respiration an inefficient process? | Some of the chemical energy released during cellular respiration is transformed into heat. Heat generated within an individual organism cannot be transformed back into chemical energy and is ultimately lost from the body. |
| Describe the second law of thermodynamics | energy transformations in ecosystems are inefficient. when energy is transformed, some must be degraded into a less useful form, such as heat. In ecosystems, the biggest losses occur during cellular respiration. |
| Describe a consumers role in a food chain | Consumers gain chemical energy from carbon (organic) compounds obtained from other organisms. Consumers have diverse strategies for obtaining energy-containing carbon compounds. Obtain carbon compounds from producers or other consumers. |
| Describe herbivores | Primary consumers - always consume producers |
| Describe saprotrophs | An organism that secretes enzymes that digest organic material before consuming e.g. mushrooms (a type of decomposer) |
| Describe Scavengers | Animals that consume dead organisms |
| Describe decomposers | Animals that digest organic material for nutrition. Two main types - saprotrophs and detritivores. Usually not included in food chains as they typically gain carbon compounds from a variety of sources |
| Describe Detritivores | Decomposers that ingest, then digest organic material. |
| Why are producers usually at the start of the food chain? | Because producers in ecosystems make their own carbon compounds by photosynthesis |
| Why is the second law of thermodynamics applicable to the food chain? | The law explains why energy transfers are never 100% efficient in a food chain. Energy is lost as heat. |
| How do consumers gain matter in a food chain? | There are a diverse ways that consumers obtain their carbon compounds in a food chain - either from producers or other consumers. e.g. herbivores, detritivores, predators, parasites, saprotrophs, scavengers and decomposers. |
| Name the stages in a food chain | Trophic levels. |
| What is lost as food is transferred along a food chain? | There are losses of energy and organic matter. Not all food available to a given trophic level is harvested: not all is consumed; not all is absorbed; not all is stored—some is lost as heat through cellular respiration. |
| Define Gross Productivity | the total gain in biomass by an organism. |
| Define Net productivity | The amount of productivity remaining after losses due to cellular respiration. (NP = GP - R). Losses due to cellular respiration are typically greater in consumers than in producers due to more energy-requiring activity. |
| Why is Net productivity important for sustainability? | The NP of any organism or trophic level is the maximum sustainable yield that can be harvested without diminishing the availability for the future. |
| Why is it unlikely to see more than 4 trophic levels in a food chain? | The number of trophic levels in ecosystems is limited due to energy losses. Energy released by respiration and heat so is unavailable to higher trophic levels. Typically 10% or less of the energy flowing to a trophic level is available to the next level. |
| Why is a food web more accurate than a food chain in an ecosystem? | Food webs show the complexity of trophic relationships in communities. Species may feed at more than one trophic level. |
| What do arrows show in food chains and food webs? | The direction of energy flow and transfer of biomass. |
| How can Biomass be measured in a trophic level? | by collecting and drying samples. Dry mass of samples is approximately equal to mass of organic matter (biomass). Energy in biomass can be measured by combustion of samples and extrapolation. |
| Name the types of ecological pyramids discussed in Topic 2 | Pyramids of number and biomass show the standing crop per unit area at a particular time. Pyramids of productivity show the amount of energy flowing to each trophic level per unit area and per unit time (usually kJ m-2 year-1). |
| Identify some examples of non-biodegradable pollutants that can change ecosystems | polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and mercury, cause changes to ecosystems through the processes of bioaccumulation and biomagnification. |
| Describe Bioaccumulation | refers to the increasing concentration of non-biodegradable pollutants in organisms or trophic levels over time (as more are absorbed). |
| Describe Biomagnification | refers to the increasing concentration of non-biodegradable pollutants along a food chain (due to the loss of biodegradable biomass through, for example, cellular respiration). |
| Describe why microplastics are concerning in the food chain | Non-biodegradable pollutants are absorbed within microplastics, which increases their transmission in the food chain. |
| Describe some examples of human activities that impact on the flow of energy and transfer of matter in ecosystems | burning fossil fuels, deforestation, urbanisation and agriculture |
| Describe how burning fossil fuels impacts the flow of energy and transfer of matter in ecosystems | burning fossil fuels may lead to increased CO2 available for photosynthesis, however, the other pollutants from combustion and impacts global warming will reduce primary productivity. |
| Describe how deforestation impacts the flow of energy and transfer of matter in ecosystems | leads to loss of ecosystem biomass, disruption of food webs, and the capacity for photosynthesis. |
| Describe how urbanisation impacts the flow of energy and transfer of matter in ecosystems | leads to loss of ecosystem biomass, disruption of food webs, and the capacity for photosynthesis. |
| Describe how agriculture impacts the flow of energy and transfer of matter in ecosystems | leads to loss of ecosystem biomass, disruption of food webs, and the capacity for photosynthesis. |
| Describe an autotroph | synthesize carbon compounds from inorganic sources of carbon and other elements. |
| Describe a heterotroph | obtain carbon compounds from other organisms. |
| Describe a biogeochemical store | remain in equilibrium with the environment; absorption is balanced by release. e.g. carbon - organic = crude oil, organisms and natural gas. Inorganic - atmosphere, soil, ocean |
| Describe a biogeochemical sink | indicate net accumulation of the element; e.g. carbon - a young forest where photosynthesis exceeds cellular respiration. |
| Describe a biogeochemical source | a net release of the element. e.g. carbon - a mature forest destroyed by fire or deforestation |
| Describe residence time of a carbon store | the average period that a carbon atom remains in a store. |
| Describe how the same organism can act as a sink, a source or a store of carbon | the difference between photosynthesis and respiration = net accumulation or release of carbon. e.g. young forest acts as a sink, a mature forest = store and a forest fire =source. |
| Describe carbon flows in the carbon cycle | photosynthesis, feeding, defecation, cellular respiration, death and decomposition. |
| Describe carbon sequestration | the process of capturing gaseous and atmospheric carbon dioxide and storing it in a solid or liquid form. Trees sequester carbon naturally by absorbing carbon dioxide and converting it into biomass. |
| Describe the residence time of the carbon in fossil fuels | unlimited residence times. They were formed when ecosystems acted as carbon sinks in past eras and become carbon sources when burned. |
| Describe an example of how agricultural systems can act as stores, sources and sinks | crop rotation, cover crops and no till = carbon sink drainage of wetland, monoculture and heavy tillage will = soil as a carbon source. Cropping over a longer timescale (for example, timber production) and the subsequent use of harvested products will als |
| Describe a biogeochemical store | remain in equilibrium with the environment; absorption is balanced by release. e.g. carbon - organic = crude oil, organisms and natural gas. Inorganic - atmosphere, soil, ocean |
| Describe a biogeochemical sink | indicate net accumulation of the element; e.g. carbon - a young forest where photosynthesis exceeds cellular respiration. |
| Describe a biogeochemical source | a net release of the element. e.g. carbon - a mature forest destroyed by fire or deforestation |
| Describe residence time of a carbon store | the average period that a carbon atom remains in a store. |
| Describe how the same organism can act as a sink, a source or a store of carbon | the difference between photosynthesis and respiration = net accumulation or release of carbon. e.g. young forest acts as a sink, a mature forest = store and a forest fire =source. |
| Describe carbon flows in the carbon cycle | photosynthesis, feeding, defecation, cellular respiration, death and decomposition. |
| Describe carbon sequestration | the process of capturing gaseous and atmospheric carbon dioxide and storing it in a solid or liquid form. Trees sequester carbon naturally by absorbing carbon dioxide and converting it into biomass. |
| Describe the residence time of the carbon in fossil fuels | unlimited residence times. They were formed when ecosystems acted as carbon sinks in past eras and become carbon sources when burned. |
| Describe an example of how agricultural systems can act as stores, sources and sinks | crop rotation, cover crops and no till = carbon sink drainage of wetland, monoculture and heavy tillage will = soil as a carbon source. Cropping over a longer timescale (for example, timber production) and the subsequent use of harvested products will als |
| Describe how oceans act as a carbon sink | Carbon dioxide is absorbed into the oceans by dissolving and is released as a gas when it comes out of a solution. |
| Describe the process of ocean acidification | Carbon dioxide is absorbed into the oceans by dissolving. Increases in concentrations of dissolved carbon dioxide cause ocean acidification, harming marine animals. |
| Describe the impacts of ocean acidification on marine animals | Small decreases in pH can interfere with calcium carbonate deposition in mollusc shells and coral skeletons. |
| Describe some measures that could alleviate the effects of human activities on the carbon cycle | low-carbon technologies, reduction in fossil-fuel burning/soil disruption/deforestation, carbon capture through reforestation and artificial sequestration. |
| Distinguish between the terms climate and weather | Climate describes atmospheric conditions over relatively long periods of time (approx 30 years), whereas weather describes the conditions in the atmosphere over a short period of time. |
| What factors are recorded to describe the weather conditions | temperature, humidity, air pressure and wind speed |
| Describe a Biome | A biome is a group of comparable ecosystems that have developed in similar climatic conditions, wherever they occur. |
| Describe the climatic conditions responsible for the formation of Biomes | Precipitation, temperature and insolation are major influences on the distribution of terrestrial biomes. |
| What factors determine terrestrial biome distribution | Abiotic factors are the determinants of terrestrial biome distribution. |
| Name the groups of biomes studied in ESS | freshwater, marine, forest, grassland, desert and tundra. |
| Describe a subcategory of the forest biome | They may be further classed into many subcategories (for example, temperate forests, tropical rainforests and boreal forests). |
| Describe the characteristic limiting factors, productivity and biodiversity of tropical rainforests | LF: high rainfall leaches nutrients from soils, thin soils, nutrients locked in biomass P: very high productivity B: very high - TR have highest diversity on Earth |
| Describe the characteristic limiting factors, productivity and biodiversity of hot deserts | LF: little precipitation, high evaporation, limited photosynthesis, extreme day/night temp differences P: low - water needed for photosynthesis B: Low: Extreme precipitation and temp are not optimal for plant or animal survival |
| Describe the characteristic limiting factors, productivity and biodiversity of Tundra | LF: short days = low insolation, water often frozen limiting photosynthesis, slow nutrient cycles P: low due to short days, low temps and frozen water and saturated soils during thaw B: Limit - too cold for reptiles, amphibians and invertebrates |
| Describe the characteristic limiting factors, productivity and biodiversity of Grassland | LF: seasonal temp extremes, low decomposition and nutrient cycling P: moderate to low - slow nutrient cycles and seasonal temp extremes limit productivity for part of the year B: high - soil rich in nutrients support extensive food webs |
| Describe the characteristic limiting factors, productivity and biodiversity of marine | LF: no light for photosynthesis in deep oceans, water absorbs some light and limits photosynthesis P: very low in deep ocean, high in tropical coral reefs B: very high on coral reefs, low in Deep ocean |
| Describe the tricellular model of atmospheric circulation | three distinct cells: the Hadley cell, the Ferrel cell and the polar cell affect the distribution of precipitation and temperature at different latitudes. These factors influence the structure and relative productivity of different terrestrial biomes. |
| What role do oceans play in atmospheric circulation? | The oceans absorb solar radiation and ocean currents distribute the resulting heat around the world. |
| How are biomes shifting during global warming? | Global warming is leading to changing climates and shifts in biomes. The general trend is of biomes moving poleward and to higher altitude. |
| Describe Zonation | changes in community along an environmental gradient. |
| What factors influence Zonation? | changes in elevation, latitude, tidal level, soil horizons or distance from a water source. |
| How can zonation be measured? | Transects can be used to measure biotic and abiotic factors along an environmental gradient in order to determine the variables that affect the distribution of species. Kite graphs can be constructed from this data |
| Describe Succession | the replacement of one community by another in an area over time due to changes in biotic and abiotic variables. |
| Distinguish between zonation and succession | Zonation is a spatial phenomenon; succession is a temporal phenomenon. |
| Describe primary succession | successions happen on newly formed substratum where there is no soil or pre-existing community, such as rock newly formed by volcanism, moraines revealed by retreating glaciers, wind-blown sand or waterborne silt. e.g Surtsey Island |
| Describe seral communities | Each seral community (sere) in a succession causes changes in environmental conditions that allow the next community to replace it through competition until a stable climax community is reached. |
| Describe a pioneer community | The first stage of succession e.g. mosses start soil formation on bare rock. The species are adapted to extreme conditions. Small plants or animals with short life cycles and rapid growth. |
| Describe secondary Succession | Succession happen on bare soil where there has been a pre-existing community, such as a field where agriculture has ceased or a forest after an intense firestorm. e.g. Broadbalk Wilderness at Rothamsted |
| Describe energy flow over time during succession | Pioneer stage: small animals and plants, decomposition starting Intermediate Stage: species interactions increase, community respiration increasing Climax: microclimate changes, larger plants and animals cover and provide shelter. complex food web |
| Describe how resilience of an ecosystem affects a community response to a disturbance | An ecosystem’s capacity to tolerate disturbances and maintain equilibrium depends on its diversity and resilience. |
| Describe productivity w over time during succession | Pioneer stage: GP is low, Intermediate Stage: GP increasing Climax Stage: larger plants increase cover and provide shelter - more animal productivity, complex food webs and food chains. Temp, wind and sun less extreme |
| Describe species diversity over time during succession | Pioneer stage: SD is low: small plants and animals with short life cycles Intermediate Stage: SD increasing - more grasses and small shrubs. More habitats for animals. Climax Stage: Larger plants provide shelter, larger animals/complex food webs |
| Describe nutrient cycling over time during succession | Pioneer : Species diversity and respiration is low. As plants die, some decomposition occurring to add organic material to the soil. Intermediate : species interactions increase, invertebrates increase Climax : stable environment with equilibrium |
| Describe a climax community | A stable and self-perpetuating community. The final stage of succession. It is exists in a steady-state dynamic equilibrium. The maximum possible development that a community can reach under the prevailing environmental condition. |
| Distinguish between a line or belt transect. | Line Transects: A line is laid out, and observations are made at specific intervals along the line. Belt Transects: A strip of habitat is marked by a quadrat, and all organisms within the strip are recorded, along with abiotic factors. |
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DrLeeAGS
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