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| Question | Answer |
| 6.1 what can be said about the flow of nutrients within an ecosystem? | the flow of nutrients within an ecosystem is cyclic |
| 6.1 describe the basic sequence of a nutrient cycle | nutrient taken up by producers as simple, inorganic molecules producer incorporates nutrient into complex organic molecules producer eaten, nutrient passed to consumers and along foodchain complex molecules in dead consumers and producers broken down by saprobionts |
| 6.1 give two reasons why the level of atmospheric CO2 has increased | combustion of fossil fuels - releases CO2 previously locked up within these fuels deforestation - removes large amounts of photosynthesising biomass so less CO2 removed from atmosphere |
| 6.1 explain how oceans act as a carbon sink | contains large reserve of CO2 excess CO2 in atmosphere dissolves in water used by phytoplankton to form the macromolecules that make up their bodies |
| 6.1 explain the role of saprobionts | secrete enzymes onto dead organisms which breaks down complex molecules into smaller soluble molecules that can be absorbed by diffusion. carbon released as CO2 during respiration of decomposers |
| 6.1 how are organisms fossilised? | organisms become fossilised into coal, oil or peat if decay prevented |
| 6.1 how are carbon-containing sedimentary rocks formed? give two examples of sedimentary rocks | shells and bones of aquatic organisms sink to bottom of oceans, form carbon-containing sedimentary rocks over millions of years, carbon returns to atmosphere as rocks weathered examples - chalk, limestone |
| 6.2 what is the greenhouse effect? explain how it works | the greenhouse effect is a natural process that keeps global temperatures around 17 degrees solar radiation reaches our planet some radiation reflected into space, some absorbed by atmosphere radiation that reaches the Earth - some reflected back as heat and lost into space some radiated back to Earth by clouds and greenhouse gases in atmosphere GG trap heat close to Earth's surface keeping it warm |
| 6.2 what is the most important greenhouse gas? why? why is it increasing? | CO2 because there's lots of it and it remains in the atmosphere longer than others increasing because of human activities |
| 6.2 how is methane produced? | produced when microorganisms break down organic molecules the organisms made out of e.g. decomposers breaking down dead remains of organisms microorganisms in intestines of primary consumers e.g. cattle, digest food that's already being eaten |
| 6.2 what has the concentration of CO2 risen from? | risen from 270ppm to 370ppm |
| 6.2 what sort of changes has global warming brought about? | global warming brings about changes in temperature, precipitation, timing of seasons, frequency of extreme events |
| 6.2 how does climate change affect a community of organisms? | affects niches available in a community each organism is adapted to a particular niche so distribution of organisms will change if RoCC slow species have time to gradually migrate to new areas and compete for available resources leads to loss of native species that already occupy those niches |
| 6.2 explain five possible changes if global warming is to continue | melting of polar ice caps - extinction of wild plants and animals, rising sea levels rise in sea level due to thermal expansion of the oceans - flooding in low lying land, salt water extends further up rivers so cultivation of crop plants difficult life cycles and populations of insects alter as they adapt to changed conditions, tropical diseases may spread towards the poles increase in rain fills reservoirs, increase temp allows crops to be grown where presently too cold so RoP increases, may be able to harvest twice a year higher temp and less rain - crops don't grow well, more desert lands, only xerophytes can survive, may affect food chains |
| 6.3 what is nitrogen needed for? | needed to manufacture proteins, nucleic acids and other nitrogen containing compounds |
| 6.3 explain ammonification | production of ammonia from organic ammonium containing compounds such as urea (breakdown of excess amino acids) proteins nucleic acids and vitamins saprobionts feed on these materials, releasing ammonia which forms ammonium ions in soil |
| 6.3 explain nitrification | ammonium ions converted into nitrate ions - oxidation reaction so releases energy carried out by free living nitrifying bacteria oxidation of NH4+ --> NO2- oxidation of NO2- --> NO3- oxygen needed so soil needs many air spaces: soil kept well aerated by ploughing good drainage prevents air spaces filling with water |
| 6.3 explain nitrogen fixation | nitrogen gas --> nitrogen containing compounds can be done using lightning or microorganisms free-living nitrogen-fixing bacteria reduce gaseous N2 --> NH3 used to make AA. nitrogen rich compounds released when they decay mutualistic nitrogen-fixing bacteria - live in root nodules of leguminous plants. obtain carbs from plant and plant gets AA from bacteria |
| 6.3 explain denitrification | when O2 levels in soil low, fewer aerobic nitrifying and nitrogen-fixing bacteria and more anaerobic denitrifying bacteria DB convert soil nitrates to N2(g). reduces availability of N2 containing compounds for plants |
| 6.4 what is the drawback of intensive food production? | mineral ions continually taken up by crops being grown on it |
| 6.4 what happens to the mineral ions in a natural ecosystem? | minerals removed from soil by plants eventually returned when broken down after death |
| 6.4 what happens to the mineral ions in an artificial ecosystem? | after crops harvested urine, faeces and dead remains of consumer not returned to same area of land so nutrient levels fall |
| 6.4 why is it important to replace mineral ions? | if not they may become the limiting factor to plant growth, reducing productivity |
| 6.4 explain the two different types of fertiliser | natural organic fertilisers -dead and decaying remains of plants and animals, animal waste artificial inorganic fertilisers mined from rocks and deposits then converted into different forms and balanced to give appropriate balance of minerals or a particular crop. compounds contain N, P and K |
| 6.4 briefly describe how the use of fertilisers increases productivity | minerals needed for growth, so greater the number the greater growth rate as a result of increased photosynthesis, hence productivity increases |
| 6.5 explain how the use of nitrogen fertilisers may lead to reduced species diversity | nitrogen rich soils favor growth of grasses, nettles and rapidly growing species out-compete other species can affect habitats etc |
| 6.5 explain how use of nitrogen fertilisers may lead to leaching. what are two possible consequences? | nutrients removed from soil rain dissolves any soluble nutrients and carry them deep into soil away from roots leached nitrates move into streams, rivers and freshwater lakes can affect humans if drinking source - increases nitrate levels can prevent efficient O2 transport in babies leached nitrate ions can cause eutrophication |
| 6.5 what is eutrophication? explain the process of eutrophication | process by which nutrients build up in bodies of water of freshwater lakes or rivers leaching causes nitrate levels to increase algae grow more near surface - algal bloom layer of algae absorb light, prevents light penetrating to lower depths plants at lower depths die as no light saprobionts feed on dead plant matter saprobionts use up oxygen fish can't get enough oxygen so die anaerobic organisms decompose dead material releasing more nitrates and toxic waste e.g. hydrogen sulphide which makes water putrid |
| 6.5 what five other things may lead/contribute to eutrophication? | organic manures animal slurry human sewage ploughing old grassland natural leaching |
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