10.2 - nutrient recycling

highlight another condition key to the optimum working of decomposers

as they respire (like any other organism) decay takes place more rapidly in the presence of oxygen (especially when there is plenty of oxygen available)

what are nitrifying bacteria?

bacteria that oxidise ammonium compounds to form nitrites and nitrates

why can't plants use nitrogen, even though the contains 78% nitrogen?

because it is an inert gas, & so therefore it's unreactive

how is most (90%) of nitrogen fixed (turned into nitrates)?

by bacteria: nitrogen-fixing bacteria

how else is carbon dioxide released into the atmosphere?

by combustion - straw, wood, fossil fuels

how is carbon dioxide removed from the air?

by green plants in photosynthesis

how are the nutrients held in the bodies of dead plants and animals + animal droppings and urine released back into the soil and air?

by the action of bacteria and fungi - the decomposers

highlight the non useful group of bacteria in the soil that are part of the nitrogen cycle

denitrifying bacteria

how is the carbon dioxide dissolved in the water taken up?

in photosynthesis by the phytoplankton that live in the surface waters in the oceans

where is there a vast pool of carbon?

in the form of carbon dioxide in the air and dissolved in the water of rivers, lakes and oceans

what is the useful form of nitrogen for plants?

in the form of nitrates - these are absorbed by plants in the form of soil water

where is the main role of decomposers?

in the natural word: decomposers have a key role in the recycling of resources, which plays a vital role in maintaining the fertility of soil + the health of our atmosphere

in the industrial world, when is the process of decomposition used?

in the treatment of sewage + production of compost

when does the decay of dead plants, animals + dung take place more rapidly?

in warm, moist conditions

highlight what occurs in the biotic phase

inorganic ions are incorporated in the tissues of living things

highlight what occurs in the abiotic phase

inorganic ions are returned to the non-living part of the ecosystem

what is particular about the supply of other resources needed by producers to build molecules like carbohydrates, proteins and lipids?

it is not exhaustible

why is carbon important for living organisms?

it is part of all of the main molecules of life: carbohydrates, proteins, fats and DNA

give an example to illustrate the point made above

it would take more or less a year to decompose a leaf in the UK but in the tropical rainforest it may only take 6 weeks

what do we find in nature?

large abiotic and biotic carbon sinks

what does soil contain?

large amounts of organic rich material - organic humus

which group of plants are important in the nitrogen cycle?

legumes - peas, beans, clover

what does 'nutrients' refer to?

materials required by an organism e.g elements such as carbon, nitrogen and phosphorous

what are the optimum conditions for most microorganisms?

moist conditions - as it makes it easier for them to dissolve food + prevents them from drying out

what do the bacteria produce?

much more ammonia than their host plant needs and so the excess passes into the soil to be used and turned into nitrates by nitrifying bacteria

do carbohydrates contain nitrogen?

no

what do some bacteria in the carbon cycle do?

produce the enzyme cellulase which breaks down the cellulose in plant cell walls - producing sugars that can then be used as food by a wide range of organisms

what does the sun do?

provides light for photosynthesis - for the foreseeable future

what do the microorganisms do?

release waste products + provide the nutrients in a form that plants can use again

what happens in the abiotic part of the system?

rocks e.g limestone and chalk + fossil fuels hold vast stores in carbon

what do plants constantly do?

take minerals e.g nitrates from the soil and compounds like carbon dioxide from the air to build macromolecules in their cells

what do complex cycles ensure?

that the chemical constituents of life are continually recycled within ecosystems

what else are microorganisms involved in?

the carbon cycle

what happens when plants are eaten by animals and those animals are eaten by predators?

the carbon is passed on and becomes part of the animals' bodies (this is how carbon is removed from the environment)

what is a massive reservoir for carbon dioxides?

the oceans

what is the nitrogen cycle?

the recycling of nitrogen between living things + their environment by the actions of microorgansisms

what is the carbon cycle?

the series of reactions by which carbon is constantly recycled between the living things and their environment

to summarise: what is there a finite amount of on Earth?

the supply of inorganic nutrients - new elements can't just be created and so they are in limited supply

what are denitrifying bacteria?

they are bacteria that break down nitrates to power the production of ATP, producing nitrogen gas as a waste product

what do nitrogen-fixing bacteria do?

they are found in the soil and they: can convert nitrogen from the soil air into ammonia, which is then converted into nitrates by the nitrifying bacteria

what are carbon sinks?

they are reservoirs where carbon is removed from the atmosphere and retained in organic or inorganic compounds

what do decomposers do?

they feed on the droppings and dead bodies - digesting them + using the nutrients for respiration to build their own cells + for reproduction

what happens to the macromolecules built in plants?

they get passed on to animals through food chains and food webs (these link all living organisms)

why do legumes have a key role in the nitrogen cycle?

they have nodules on their roots which contain a lot of nitrogen-fixing bacteria (this = an example of mutualism, both organisms live together + both benefit)

overall what do denitrifying bacteria do?

they reduce the amount of nitrates in the soil

when do the chemical reactions in microorganisms work best?

they work faster in warmer conditions note: as they're controlled by enzymes, if the temperature is too hot they stop working altogether as their enzymes denature (this also happens in cold conditions)

what is carbon used for by plants?

to make carbohydrates, proteins and fats that make up the body of the plant

what do plants use nitrates for?

to make proteins, + the protein gets passed along the food chain/web - therefore nitrogen from the soil becomes incorporated into the bodies of all different types of living organisms

highlight the general stages in nutrient recycling

- autotrophs obtain inorganic compounds from the air, water + soil and convert them into organic compounds - heterotrophs ingest organic compounds + use them for growth, respiration + therefore releasing the inorganic products - when organisms die, decomposers digest their remains + free (return) the inorganic materials into the soil and air - the return of inorganic nutrients to the soil ensures a continuous supply of raw materials for autotrophs

highlight how this is an example of mutualism

- bacteria are protected + have a supply of organic food from the plant - the plant gets ammonia needed to form amino acids

how can some nitrogen be fixed (turned into nitrates)?

- fixation by lightening - fixation by the Haber process (the fertiliser contains ammonium ions and nitrate ions which end up in the soil) note: these two processes = only 10% of nitrogen fixation on Earth

where can the importance of microorganisms in nutrient recycling be seen?

- in the nitrogen cycle - in the carbon cycle

what are the two main phases of these cycles?

- the biotic phase - the abiotic phase

highlight the situation in a stable community of plants and animals living in an environment

- the processes that remove materials from the soil are balanced by the processes that return materials (materials are constantly recycled through the environment) - by the time the microbes and detritus feeders have broken down waste products + dead bodies of organisms, most of the energy originally captured by green plants in photosynthesis = has been transferred to other organisms or back into the environment

what is nitrogen key in?

- the structure of many biological molecules - DNA and RNA (in the bases)

how is carbon dioxide returned to the atmosphere?

- when green plants respire - when animals respire (carbon dioxide is released as a waste product) - also when plants and animals die & their bodies are broken down by decomposers, these microbes respire and they release carbon dioxide into the atmosphere (this carbon dioxide is ready to be removed by plants again in photosynthesis)

what happens in the biotic part of the system?

carbon is removed from the atmosphere by photosynthesis + it is stored in the body of living organisms