energy transfers in and between organisms (nutrient cycles) Flashcards
what are the four stages of the nitrogen cycle?
-nitrogen fixation
-ammonification
-nitrification
-dentrification
explain nitrogen fixation
nitrogen fixing bacteria in root nodules of legumes and free-living bacteria in soils use the enzyme nitrogenase to reduce gaseous nitrogen into ammonia, which produces ammonium ions.
explain ammonification
-saprobiotic microorganisms feed on faeces and dead organisms
-this causes the production of ammonia from organic nitrogen containing compounds
-the released ammonia forms ammonium ions in the soil
explain nitrification
-ammonia ions are oxidised to produce nitrite by nitrifying bacteria
-more nitrifying bacteria oxidise the nitrites into nitrates
explain denitrification
-anaerobic denitrifying bacteria convert nitrate ions to nitrogen gas.
-this process is wasteful as nitrogen gas cannot be absorbed by plants
-it can be prevented through ensuring that the soil is well aerated and drained.
why is nitrogen significant to organisms
plant roots uptake nitrates via active transports and use them to compose biological compounds including nucleic acids, amino acids, NAD/NADP
outline the role of mycorrhizae.
symbiotic relationship between plant and fungus
the mycorrhizae has long thin strands called hyphae that connects to plant roots and increases the surface area. this helps the plants increase their uptake of water and mineral ions
they act as a sponge to hold water and minerals around the root which makes them more drought resistant
the plant provides the fungus with carbohydrates produced in photosynthesis
why is phosphorus significant to organisms
-phosphate ions are absorbed by plants to compose biological compounds including phospholipids in cell membranes, nucleic acids, and ATP
-phosphorus is transferred to plant consumers through feeding and digestion. they use the ions to synthesis organic matter
-excess phosphate ions are excreted by animals such as in guano/bird waste
-on death decomposer break these animals down and release the phosphate ions into the water or soil
-some phosphate ions are transported by streams and they form sedimentary rock
why can’t organisms use nitrogen directly from the atmosphere?
nitrogen is very stable due to a strong covalent triple bond
how do saprobionts get the nutrients they need?
saprobiont nutrition
extracellular digestion occurs which is when the saprobionts secrete enzymes and digest food externally.
organic molecules are are broken down into inorganic ions
they then absorb the nutrients they require
why are fertilisers used?
fertilisers are used to provide or replace plants with minerals so to increase gross productivity for higher crop yield
organic fertilisers consist of dead and decaying organic matter and animal waste
inorganic fertilisers consist of minerals mined from rocks
how are nutrients lost when crops are harvested?
crops uptake minerals from the soils for growth
when the crops are harvested they are removed from the field which stops mineral ions from returning to the soil by decomposers
what environmental issues do fertilisers raise?
-reduced species diversity as nitrogen rich soils favour rapidly growing species
-leaching occurs when rainwater dissolves soluble nitrates and runoff transports the nitrates into water sources like lakes, rivers
-eutrophication
explain eutrophication.
nitrate levels in water sources increase due to leaching and stimulate rapid growth of algae.
the algae bloom prevents light from reaching water under the surface and the plants below
the plants are unable to photosynthesis due to a lack of light so they die
saprobiontic bacteria feed on the dead plant matter which increases the population of saprobiontic bacteria
as they respire anaerobically there is a reduced oxygen concentration in the water source which causes the death of aquatic organisms like fish
define biomass
the chemical energy stored in the plant
