C.6 The Nitrogen and Phosphorus Cycles

outline how human activity impacts the phosphorus cylce

-phosphate is mined and converted into phosphate based fertlilizer (this increases the rate of turnover) -the fertlilizer is then (transported great distances and) applied to crops (these processes remove phosphorus from the cycle in one location and adds it to another -phosphorus in the biomass of crops is transferred from fields in one area to markets in other areas

what are the uses of phosphate for organisms

ATP DNA and RNA cell membranes skeletons in vertebrates

distinguish between the bacteria from the genii Rhizobium and Azotobacter

Azotobacter are free-living in the soil Rhizovium live in a close symbiotic association in the roots of plants such as the legume familty

state the name of the genus of the bacteria that contains many species that can perform dentirification

Pseudomonas sp.

outline how there are lower levels of dissolved oxygen in rivers and lakes

algal growth is normally limited by the availability of nutrients such as nitrates and phosphates rapid growth in the algal propulations occur, these increases are called 'algal blooms' as the population of algae increase so naturally does the numbers of dead algae the numbers of (saprotrophic ) bacteria and microbes feed on the dead algae also increase an increase in biochemical oxygen demand (BOD) by the saprotrophic bacteria results in deoxygentation of the water supply (reduced dissolved O2)

explain why rocks rich in phosphate minerals are classified as a non renewable resource

as the reserves of phosphate rock are depleted the production of phosphorus is likely to peak and decline though some sources say the peak is likely to occur in the next 30 years it is difficult to judge particularly due to the fact that new phosphate mineral deposits are still being discovered

briefly outline the process of nitrification that produces the nitrates, which plants can absorb and assimilate

converting ammonia into nitrations (nitrosomonas and nitrobacter are bacteria that complete this process)

what are the consequences to organisms of low levels of dissolved oxygen

death or emigration of oxygen sensitive organisms (fish) proliferation of low dissolved oxygen tolerant organisms reduction of biodiversity decrease in water transparency (an increase in turbidity stresses photosynthetic organisms which in turn will affect the whole food chain, no light getting through) increased levels of toxins and greater numbers of pathogens means affected water is no longer suitable for bathing or drinking

outline how insectivorous plants absorb the nitrogen contained in the insects and other animals

modified leaves have evolved to trap insects enzymes are secreted to (extracellularly) digest the animal the products of digestion are absorbed by the modified leaves

which nitrogen compounds can plants absorb and assimilate

nitrates and ammonia

state the name of the key processes carried out by the bacteria Rhizobium and Azotobacter and the nitrogen contain compound produced

nitrogen fixation (nitrogen to ammonia)

explain why these plants cannot be truly considered carnivourous

only nitrogen compounds are absorbed. the plant still obtains its energy from light via photosynthesis

explain why the rate of turnover (the speed of movement of phosphorus from one pool/sink to another) is relatively slow compared with nitrogen

phosphate is only slowly released to ecosystems by weathering

state the reason why nitrogen is frequently a limiting factor for plant growth when 78% of the atmosphere is nitrogen gas

plants cannot directly absorb and assimilate nitrogen

explain how increased concentrations of nutrients can cause a lack of dissolved oxygen in rivers and lakes

poorly drained, waterlogged soils encourage leaching an increase in nutrients in aquatic ecosystems leads to eutrophication

explain how more nutrients end up in rivers and lakes

rainfall leaches water-solublem nutrients (phosphates, ammonia and nitrates) from soil and carries them into rivers and lakes. The nutrients can come either from artificial fertilizers, natural fertilizers such as manure or the urine of livestock

define the term dentrification

reduces the availability of nitrogen compounds to plants nitrate to nitrogen

outline the impact of waterlogging on the nitrogen cycle

soil can become inundated by water, waterlogged, through flooding or irrigation with poor drainage waterlogging reduces the oxygen availability in soils this encourages the process of dentrification by bacteria ex. pseudomonas sp.

list three example of insectivorous plants and explain how the specialized leaves act as a trap in each case

sundews (drosera)- flypaper traps that are sticky or adhesive. the leaves are covered in slaked glands that exude sticky mucilage venus flytrap(dionaea)- snap traps (steel traps) are hinged leaves that snap shut when trigger hairs are touched bladderwort (utricularia)- suction traps (unique to this plant) are highly modified leaves in the shape of a bladder with a hinged door line with trigger hairs

explain why phosphate minerals are classified as a non-renewable resource

the demand for artificial fertilizer in modern intensive farming is very high consequently phosphate mining is being carried out at a much faster rate than the rocks can be naturally formed and hence replenished

outline why the relationship between Rhizobium and legumes is described and being symbiotic (an example of mutualism)

the legume supplies carbohydrates to the bacteria. the bacteria use the carbohydrates for processes such as respiration the bacteria supply ammonia (fixed from atmospheric nitrogen) to the legume the legume requires ammonia for the synthesis of amino acids mutualism describes relationships between organisms in which organisms benefit they grow together to form nodules on the roots of the legume

describe the conditions in which dentrifying bacteria would perform dentrification

though oxygen is preferred, in oxygen poor conditions nitrate is used and the process releases nitrogen gas as a product oxygen or nitrate is used in cell respiration as an electron acceptor in electron transport