Nutrient Cycles Flashcards
nitrogen
nitrogen is finite so it is recycled
proteins, ATP and nucleotides contain nitrogen
nitrogen in the atmosphere is stable + unreactive due to a triple covalent bond so plants can’t access this
nitrogen can be fixed- converted by nitrogen fixing bacteria into nitrogen containing compunds
plants absorb nitrate ions from soil by active transport
saprobiotic digestion
extracellelular digestion of proteins in dead matter to amino acids by decomposers
ammonification
formation of ammonium compounds from amino acids
NH2 (amine) group removed and converted to NH4
nitrification
conversion of ammonium compounds to nitrates
ammonium ions converted to nitrite ions (NO2-)
nitrite ions converted to nitrate ions (NO3-) which can be taken up by the plant
requires nitrifying bacteria which need O2 to respire so if the soil is waterlogged and there is less oxygen, nitrates are converted to nitrogen gas by denitrifying bacteria which work anaerobically
nitrogen fixation
nitrogen converted into nitrogen containing compounds
nitrogen can be fixed with oxygen using lightning to form nitrogen oxides which can be taken up as nitrates
by nitrogen fixing bacteria which reduce nitrogen to ammonia which is used to make amino acids which release nitrates when they die and decay
mutualism
rhizobium bacteria- nitrogen fixing bacteria
found in nodules of leguminous plants, contain nitrogenase which converts nitrogen gas to ammonia
ammonia used to make aa, releases nitrates after death
plant benefits from amino acids produced by bacteria (still have aa even if nitrates are scarce)
bacteria benefits from the sugars from the plant eg carbohydrates used for growth
crop rotation
different crops on same field
leguminous plants (NF bacteria) + other crops
NF bacteria doesn’t deplete soil of nitrates
roots stay in soil (nodules containing ammonia) so other crops benefit as it increases nitrogen compound level in soil
phosphorus
needed in ATP (energy for growth), nucleic acids (production of cells/proteins) and phospholipids (cell membranes)
cycle
plants have phosphorus in biological molecules
digestion + assimilation by consumers
consumers have phosphorus in biological molecules
excretion (guano) and death of consumers
decompose dead material- saprophytic
aquatic sedimentation
phosphate in rocks which is released by erosion
phosphate ions in soil and plants take this up
assimilation
transformation of absorbed substances into biomass
aquatic sedimentation
when solid material eg dead aquatic organisms (containing phosphate) is deposited at the bottom of the sea or on land and gets covered in sediment, forming sedimentary rock
chemical weathering
breaking down and erosion of rocks over time
releases phosphate ions from rocks
mycorrhiza funghi
have thread like structures (hyphae) which grow around the roots of the plant, increasing the surface area for more uptake of water and mineral ions eg phosphate
-can communicate with other plants for direct, fast plant to plant transmission
mutualistic as the plant gains water and phosphate ions
fungus gains sugars eg starch from the plant
why is land depleted of minerals
crop is harvested and transported from its point of origin so plants don’t decompose where they are grown
livestock is removed from where it is grazed so urine, faeces and dead remains aren’t returned
types of fertiliser
natural (organic)- consists of dead and decaying remains of plants, animals and animal waste
ad-cheap, improves soil structure and aeration
dis- don’t know exact ion amounts, dirty and bulky
artificial- consists of minerals mined from rocks and blended together to give an appropriate balance of minerals for the crop
ad- know precise amounts of ions, clean, ions are readily available
dis- expensive, doesn’t help soil structure
