nitrogen cycle

Explain the role of saprobionts in recycling chemical elements

● Decompose organic compounds eg. proteins / urea / DNA, in dead matter / organic waste

● By secreting enzymes for extracellular digestion (saprobiotic nutrition)

● Absorb the needed nutrients and release/leave minerals ions in soil eg. phosphate ions for plants to reabsorb

of biological molecules that contain nitrogen

Amino acids / proteins or enzymes / urea / DNA or RNA / chlorophyll / ATP or ADP / NAD or NADP

role of bacteria in nitrogen fixation

● Nitrogen gas (N2) converted into ammonia (NH3), which forms ammonium ions (NH4+) in wet soil

● By nitrogen-fixing bacteria (may be found in root nodules)

Describe the role of bacteria in ammonification

● Nitrogen-containing compounds eg. proteins / urea / DNA from dead organisms / waste are hydrolysed into its monomers

● Converted to ammonia, which forms ammonium ions in wet soil

● By saprobionts - secrete enzymes for extracellular digestion

ammonia goes onto be nitrified in order for plants to absorb

Describe the role of bacteria in nitrification

● Ammonium ions in soil converted into nitrites then nitrates, via a two-step oxidation reaction

○ For uptake by plant root hair cells by active transport

● By nitrifying bacteria in aerobic conditions (oxygen)

Mutualistic bacteria in N cycle

Nitrogen fixing bacteria found in root nodules that fix nitrogen (even in soil with low nitrogen contents) in return for carbohydrates from the host plant.

Describe the role of bacteria in denitrification

● Nitrates in soil converted into nitrogen gas (reduction)

● By denitrifying bacteria in anaerobic conditions (no oxygen, eg. waterlogged soil)

Suggest why ploughing (aerating) soil increases its fertility

● More ammonium converted into nitrite and nitrate / more nitrification / more (active) nitrifying bacteria because it introduced oxygen and prevents anaerobic conditions

● Less nitrate converted to nitrogen gas / less denitrification / fewer (active) nitrifying bacteria

decomposers

break down dead plant'/animal matter e.g. urea and protein, they absorb what they need and leave vital nutrients that plants require

nitrogen cycle

purpose of n cycle

• 78% of air is nitrogen

• triple bond hard to break, can’t obtain nitrogen through gas exchange

• microorganisms needed to convert nitrogen gas into nitrogen containing molecules that can be absorbed:

→ plants: via active transport to roots

→ animals: via digesting plant material