13.3: Nutrient cycles Flashcards
N2
atmospheric nitrogen
Extracellular digestion
A process carried out by saprobionts in which they secrete enzymes onto dead organic matter which break down large, insoluble molecules
What are saprobionts
Microorganisms for example: fungi and bacteria
Importance of extracellular digestion
vital so that continuously reusing nutrients
What happens to the products of extracellular digestion?
they are small, soluble molecules which can be absorbed by the saprobiont and used in respiration or stored
4 steps in nitrogen cycle
1: Nitrogen fixation
2: Ammonification
3: Nitrification
4: Denitrification
Nitrogen fixation
step 1
N2 into NH3
by nitrogen fixing bacteria in the soil
Nitrogen fixing bacteria (mutualistic)
Form a mutualistic relationship with leguminous plants by inhabiting their root nodules and provide a source of ammonium ions for the plants and the plants provide them with sugars
Leguminous plants
eg: beans and peas
Ammonification
step 2
Saprobionts decompose a dead organism by extracellular digestion they release inorganic ammonium ions into the soil
Nitrification
step 3
NH4 + ions (that are released from step 2)
are converted into nitrates by nitrifying bacteria into nitries and then another bacteria convert them into nitrates
Denitrification
step 4
Denitrifying bacteria convert nitrates back into N2
a process that occurs in anaerobic conditions when the soil is waterlogged
2 types of nitrogen fixing bacteria
free-living nitrogen fixing bacteria
mutualistic nitrogen fixing bacteria
Free-living nitrogen fixing bacteria
reduce gaseous nitrogen to ammonia then they manufacture amino acids
The phosphorus cycle
Phosphorus exists mostly of PO4 3-
(phosphate ions) into sedimentary rock deposits in the sea but are often brought up to the surface by the geographical uplifting of rocks
Mycohorrizae associations
Fungi form symbiotic relationships with the roots of plants and act like extensions of the plants roots
Mycohorrizae role
3
vastly increase the SA of plants for the absorption of water and minerals and act like a sponge
enables plants resist droughts more easily
improves the uptake of quite scarce ions eg: phosphate ions
