Nutrient Cycles Flashcards
(12 cards)
Explain the role of saprobionts
They decompose organic compounds by secreting digestive enzymes for extracellular digestion. They also absorb soluble nutrients and release minerals ions.
Explain the role of mycorrhizae
- Fungi (hyphae) act as an extension of plant roots to increase surface area of root system
- To increase rate of uptake / absorption of water and inorganic ions
- Fungi receive organic compounds eg. carbohydrates
Give examples of biological molecules that contain nitrogen
Amino acids, proteins, enzymes, urea, DNA, RNA, chlorophyll, ATP, ADP, NAD, NADP
Describe the role of bacteria in nitrogen fixation
Nitrogen gas (N2) is converted into ammonia (NH3), which forms ammonium ions (NH4+) in soil by nitrogen-fixing bacteria
Describe the role of bacteria in ammonification
Nitrogen-containing compounds from dead
organisms and waste are decomposed by saprobionts (which secrete digestive enzymes) and converted to ammonia, which forms ammonium ions in soil.
Describe the role of bacteria in nitrification
Ammonium ions in soil are 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
Describe the role of bacteria in denitrification
Nitrates in soil are converted into nitrogen gas via reduction by denitrifying bacteria in anaerobic conditions
Suggest why ploughing (aerating) soil increases its fertility
More ammonium is converted into nitrite and nitrate (more nitrification). Less nitrate is converted to nitrogen gas (less denitrification)
Give examples of biological molecules that contain phosphorus
Phospholipids, DNA, RNA, ATP, ADP, NADP, TP, GP, RuBP
Describe the nitrogen cycle
Ammonification: Saprobionts decompose nitrogen containing compounds from dead organisms and waste into ammonia. The saprobionts secrete protease enzymes for extracellular digestion so proteins are converted to ammonia which then form ammonium ions in the soil
Nitrification: Nitrifying bacteria convert the ammonium ions from ammonification into nitrite ions and then nitrate ions via a two step oxidation. The nitrate ions are absorbed by plants by active transport via the roots. Nitrifying bacteria require aerobic conditions.
Denitrification: If conditions are anaerobic, nitrate ions are converted to nitrogen gas by denitrifying bacteria. This is wasteful and can be prevented by aerating and draining soil
Nitrogen fixation: Nitrogen gas from the atmosphere can be fixed into other compounds by nitrogen fixing bacteria. These bacteria can reduce nitrogen gas into ammonia which then dissolves to ammonium ions.
Describe the phosphorous cycle
Phosphate ions are found in rocks and are released into the soil/water via erosion and weathering. The phosphate ions are taken up by producers and become incorporated in their biomass. This absorption is increased by mycorrhizae. The phosphate ions are moved through the tropic levels and are excreted by animals, then saprobionts decompose the organic material and release the phosphate ions.
What is leaching and eutrophication?
Use of fertilisers can lead to mineral ions e.g. phosphates and nitrates dissolving into rainwater and leaching into rivers . This can lead to eutrophication, where the excess mineral ions in the water causes a rapid growth of algae which blocks light. This means water plants die as they do not receive sufficient light for photosynthesis. When they die, saprobionts decompose the dead matter, using up oxygen for aerobic respiration. This reduces the level of oxygen in the water, so fish and other organisms die due to lack of oxygen for respiration.
