Nutrient cycles Flashcards
Why is it important that nutrients are recycled?
Because there is a limited availability of nutrient ions in a usable form. It is important therefore that nutrients such as carbon, nitrogen and phosphorus are recycled - the flow is cyclic rather than linear
What is the simple sequence of a nutrient cycle?
- nutrients are taken up by producers as simple, organic molecules
- the producer incorporates the nutrient into complex organic molecules
- when the producer is eaten, the nutrient passes into consumers
- nutrient passes along the food chain as consumers are eaten
- when producers and consumers die, they are broken down by saprobiontic microorganisms which release the nutrient in its simple, original form
What would happen without saprobionts?
Nutrients would remain locked up as part of complex molecules that cannot be taken up or used by plants again
Why are nitrates needed in plants?
- manufacture amino acids, proteins and nucleic acids needed for growth
How do plants take up nitrate ions?
Through active transport in the soil
What are the 4 main stages in the nitrogen cycle?
- ammonification
- nitrification
- nitrogen fixation
- denitrification
What is ammonification?
nitrogen compounds in waste products and dead organisms are converted into ammonia by saprobionts
What is nitrification?
Ammonium ions in soil are converted by nitrifying bacteria into nitrite ions (NO2-) and then nitrate ions (NO3-), which are nitrogen compounds that can be used by plants
What is nitrogen fixation?
Nitrogen gas is converted into nitrogen containing compounds by nitrogen-fixing bacteria
- bacteria reduce gaseous nitrogen to ammonia, which they use to manufacture amino acids. Nitrogen rich compounds are released when they die
What is denitrification?
when soil becomes waterlogged, there is an increase in anaerobic gentrifying bacteria. These convert soil nitrates into gaseous nitrogen during respiration, which reduces the availability of nitrogen containing compounds for plants. (therefore soil must be kept aerated to reduce denitrifying bacteria)
Why is phosphorus important?
Component of ATP, phospholipids and nucleic acids - life therefore depends on it being constantly recycled
How are nitrates made available to plants?
- proteins are converted into ammonium compounds by saprobionts
- ammonium converted to nitrite, which is converted into nitrate by nitrifying bacteria
- nitrate is converted to ammonium by nitrogen fixing bacteria
What are the stages of the phosphorus cycle?
- phosphate ions found mostly in the form of sedimentary rocks - erosion and weathering of these rocks helps phosphate ions to become dissolved
- available for absorption, so taken up by plants (assimilation)
- phosphate ions pass to animals which feed on plants
- after death and excretion, decomposers break them down and release phosphate ions into the water/soil
- phosphate ions in streams/rivers are transported to oceans where sedimentation occurs
What are mycorrhizae and what is their role?
- fungi which act like extensions of the plants root system, which vastly increases surface area for the absorption of water and minerals
- plants benefit from improved water and ion uptake whist fungus receives organic compounds such as sugars and amino acids from the plant
Why are fertilisers used?
- in agricultural systems, crops are harvested meaning that nutrients cannot be recycled - necessary to replenish them so that they will become a limiting factor to plant growth, reducing productivity and yield
