Nutrient cycles Flashcards
What are the common features of all nutrient cycles?
- Nutrients are taken up by producers (plants) as simple inorganic molecules
- Producer incorporates nutrient into complex inorganic molecules
- When producers are eaten, nutrients passes into consumers
- Passes along the food chain + animals eaten by other consumers
- When producers + consumers die, their complex molecules are broken down by saprobionts which release nutrients
(Then, the cycle repeats)
Why do plants need nitrogen?
To manufacture proteins, nucleic acids + other nitrogen-containing compounds
Nitrate ions are very soluble. What does this mean when it is in soil?
They easily leach (wash) through the soil, beyond the reach of plant roots
How can concentration of soil nitrate be further increased?
By the addition of fertilisers
What is assimilation?
When nitrates are taken up by the roots
Name the four main stages of the nitrogen cycle in order
Ammonification, nitrification, denitrification + nitrogen fixation (nitrates made by nitrification can either be absorbed by roots or denitrification + nitrogen fixation can take place - produce ammonium ions)
Describe the process of ammonification
Saprobionts break down dead organisms + release nitrogen contained as NH3 and are converted to NH4+ (ammonia to ammonium ions)
Describe the process of nitrification
-It is carried out by nitrifying bacteria
- Ammonium ions are converted to nitrite ions
- Nitrite ions are then converted to nitrate ions
(Both of these are oxidation reactions)
Describe the process of nitrogen fixation
- It is carried out by nitrogen fixing bacteria
- Nitrogen gas is converted into ammonium ions
Describe the two ways in which nitrogen fixation can occur
- Happens naturally during lightning
- Carried out by bacteria
- Mutualistic (nitrogen fixing) bacteria that live inside roots nodules of leguminous plants
- Free living nitrogen fixing bacteria in the soil
Why do the plants and the bacteria have a mutualistic relationship?
They both benefit one another:
The plant provides bacteria with carbohydrates and the bacteria provide plants with nitrates
What do the free living nitrogen fixing bacteria do?
Nitrogen gas can be reduced to ammonia (which can then be used to make amino acids)
Describe the process of denitrification
- Nitrates in soil are converted to nitrogen gas by denitrifying bacteria
- This requires anaerobic conditions
Why does denitrification occur?
- It happens when the soil becomes waterlogged
- There is low O2 concentration so there are fewer aerobic bacteria (nitrifying + nitrogen fixing bacteria) and more anaerobic denitrifying bacteria
Why is denitrification bad and how can you prevent denitrifying bacteria from building-up?
- Denitrification reduces availability of nitrogen-containing compounds for plants
- You can prevent build-up of denitrifying bacteria by keeping the soil well aerated (make sure there is plenty of O2 available)
What important biological elements need phosphorus (or phosphate ions)?
ATP, phospholipids + nucleic acids
Where is phosphorus found (and in what form)?
Phosphorus exists mostly as phosphate ions in the form of sedimentary rock deposits
Define weathering
The break down of rocks on the Earth’s surface
Define erosion
The act of taking broken down rocks away
What is guano? Why does it contain lots of phosphate ions?
Seabirds faeces. They have lot of phosphate ions from the fish that they eat from the sea - the sea contains phosphate ions that are be dissolved out of rocks
What is uplifting?
Rocks that were underground being forced/brought up the Earth’s surface
How do animals get phosphate ions?
They eat the plants that absorb the phosphorus ions from the soil
How do phosphate ions form sedimentary rocks?
The phosphate ions from guano and decomposition remains are transported by streams and rivers into lakes and oceans where they form sedimentary rocks - this completes the cycle
How can plants get phosphate ions?
- Guano contains lots of phosphate ions (from the fish that seabirds eat) which the soil can absorb
- Decomposition of dead organisms leaving remains e.g bones + shells releasing phosphate ions into the water/soil
What is mycorrhizae?
Mycorrhizae are associations between certain types of fungi and the roots of plants
How/why does mycorrhizae play an important part in nutrient cycles?
- Fungi increase SA for absorption of water + minerals
- Helps increase uptake of scarce ions e.g phosphate ions
Why is the relationship between the fungi and plant described as mutualistic?
Both the plant and the fungi benefit:
- Plants get water + nutrients from fungi
- Fungi get organic compounds (e.g amino acids & sugars) from plants
