Chapter 13 - Energy And Cycles Flashcards
Explain the importance of the nitrogen cycle
- There is 78% nitrogen in the air however plants and animals cannot obtain nitrogen through gas exchange due to nitrogen containing a triple bond which is difficult to break
- This explains the importance of the nitrogen cycle as microorganisms are needed to convert nitrogen gas into nitrogen containing substances that plants and animals can absorb
Which biological molecules contain nitrogen
- proteins
- ATP
- Nucleic acids
Key processes of nitrogen cycle
1) Nitrogen fixation
2) Ammonification
3) Nitrification
4) Denitrification
What occurs in the first step of the nitrogen cycle (nitrogen fixation)
Atmospheric nitrogen gas can be fixed by:
- Rhizobium (Nitrogen-fixing bacteria) in the root nodules of leguminous plants - They turn N2 into NH3 (ammonia) , which is then converted into an ammonium ions that can be used by the plant, the bacteria form a Mutualistic relationship with the plants as they provide the plant with nitrogen compounds and the plant provides them with carbohydrates
- Free-living bacteria - They fix N2 into NH3 and then amino acids. When they die and are decomposed by saprobionts it causes the nitrogen-rich compounds to be released and converted into a form that can be assimilated by plants.
- Abiotic processes - Lightning, artificial fertilisers, and the Haber process also fix N2.
What does nitrogen fixing mean
Converting a nitrogen gas in the air to a nitrogen containing compound
What is ammonification
This process converts organic nitrogen-compounds in dead organisms or waste to ammonia by saprobionts which then go on to form ammonium ions
What occurs in the second stage of the nitrogen cycle (ammonification)
- Animal waste (urine and faeces), are nitrogen containing compounds, and are converted into ammonia by saprobionts and go in to form ammonium ions which can be absorbed and assimilated by plants
What occurs in the 3rd stage of the nitrogen cycle (nitrification)
- nitrifying bacteria (nitrosomanas) change ammonium ions into nitrites
- other nitrifying bacteria (nitrobacter) change nitrites to nitrates
What is nitrification
When ammonium ions in the soil are changed into nitrogen compounds (nitrates) which can be used by plants
What occurs in the last stage of the nitrogen cycle (denitrification)
It converts nitrates into atmospheric nitrogen using denitrifying bacteria under anaerobic conditions, such as in waterlogged soils.
What is a natural ecosystem
An ecosystem that hasn’t been changed by human activity
Why are saprobionts important for nutrient recycling
As they feed on the remains of dead plants and animals and on their waste products, breaking them down allowing chemical elements in the remains to be recycled
How do saprobionts digest dead organisms
Through saprobiotic nutrition
- This is where saprobionts undergo extracellular digestion by secreteing enzymes, digesting their food externally then absorb the nutrients they need
What is a mycorrhizae relationship
When fungi form a symbiotic relationship with the roots of plants (they both benefit each other)
How do some fungi form a mycorrhizae relationship with the roots of plants
- the fungi are made up of long thin strands called hyphae which connect to the plants root
- the hyphae greatly increase the surface area of the plants root system helping the plant to absorb ions form the soil that are usually scarce
- the hyphae also increases the uptake of water by the plant
- in turn the fungi obtain organic compounds such as glucose from the plant
What do plants need phosphorus
To make
- DNA
- ATP
- Phosphorus bilayer
What does it mean by assimilated
Absorbed then used to make more complex molecules
Explain the whole phosphorous cycle
1) Phosphate ions in rocks are released into the soil by weathering
2) Phosphate ions are taken into the plants through the roots and the mycorrhizae increase the rate at which the phosphorous can be assimilated
3) Phophate ions are transferred through the food chain as animals eat the plants and in turn are eaten by other animals
4) Phosphate ions are lost from the animals in waste products
5) When plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants, these microorganisms also release the phosphate ions from urine and faeces
6) Weathering of rocks release phosphate ions into seas lakes and rivers, this is taken up by aquatic produces e.g algae and passed along the food chain to birds
7) Guano (the waste produced by sea birds) contains a high proportion of phosphate ions, guano returns phosphate ions to soils and is also used as a natural fertiliser
Explain how are nutrients lost when crops are harvested
1) Crops take in minerals from the soil for growth and to build their own tissues
2) When crops are harvested they’re removed from the field where they’re grown, rather then letting them die and decompose, this means the mineral ions they contain are not returned to the soil by decomposers in the nitrogen or phosphorus cycle
3) Phosphates and nitrates are also lost from the system when animals or animal products are removed from the land, this is because animals eat plants they take in their nutrients so when they are taken elsewhere, the nutrients aren’t replaced through their remains or waste product
Advantages of fertaliser
- they replace the lost minerals so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer
