1
Q
How does energy enter the ecosystem?
A
- the energy enters an ecosystem as sunlight and is lost as heat
- this heat cannot be recycled
- the flow of energy through an ecosystem is therefore in one direction, (linear)
- provided the sun continues to supply energy to the earth, this is not a problem
2
Q
What is the sequence of the nutrient cycle?
A
- the nutrient is taken up by producers as simple, inorganic molecules
- the producer incorporates the nutrient into complex organic molecules
- when the producer is eaten, the nutrient passes into consumers
- it then passes along the food chain when these animals are eaten by other consumers
- when the producers and consumers die their complex molecules are broken down by saprobiontic microorganisms that release the nutrient in its original simple form, the cycle is then complete
3
Q
What is the nitrogen cycle?
A
- living organisms require a source of nitrogen from which to manufacture proteins, nucleic acids and other nitrogen-containing compounds
- although 78% of the atmosphere is nitrogen, there are very few organisms that can use nitrogen gas directly
- plants take up most of the nitrogen they require in the form of nitrate ions from the soil
- these ions are absorbed using active transport by the roots
- this is where nitrogen enters the living component of the ecosystem
- animals obtain nitrogen-containing compounds by eating and digesting plants
- nitrate ions are very soluble and easily leach (wash) through the soil, beyond the reach of plant roots
- in natural ecosystems, the nitrate concentrations are restored largely by the recycling of nitrogen-containing compounds
- in agricultural ecosystems, the concentration of soil nitrate can be further increased by the addition of fertilisers
- when plants and animals die, the process of decomposition begins, in a series of steps by which microorganisms replenish the nitrate ions by decomposition is most important because, in natural ecosystems, there are very few nitrate ions available from other sources
4
Q
What are the main stages of the nitrogen cycle?
A
- ammonification
- notification
- nitrogen fixation
- gentrification
- each stage involves saprobiontic microorganisms
5
Q
What is ammonification?
A
- the production of ammonia from organic nitrogen-containing compounds like urea from the breakdown of excess amino acids and proteins
- saprobiontic microorganisms release ammonia, from organic matter which forms ammonium ions in soil
6
Q
What is nitrification?
A
- plants use light energy to produce organic compounds
- some bacteria, however, obtain their energy from chemical reactions involving inorganic ions
- like the oxidation of ammonium ions to nitrate ions
- which is carried out by nitrifying bacteria which require oxygen
- farmers should keep soil structure light and aerated by ploughing
- good drainage prevents the air spaced from being blocked with water
- this increases productivity
7
Q
Which stages does conversion occur in during nitrification?
A
- oxidation of ammonium ions to nitrate ions
- oxidation of nitrate ions to nitrate ions
8
Q
What is nitrogen fixation?
A
- nitrogen gas is converted into nitrogen-containing compounds
- it can be carried out industrially or naturally when lightning passes through the atmosphere
- the most important form of nitrogen fixation is carried out by microorganisms
- free-living nitrogen-fixing bacteria
- mutuality nitrogen-fixing bacteria
9
Q
What is free-living nitrogen-fixing bacteria?
A
- these bacteria reduce gaseous nitrogen to ammonia, which they then use o manufacture amino acids
- nitrogen-rich compounds are released from them when they die and decay
10
Q
What is mutualistic nitrogen-fixing bacteria?
A
- these bacteria live in nodules on the roots of plants such as peas and beans
- they obtain carbohydrates from the plant and the plant acquired amino acids from the bacteria
11
Q
What is gentrification?
A
- when soils become waterlogged and have a low oxygen concentration there are fewer aerobic nitrifying and nitrogen-fixing bacteria are found and more anaerobic denitrifying bacteria
- these convert soil nitrates into gaseous nitrogen which reduces the availability of nitrogen for plants
- so the soils on which crops grow must therefore be kept well aerated to prevent this
12
Q
What is the phosphorus cycle?
A
- phosphorus is an important biological element as it is a component of ATP, phospholipids and nucleic acids
- so life depends on it being constantly recycled
- in the phosphorus cycle the main reservoir is in mineral form as phosphate ions in rock deposits
- they originate in the sea but are brought to the surface by the geological uplifting of rocks
- the weathering and erosion of these rocks helps phosphate ions to become dissolved and so available for absorption by plants which incorporate them into their biomass
- the phosphate ions pass into animals which feed on the plants
- on the death of plants and animals, decomposes such as certain bacteria and fungi break them down releasing phosphate ions into the water or soil
- some phosphate ions remain in parts of animals, such as bones or shells, that are very slow to breakdown
- these are then transported by streams and rivers into lakes and oceans where they form sedimentary rocks thus completing the cycle
13
Q
What is the role of mycorrhizae in nutrient cycles?
A
- mycorrhizae act like extensions of the plant’s root system and vastly increase the total surface area like a sponge and so holds water and minerals in the neighborhood of the roots
- this enables the plant to better resist drought and to take up inorganic ions like phosphate ions more readily
- the relationship is mutualistic as plant benefits from improved water and ion uptake while the fungus receives organic compounds such as sugars and amino acids from the plant
14
Q
How do nutrients enter the ecosystem?
A
- nutrients, by contrast, do not have an extraterrestrial source
- there is limited availability of nutrient ions in a usable form
- it is important therefore that elements such as carbon, nitrogen and phosphorus are recycles
- the flow of nutrients within an ecosystem is not linear, but mostly cyclic
