B3. Nutrient Cycles in Natural Ecosystems Flashcards
The role of microorganisms
Microorganisms, such as ___________and ______, are an important part of food
webs and ecosystems. Many are saprobionts. Saprobionts do two things:
- They _____on the remains of ____ _______and _______and on their ______products (faeces and urine), __________them down. This makes saprobionts a type of decomposer and it allows important __________elements in the remains and waste to be ____________.
- They secrete _________and ________their ____ _________, then _______the ________they need. This is known as _______________ _________. During this process, ________ _________are broken down into ___________ _____. Obtaining nutrients from dead organic matter and animal waste using extracellular digestion is known as __________ _________.
The role of microorganisms
Microorganisms, such as bacteria and fungi, are an important part of food
webs and ecosystems. Many are saprobionts. Saprobionts do two things:
- They feed on the remains of dead plants and animals and on their waste products (faeces and urine), breaking them down. This makes saprobionts a type of decomposer and it allows important chemical elements in the remains and waste to be recycled.
- They secrete enzymes and digest their food externally, then absorb the nutrients they need. This is known as extracellular digestion. During this process, organic molecules are broken down into inorganic ions. Obtaining nutrients from dead organic matter and animal waste using extracellular digestion is known as saprobiotic nutrition.
The role of microorganisms - Mycorrhizae
Some fungi form _____________ relationships with the _____of _______. These relationships are known as mycorrhizae. The ______are made up of _____, _____ _______called _________, which connect to the _______ _____-see Figure 1. The _______greatly increase the ________ ____of the _______ _____ _______, helping the ______to ________ ___from the ____that are usually scarce (eg, phosphorus). _________also increase the _________of _____by the plant. In turn, the fungi obtain organic compounds, such as ________, from the plant.
Some fungi form symbiotic relationships with the roots of plants. These relationships are known as mycorrhizae. The fungi are made up of long, thin strands called hyphae, which connect to the plant’s roots-see Figure 1. The hyphae greatly increase the surface area of the plant’s root system, helping the plant to absorb ions from the soil that are usually scarce (eg, phosphorus). Hyphae also increase the uptake of water by the plant. In turn, the fungi obtain organic compounds, such as glucose, from the plant.
Figure 1: A plant without mycorrhizae (left) and with mycorrhizae (right).
The nitrogen cycle
Plants and animals need nitrogen to make ________and ________ ____(____and ____). The atmosphere’s made up of about 78% nitrogen gas, but plants and animals can’t use it in that form they need bacteria to convert it into nitrogen-containing compounds first. The nitrogen cycle shows how nitrogen is converted into a usable form and then passed on between different living organisms and the non-living environment.
It includes food chains (nitrogen is passed on when organisms are eaten), and four different processes that involve bacteria: (4 ways)
Other ways that nitrogen gets into an ecosystem are by ____________(which fixes atmospheric nitrogen into nitrogen oxides) or by __________ ____________(they’re produced from atmospheric nitrogen on an industrial scale in the Haber process).
Plants and animals need nitrogen to make proteins and nucleic acids (DNA and RNA). The atmosphere’s made up of about 78% nitrogen gas, but plants and animals can’t use it in that form they need bacteria to convert it into nitrogen-containing compounds first. The nitrogen cycle shows how nitrogen is converted into a usable form and then passed on between different living organisms and the non-living environment.
nitrogen fixation, ammonification, nitrification and denitrification
Other ways that nitrogen gets into an ecosystem are by lightning (which fixes atmospheric nitrogen into nitrogen oxides) or by artificial fertilisers (they’re produced from atmospheric nitrogen on an industrial scale in the Haber process).
Figure 3: The four main processes in the nitrogen cycle.
The Nitrogen Cycle - Nitrogen Fixation
Nitrogen fixation is when ___________ ___in the ___________is turned into __________-____________ ______________. Biological nitrogen fixation is carried out by ____________such as Rhizobium. It turns __________into ____________, which goes on to form _______________ ____in solution that can be used by _______. Rhizobium are found inside root nodules (growths on the roots) of leguminous plants (e.g. peas, beans and clover). They form a mutualistic relationship with the plants -they provide the plant with nitrogen compounds and the plant provides them with carbohydrates. Other nitrogen-fixing bacteria are found in the soil.
Nitrogen fixation is when nitrogen gas in the atmosphere is turned into nitrogen-containing compounds. Biological nitrogen fixation is carried out by bacteria such as Rhizobium. It turns nitrogen into ammonia, which goes on to form ammonium ions in solution that can be used by plants. Rhizobium are found inside root nodules (growths on the roots) of leguminous plants (e.g. peas, beans and clover). They form a mutualistic relationship with the plants -they provide the plant with nitrogen compounds and the plant provides them with carbohydrates. Other nitrogen-fixing bacteria are found in the soil.
The Nitrogen Cycle - Ammonification
Ammonification is when _____________ ____________from _____ _____________are turned into ___________by _____________, which goes on to form _____________ ____. __________ ______also contains _________ ____________. These are also turned into _____________by _______________and go on to form ________________ ____.
Ammonification is when nitrogen compounds from dead organisms are turned into ammonia by saprobionts, which goes on to form ammonium ions. Animal waste (urine and faeces) also contains nitrogen compounds. These are also turned into ammonia by saprobionts and go on to form ammonium ions.
The Nitrogen Cycle - Nitrification
Nitrification is when ______________ ____in the ____are changed into __________ _____________that can then be used by _______(nitrates). First ___________ _________called Nitrosomonas change ____________ ____into _______. Then other _________ ___________called Nitrobacter change ________into __________.
Nitrification is when ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants (nitrates). First nitrifying bacteria called Nitrosomonas change ammonium ions into nitrites. Then other nitrifying bacteria called Nitrobacter change nitrites into nitrates.
The Nitrogen Cycle - Denitrification
Denitrification is when __________in the ______are converted into __________ ___ by ____________ _________-they use -_______in the ____to carry out _____________and produce ____________ ____. This happens under ____________ ___________(where there’s no oxygen), e.g. in ____________ ____.
Denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria-they use nitrates in the soil to carry out respiration and produce nitrogen gas. This happens under anaerobic conditions (where there’s no oxygen), e.g. in waterlogged soils.
Tip: A _____________relationship is a type of symbiotic relationship where both species benefit.
Tip: A mutualistic relationship is a type of symbiotic relationship where both species benefit.
The phosphorus cycle
Plants and animals need phosphorus to make biological molecules such as _______________(which make up ____ ____________), ___and ____. Phosphorus is found in _____and _____________in the _______in the form of ____________ ___. Phosphate ions dissolved in water in the soil can be _____________(absorbed and then used to make more complex molecules) by _________and other __________.
Plants and animals need phosphorus to make biological molecules such as phospholipids (which make up cell membranes), DŇA and ATP. Phosphorus is found in rocks and dissolved in the oceans in the form of phosphate ions. Phosphate ions dissolved in water in the soil can be assimilated (absorbed and then used to make more complex molecules) by plants and other producers.
The phosphorus cycle (Steps 1 to 7)
- Phosphate ions in rocks are released into the soil by weathering.
- Phosphate ions are taken into the plants through the roots. Mycorrhizae greatly increase the rate at which phosphorus can be assimilated.
- Phosphate ions are transferred through the food chain as animals eat the plants and are in turn eaten by other animals.
- Phosphate ions are lost from the animals in waste products.
- 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.
- Weathering of rocks also releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, such as algae, and passed along the food chain to birds.
- The waste produced by sea birds is known as guano and contains a high proportion of phosphate ions. Guano returns a significant amount of phosphate ions to soils (particularly in coastal areas). It is often used as a natural fertiliser.
