Why are nutrient cycles essential in natural ecosystems?
Recycling of nutrients
Matter is continually reused so elements like nitrogen and phosphorus remain available for organisms.
What type of organism feeds on dead organic matter and releases enzymes externally to break it down?
Saprobionts
Commonly fungi and bacteria that carry out extracellular digestion during decomposition.
During decomposition, which process converts organic nitrogen compounds in dead organisms into ammonium ions?
Ammonification
Carried out by microorganisms during decay of proteins, nucleic acids and other nitrogen-containing molecules.
What process converts ammonium ions in soil into nitrite and then nitrate ions?
Nitrification
This occurs in two oxidation stages carried out by nitrifying bacteria.
What process converts atmospheric nitrogen gas into biologically usable nitrogen compounds?
Nitrogen fixation
This can occur in soil bacteria or in mutualistic bacteria in root nodules of legumes.
True or False:
Denitrifying bacteria convert nitrates in the soil into nitrogen gas released into the atmosphere.
True
Denitrification reduces nitrate to nitrogen gas, returning nitrogen to the atmosphere.
Fill in the blank:
In the nitrogen cycle, ammonium ions are oxidised to nitrites and then nitrates in a process called ______.
Nitrification
This process is carried out by nitrifying bacteria in aerobic soil conditions.
What mutualistic association between fungi and plant roots increases the uptake of water and mineral ions?
Mycorrhizae
Fungal hyphae increase the effective surface area for absorption from the soil.
True or False:
Mycorrhizae benefit only the fungus and not the plant.
False
The plant gains improved mineral and water uptake, while the fungus receives carbohydrates.
What role do decomposer microorganisms play in nutrient cycles?
Decomposition
They break down organic material and return inorganic ions to the soil.
Fill in the blank:
Farmers add natural or artificial ______ to soils to replace nutrients lost during harvesting.
fertilisers
Fertilisers commonly supply nitrates, phosphates and potassium ions.
What environmental process occurs when excess nitrates are washed from soil into rivers and lakes?
Leaching
Highly soluble nitrate ions move through soil with water.
What process occurs when nutrient enrichment causes rapid algal growth in aquatic ecosystems?
Eutrophication
Often caused by fertiliser runoff entering lakes or rivers.
True or False:
Eutrophication can lead to oxygen depletion in water.
True
Decomposition of large algal populations increases microbial respiration and reduces dissolved oxygen.
What group of microorganisms converts nitrates in soil back into atmospheric nitrogen?
Denitrifying bacteria
This occurs in anaerobic soil conditions, completing the nitrogen cycle.
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3.1.1 Monomers & Polymers9
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3.1.2 Carbohydrates22
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3.1.3 Lipids17
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3.1.4 Proteins39
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3.1.5 Nucleic Acids32
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3.1.6 ATP11
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3.1.7 Water11
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3.1.8 Inorganic ions8
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3.2.1 Cell structure52
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3.2.2 Cell division20
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3.2.3 Transport across cell membranes20
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3.2.4 Cell recognition & the immune system36
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3.3.1 Surface area to volume ratio13
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3.3.2 Gas exchange24
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3.3.3 Digestion & absorption16
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3.3.4 Mass transport39
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3.4.1 DNA, genes & chromosomes13
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3.4.2 DNA & protein synthesis14
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3.4.3 Genetic diversity & meiosis14
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3.4.4 Genetic diversity & adaptation20
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3.4.5 Species & taxonomy20
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3.4.6 Biodiversity within a community12
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3.4.7 Investigating diversity12
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3.5.1 Photosynthesis23
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3.5.2 Respiration17
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3.5.3 Energy & ecosystems20
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3.5.4 Nutrient cycles15
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3.6.1 Stimuli & Response62
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3.6.2 Nervous coordination53
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3.6.3 Skeletal muscles14
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3.6.4 Homeostasis57
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3.7.1 Inheritance12
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3.7.2 Populations15
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3.7.3 Evolution may lead to speciation22
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3.7.4 Populations in ecosystems24
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3.8.1 Gene Mutations and Protein Structure14
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3.8.2 Control of Gene Expression44
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3.8.3 Applications of Genome Projects10
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3.8.4 Gene Technologies and Their Applications46
