Unit 7 - Nutrient Cycles Flashcards
Which biological molecules contain nitrogen?
-amino acids
-proteins + enzymes
-ATP
-DNA/RNA nucleotides
In what form does nitrogen exist in the nitrogen cycle?
Nitrogen gas (N2)
Ammonium ions (NH4+)
Nitrate ions (NO3-)
Nitrite ions (NO2-)
How do animals in the food chain obtain their nitrogen and what do they use it for?
Consumers eat and digest the nitrogen-containing compounds e.g. proteins and DNA.
The amino acids are used to make proteins and nucleotides make DNA and RNA.
Explain how nitrogen returns to the environment from organisms in the food chain? (Ammonification)
Saprobiotic bacteria and fungi secrete enzymes into dead organisms, faeces and urine. They hydrolyse the nitrogen containing compounds e.g. proteins by extra cellular digestion and absorb the products. Ammonium ions are released into the soil.
Explain how nitrogen in the soil is converted into a form which plants can absorb? (Nitrification)
(Aerobic) nitrifying bacteria oxidise ammonium ions in 2 stages:
1) Ammonium to nitrite ions (NO2-)
2) Nitrite ions to nitrate ions (NO3-)
Plants absorb nitrate ions via active transport and use them to make proteins etc.
Explain how nitrates in the soil are converted back into the nitrogen gas? (Denitrification)
Denitrifying bacteria reduces nitrate ions to nitrogen gas. Denitrifying bacteria require anaerobic conditions.
Explain why farmers keep their soil well drained and regularly ploughed?
To maintain aerobic conditions for nitrifying bacteria to oxidise ammonium ions to nitrates. To prevent anaerobic conditions so denitrifying bacteria do not convert nitrates to nitrogen gas via denitrification.
Explain how nitrogen gas in the atmosphere is converted into nitrogen compounds in the soil? (Nitrogen fixation)
Nitrogen gas is reduced to ammonium ions by:
1) nitrogen fixing bacteria in the soil
2! Nitrogen fixing bacteria in the root nodules of legumes.
The plant gets nitrogen containing compounds and the bacteria get carbohydrates from the plant (symbiotic relationship)
What is mycorrhizal fungus and how does the plant and fungus benefit?
Mycorrhizae are relationships between fungi and plant roots. They hyphae of the fungi increase the surface area for the absorption of water and nitrates/phosphates for plants. Fungus received carbohydrates from the (photosynthesising) plant such as glucose. This is an example of a symbiotic relationship.
The nitrogen cycle overview?
What biological molecules contain phosphorus?
-ATP, Pi and ADP
-Phospholipids
-DNA/RNA nucleotides
-RuBP/NADP in photosynthesis
Where is the main source of the mineral phosphorus found?
Phosphate ions (PO4^3-) in sedimentary rocks.
Phosphate ions dissolve in water. Explain how the phosphate ions get from the rocks into soils, lakes and oceans?
Weathering and erosion of these rocks cause phosphate ions to dissolve into soils and oceans/lakes.
Explain how dissolved phosphate ions get into plants. Describe what facilitates this process?
Phosphates are absorbed by plants via active transport. Mycorrhizae increase the surface area for absorption as concentrations of phosphate in soil are low so require a large surface area.
Explain how animals get their phosphate?
Consumers then eat the plants and hydrolyse biological molecules such as DNA via digestion. The phosphate ions are absorbed and assimilated into new tissue in the consumer.
Explain how the phosphate ions from organisms return to the soil?
When organisms die, saprobiotic bacteria and fungi secrete extracellular enzymes which hydrolyse the phosphorous containing molecules e.g. DNA into phosphate ions. Excess phosphate ions are excreted into waste products such as urine or guano in birds.
Explain how phosphate ions get back to the rock?
Phosphate ions can form sedimentary rocks through deposition. This takes a long time.
Steps of the phosphorous cycle?
1) Phosphate ions present in rocks are released through erosion.
2) The phosphate ions dissolve into water in lakes, oceans and soil.
3) Plants absorb the phosphate ions into their roots via active transport. Mycorrhizae increase the surface area for this absorption as the concentration of phosphate ions in the soil is low.
4) Plants use the phosphate ions to make molecules.
5) The phosphates are then transferred to consumers when they eat the plant, digest and absorb the molecules. The animals then assimilate the phosphate into their own molecules.
6) When the animals and plants die they are decomposed by saprobiotic organisms such as bacteria and fungi which extracellularly digest the phosphate containing molecules, returning the phosphate to the soil.
7) Phosphate is also excreted from animals in their urine and in guano from birds which is digested by saprobiotic bacteria.
8) The phosphate in the soil can return to rocks when sedimentary rocks are formed by deposition.
Overview of the phosphorous cycle?
What do fertilisers do?
They add nitrates and phosphate into the soil to replace those lost after harvesting the crops or if livestock has been removed.
Explain how harvesting crops and removing livestock cause nitrates and phosphates to be lost?
The crops do not decompose to replace the nitrates/phosphates they have absorbed.
Livestock no longer excrete replacing the nitrates/phosphates they have consumed from the plants they have eaten.
What molecules are made with nitrate and how are they used in the plant?
Amino acids = To make polypeptides such as enzymes
DNA = Codes for proteins and functional RNA
RNA = Used in protein synthesis
ATP = Immediate energy source for processes such as active transport, mitosis, protein synthesis, DNA replication
Chlorophyll = light dependent reaction of photosynthesis
What molecules are made with phosphate and how are they used in the plant?
Phospholipids = makes up phospholipid bilayer of cell membranes
DNA, RNA, ATP
What makes up natural fertilisers and what makes up artificial fertilisers?
Natural = compost and manure
Artificial = chemical compounds that can be added to the soil.
Explain why natural fertilisers take longer to provide plants with an absorbable form of nitrogen than artificial fertilisers?
Natural fertilisers need saprobiotic bacteria to hydrolyse the nitrogen-containing compounds e.g. proteins into ammonium ions first and the phosphate containing compounds e.g. DNA/RNA into phosphate ions. Whereas the artificial fertilisers add nitrates/ammonium ions and phosphate ions straight into the soil.
Explain why the addition of fertiliser at high concentrations decrease the productivity of the crop?
High concentrations of fertiliser lowers the water potential of the soil;
Plant root cells have a higher water potential than the soil;
Water moves out of the plant root cells by osmosis.
What is leaching?
It is the removal of nitrates and phosphates from the soil by rain into rivers and lakes.
What is eutrophication?
Nitrates and phosphates from the leaching of fertilisers, enter streams and rivers
The nitrates and phosphates increase the growth of algae on the surface of rivers - this is called an ‘algal bloom’
This reduces the light available to plants in the water, so these plants stop photosynthesising and die
Saprobiotic bacteria reproduce rapidly and decompose the dead plant matter, using oxygen for aerobic respiration
This reduces the oxygen available for other organisms in the river such as fish, so they cannot aerobically respire and die.
