Nutrient Cycles Flashcards
Nitrogen cycle stages
Nitrogen fixation
Nitrification
Ammonification
Denitrification
Microorganism for
nitrogen fixation
Nitrogen fixing bacteria
Nitrogen fixing
bacteria location
Root nodules
OR
Free in the soil
nitrogen fixing bacteria reaction
Convert atmospheric nitrogen
Describe nitrification
Ammonia into nitrites;
Nitrites into nitrates;
By nitrifying bacteria
Microorganism that returns nitrogen to the atmoshphere
Denitrifying bacteria
Denitrifying bacteria reaction
Convert nitrates in the soil into atmospheric nitrogen
Denitrifying bacteria conditions
Anerobic / waterlogged soil
After nitrates have been absorbed from the soil via the plant roots. This nitrogen is _________ into the plant’s tissues.
assimilated
ammonification microorganism
Saprobionts
Describe the role of saprobionts in the nitrogen cycle (Ammonification stage) (2 marks).
- (use enzymes to decompose) proteins / DNA / RNA / urea;
- Producing ammonia / ammonium ions;
Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants (5 marks).
(Nitrogen fixation)
1. Nitrogen into ammonia;
2. By nitrogen-fixing bacteria;
(Nitrification)
3. (oxidation of) ammonia into nitrite;
4. Nitrite into nitrate;
5. By nitrifying bacteria;
(Ammonification)
6. protein / amino acids / DNA into ammonia
7. (use enzymes to decompose) by saprobionts;
Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.
Any two from:
1. amino acid / protein / polypeptide / peptide;
nucleic acid / nucleotide / base;
DNA;
RNA;
ATP / ADP;
NAD / NADP (reduced or not);
Cyclic AMP / cAMP;
Chlorophyll;
After harvesting, the remains of crop plants are often ploughed into the soil.
Explain how microorganisms in the soil produce a source of nitrates from these remains (5 marks).
(Ammonification)
1. Protein/amino acids/DNA/urea into ammonia;
2. By saprobionts
(Nitrification)
3. Ammonia into nitrite;
4. Nitrite into nitrate ;
5. By nitrifying bacteria;
Denitrification requires anaerobic conditions.
Ploughing aerates the soil.
Explain how ploughing would affect the fertility of the soil (2 marks).
- (Fertility increased as) less nitrate removed;
Accept: Nitrate remains
- Less denitrification / fewer denitrifying bacteria.
How can a farmer replace the nitrates and phosphates lost from the soil following the harvest of crops?
Add natural (e.g. manure / compost) AND/OR
artificial (e.g. liquid ammonia) fertilisers
Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.
Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions (2 marks).
- Less nitrification
- (Less) oxidation/conversion of ammonia to nitrite (ions) and to nitrate (ions);
- More denitrification
Name of symbiotic relationship between plant roots and fungus
Mycorrhizae
Role of mycorrhizae
Increase uptake of water and inorganic / mineral ions (e.g. phosphate and nitrate) by plants
TRUE OR FALSE
Mycorrhizal networks can connect the roots of plants growing next to each other so the plants can exchange biological molecules.
TRUE
Explain how mycorrhizae networks can increase plant growth
Increase surface area;
For absorption of water and inorganic / mineral ions;
Which are used for growth / protein synthesis / respiration / photosynthesis
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced.
When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit.
Explain how (2 marks).
- Less/no ATP/energy required/used
OR More ATP/energy available;
- ATP/energy can be used for growth/synthesis/replication
One farming practice used to maintain high crop yields is crop rotation. This involves growing a different crop each year in the same field.
Suggest two ways in which crop rotation may lead to high crop yields.
- Grow crops / plants with nitrogen-fixing (bacteria);
Accept: grow legumes / named example e.g. peas, beans, clover
Accept: fallow year
- (Different crops use) different minerals / salts / nutrients / ions (from the soil);
- (Different crops have) different pests / pathogens / diseases.
Describe the phosphorus cycle
(5 marks).
Phosphate ions in rocks are eroded by water/weather
Dissolve into water systems and soil
Absorbed by plants and assimilated into compounds such as nucleic acids and phospholipids
These can be passed on during feeding to higher trophic levels
Excretion of phosphate ions in waste and decomposition of remains by saprobionts
Deposition of these phosphate ions leads to phosphate held in rocks
Name the process by which some bacteria oxidise ammonia to nitrate.
Nitrification
As fertiliser use increases and soil quality decreases, excess Nitrogen, Phosphorus (and potassium) used on farmlands can be picked up by rainfall in a process known as ________________.
leaching
What happens after leaching?
crease concentration of nitrate and phosphate in freshwater;
Leds to algal growth / algal bloom which block light
Why do fish die during eutrophication?
Saprobionts decompose dead plant material;
Aerobically respire / use oxygen in respiration;
Less oxygen for fish to aerobically respire so they die;
Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water (5 marks).
(Eutrophication)
1. Growth of algae / surface plants / algal bloom blocks light;
Reduced / no photosynthesis so submerged plants die;
Saprobiont;
Aerobically respire / use oxygen in respiration;
Less oxygen for fish to respire / aerobic organisms die;
One environmental issue arising from the use of fertilisers is eutrophication.
Eutrophication can cause water to become cloudy.
You are given samples of water from three different rivers.
Describe how you would obtain a quantitative measurement of their cloudiness (3 marks).
- Use of colorimeter;
- Measure the absorbance/transmission (of light);
- Example of how method can be standardised eg same volume of water, zeroing colorimeter, same wavelength of light, shaking the sample;
