6.3 The nitrogen cycle Flashcards
EXAM QUESTION
Name the process by which some bacteria oxidise ammonia to nitrate. (1)
Nitrification;
EXAM QUESTION
Reeds have hollow, air-filled tissue in their stems which supplies oxygen to their roots.
Explain how this enables the roots to take up nitrogen-containing substances.
- Uptake (by roots) involves
active transport; - Requires ATP/ aerobic
respiration;
EXAM QUESTION
There is an optimum rate at which human sewage should flow through the reed bed.
If the flow of human sewage is too fast, the nitrate concentration at point A falls.
Explain why. (2)
1. Not enough time / fast flow washes bacteria away; 2. (Not all/less) ammonia converted to nitrate/less nitrification;
EXAM QUESTION
Upwelling is a process where water moves from deeper parts of the sea to the surface. This water contains a lot of nutrients from the remains of dead organisms.
a) Nitrates and phosphates are two of these nutrients. They provide a source of nitrogen and phosphorus for cells.
Give a biological molecule that contains: (2)
1. nitrogen
2.phosphorus
b) Upwelling often results in high primary productivity in coastal waters. Explain why some of the most productive fishing areas are found in coastal waters. (2)
1. Amino acid/protein/enzyme/urea/nucleic acid/chlorophyll/DNA/RNA//ATP/ADP/AMP/ NAD/NADP; 2. DNA/RNA/nucleic acid/ATP/ADP/AMP/ NADP/TP /GP/ RuBP /phospholipids;
- Nitrate/phosphate/named ion/nutrients for growth
of/absorbed/used by plants/algae/producers; - More producers/consumers/food so more fish /
fish reproduce more / fish grow more / fish move
to area;
(nitrate/nutrients used for growth of plants/producers, more producers, so more fish)
EXAM QUESTION
Describe the role of microorganisms in producing nitrates from the remains of dead organisms. (3)
- Saprobiotic (microorganisms/bacteria) break
down remains/dead material/protein/DNA into
ammonia/ammonium; - Ammonia/ammonium ions into nitrite and then
into nitrate; - (By) Nitrifying bacteria / nitrification;
EXAM QUESTION
Much of Indonesia is covered with forest. Large areas of forest have been cleared and
planted with oil-palm trees to be used in the production of fuel.
In these forests, nitrogen in dead leaves is made available to growing plants by the action of bacteria. Describe the role of bacteria in making the nitrogen in dead leaves
available to growing plants. (5)
- Saprobionts/saprophytes;
- Digest/break down proteins/DNA/nitrogen-containing
substances; - Extracellular digestion/release of enzymes;
- Ammonia/ammonium produced;
- Ammonia converted to nitrite to nitrate/ammonia to nitrate;
- Nitrifying (bacteria)/ nitrification;
- Oxidation;
EXAM QUESTION
Nitrogen gas —-> ammonium ions —> nitrates —-> nit. gas
Q R P
Which one of the processes P, Q or R involves nitrification? (1)
Figure includes one process in which microorganisms add ammonium ions to soil.
Describe another process carried out by microorganisms which adds ammonium ions to soil. (2)
R
- Protein/amino acids broken down (to
ammonium ions/ammonia); - By saprobionts / saprobiotic
(microorganisms);
EXAM QUESTION
Denitrification requires anaerobic conditions. Ploughing aerates the soil.
Explain how ploughing would affect the fertility of the soil.(2)
1. (Fertility increased as) more nitrate formed / less nitrate removed/broken down; 2. Less/no denitrification / process P is decreased / fewer denitrifying bacteria;
EXAM QUESTION
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. (2)
- Grow crops/plants with nitrogen fixing
(bacteria); (e.g. peas, beans, clover) - (Different crops use) different
minerals/salts/nutrients/ions (from
the soil); - (Different crops have) different
pests/pathogens/diseases;
Absorption:
Producers obtain?
By? (3)
Feeding/digestion:
Consumers obtain?
By?
Nitrate ions
Absorption, through root hairs, using active transport (requires ATP from aerobic respiration)
Nitrogen-containing compounds
Feeding on/digesting producers.
Recycling:
Why is it important to recycle nitrate ions?
Nitrate ions soluble and easily leach through soil, beyond reach of root hair cells
Ammonification:
= ? —> ?
What microorganism?
Breaks down nitrogen-containing compounds of? (2)
Releases ammonium ions into?
= Nitrogen-containing compounds —> ammonium ions
Saprobiotic microorganisms (decomposers)
faeces/dead organisms (e.g. urea, nucleic acids).
Soil (non-living component)
Nitrification:
= ? —> ?
What microorganism?
What type of reaction?:
2 steps? (4)
Why does soil need air spaces?
Ploughing and drainage =? (3)
= Ammonium ions —> nitrate ions
Nitrifying bacteria
Oxidation reaction (releases energy):
Of ammonium ions to nitrite ions
Of nitrite ions to nitrate ions
Requires oxygen
= aeration = prevents waterlogging = prevents denitrifying bacteria
Nitrogen fixation:
= ? —> ?
What microorganism? Manufacture?
What microorganism? live in?
What type of reaction?
Alternatives? (2)
= Nitrogen gas —> Ammonium ions/nitrogen-containing compounds
Free-living nitrogen-fixing bacteria
Use ammonium ions to manufacture amino acids.
Nitrogen-containing compounds released when they decompose.
Mutualistic nitrogen-fixing bacteria
Live in root nodules
Obtain carbohydrates from plant, give amino acids to plant.
Reduction reaction (takes in energy)
Alternatives = industrial/lightning
Denitrification:
= ? —> ?
Soil becomes?
How do microorganisms present change? (2)
Ploughing and drainage = ? (3)
= Nitrate ions —> nitrogen gas
waterlogged
More anaerobic denitrifying bacteria
Less aerobic nitrifying and nitrogen-fixing bacteria
= aeration = prevents waterlogging = prevents denitrifying bacteria
