nutrient cycles exam questions Flashcards
The diagram above includes one process in which microorganisms add ammonium ions to soil.
(1)
Describe another process carried out by microorganisms which adds ammonium ions to soil.
………………………………………………………………………………………………………… …………………………………………………………………………………………………………
-proteins broken down into ammonia
-by saprobionts.
Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil.
…………………………………………………………………………………………………..
-increased fertilit as more nitrates
-less denitrification
One farming practice used to maintain high crop yields is crop rotation. This involves growing a different crop each year in the same field.
(d)
Suggest two ways in which crop rotation may lead to high crop yields.
1 …………………………………………………………………………………………………….
-plants with nitrogen fixing bacteria
-different crops have different pests/diseases
cScientists investigated the effect of a mycorrhizal fungus on the growth of pea plants with a nitrate fertiliser or an ammonium fertiliser. The fertilisers were identical, except for nitrate or ammonium.
The scientists took pea seeds and sterilised their surfaces. They planted the seeds in soil that had been heated to 85 °C for 2 days before use. The soil was sand that contained no mineral ions useful to the plants.
(a) Explain why the scientists sterilised the surfaces of the seeds and grew them in soil that had been heated to 85 °C for 2 days.
…………………………………………………………………………………………………………
-to kill fungus/bacteria on the surface of the seed
-so only the effect of the added fungi can be seen.
Explain why it was important that the soil contained no mineral ions useful to the plants.
…………………………………………………………………………………………………………
so that only the type of fertiliser affects growth
The pea plants were divided into four groups, A, B, C and D.
• Group A – heat-treated mycorrhizal fungus added, nitrate fertiliser
• Group B – mycorrhizal fungus added, nitrate fertiliser
• Group C – heat-treated mycorrhizal fungus addede, ammonium fertiliser
• Group D – mycorrhizal fungus added, ammonium fertiliser
The heat-treated fungus had been heated to 120 °C for 1 hour. Explain how groups A and C act as controls.
…………………………………………………………………………………………………………
-so that effect of nitrogen or ammonia fertiliser can be seen
so that effect of fungi can be seen.
After 6 weeks, the scientists removed the plants from the soil and cut the roots from the shoots. They dried the plant material in an oven at 90 °C for 3 days. They then determined the mean dry masses of the roots and shoots of each group of pea plants.
Suggest what the scientists should have done during the drying process to be sure that all of the water had been removed from the plant samples.
………………………………………………………………………………………………………… …………………………………………………………………………………………………………
-weigh samples at intevals during drying
-to see if constant mass reached.
The scientists determined the dry mass of the roots and shoots separately. The reason for this was they were interested in the ratio of shoot to root growth of pea plants. It is the shoot of the pea plant that is harvested for commercial purposes.
(f) Explain why determination of dry mass was an appropriate method to use in this investigation.
…………………………………………………………………………………………………………
-dry mass measures increase in organic material
-water content varies.
Freshwater marshes have one of the highest rates of gross primary production
(GPP) and net primary production (NPP) of all ecosystems.
Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have
a high CUE.
(a) Use your knowledge of NPP to explain why freshwater marshes have a
high CUE and the advantage of this.
Do not refer to abiotic factors in your answer. (2)
-low respiration
-more growth
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)
-less nitrification as requires aerobic conditions
-less ammonium oxidised to nitrite ions and less nitrite ions oxidised to nitrate ions.
Describe the role of saprobionts in the nitrogen cycle (2)
-decomposes urea
-producing ammonia
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)____________________________________________________
-use colorimeter
-measure light absorbance/transmission
-standardise colorimeter e.g. by zeroing colorimeter.
denitrification requires anaerobic conditions.
Ploughing aerates the soil.
explain how ploughing would affect the fertility of the soil. (2)
-less denitrification
-less nitrate broken down
upwelling results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters. (2)
-nutrients used by plants
-more producers- more fish
nitrate from fertiliser applied to crops may enter ponds and lakes. explain how nitrate may cause the death of fish in freshwater. (5)
-growth of algal blooms block light
-plants below cannot photosynthesise so die
-saprobionts
-use oxygen to respire aerobically
-less oxygen for fish to respire and aerobic organisms die
