3.3.5 NUTRIENT CYCLES
Q: Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen-containing compounds to a field. (2 MARKS)
- growing legumes / named legume - ploughed in/ allowed to decompose/ nitrogen-fxing (bacteria in nodules) OR - allow cattle / named species/ (farm) animals (to graze), - add dung/ urine OR - spread/add manure/slurry - decomposed to release nitrates/ ammonia/ nitrites
Q: Describe the diferences between nitrogen fixation and nitrification. (2 MARKS)
- nitrogen fixation is the conversion of (atmospheric) nitrogen into ammonia/ ammonium compounds/ ammonium ions - nitrification is the conversion of ammonia ammonium compounds ammonium ions into nitrite/ nitrate
Q: In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how. (5 MARKS)
1. Carbon dioxide combines with ribulose bisphosphate / RuBP; 2. To produce two molecules of glycerate 3-phosphate/ GP, 3. Reduced to triose phosphate /TP; 4. Requires reduced NADP 5. Energy from ATP;
Q: Scientists 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. 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 added, ammonium fertiliser • Group D - mycorrhizal fungus added, ammonium fertiliser The heat-treated fungus had been heated to 120 °C for 1 hour. 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. 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. Explain why determination of dry mass was an appropriate method to use in this investigation. (2 MARKS)
1. Dry mass measures / determines increase in biological / organic material; 2. Water content varies.
Q: Explain how farming practices increase the productivity of agricultural crops. (5 MARKS)
1. Fertilisers/ minerals / named ion (added to soil); 2. Role of named nutrient or element e.g. nitrate / nitrogen for proteins / phosphate/ phosphorus for ATP /DNA; 3. Selective breeding/ genetic modification (of crops); 4. Ploughing/ aeration allows nitrification/ decreases denitrification 5. Benefit of crop rotation in terms of soil nutrients / fertility / pest reduction
EQ: Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate. Scientists investigated the effects of different AMF species on the productivity of the plant community of a prairie grassland ecosystem when growing in/on soil containing different phosphate concentrations. The scientists set up identical plots of prairie grassland soil containing seeds of the plant species found in the ecosystem. The scientists added different AMF species and different concentrations of phosphate to particular plots. Control plots without AMF species were also set up. After 20 weeks the scientists determined the shoot biomass for each plot. The results the scientists obtained are shown in Figure 5. Using the data from Figure 5, evaluate the effect on plant productivity of adding AMF species and adding phosphate to the soil. (4 MARKS)
1. For the control an increase in phosphate increases (plant) growth; 2. For Entrophospora an increase in phosphate reduces (plant) growth; 3. Scutellospora reduces (plant) growth (compared to control); 4. Entrophospora and Glomus increases (plant) growth(compared to control); 5. No SD/statistical test to determine significance; 6. Only 20 weeks of growth; 7. Underground/root growth not known;
How are natural fertilisers broken down?
Need to be broken down by saprobionts → slow release of Nitrogen + Phosphorus in comparison to artificial fertilisers
TIP!
Nitrification is when you are converting something into a good form of nitrogen that you want, whereas denitrification is when you are converting something into an unwanted form of nitrogen, as nitrogen gas in the atmosphere is in an unwanted form.
Give examples of natural fertilisers.
Nitrogen and Phosphorus in organic compounds, eg manure or compost
TIP!!
Nitrogen fixation can be thought of as taking nitrogen gas in the atmosphere (a useless form) and fixing it into a good form in plants
The oceans contain a massive reserve of carbon dioxide. This store is some 50 times greater than that in the atmosphere. It helps to keep the concentration of atmospheric carbon dioxide more or less constant. Some of any excess carbon dioxide in the atmosphere dissolves in the waters of the oceans. What happens when atmospheric concentration of CO2 is low?
The reverse occurs: CO2 in the oceans go into the atmosphere.
Describe leaching (an impact of artificial fertilisers).
When soluble compounds are washed off land by rain into waterways → more common in artificial fertilisers (worse when fertiliser added in excess (more added than used)) → harmful in drinking water
EQ: Ammonia in soil is oxidised to nitrites and nitrates by species of nitrifying bacteria. Scientists investigated whether two soils with a different pH contained different communities of nitrifying bacteria. These communities consist of all the nitrifying bacteria of different species in each soil. They took samples of soil from two sites, A and B. They measured the pH of the samples and found that • the soil from site A had a pH of 6.9 • the soil from site B had a pH of 4.3 The scientists measured the concentration of ammonia in soil samples over 20 days. Each sample contained the same concentration of ammonia at the start and had the same mass. They recorded the concentration of ammonia in • soil A with a pH of 6.9 • soil B with a pH of 4.3 • a mixture of equal masses of soils A and B with its pH adjusted to 6.9 Their results are shown in Figure 6. The oxidation of ammonia by nitrifying bacteria involves the enzyme ammonia monooxygenase. Each species of nitrifying bacteria has its own specific amoA gene that codes for production of ammonia monooxygenase. In a second investigation, the scientists determined the expression of the amoA gene in two species of bacteria, S and T. Species S was from acid soil and species T was from soil with a neutral pH. The scientists grew cultures of each species separately in soils of different pH. They determined the amount of mRNA from the amoA gene in each culture. Their results are shown in Figure 7. In which species was the number of copies of mRNA more affected by changes in soil pH from 4.9 to 7.5? Use a calculation to support your answer. (2 MARKS)
(Species S because) no mark 1. Species S change of 990,000 (per gram of soil); 2. Species T change of 9,900 (per gram of soil); OR (Species T because) no mark 3. Species S has 99% change; 4. Species T has 9900% change;
Q: Arctic tundra is an ecosystem found in very cold climates. Figure 1 shows some parts of the carbon and nitrogen cycles in arctic tundra. (a) An increase in temperature causes an increase in carbon input. Explain why. (2 MARKS) (b) The nitrogen compounds in the organic matter in soil are converted to nitrates Explain how nitrogen output can occur from these nitrates (3 MARKS)
(a) - Increase in photosynthesis; - As enzyme activity increased (b) - Secretion / release of enzymes; - Extracellular digestion; - Absorb soluble products / named product e.g. glucose, amino acids
Q: Scientists 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. (i) 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. (2 MARKS) (ii) Explain why it was important that the soil contained no mineral ions useful to the plants. (1 MARK)
(a) 1. To kill any fungus / bacteria on surface of seeds or in soil; 2. So only the added fungus has any effect. (b) So that only nitrate or ammonia / type of fertiliser affects growth.
Q: Arctic tundra is an ecosystem found in very cold climates. Figure 1 shows some parts of the carbon and nitrogen cycles in arctic tundra. Name the process represented by: (i) carbon output (ii) nitrogen input.
(i) Respiration / decomposition (ii) Nitrogen fixation / death of animals / organisms / excretion
Q: Describe the differences between decomposition and denitrification. (2 MARKS)
- decomposition is break down of dead matter/waste OR decomposition is conversion of organic matter to inorganic OR decomposition increases mineral nitrate supply - denitrification is conversion of nitrates to nitrogen (gas) OR denitrification reduces mineral/ nitrate supply
Q: Inorganic fertilisers are not directly toxic to living organisms. However, the excessive use of these fertilisers can lead to a reduction in the biodiversity of farmland. Suggest how the excessive use of inorganic fertilisers on farmland can cause a reduction in its biodiversity. (2 MARKS)
- (fertiliser) promotes growth of one/ few (plant) species - other (plant) species out-competed (as a result of competition from crop species) OR disruption of food chains OR reduction in soil quality humus over time
Q: Give one advantage of using natural fertiliser rather than an artificial fertiliser. (1 MARK)
- Acts as soil conditioner/improves drainage/ aerates soil/increases organic content of soil OR Contains elements/ wider range of elements OR Production of artificial fertiliser energy-consuming OR Less leaching / slow release (of nutrient)
Name the benefits of natural fertilisers vs artificial fertilisers.
- Aerate soil - Contain a wider range of elements - Less leaching - Consume less energy - Cheaper / free
Q: It is estimated that, each year, a total of 3 x 10 tonnes of ammonia are converted to nitrate. Only 2 x 10 tonnes of ammonia are produced from nitrogen gas. Explain the difference in these figures (2 MARKS)
- Ammonia formed by decay/ decomposition/putrefying/ ammonitying by action of decomposers/saprobionts - On nitrogenous waste/ urea or nitrogenous compounds (eg. proteins, amino acids, DNA, ATP);
Variations in rates of respiration and photosynthesis give rise to short term fluctuations in proportions of oxygen and carbon dioxide in the atmosphere, give examples.
- Concentration of CO2 is greater at night than in day as absence of light means no photosynthesis takes place - The daytime concentration of CO2 in summer day (when photosynthesis is greatest) is lower than on a winters day
Q: A wheat crop was growing on clay soil. Clay is easily waterlogged. The amount of denitrification taking place would be lower on a farm with sandy soil that does not become waterlogged. Explain why. (2 MARKS)
- Denitritying bacteria found in anaerobic conditions - Sandy soils contain more oxygen [Accept converse argument for clay soils]
What is saprobiontic nutrition?
- Digestion/decay of dead organic matter and their waste products (faeces, urea) - By secreting extracellular enzymes → soluble products are absorbed
How do fertilisers increase productivity?
- E.g. Nitrogen - Nitrogen needed for proteins and DNA for plant growth - Availability of nitrates means plants can develop earlier, grow taller and have greater leaf area - This increases rate of photosynthesis and improves crop productivity
Q: Dead leaves contain starch. Describe how microorganisms make carbon in starch available to plants. (3 MARKS)
- Extracellular digestion / releases enzymes - Starch to monosaccharides /glucose/sugars/smaller molecules - Respire product of digestion OR Produce carbon dioxide from respiration
Q: Since 1965 there has been a steady rise in the phosphate concentration in the water of Lake Windermere. Scientists have monitored the phosphate concentration and plant biomass over a period of time. The results are shown in the graphs. From these graphs, a student concluded that changes in phosphate concentration caused changes in plant biomass. Explain why this conclusion may not be valid. (2 MARKS)
- Have continuous data for phosphate but not for biomass; - Effect of named factor explained;
Describe artificial fertilisers.
- Inorganic - Contain pure chemicals e.g. ammonium nitrate as powders / pellets - Chemicals contain exact proportions of minerals - Inorganic substances more water soluble so larger quantities washed away, impacting the environment - Concentrated so smaller amounts are needed
Q: Microorganisms make the carbon in polymers in a dead worm available to cells in a leaf. Describe how. (5 MARKS)
- Microorganisms are saprobionts [Accept saprophytes, although not strictly correct]. - Secrete enzymes (onto dead tissue)/ extracellular digestion - Absorb products of digestion/smaller molecules/named relevant substance - Respiration (by microorganisms) produces carbon dioxide - Carbon dioxide taken into leaves / through stomata
Q: Why is leaching less likley with natural fertilisers? (2 MARKS)
- Nitrogen / phosphorus contained in organic molecules - Organic molecules less soluble in water so need to be decomposed by saprobionts before nitrogen and phosphorus are released (as soluble inorganic molecules)
Why is the nitrogen cycle important?
- Nitrogen gas (N2) is unreactive and not easily converted into other compounds - Most plants can only take up nitrogen (by active transport in roots) in the form of nitrate - Used by plants / animals to make proteins / nucleic acids (assimilated) → growth
How can fertiliser improve the efficiency of energy transfer (more energy can be used for growth)?
- Nutrient could no longer be a limiting factor - Increase productivity of agricultural land
Describe natural fertilisers.
- Organic - E.g. manure, compost, sewage, bonemeal - Cheaper / free but exact nutrients cannot be controllled - Not very concentrated so large amounts are needed
Q: Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants. (7 MARKS)
- Protein/amino acids/DNA (converted/ broken down/digested) into ammonium compounds/ ammonia [Accept any named nitrogen containing compound e.g. urea - By saprobionts [Accept saprophytes] - Ammonium/ammonia (converted) into nitrite - Nitrite (converted) into nitrate - By nitrifying bacteria/microorganisms - Nitrogen (converted) to ammonia/ammonium - By nitrogen-fixing bacteria/microorganisms in soil
Describe why fertiliser helps in harvesting crops / livestock.
- Removes Nitrogen and phosphorus from their cycles - Soil nitrogen and phosphorus become depleted - Add fertiliser to replace Nitrogen & Phosphorus
Q: Describe the role of microorganisms in producing nitrates from the remains of dead organisms. (4 MARKS)
- Saprobiotic (microorganisms/bacteria) [Accept: saprobionts /saprophytes/saprotrophs] - break down remains/dead material/ protein/DNA into ammonia/ammonium - Ammonia/ammonium ions (converted) into nitrite and then into nitrate - (By) Nitrifying bacteria OR nitrification
Q: Over a million tonnes of salmon per year are produced in fish farms. The salmon are grown in large cages in sheltered waters, such as off the west coast of Scotland. The cost of these farmed salmon is much lower than that of wild salmon. Large amounts of waste food and faeces fall through the bottom of the cages. This results in a much reduced diversity of marine organisms below and around the cages. Explain how the organic matter in the water causes this reduction in diversity. (2 MARKS)
- activity of decomposers / microorganisms reduced oxygen content; - few species adapted to low oxygen conditions;
Q: Describe and explain how one farming practice results in the removal of nitrogen- containing compounds from a field. (2 MARKS)
- bare soil / fallow in winter/ hedge removal; leaching - (of nitrates)/ soil erosion OR - uptake of nitrates/ ammonium compounds by crop - harvesting crop / named crop which would be harvested: OR - (farm) animals eat plants - (in field), (then) animals removed,
Q: Crop yield can be improved by the use of fertilisers. In the eighteenth century, these are likely to have been organic fertilisers in the form of manure or compost. Suggest how organic fertilisers improve the yield of plant crops. (2 MARKS)
- broken down by decomposers/ bacteria fungi - add mineral(s) to soil/ nitrate and phosphate and potassium /mineral(s) nutrient(s) / ion(s), is limiting factor (for growth of crops)
Q: In the activated sludge method of sewage treatment, organic matter in untreated sewage supplies nutrients to bacteria in the treatment tank. These bacteria include decomposers and nitrifying bacteria. The bacteria are eaten by ciliated protoctistans, which are, in turn, eaten by carnivorous protoctistans. Nitrifying bacteria are one kind of bacteria that are important in the nitrogen cycle; nitrogen-fixing bacteria are another kind. Describe the part played by nitrogen- fixing bacteria in the nitrogen cycle. (2 MARKS)
- convert nitrogen (gas) into ammonium / ammonia / amino acids; - add usable / available nitrogen to an ecosystem / eq.;
Q: In the activated sludge method of sewage treatment, organic matter in untreated sewage supplies nutrients to bacteria in the treatment tank. These bacteria include decomposers and nitrifying bacteria. The bacteria are eaten by ciliated protoctistans, which are, in turn, eaten by carnivorous protoctistans. Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen in organic compounds in the sewage into a soluble, inorganic form. (3 MARKS)
- decomposers convert (nitrogen in organic compounds) into ammonia / ammonium; - suitable example of "organic nitrogen" - protein / urea / amino acid etc. (e.g. linked to process); - nitrifying bacteria / correctly named convert ammonium to nitrate; via nitrite;
Artificial fertilisers can lead to leaching, which can further lead to eutrophication. Explain what happens in eutrophication.
1) Nitrate / phosphate ions leach into fresh water 2) Rapid increase in algal bloom 3) Blocks out the light as on surface on water → Plants cant photosynthesise + die due to competition 4) Saprobionts break down dead plants due to increase food supply 5) They respire aerobically and use up oxygen 6) Fish and other organisms die as less oxygen 7) Less competition for anaerobic organisms → populations rise exponentially 8) Anaerobic organisms further decompose dead material, releasing more nitrates and toxic wastes, such as hydrogen sulfide, making water putrid
Q: Leguminous crop plants have nitrogen-fixing bacteria in nodules on their roots. On soils with a low concentration of nitrate ions, leguminous crops often grow better than other types of crop. Explain why. (2 MARKS)
1. (Nitrogen) to ammonia / NH3 / ammonium; 2. Produce protein / amino acids / named protein / DNA / RNA;
EQ: Describe the role of saprobionts in the nitrogen cycle. (2 MARKS)
1. (They use enzymes to) decompose proteins/DNA/RNA/urea; 2. Producing/releasing ammonia/ammonium compounds/ammonium ions;
EQ: Ammonia in soil is oxidised to nitrites and nitrates by species of nitrifying bacteria. Scientists investigated whether two soils with a different pH contained different communities of nitrifying bacteria. These communities consist of all the nitrifying bacteria of different species in each soil. They took samples of soil from two sites, A and B. They measured the pH of the samples and found that • the soil from site A had a pH of 6.9 • the soil from site B had a pH of 4.3 The scientists measured the concentration of ammonia in soil samples over 20 days. Each sample contained the same concentration of ammonia at the start and had the same mass. They recorded the concentration of ammonia in • soil A with a pH of 6.9 • soil B with a pH of 4.3 • a mixture of equal masses of soils A and B with its pH adjusted to 6.9 Their results are shown in Figure 6. The scientists used units of µg g−1 for the concentration of ammonia in soil. Suggest why, in this investigation, the scientists used these units. (2 MARKS)
1. (µg because) very little ammonia (in soil); 2. (µg because) avoids use of (lots of) decimal places (in their results) / avoids the use of powers of 10 / avoids the use of standard form; 3. (g-1 ) to allow comparisons (between samples);
Q: Knowledge of the nitrogen cycle can be used to make decisions about management of farmland. A farmer uses her grass meadow to raise sheep. In a separate field she grows cabbages. Fig. 1.1 shows part of the nitrogen cycle. The four boxes on the bottom line of the diagram refer to substances in the soil. 1. Briefly describe the steps that must occur for plant protein to be converted to animal protein in the farmer's sheep as shown by arrow A on Fig. 1.1. (3 MARKS) 2. List the processes which contribute to B in the meadow where sheep are raised. (2 MARKS) 3. Name the bacteria that carry out processes C and D, and expiain the significance of these bacteria for the growth of plants. (4 MARKS)
1. - (sheep/ animals) ingest / consume/ eat/ feed on (grass / plants) - digest/ hydrolyse (protein) to amino acidsl amino acids move into blood/ cells - synthesis of proteins/ translation 2. - death OR leaf loss OR decomposition OR decay - excretion urination/ egestion/ defaecation 3. - C is Nitrosomonas - D is Nitrobacter - C and D are nitrifying bacteria - plants need nitrates to make amino acids/ protein(s) / enzymes/ DNA / RNA /nucleic acids chlorophyll/ cytoplasm/ new cells
Q: Intensive rearing of livestock produces large quantities of waste. Some farmers use an anaerobic digester to get rid of the waste. In an anaerobic digester, microorganisms break down the large, organic molecules in the waste. This produces methane, which is a useful fuel. It also produces organic substances that can be used as a natural fertiliser. The diagram shows an anaerobic digester. Give one advantage of using natural fertiliser produced in the digester rather than an artificial fertiliser. (1 MARK)
1. Acts as soil conditioner / improves drainage / aerates soil / increases organic content of soil; 2. Contains other elements / named element / wider range of elements; 3. Production of artificial fertiliser energy-consuming; 4. Less leaching / slow release (of nutrient);
EQ: Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate. Scientists investigated the effects of different AMF species on the productivity of the plant community of a prairie grassland ecosystem when growing in/on soil containing different phosphate concentrations. The scientists set up identical plots of prairie grassland soil containing seeds of the plant species found in the ecosystem. The scientists added different AMF species and different concentrations of phosphate to particular plots. Control plots without AMF species were also set up. After 20 weeks the scientists determined the shoot biomass for each plot. The results the scientists obtained are shown in Figure 5. Using the ex button on your calculator, determine the rate of shoot biomass production in grams per day for the control plot in soil with normal phosphate concentration. (2 MARKS)
1. Answer in range 0.07 to 0.09 = 2 marks;; 2. Answer in range 9.97 to 12.2 OR Shows division by 140 or 20 x 7 = 1 mark;
Compare artificial and natural fertilisers.
1. Artificial fertilisers are inorganic whereas natural fertilisers are organic. 2. Artificial fertilisers contain pure chemicals e.g. ammonium nitrate as powder / pellets, whereas natural fertilisers are made from manure, compost, sewage and bonemeal 3. Artificial fertilisers contain chemicals with exact proportions of minerals whereas natural fertilisers are cheaper / free but exact nutrients cannot be controlled 4. Artificial fertilisers are more water soluble than natural fertilisers, so larger quantities are washed away, impacting the environment 5. Artificial fertilisers are concentrated so smaller amounts are needed, whereas natural fertilisers are not very concentrated so larger amounts are needed.
What are the consequences of global warming?
1. Bring changes in temperature, precipitation, the timing of seasons, frequency of storms, floods and drought 2. Affect the niches available in a community → as each organism is adapted to a specific niche, the distribution of species will change. If climate change is slow, species may have time to gradually migrate to new areas, where they will compete for available niches. This can lead to the loss of native species that occupy those niches. 3. Melting of polar ice caps can cause extinction or organisms 4. Rise in sea level due to thermal expansion of oceans, flooding low-lying land 5. Saltwater extends further up rivers making cultivation of crops difficult 6. Can cause failure of crops due to high temperatures and less rainfall 7. Land may become desert, where only xerophytes will survive.
Q: Scientists 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. 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 added, ammonium fertiliser • Group D - mycorrhizal fungus added, ammonium fertiliser The heat-treated fungus had been heated to 120 °C for 1 hour. 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. 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. Which treatment gave the best result in commercial terms? Justify your answer. (2 MARKS)
1. Fungus with nitrate-containing fertiliser gave largest shoot: root ratio; 2. And largest dry mass of shoot; 3. 6.09:1 compared with ammonium-containing fertiliser 4.18:1
Q: Intensive rearing of livestock produces large quantities of waste. Some farmers use an anaerobic digester to get rid of the waste. In an anaerobic digester, microorganisms break down the large, organic molecules in the waste. This produces methane, which is a useful fuel. It also produces organic substances that can be used as a natural fertiliser. The diagram shows an anaerobic digester. Suggest two advantages of processing waste in anaerobic digesters rather than in open ponds. (2 MARKS)
1. Gases / correct named gas not released; 2. Conditions (in digester) can be controlled; 3. Products / named product can be collected; 4. Open ponds associated with health risk / environmental damage / eutrophication;
Describe the greenhouse effect.
1. Heat and light of sun reach earth, some solar radiation is reflected into space, some is absorbed by atmosphere and some is absorbed by earth 2. Some of the radiation reaching earth is reflected back as heat into space 3. However some is reflected back to earth by clouds and greenhouse gases in atmosphere 4. Greenhouse gases trap this heat, keeping earth's surface warm
Q: The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur (5 MARKS)
1. High concentration of carbon dioxidelinked with night/ darkness 2 No photosynthesis in dark/ night/ light required for photosynthesis / light dependent reaction; 3. (in dark) plants (and other organisms) respire 4. In light net uptake of carbon dioxide by plants/ plants use more carbon dioxide than they produce/ rate of photosynthesis greater than rate of respiration 5. Decrease in carbon dioxide concentration with height, 6. At ground level fewer leaves/ less photosynthesising tissue/more animals/ less light
Q: Since 1965 there has been a steady rise in the phosphate concentration in the water of Lake Windermere. Scientists have monitored the phosphate concentration and plant biomass over a period of time. The results are shown in the graphs. Between 1982 and 1992 the number of fish in the lake decreased. Explain how the change in phosphate concentration may have resulted in this decrease in the fish population. (6 MARKS)
1. Increased phosphate causes increase in plant growth / algal bloom; 2. Plants (cover surface and) block out light so plants (under surface) die; 3. Increase in (aerobic) bacteria / decomposers (which break down plants); 4. Bacteria / decomposers use up oxygen / reduce oxygen conc. in water; 5. In respiration; 6. Plants unable to photosynthesise so less oxygen produced;
State the 3 impacts of artificial fertilisers.
1. Leaching 2. Eutrophication 3. Reduced species diversity
Describe ammonification.
1. Nitrogen-containing compounds e.g. proteins from dead organisms / animal waste is broken down and converted into ammonia which goes to form ammonium ions (NH4+) in the soil by saprobionts which secrete enzymes for extracellular digestion.
Describe the whole nitrogen cycle.
1. Nitrogen-containing compounds e.g. proteins from dead organisms / animal waste is broken down and converted into ammonia which goes to form ammonium ions (NH4+) in the soil by saprobionts which secrete enzymes for extracellular digestion. 2. Ammonium Ions go through nitrification [oxidation reaction] to be converted into Nitrite ions (Nitr1te [1st]) (NO2 -), then go through further nitrification [oxidation] to become Nitrate ions (Late) (NO3 -). Bacteria need oxygen to carry out conversion. 3. Nitrate ions then go through denitrification in anaerobic conditions by denitrifying bacteria (e.g. waterlogged soil) to become nitrogen gas in atmosphere 4. Plants receive nitrogen in two ways - Absorbed directly from Nitrate through plant root hair cells by active transport - Nitrogen gas in the atmosphere is converted into nitrogen-containing compounds through nitrogen fixation by either mutalistic nitrogen fixing bacteria which live in nodules on the roots of leguminous plants such as peas and beans. - Free-living nitrogen-fixing bacteria can reduce gaseous nitrogen to ammonia. 5. Plants use nitrates for proteins and DNA, animals consume plants to get nitrate to make proteins and DNA 6. When both animals and plants die, saprobiotic nutrition occurs when decomposers digest the decay of their dead organic matter by extracellular enzymes by saprobiotic microbes. They use this nitrate for synthesising proteins and DNA 7. The decomposers feed on nitrates in compounds and release ammonia go through ammonification to become ammonium ions again, and the cycle repeats.
Describe the simple sequence of a nutrient cycle.
1. Nutrients taken up by producer as an inorganic ion (simple inorganic molecule) 2. Producer incorporates nutrients into complex organic molecules 3. Producer eaten and nutrients passed to consumer and along food chain 4. When producers / consumers die, complex molecules are broken down by saprobiontic microorganisms (decomposition) 5. Inorganic ion released
EQ: A scientist investigated the effects of different fertilisers on the growth of spinach plants. The scientist: • set up a large sample of identical pots of soil • added different masses of different fertilisers to selected pots • did not add fertiliser to the control pots • planted the same number of young spinach plants in each pot • after 20 days, determined the biomass of spinach plants in each pot. The results the scientist obtained after 20 days are shown in Figure 4. Using all the information, evaluate the effect on plant growth of adding the different fertilisers to the soil. (5 MARKS)
1. Potassium nitrate most effective and chicken manure least effective; 2. All fertilisers more effective than control; 3. No increase (in growth) with potassium nitrate above 30g; 4. Ammonium sulfate (shows) small/gradual increase after 30g; 5. Chicken manure effectiveness decreases after 45g OR Chicken manure effectiveness decreases at 60g; 6. Fertiliser/s provide nitrogen source for protein; 7. No statistical test (to determine if differences are significant); 8. Only shows (results for) spinach;
Q: Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants. (5 MARKS)
1. Protein/ amino acids / DNA into ammonium compounds/ ammonia, 2. By saprobionts 3. Ammonium/ ammonia into nitrite, 4. Nitrite into nitrate 5. By nitriflying bacteria / microorganisms 6. Nitrogen to ammonia/ ammonium 7. By nitrogen-fixing bacteria/microorganisms in soil,
EQ: Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate. Scientists investigated the effects of different AMF species on the productivity of the plant community of a prairie grassland ecosystem when growing in/on soil containing different phosphate concentrations. The scientists set up identical plots of prairie grassland soil containing seeds of the plant species found in the ecosystem. The scientists added different AMF species and different concentrations of phosphate to particular plots. Control plots without AMF species were also set up. After 20 weeks the scientists determined the shoot biomass for each plot. The results the scientists obtained are shown in Figure 5. Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity. (2 MARKS)
1. Represents dry mass / mass of carbon; 2. Represents gross production minus respiratory losses;
Q: Intensive rearing of livestock produces large quantities of waste. Some farmers use an anaerobic digester to get rid of the waste. In an anaerobic digester, microorganisms break down the large, organic molecules in the waste. This produces methane, which is a useful fuel. It also produces organic substances that can be used as a natural fertiliser. The diagram shows an anaerobic digester. The anaerobic digester has a cooling system, which is not shown in the diagram. Without this cooling system the digester would soon stop working. Explain why. (2 MARKS)
1. Respiration causes temperature increase / release of heat; 2. Enzymes would be denatured / microorganisms killed;
Q: Scientists 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. 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 added, 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. (2 MARKS)
1. So that effects of nitrate or ammonium alone could be seen; 2. So that effects of fungus can be seen.
Q: Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your knowledge of water potential to explain why. (2 MARKS)
1. Soil has low(er) water potential / plant / roots have higher water potential; 2. Osmosis from plant / diffusion of water from plant;
What are the advantages of global warming?
1. Some areas have increased rainfall which fills reservoirs 2. Warmer temperatures can allow crops to grow where presently too cold 3. Rate of photosynthesis (and productivity) can increase, so can be possible to harvest twice a year instead of once
EQ: Ammonia in soil is oxidised to nitrites and nitrates by species of nitrifying bacteria. Scientists investigated whether two soils with a different pH contained different communities of nitrifying bacteria. These communities consist of all the nitrifying bacteria of different species in each soil. They took samples of soil from two sites, A and B. They measured the pH of the samples and found that • the soil from site A had a pH of 6.9 • the soil from site B had a pH of 4.3 The scientists measured the concentration of ammonia in soil samples over 20 days. Each sample contained the same concentration of ammonia at the start and had the same mass. They recorded the concentration of ammonia in • soil A with a pH of 6.9 • soil B with a pH of 4.3 • a mixture of equal masses of soils A and B with its pH adjusted to 6.9 Their results are shown in Figure 6. The oxidation of ammonia by nitrifying bacteria involves the enzyme ammonia monooxygenase. Each species of nitrifying bacteria has its own specific amoA gene that codes for production of ammonia monooxygenase. In a second investigation, the scientists determined the expression of the amoA gene in two species of bacteria, S and T. Species S was from acid soil and species T was from soil with a neutral pH. The scientists grew cultures of each species separately in soils of different pH. They determined the amount of mRNA from the amoA gene in each culture. Their results are shown in Figure 7. The scientists set up their cultures in sterile glass bottles. Suggest one suitable method for sterilising the bottles and explain why it was necessary to sterilise them. (2 MARKS)
1. Suitable method; eg in boiling water / steam / autoclave / wash in disinfectant / wash in alcohol 2. (Reason) to remove / kill other bacteria / organisms that might break down ammonia;
Describe the carbon cycle.
1. The carbon in photosynthetic organisms passes along food chains to animals. On their death, both plants and animals are broken down by saprophytic microorganisms → decomposers. 2. Saprophytic microorganisms secrete extracellular enzymes on to the dead organisms. These break down complex molecules into smaller, soluble molecules that they absorb by diffusion. 3. The carbon in dead organisms is then released as CO2 during respiration by the decomposer. 4. If decay is prevented, the organisms may become fossilised into coal, oil, or peat. 5. Not all parts of organisms decompose, shells and bones of aquatic organisms sink to the bottom of the oceans and, over millions of years, form carbon-containing sedimentary rocks such as chalk and limestone. 6. This carbon eventually returns to the atmosphere as these rocks are weathered.
Global CO2 concentration in the atmosphere has increased due to human activities of...
1. The combustion of fossil fuels 2. Deforestation, removing enormous amounts of photosynthesising biomass so less CO2 removed from atmosphere
EQ: Ammonia in soil is oxidised to nitrites and nitrates by species of nitrifying bacteria. Scientists investigated whether two soils with a different pH contained different communities of nitrifying bacteria. These communities consist of all the nitrifying bacteria of different species in each soil. They took samples of soil from two sites, A and B. They measured the pH of the samples and found that • the soil from site A had a pH of 6.9 • the soil from site B had a pH of 4.3 The scientists measured the concentration of ammonia in soil samples over 20 days. Each sample contained the same concentration of ammonia at the start and had the same mass. They recorded the concentration of ammonia in • soil A with a pH of 6.9 • soil B with a pH of 4.3 • a mixture of equal masses of soils A and B with its pH adjusted to 6.9 Their results are shown in Figure 6. The oxidation of ammonia by nitrifying bacteria involves the enzyme ammonia monooxygenase. Each species of nitrifying bacteria has its own specific amoA gene that codes for production of ammonia monooxygenase. In a second investigation, the scientists determined the expression of the amoA gene in two species of bacteria, S and T. Species S was from acid soil and species T was from soil with a neutral pH. The scientists grew cultures of each species separately in soils of different pH. They determined the amount of mRNA from the amoA gene in each culture. Their results are shown in Figure 7. This method allowed the scientists to estimate the expression of the amoA gene in each culture but not the growth of the bacterial population in each culture. Explain why. (4 MARKS)
1. They didn't count bacteria / cells / population(s); 2. Copies / number of mRNA related to amount of enzyme / amoA produced / translated; 3. Don't know how much mRNA / amoA produced by each cell; 4. Don't know if amoA (mRNA / enzyme) is linked to cell division / growth (of population);
EQ: 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)
1. Use of colorimeter; 2. Measure the absorbance/transmission (of light); 3. Example of how method can be standardised eg same volume of water, zeroing colorimeter, same wavelength of light, shaking the sample;
EQ: Farmers use artificial fertilisers to maintain or increase yield from grain-producing crop plants such as wheat. Scientists investigated changes in the use of artificial fertiliser in India between 1970 and 2005. They also investigated changes in the fertiliser response ratio. This ratio shows how many kg of grain are produced for each kg of fertiliser used. Figure 4 shows their results in the form the scientists presented them. (A hectare is a unit of area commonly used in agriculture) Use the data in Figure 4 to evaluate the use of artificial fertilisers on grain-producing crops in India. (2 MARKS)
1. Using more but getting less response over time; 2. The graph shows correlation but doesn't prove changes in yield due to fertiliser/but there could be other factors; 3. Becomes less cost effective with time;
Q: Scientists 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. 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 added, ammonium fertiliser • Group D - mycorrhizal fungus added, ammonium fertiliser The heat-treated fungus had been heated to 120 °C for 1 hour. 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. (2 MARKS)
1. Weigh samples at intervals during drying; 2. To see if weighings became constant (by 3 days).
Q: In the activated sludge method of sewage treatment, organic matter in untreated sewage supplies nutrients to bacteria in the treatment tank. These bacteria include decomposers and nitrifying bacteria. The bacteria are eaten by ciliated protoctistans, which are, in turn, eaten by carnivorous protoctistans. The organic matter in untreated sewage consists of small particles, which are suspended in water. Activated sludge consists of solid lumps (flocs) of organic matter and bacteria. When the two are mixed in the treatment tank, bacteria from the flocs become dispersed in the water and feed on the suspended organic matter, converting it to flocs. Different types of ciliated protoctistans feed on the bacteria. • Free-swimming protoctistans are able to move throughout the tank. • Crawling protoctistans can only move over the surface of the flocs. The diagram shows the change in the nature of the organic matter in the treatment tank and the changes in the numbers of the different types of organisms present. Explain the changes in the numbers of dispersed bacteria and the numbers of free-swimming protoctistans. (3 MARKS)
1. numbers of dispersed bacteria increase as they feed on organic matter; 2. numbers of free-swimming protoctistans increase because number of bacteria increase; 3. dispersed bacteria decrease as amount of dispersed organic matter decreases / due to lack of food / as organic matter is converted to flocs / are preyed on by free-swimming protoctistans;
EQ: Ammonia in soil is oxidised to nitrites and nitrates by species of nitrifying bacteria. Scientists investigated whether two soils with a different pH contained different communities of nitrifying bacteria. These communities consist of all the nitrifying bacteria of different species in each soil. They took samples of soil from two sites, A and B. They measured the pH of the samples and found that • the soil from site A had a pH of 6.9 • the soil from site B had a pH of 4.3 The scientists measured the concentration of ammonia in soil samples over 20 days. Each sample contained the same concentration of ammonia at the start and had the same mass. They recorded the concentration of ammonia in • soil A with a pH of 6.9 • soil B with a pH of 4.3 • a mixture of equal masses of soils A and B with its pH adjusted to 6.9 Their results are shown in Figure 6. The scientists concluded that the soil mixture experiment showed there were different communities of bacteria in soils A and B. What evidence from Figure 6 supports their conclusions? Give reasons for your answer. (3 MARKS)
1. pH 4.3 / B has fastest rate of breakdown (of ammonia); 2. A + B / mixture at pH 6.9 slowest / slower (than A or B); 3. Suggests (community / bacteria at) pH 4.3 / B doesn't work (well) at pH 6.9 / pH of mixture;
Q: Tomato growers have increased the yield of fruit from 100 to 400 tonnes per hectare by growing the tomato plants in automatically heated glasshouses and enhancing the carbon dioxide concentration. To control the nutrient supply to the roots, the plants are grown without soil in plastic troughs, as shown in the diagram. 1. Explain how enhancing the carbon dioxide concentration helps to increase the yield. (2 MARKS) 2. Maintaining a high temperature in a glasshouse in winter, when the light intensity is low, may reduce the yield. Explain how. (2 MARKS) 3. Tomato fruits have a high percentage of water. When making tomato ketchup, it is more economical to use fruits which have a low percentage of water. Growers can reduce the water content of the fruit by adding sodium chloride to the nutrient solution in the plastictrough. Explain how adding sodium chloride can reduce the water content of the fruit. (2 MARKS)
1.- rate of photosynthesis increased; - normal atmospheric concentration a limiting factor/ more /faster production of biomass or sugars / more products of photosynthesis transported to fruits; 2. - (increased temperature) increases rate of respiration - rate of photosynthesis too low to replace respiratory loss 3. - lower water potential of nutrient solution; - less water absorbed into roots (by osmosis);
EQ: A scientist investigated the effects of different fertilisers on the growth of spinach plants. The scientist: • set up a large sample of identical pots of soil • added different masses of different fertilisers to selected pots • did not add fertiliser to the control pots • planted the same number of young spinach plants in each pot • after 20 days, determined the biomass of spinach plants in each pot. The results the scientist obtained after 20 days are shown in Figure 4. Calculate how many times greater the mean growth rate per day was using 37.5 g potassium nitrate than using 37.5 g ammonium sulfate. Assume the mean biomass of the spinach plants at the start of the investigation was 0.5 g per pot. (1 MARK)
1.375 / 1.3746 / 1.38 / 1.4 (times greater);
Describe nitrification.
2. Ammonium Ions go through nitrification [oxidation reaction] to be converted into Nitrite ions (Nitr1te [1st]) (NO2 -), then go through further nitrification [oxidation] to become Nitrate ions (Late) (NO3 -). Bacteria need oxygen to carry out conversion.
Describe denitrification.
3. Nitrate ions then go through denitrification in anaerobic conditions by denitrifying bacteria (e.g. waterlogged soil) to become nitrogen gas in atmosphere
Describe nitrogen fixation.
4. Plants receive nitrogen in two ways - Absorbed directly from Nitrate through plant root hair cells by active transport - Nitrogen gas in the atmosphere is converted into nitrogen-containing compounds through nitrogen fixation by either mutalistic nitrogen fixing bacteria which live in nodules on the roots of leguminous plants such as peas and beans. - Free-living nitrogen-fixing bacteria can reduce gaseous nitrogen to ammonia.
EQ: Ammonia in soil is oxidised to nitrites and nitrates by species of nitrifying bacteria. Scientists investigated whether two soils with a different pH contained different communities of nitrifying bacteria. These communities consist of all the nitrifying bacteria of different species in each soil. They took samples of soil from two sites, A and B. They measured the pH of the samples and found that • the soil from site A had a pH of 6.9 • the soil from site B had a pH of 4.3 The scientists measured the concentration of ammonia in soil samples over 20 days. Each sample contained the same concentration of ammonia at the start and had the same mass. They recorded the concentration of ammonia in • soil A with a pH of 6.9 • soil B with a pH of 4.3 • a mixture of equal masses of soils A and B with its pH adjusted to 6.9 Their results are shown in Figure 6. Calculate the difference in the rate of breakdown of ammonia per day between day 0 and day 2 in soil A and soil B. Show your working and the units for your answer. (2 MARKS)
Answer between 4.5 and 4.6 µg g-1 day-1 ;;
Artificial fertilisers can leading to reduced species diversity. Explain how.
Artificial fertilisers favour fast growing plants e.g. grass / nettles → slower plants lose out out → less organisms who feed off them
How do microorganisms play a vital role in recycling nutrients such as nitrogen and phosphorus?
Breakdown large organic compounds into small inorganic (soluble) compounds → these can be absorbed by producers
What is the most important greenhouse gas and why?
CO2 - most abundant - remains on earth for a long time
Name the 2 most important greenhouse gases.
CO2 & Methane
Why is too much fertiliser harmful to the soil?
Can change their water potential (more negative) and make it harder to absorb nutrients such as magnesium (rare) for chlorophyll
Q: Describe what bacteria do in denitrification. (1 MARK)
Conversion of nitrate to nitrogen.
EQ: Farmers use artificial fertilisers to maintain or increase yield from grain-producing crop plants such as wheat. Scientists investigated changes in the use of artificial fertiliser in India between 1970 and 2005. They also investigated changes in the fertiliser response ratio. This ratio shows how many kg of grain are produced for each kg of fertiliser used. Figure 4 shows their results in the form the scientists presented them. (A hectare is a unit of area commonly used in agriculture) Use these data to calculate the difference in the mass of grain produced per hectare in 1970 compared with 2005. Show your working. (2 MARKS)
Correct answer in the range 90 to 133.2 scores 2 marks;;
Describe an application of nitrification.
Farmers aerate their soil → increase O2 → allowing number of nitrifying bacteria to increase and denitrifying bacteria to decrease → maximise nitrogen availability
Q: Since 1965 there has been a steady rise in the phosphate concentration in the water of Lake Windermere. Scientists have monitored the phosphate concentration and plant biomass over a period of time. The results are shown in the graphs. Suggest one source of the phosphate in the lake. (1 MARK)
Fertilisers / detergents / slurry / manure / sewage / faeces;
What are mycorrhizae?
Fungi that grows in a mutualistic / symbiotic relationship with plant roots
Draw the nitrogen cycle.
Look at the image and compare.
Name the benefits of mycorrhizae and plants because of their mutualistic / symbiotic relationship.
Plant: - Increase in surface area of the roots as fungi acts as extension of root - Increases the absorption of rare minerals + water, eg magnesium - Mycorrhizae acts like a sponge and holds water and minerals around the roots → makes plant more drought resistant and able to take up more inorganic ions Fungi: - Plant exchanges these for organic compounds, eg sucrose (carbohydrates)
How is methane produced?
Produced when microorganisms break down organic molecules of which organisms are made 1. When decomposers break down the dead remains of organisms 2. When microorganisms in the intestines of primary consumers, such as cattle digest the food that has been eaten
Q: Specialised biotechnology companies have managed to culture some nitrifying bacteria. The bacteria are sold in water-suspension by aquarium suppliers. Aquarium owners use these bacteria to prevent fish death due to toxic levels of ammonia. With reference to the role of Rhizobium in the nitrogen cycle, why would the aquarium suppliers be unlikely to sell Rhizobium? (1 MARK)
Rhizobium is involved in) nitrogen fixation / not involved in nitrification OR (Rhizobium) will not reduce increases levels of ammonia/ ammonium ions
What are the main stages of the nitrogen cycle?
Summary of main stages: 1. Ammonification 2. Nitrification 2. Nitrogen fixation 4. Denitrification Each stage involves saprophytic microorganisms.
What are saprobionts?
Type of decomposer, bacteria or fungi, that digest their food by saprobiotic nutrition --> digesting dead organic matter and their waste products by secreting extracellular enzyme
EQ: Farmers use artificial fertilisers to maintain or increase yield from grain-producing crop plants such as wheat. Artificial fertiliser is used to replace mineral ions removed from the land when crops are harvested. One of the mineral ions is nitrate. Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested. (2 MARKS)
Two suitable examples;; Examples 1. amino acid/protein/ polypeptide/peptide; 2. nucleic acid/nucleotide/base; 3. DNA; 4. RNA; 5. ATP/ADP; 6. NAD/NADP (reduced or not); 7. Cyclic AMP/cAMP; 8. Chlorophyll;
Q: Scientists 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. 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 added, ammonium fertiliser • Group D - mycorrhizal fungus added, ammonium fertiliser The heat-treated fungus had been heated to 120 °C for 1 hour. 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. The scientists' results are shown in the table below What conclusions can be drawn from the data in the table about the following? (i) The effects of the fungus on growth of the pea plants. (ii) The effects of nitrate fertiliser and ammonium fertiliser on growth of the pea plants. (4 MARKS)
With live fungus - showing effects of the fungus: 1. Fungus increases growth of roots and shoots in both; 2. Produces greater growth with nitrate. With heat-treated fungus - showing effects of fertiliser: 3. Similar dry masses for roots and shoots; 4. (Probably) no significant difference because SDs overlap.
Q: State the term used to describe the conversion of nitrogen gas to ammonium compounds in the soil. (1 MARK)
nitrogen fixation
