Energy and ecosystems Flashcards
Suggest how you could determine the dry mass of a sample of plant material. (2)
Heat to temp to evaporate water;
Value which would not burn material
Weigh and heat until no further change in mass;
What is the advantage of using dry mass and not fresh mass to compare the yield of plants?
Amount of water present will vary;
This will affect fresh mass / will not affect dry mass;
Give the equation that links gross productivity and net productivity.
Gross productivity = net productivity + respiratory loss / respiration;
A horse was kept in the field from March to October. During the summer months, the horse was able to eat more than it needed to meet its minimum daily requirements.
Suggest how the horse used the extra nutrients absorbed. (1)
- Stored as fat / glycogen / biomass;
Reject stored energy. Ignore respiration
- Used for growth / movement / reproduction / process involved in growth / movement / reproduction;
During the dry season the protein content of the plants decreases. Suggest one way in which a lack of rain could account for this change. (2)
less nitrate taken up;
less amino acid / protein synthesis;
OR
parts of plant higher in protein die;
higher proportion of cellulose / non-protein components in diet;
Suggest an explanation for the percentage of energy lost in faeces for the herbivore being larger than that for the carnivore. (2)
cellulose present in faeces;
cellulose / much of food indigestible;
indigestible material contains energy;
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)
- (Nitrogen) to ammonia / NH3 / ammonium;
- Produce protein / amino acids / named protein / DNA / RNA;
Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your knowledge of water potential to explain why. (2)
- Soil has low(er) water potential / plant / roots have higher water potential;
Reference to water potential gradient is sufficient if correct direction of gradient or water movement is outlined Accept WP or Ψ for water potential
- Osmosis from plant / diffusion of water from plant;
Accept plant takes up less / not enough water by osmosis Reference to movement of minerals by osmosis negates mark
Explain how farming practices increase the productivity of agricultural crops. (5)
- Fertilisers / minerals / named ion (added to soil);
Accept any named examples of natural fertilisers for mark point 1 e.g. manure, bone meal etc. Ignore named elements
- Role of named nutrient or element e.g. nitrate / nitrogen for proteins / phosphate / phosphorus for ATP / DNA;
Accept fertilisers / minerals / named nutrient / element removes limiting factor for mark point 2
- Selective breeding / genetic modification (of crops);
Accept idea of choosing particular variety of crop for mark point 5
- Ploughing / aeration allows nitrification / decreases denitrification;
- Benefit of crop rotation in terms of soil nutrients / fertility / pest reduction;
Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants. (5)
- Protein / amino acids / DNA into ammonium compounds / ammonia;
Accept any named nitrogen containing compound e.g. urea for mark point 1
- By saprobionts;
Accept saprophytes for mark point 2
- Ammonium / ammonia into nitrite;
Accept marks for conversion i.e. mark points 1, 3, 4 and 6 even if incorrect type of bacteria named as being involved
- Nitrite into nitrate;
However, reject marks for type of bacteria i.e. mark points 2, 5 and 7 if linked to incorrect process e.g. nitrite converted to nitrate by saprobionts
- By nitrifying bacteria / microorganisms;
- Nitrogen to ammonia / ammonium;
Award one mark for ammonia / ammonium into nitrate if neither mark point 3 or 4 awarded
- By nitrogen-fixing bacteria / microorganisms in soil;
Ignore reference to nitrogen-fixing bacteria in root nodules. If not specified, assume nitrogen-fixing bacteria are in the soil
It is estimated that, each year, a total of 3 × 109 tonnes of ammonia are converted to nitrate. Only 2 × 108 tonnes of ammonia are produced from nitrogen gas.
Explain the difference in these figures. (2)
Ammonia formed by decay / decomposition / putrefying / ammonifying / by action of decomposers / saprobionts;
On nitrogenous waste / urea or nitrogenous compounds (e.g. proteins, amino acids, DNA, ATP);
Describe and explain the effect of Rhizobium bacteria on the growth of soybeans. (3)
Forms mutualistic / symbiotic union with soyabean / forms root nodules / mutual benefits ( / described);
makes ammonia / ammonium;
Helps produce organic-N / amino acids / protein;
Explain how farming practices might be responsible for the change in nitrate concentration in the water between point X and point Y. (2)
excessive use of fertilisers;
run-off / leaching;
The species that are present change during succession. Explain why. (2)
- Species / plants / animals change the environment / conditions / add humus / nutrients etc. / less hostile (habitat);
Accept ‘they’ for species / plants in mark points 1 and 2
- Species / plants better competitors;
Explain the advantage of this to these pioneer plants. (2)
Bare soil temperatures fluctuate;
Reject: environmental temperature Accept: converse
More bare soil, early / at start of succession / when few plants;
Explain the advantage to a plant that colonises after 50 years of having a high rate of photosynthesis at low light intensities. (1)
Plant will grow / survive in the shade / when overshadowed (by taller plants) / when receiving less light;
Effect on plant with reason for effect
Ignore reference to competition
explain what is meant by succession
change in community over time;
either due to change environmental / abiotic factors / change is due to species present;
explain what is meant by climax community
stable community / no further succession / final community;
Explain why the number of other plant species decreases between 4 and 12 years after burning. (2)
(increased) interspecific competition;
for light / nutrients / named nutrient / water;
Explain how succession resulted in the formation of the forest. (4)
pioneers / suitable example colonise land;
example of change in environment;
enables change in species;
conditions change further / example to favour trees;
Waterlogged soils lack oxygen. Suggest why trees are unable to survive in waterlogged soils
roots unable to respire (aerobically);
active transport of minerals / other metabolic effect stops;
The water and soil in Sphagnum bogs are usually acidic. Suggest why Sphagnum is not fully decomposed after it dies. (3)
action of bacteria / decomposers inhibited / fewer bacteria / decomposers;
acid conditions inhibits enzymes / enzymes denatured / changes active site;
H+ ions affect active site;
anaerobic conditions;
Explain the decrease in biochemical oxygen demand with distance downstream from the sewage outlet. (
high initially because sewage contains large numbers of
microorganisms / bacteria;
less organic material therefore fewer bacteria;
less oxygen used for breakdown / respiration;
Suggest an explanation for the changes in the population density of Asellus with distance downstream from the sewage outlet. (3
decrease due to low oxygen;
increase due to large food supply / organic matter / sufficient
oxygen / little or no competition;
decrease due to increased (interspecific) competition from other
invertebrates / less food / organic matter;
