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Suggest two reasons for conserving rainforests. (2)
• protect species • protect habitats • reduce climate change • source of medicines • for tourism
Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem. (3)
• heat loss from respiration • not all organism eaten • excretion
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why. (2)
• energy is lost between trophic levels • energy is lost via respiration
The tomato seeds were planted into sterilised soil. Suggest two reasons why the soil was sterilised. (2)
• kill pathogens • kill pests
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 (nitrifying bacteria require aerobic conditions) • less oxidation of ammonium ions to nitrite ions and nitrate ions
describe what happens during photoionisation in the light-dependent reaction. (2)
• chlorophyll absorbs light • electrons are lost
explain why the students marked the origin using a pencil rather than using ink. (1)
with a pencil the origin line would still be visible
suggest and explain the advantage of having different coloured pigments in leaves. (1)
allows leaves to absorb different wavelengths of light for photosynthesis
explain why an increase in shoot biomass can be taken as a measurement of net primary productivity. (2)
• represents dry mass of carbon • represents gross production minus respiratory losses
In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest two reasons why. (2)
• light is reflected • light misses photosynthetic tissue
Explain why determination of dry mass was an appropriate method to use in this investigation. (2)
• dry mass determines increase in organic material • water content varies
Heat stress decreases the light-dependent reaction of photosynthesis. Explain why this leads to a decrease in the light-independent reaction. (2)
• less reduced NADP • less ATP
Where precisely is rubisco found in a cell? (1)
stroma
explain why a log scale is used to record the number of cells. (1)
there is a large range in the number of cells
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 transmission • use the same volume of water each time
In muscles, pyruvate is converted to lactate during prolonged exercise. Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration. (2)
• NAD is regenerated • glycolysis continues
The student repeated the experiment using yeast in maltose solution. She found the rate of carbon dioxide production was slower than with yeast in glucose solution. Suggest why. (2)
• maltose is a dissacharide • time was taken to hydrolyse the glycosidic bond in maltose
describe how the products of the LDR and used in the LIR to produce triose phosphate - don’t include details of RuBP in your answer. (3)
• reduced NADP and ATP • reduced NADP used to reduce glycerate 3-phosphate to triose phospate • ATP is hydrolysed to release energy for this
suggest two ways in which crop rotation may lead to high crop yields. (2)
• different crops use different nutrients from soil • grow crops with nitrogen-fixing bacteria
explain the decrease in gross productivity as the woodland matures. (2)
• more shading • reduced photosynthesis
Explain how the increase in soil nitrate could account for the higher wheat biomass in NB-17 plots. (2)
• nitrate used to make amino acids which are needed for protein synthesis • more nitrate means higher rate of protein synthesis so biomass increases