Azotobacter is a nitrogen- fixing bacterium. it produces the enzyme nitrogenase. the enzyme only works in the absence of oxygen. Azotobacter has a very high rate of aerobic respiration compared with bacteria that do not fix nitrogen. suggest 2 advantages of the very high rate of aerobic respiration. (2)
- provides energy for nitrogen- fixation
- nitrogenase produced quicker
if scientists could transfer the gene that codes for nitrogenase to cereal plants, these cereal plants would be able to fix nitrogen. however, the scientists would expect these genetically engineered cereal plants to grow more slowly than coral plants that get their nitrogen from fertiliser. explain why they would grow more slowly. (2)
- ATP needed for nitrogen fixation
- so less ATP available for growth
what does the Hardy- Weinberg principle predict? (3)
- the frequency of alleles of a particular gene
- will stay constant from one generation to the next
- providing no mutations
the respiration energy: absorbed energy from gut ratio is higher in mammalian primary consumers than in insect primary consumers. suggest a reason for this higher value. (1)
mammals have a high body temperature
describe the part played by the inner membrane of a mitochondrion in producing ATP. (3)
- electrons transferred down ETC
- provide energy to take H+ into space between membranes
- H+ pass back, through ATP synthase
a scientist investigated ATP production in a preparation of isolated mitochondria. He suspended the mitochondria in an isotonic solution and added a suitable respiratory substrate together with ADP and Pi. he bubbled oxygen through the preparation. explain why the scientist did not use glucose as the respiratory substrate. (2)
- glycolysis in cytoplasm
- glucose cannot cross mitochondrial membrane
the ratio of dry biomass of animals to the dry biomass of seaweed is always a lot less than 1. explain why. (2)
- seaweeds are producers
- loss of energy between trophic levels
- as a result of respiration
the concentrations of CO2 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)
- high concentration of CO2 at night
- no photosynthesis at night
- in dark plants respire
- in light plants use more CO2 than they produce
- decrease in CO2 concentration with height
- at ground less light
in the light- independent reaction of photosynthesis, the carbon in CO2 becomes carbon in triode phosphate. describe how. (5)
- CO2 combines with RuBP
- to produce 2 molecules of GP
- reduced to TP
- requires reduced NADP
- energy from ATP
humans synthesis more than their body mass of ATP each day. explain why it is necessary for them to synthesis such a large amount of ATP. (2)
- ATP cannot be stored
- used for active transport, muscle contractions etc
scientists measured the mean temperature in a field each month between March and October. The gross productivity of the plants in the field was highest in July. explain why. (2)
- high temperature allows enzymes to work faster
- photosynthesis reactions are faster
the net productivity of the plants in the field was higher in August than in July. use the equation in part and your knowledge of photosynthesis and respiration to suggest why. (2)
- less respiration
- photosynthesis less affected by temperature increase
- lower energy loss
suggest 2 advantages of processing waste in anaerobic digesters rather than in open ponds. (2)
- conditions can be controlled
- open ponds associated with eutrophication
give 1 advantage of using natural fertiliser produced in the digester rather than an artificial fertiliser. (1)
- less leaching
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
- break down proteins
- ammonium produced
- ammonia converted to nitrite to nitrate
- nitrifying bacteria
- oxidation
during photosynthesis, oil- palm trees convert CO2 into organic substances. describe how. (6)
- CO2 combines with RuBP
- provides 2 GP
- reduces to TP
- using reduced NADP
- using ATP
- TP converted to glucose
suggest and explain one advantage to the fish of occupying different depths in the lake. (2)
- less competition
- for food
describe how the action of microorganisms in the soil produced a source of nitrates for crop plants. (5)
- proteins into ammonia compounds
- by saprobionts
- ammonia into nitrite
- by nitrifying bacteria
- nitrogen to ammonia
- by nitrogen- fixing bacteria
explain how the use of pesticides can result in resistant strains of insect pests. (5)
- variation
- due to mutation
- allele for resistance
- selection pressures
- pests with resistance survive and breed
the species that present change during succession. explain why. (2)
- species change the environment
- less hostile habitat
- species better competitors
a scientists investigated the uptake of radioactively labelled carbon dioxide in chloroplasts. she used 3 tubes, each containing different components of chloroplasts. she measured the uptake of CO2 in each of these tubes.
A=> stroma and grana uptake of CO2= 96000
B=> stroma, ATP and NADPH uptake of CO2= 97000
C=> stroma uptake of CO2= 4000
explain why the results in tube B are similar to those in tube A. (1)
ATP and NADPH are produced in grana
a scientists investigated the uptake of radioactively labelled carbon dioxide in chloroplasts. she used 3 tubes, each containing different components of chloroplasts. she measured the uptake of CO2 in each of these tubes.
A=> stroma and grana uptake of CO2= 96000
B=> stroma, ATP and NADPH uptake of CO2= 97000
C=> stroma uptake of CO2= 4000
use the information in the table to predict the uptake of radioactively labelled CO2 if tube A was placed in the dark. explain your answer. (2)
- 4000
- light- dependent reaction does not occur
a scientists investigated the uptake of radioactively labelled carbon dioxide in chloroplasts. she used 3 tubes, each containing different components of chloroplasts. she measured the uptake of CO2 in each of these tubes.
A=> stroma and grana uptake of CO2= 96000
B=> stroma, ATP and NADPH uptake of CO2= 97000
C=> stroma uptake of CO2= 4000
use your knowledge of the light- independent reaction to explain why the uptake of CO2 in tube C was less than the uptake in tube B. (2)
- less GP converted to TP
- so less TP concerted to RuBP
DCMU us used as a weed killer. it inhibits electron transfer during photosynthesis. the addition of DCMU to tube A decreased the uptake of CO2. explain why. (2)
- no ATP produced during electron transport chain
- no NADPH produced as a result
