Visit for Videos, Questions and Revision Notes. (a) (i) Name all the secondary consumers in this food web. ...

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1 Q. The diagram shows organisms in a food web. (a) (i) Name all the secondary consumers in this food web..... Use the diagram to explain the likely effect of a sudden decrease in the stickleback population on the population of mayfly larvae (b) A pyramid of energy for this food web is shown below. The bars are drawn to the same scale. (i) Use the pyramid of energy to calculate the percentage efficiency of energy Page

2 transfer between producers and primary consumers. Show your working. efficiency =... % The average efficiency of energy transfer between producers and primary consumers in pyramids of energy is around 0 %. Suggest why the efficiency of energy transfer from producers to primary consumers in this food web is higher than 0 % (c) Energy from the sun may ultimately end up in dead plant matter. Describe how (Total 9 marks) Q2.(a) Energy enters most ecosystems through the light-dependent reaction of photosynthesis. Describe what happens during the light-dependent reaction. (5) Page 2

3 (b) Describe the reasons for the low efficiency of energy transfer through ecosystems. (5) (c) Changes in ecosystems can lead to speciation. A high concentration of copper in soil is toxic to most plants. In some areas where the soil is polluted with copper, populations of grasses are found to be growing. These populations of grass belong to a species also found growing on unpolluted soils. It has been suggested that a new species of grass may evolve on soil that has been polluted with copper. Explain how this new species might evolve. (5) (Total 5 marks) Q3. The herring is a fish found in the North Sea. In the food chain below, the figures represent biomass. The units are g m 3. Phytoplankton Zooplankton Herring (a) Sketch and label a pyramid of biomass to represent this food chain. (b) In this food chain, the phytoplankton reproduce very rapidly. Suggest why this rapid rate of reproduction is essential to sustain the food chain. (Total 3 marks) Page 3

4 Q4. Phytoplankton are microscopic photosynthesising organisms which live in water. In favourable environmental conditions they have a very high rate of reproduction. They are eaten by microscopic animals called zooplankton. In an investigation, samples of water were removed from a lake at intervals over a twelve-month period and the biomasses of these organisms were determined. The results are shown in the graph. The diagram shows the relationship between the biomass of the phytoplankton and the biomass of the zooplankton for one of the months during this investigation. (a) Use the graph to give one month in which this relationship would have been found. (b) Explain why the biomass of the primary consumers is less than the biomass of the producers in most communities. Page 4

5 (3) (c) Explain why the biomass of the phytoplankton in the lake could be less than that of the zooplankton, as shown in the diagram. (Total 5 marks) Q5. 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. (a) (i) Sketch and label a pyramid of energy for the organisms found in the treatment tank. Explain what causes this pyramid of energy to be this shape. Page 5

6 (b) (i) 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) 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. (c) 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. Page 6

7 (i) Explain the changes in the numbers of dispersed bacteria and the numbers of free-swimming protoctistans. (3) Page 7

8 Explain how the changes that occur in the treatment tank illustrate the process of succession. (4) (Total 5 marks) Q6. Scientists measured the mean temperature in a field each month between March and October. The table shows their results. Month Mean temperature / C March 9 April May 4 June 7 July 20 August 8 September 6 October 4 (a) The gross productivity of the plants in the field was highest in July. Page 8

9 Use the data in the table to explain why. (b) (i) Give the equation that links gross productivity and net productivity. The net productivity of the plants in the field was higher in August than in July. Use the equation in part (b)(i) and your knowledge of photosynthesis and respiration to suggest why. (c) 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. (d) The horse s mean energy expenditure was higher in March than it was in August. Use information in the table to suggest why. Page 9

10 (Total 8 marks) Q7. (a) In the light-dependent reaction of photosynthesis, light energy generates ATP. Describe how. (5) (b) Energy is transferred through an ecosystem. Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer. Page 0

11 (6) (c) Explain how the intensive rearing of domestic livestock increases net productivity. (4) (Total 5 marks) Q8. Dogwhelks are small, carnivorous snails which live on rocky seashores. They cling to, and move over, the surface of the rocks and feed on animals such as mussels. S (a) Mussels are permanently attached to rocks. They feed on small photosynthetic organisms which they filter from the water. (i) Suggest why dogwhelks lose more energy by respiration than do mussels. Page

12 A greater proportion of the energy in food eaten is lost in the faeces of mussels compared with the faeces of dogwhelks. Suggest why. (b) Boats used to be painted with a paint that contains the poisonous substance tributyl tin (TBT). TBT is absorbed into the bodies of animals and cannot be broken down. Explain why there is a higher concentration of TBT in the tissues of dogwhelks than in the mussels on which they feed. (Total 5 marks) Q9. Scientists constructed a mathematical model. They used this model to estimate the transfer of energy through consumers in a natural grassland ecosystem. The table shows their results. Energy transferred as percentage of energy in biomass of producers Ingested food (F) Absorbed from gut (A) Egested (E) Net production (P) Respired (R) Primary consumers Page 2

13 Mammals Insects Secondary consumers Mammals Insects (a) Complete the equation to show how net production is calculated from the energy in ingested food. P = (b) Describe and explain how intensive rearing of domestic livestock would affect (i) the figure for A in the first row of the table the figure for R in the first row of the table. (c) (i) Calculate the ratio of R : A for mammalian primary consumers. The R : A ratio is higher in mammalian primary consumers than in insect primary consumers. Suggest a reason for this higher value. Page 3

14 (d) The scientists tested their model by comparing the values it predicted with actual measured values. The graph shows their results. Are the values predicted by the model supported by the actual measured values? Evaluate the evidence in the graph. (3) (Total 8 marks) Page 4

15 Q0. S A fire destroyed a large area of forest in North America. The process of succession was studied until the forest was re-established. The rate of increase in plant biomass, P, was determined at regular intervals. Also, the total biomass of the parts of plants above ground, B, was measured in sample areas. The graph shows the results for the first 00 years after the fire. (a) Ten years after the fire most of the area was covered with herbaceous plants. (i) Describe how you could measure the dry biomass of the parts of the herbaceous plants above ground in a sample area of m 2. (3) How could the researchers make sure that they obtained reliable data for the total biomass (B)? Page 5

16 (iii) Suggest two limitations involved in measuring the rate of increase in plant biomass (P) which would affect the accuracy of the data (b) The ratio of P to B after 0 years was : 0. (i) Calculate the ratio of P to B after 00 years. Ratio... Explain the change in the ratio between 0 years and 00 years. (Total 0 marks) Page 6

17 M. (a) (i) Stickleback + caddis fly (larva) + stonefly (larva); All three required for mark. In any order.. (With fewer fish) reduced predation / not being eaten results in more freshwater shrimps; Principles. Effect of fish on shrimps 2. Increased competition for food/resources / more producers eaten by shrimps / more shrimps eating producers; 2. Effect of shrimps on producer 3. Less food/resources for mayfly; 3. Effect of food on mayfly 2 max (b) (i). Two marks for correct answer in range 6.8 to 8.9; Ignore additional decimal places. 2. One mark for incorrect answer in which candidate divides 9 to 2 by to 3; Working shown in mm. Accept working in cm/2mm squares (0/56) for mark. 2. Single-celled producers are more digestible / contain less cellulose (than plants) / less energy lost in faeces; 2. All of producer eaten/parts of plant not eaten; 3. Less heat/energy lost / less respiration; 3. May refer to either trophic level 2 max (c). Photosynthesis/light dependent reaction/light independent reaction; 2. Carbon-containing substances; Allow organic substance or named organic substance 2 [9] Page 7

18 M2.(a). Chlorophyll absorbs light energy;. Accept light energy hits chlorophyll. Accept photon for light energy 2. Excites electrons / electrons removed (from chlorophyll); 2. Accept higher energy level as excites 3. Electrons move along carriers / electron transport chain releasing energy; 3. Accept movement of H + / protons across membrane releases energy 4. Energy used to join ADP and Pi to form ATP; Negate produces energy for either mark but not for both 4. Accept energy used for phosphorylation of ADP to ATP 4. Do not accept P as Pi 5. Photolysis of water produces protons, electrons and oxygen; 3. and NADP reduced by electrons / electrons and protons / hydrogen; 6. Accept NADP to NADPH (or equivalent) by addition of electrons / hydrogen 6. Do not accept NADP reduced by protons on their own 5 max (b). Some light is reflected / not of appropriate wavelength;. Light not absorbed is not enough on its own 2. Some light misses leaves / photosynthetic tissue / chloroplasts / chlorophyll; 3. Heat loss; 3. Accept (energy used to) maintain body temperature but do not accept to keep warm or warm blooded 4. (Energy loss via) respiration; 4. Do not accept energy used in respiration 5. Loss via faeces / undigested food / part of organism not eaten; 6. Excretion / named excretory product; 5 max (c). Variation / variety; Page 8

19 2. Mutation; 2. Do not accept answers which suggest the mutation is caused by copper 3. Some plants have allele to survive / grow / live in high concentration of copper / polluted soils; 3. Reference to immunity disqualifies this mark 3. Do not disqualify mark for references to allele providing resistance to copper 4. (Differential) reproductive success / adapted organisms reproduce; 5. Increase in frequency of allele; 6. No interbreeding (with other populations) / separate gene pool / gene pool differs (from other populations); 6. Accept reproductive isolation 5 max [5] M3. (a) Pyramid correctly drawn and trophic levels labelled; Must be in proportion, and labelled using: Phytoplankton / Zooplankton / Herring OR Producer / Primary Consumer / Secondary Consumer OR Candidate s own key (b) Idea of rapid reproduction to replace population/standing crop / so they don t become extinct; Idea of supplying energy/biomass to zooplankton; Idea of taking account of energy losses between trophic levels; max 2 [3] M4. (a) May/June/July; (b) Loss of energy/heat/use of energy/loss of materials/loss of mass; By respiration/movement/excretion/excreta/egestion/egesta IGNORE waste REJECT growth Less energy/mass/matter left to sustain higher level/to be passed on inedible parts/non-digestible parts; Page 9 3

20 (c) Phytoplankton reproduce at rate rate of their consumption; [5] M5. (a) (i) pyramid correctly drawn and labelled; ignore organic matter energy lost/not transferred between trophic levels; in respiration /as heat / in excretory products / movement; ignore in urea / in faeces. Growth cancels 2 nd marking point only 2 (b) (i) 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; 3 max convert nitrogen (gas) into ammonium / ammonia / amino acids; add usable/available nitrogen to an ecosystem / eq.; 2 (c) (i) 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; 4 decrease as are preyed on by free-swimming protoctistans; 5 decrease in free-swimming protoctistans due to lack of dispersed bacteria; 3 max (in a succession) organisms (enter an area and) change the environment/conditions; Page 20

21 2 creating new niches / habitats; 3 allows different species / different types of organisms to enter / be successful; 4 dispersed bacteria change dispersed organic matter to flocs; 5 presence of flocs allows crawling protoctistans to enter / to increase / to be successful; 4 max [5] M6. (a). High temperature allows enzymes to work faster/allows more collisions/ allows more e-s complexes to be formed OR A lot of light so light not limiting; 2. Photosynthesis reactions are faster/more photosynthesis;. Accept enzymes more effective. Ignore references to respiration. Ignore references to optimum (temperature or light). 2 (b) (i) Gross productivity = net productivity + respiratory loss/respiration; Accept any correct rearrangement of this equation Accept recognisable abbreviations Reject respiratory rate.. Respiration slower / less respiration; 2. Light-dependent reaction/photosynthesis less affected by temperature increase; 3. Lower (energy) loss;. Unspecified references refer to August. Allow converse of respiration faster but must specify July / higher temperature 3. Unspecified references refer to August. Allow converse of higher loss but must specify July "Lower respiratory losses (in August)" can meet both points and 3 and gain 2 marks. Page 2

22 2 max (c). Stored as fat/glycogen/biomass; 2. Used for growth/movement/reproduction / process involved in growth/movement/reproduction;. Reject stored energy. Ignore respiration 2 max (d). More heat/energy is lost (in March)/colder (in March); 2. Maintain/regulate body temperature/more heat generated; 3. By respiration/metabolism; 2. Accept keep warm. 2 max [8] M7. (a) Light (energy) excites/raises energy level of electrons in chlorophyll; 2 Electrons pass down electron transfer chain; Q Accept any reasonable alternative for electron transfer chain. 3 (Electrons) reduce carriers/passage involves redox reactions; 4 Electron transfer chain/role of chain associated with chloroplast membranes/in thylakoids/grana; Example such as chemiosmosis; 5 Energy released/carriers at decreasing energy levels; 6 ATP generated from ADP and phosphate/ Pi /phosphorylation of ATP; 5 max (b) Some light energy fails to strike/is reflected/not of appropriate wavelength; 2 Efficiency of photosynthesis in plants is low/approximately Page 22

23 2% efficient; 3 Respiratory loss/excretion/faeces/not eaten; 4 Loss as heat; 5 Efficiency of transfer to consumers greater than transfer to producers/approximately 0%; 6 Efficiency lower in older animals/herbivores/primary consumers/ warm blooded animals/homoiotherms; 7 Carnivores use more of their food than herbivores; Q Accept figures below 5%. Accept figures over 5% but below 0% if clearly related to maximum efficiency. 6 max (c) Slaughtered when still growing/before maturity/while young so more energy transferred to biomass/tissue/production; 2 Fed on concentrate/controlled diet/controlled conditions/so higher proportion of (digested) food absorbed/lower proportion lost in faeces/valid reason for addition; 3 Movement restricted so less respiratory loss/less energy used; 4 Kept inside/heating/shelter/confined so less heat loss/no predators; 5 Genetically selected for high productivity; Q The principle here is one mark for identifying a relevant point and offering an explanation. Accept other equivalent answers. 4 max [5] M8. (a) (i) dogwhelks move more; their food contains more material that cannot be digested / no enzymes to digest; such as cell walls/cellulose; 2 Page 23

24 (b) TBT is accumulated; dogwhelks eat many mussels; 2 [5] M9. (a) F E R/F (E + R); Accept: F (R + E)/F R E (b) (i) Increase because fed concentrates/food with high nutritive value/food with high digestibility/food with little waste/because less egested; Decrease because movement restricted/heat loss reduced; Accept: less movement/less muscle contraction Ignore references to keeping warm (c) (i) 0.98 : /98 : 00; Answer must be this way round and expressed in its simplest terms Reject: 0.98 Mammals maintain (body) temperature/have high (body) temperature; Accept: mammals are endotherms/warm-blooded Accept: converse for insects (d) (Results show) positive correlation/positive correlation described; Reject: reference to line/curve of best fit Most/higher values close to line/curve shows good agreement; Lower values less close to line/less correlation; Ignore reference to anomalies (Generally) predicted values are higher/actual values lower; Reference to predicted or actual required 3 max Page 24

25 [8] M0. (a) (i) (collect and) dry all above ground plant material; (reject collect one/ small sample/whole plants) in an oven at or just below 00 o C; weigh and repeat until constant mass; other precaution, e.g. cooling in desiccator; 3 max large number of sample areas / repeats; randomly selected; 2 (iii) drying destroys plants, so different samples needed; large area, so difficult to get representative samples; difficult to measure biomass of trees; variability in growing conditions; variability of abiotic conditions in different areas of forest; 2 max (b) (i) :25 most of the plants are trees/large; high proportion of dead / non-photosynthesising biomass; herbs grow rapidly/small so large percentage increase; herbs have higher productivity, so ratio lower at 0 years; 2 max [0] Page 25