Mocks, Exams, Past paper corrections

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Describe the changes that occur in the size of the population during the demographic transition model
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Population increases then levels out
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Suggest one reason for the difference in the average life expectancy for males and females in the USA in 2010.
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-Sex linked diseases e.g. prostate cancer -War -Less likely to visit a doctor
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Describe another process(other than nitrification) carried out by organisms which adds ammonium ions to soil.
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-Saprobionts -decompose and break down proteins/amino acids to ammonia
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Denitrification requires anaerobic conditions. Ploughing aerates (adds air to the soil)Explain how ploughing would affect the fertility of the soil.
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-Fertility is increased because less nitrate is removed -(Due to) no/less denitrification
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Suggest two ways in which crop rotation may lead to high crop yields.
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-Different crops use different minerals -Different crops have different pests and diseases -Can grow legumes with nitrogen fixing bacteria
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Suggest units for gross productivity
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Kjm-2y-1
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Explain the decrease in gross productivity as the woodland matures.
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-Less light/more shading/more competition for light -Reduced photosynthesis
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Use the information in figure 3 and your knowledge of net productivity to explain why biomass shows little increase after 100 years.
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– Net productivity= Gross productivity + respiratory losses -Decrease in gross productivity/photosynthesis or Increase in respiration
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Some cat breeders select for polydactyly. Describe how this would affect the frequencies of homozygous genotypes for this gene in their breeding populations over time.
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-Homozygous dominant increases and homozygous recessive decreases
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What measurements should have the student taken to determine the rate of photosynthesis
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-Oxygen production/concentration over a certain period of time
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The student did not use a buffer solution to maintain the pH the solution. Explain what would happen to the pH of the solution during this investigation.
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-As more CO2 removed for photosynthesis -pH would increase
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Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. this inuces a changes in the enzyme, which enables the acetykycoenzymeA to bind. Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme.
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-Changes shape of active site -Substrate/active site is now complementary
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In muscles , some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this.
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– lactic acid is toxic/causes cramps (reliefs pain/harm) -Pyruvate is used in aerobic respiration (increases respiration)
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Suggest how climate change could cause an increase in soil salinity.
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1. Increase in temperature/global warming 2. (causes)Eapouration of water from the soil/flooding by seawater
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Explain why the CFRR fungus was isolated from several cucumber plants and why these plants were grown in salinated soils.
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1.Representative of populations/strains 2.Natural/normal conditions of these cucumbers grow in salinated soils
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Explain why scientists set up control A.
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– (To act as a)Benchmark/ Standard/ Comparison
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Suggest one way in which these bacteria could stimulate an increase in dry mass of cucumber plants.
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-Bacteria are nitrogen fixing/nitrifying/reduce infection
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Use your knowledge of photosynthesis and respiration to describe and explain how the concetration of carbon dioxide in the air changes. -Over a period of 24 hours -At different heights above ground
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1.High concentration/increase in CO2 linked with respiration at night/in darkness 2. No photosynthesis in dark/night or only photosynthesis in light/day 3.Rate of photosynthesis greater than rate of respiration -> more CO2 is used than produced 4. Decrease in CO2 concetration with height
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Suggest how the shape of mouth is an adaptation to its niche.
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1. With different mouths eat different foods 2. Competition between / Inter specific competition is reduced
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Suggest why the efficiency of energy transfer from producers to primary consumers in the food web is higher than 10%.(3)
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1. heat loss 2. indigestible parts 3. less energy loss to faeces
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Describe how you would investigate the distribution of marram grass from one side of the dune to the other.(3)
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1.Transect (from one side of the dune to the other); *2. Place quadrats at regular intervals along the line;* 3.Count plants and record where they touch line/transect;
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Marram grass is a pioneer species that grows on sand dunes. It has long roots and a vertically growing stem that grows up through the sand. Sand dunes are easily damaged by visitors and are blown by the wind. Planting marram grass is useful in helping sand dune ecosystems to recover from damage. Use your knowledge of succession to explain how.
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1. Stabilises sand / stops sand shifting; 2. Forms/improves soil / makes conditions less hostile;
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Three factors can limit the speed of photosynthesis:
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1.light intensity 2.carbon dioxide concentration 3.temperature.
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Scientists measured the concentration of carbon dioxide in the air in one part of the forest. They took measurements at different times of day and at two different heights above the ground. Their results are shown in the bar chart.Use your knowledge of photosynthesis and respiration to explain the data in the bar chart.
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*Explanation for differences between day and night* 1. photosynthesis only during the daytime / no photosynthesis at night; 2. No carbon dioxide taken up at night/in dark *Explanation comparing leaves with ground level* 3. At ground level more respiration 4. Carbon dioxide produced at ground level
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The population of trees in the forest evolved adaptations to the mountain environment. Use your knowledge of selection to explain how.
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1. Variation in original colonisers 2. Some better (adapted for) survival (in mountains); 3. Greater reproductive success; 4. Allele frequencies change;
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Use evidence from the diagram to explain that hairlessness is caused by a recessive allele
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1.Animal 5&6 has hair but offspring do not; *2. So 5&6 parents must be heterozygous/carriers;*
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Reads have hallow, air filled tissu in their stems which supplies oxygen to their rooots. Explain how this enables the roots to take up nitrogen-containing substance.
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1. Uptake by roots involves active transport 2. (Which) Requires ATP produced by aerobic respiration
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In the investigation the scientists used the same breed of pigs with similar genotypes. Explain Why.
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1.Same breed so similar alleles; 2. Controls/removes variable
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Some pigs were allowed to eat as much as they wanted. Explain how this could have reduced the reliability of any conclusions drawn from this investigation.
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1. (This would have caused)Different growth rates / gained different biomass / grew different amount; 2. (So can not be sure if results are or are)Not due to temperature / the independent variable;
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A student concluded from these data that the mean growth rate of the pigs was fastest at 20 oC. Do you agree with this conclusion? Explain your answer.
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1. Temperature may be between 10 and 30/10 and 20/20 and 30; 2. Intervals are 10 C/large/not small enough
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Pigs can survive at temperatures above 35 o C. Use the data to suggest why scientists did not carry out any investigations at temperatures higher than 35 o C.
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1. Growth rate decreasing after 35 C 2.(Scientists would be) looking for high growth rate/ conversion 3. Wastes time/resources/
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The efficiency of conversion of food to biomass is lower at 0 oC than it is at 20 oC. Suggest an explanation for the lower efficiency
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1. Will lose more heat/energy 2. Heat results from respiration so more respiration (will occur for thermoregulation); 3. More food used in respiration(than in biomass);
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Explain why CO2 is a measure of net productivity(1)
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1.Net productivity= photosynthesis – respiration 1.More CO2 used in photosynthesis than used in respiration
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Use the information in figure 2 to explain how the shade plant is better adapted than the sun plant to growing at low light intensities.
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1. Shade plant has low respiration rate 2. (because ) Less CO2 is released at low light intensities 3. Less glucose used
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In birds, males are XX and females are XY. Use this information to explain why recessive, sex-linked characteristics are more common in female birds than in male birds.
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1. Males have to be homozygous recessive 1. Recessive allele is always expresses (in XY female)
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Explain one piece of evidence from Figure 3 which shows that the allele for rapid feather production is recessive.
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1. One(XX male) and Two(XY female) are slow feather but 5 (XY female) is rapid 2. So One (XX male) must be heterozygous – > if rapid was dominant One would have rapid feather production
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The allele for normal haemoglobin in red blood cells is HbA. In some parts of Africa where malaria occurs there is a high frequency in the population of the allele HbC. Individuals possessing the HbC allele have a lower chance of developing severe malaria. Severe malaria causes a large number of deaths in Africa. Explain the high frequency of the HbC allele in areas where malaria occurs.
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1. Individuals with the HbC (allele) survive and reproduce; 2. Pass on HbC (allele) which increases in frequency; 3. HbA HbA individuals less likely to survive and reproduce
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Respiration produces more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent. Explain why.
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1. Oxygen is final/terminal (electron) acceptor (oxygen combines with electrons and protons;) 2. Electron transport chain provides ATP; 3. no Krebs/ no link reaction; (with out oxygen removing the hydrogens and electrons(need NAD for link and krebs))
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The scientists obtained the biomass of each sample by heating it at 75 ÂșC for 2 hours. They then weighed the sample, reheated it for 15 minutes and weighed it again. They continued this cycle of reheating and weighing until they found the sample had a constant mass. Explain how this method helped to provide a reliable measurement of the biomass.
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1. Water content can vary in plants 2. Removes *all* water

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