AQA A Level Biology Paper 2 – Questions and Answers A+ Graded 100% Verified

AQA A Level Biology Paper 2 – Questions and Answers A+ Graded 100% Verified In an investigation into taxis, termites were split into 3 groups Group A had their eyes covered (moved straight up) Group B had their antenna covered (moved straight to light) Group C were the control (moved diagonally up and towards light) What does Group A show about the factors controlling termite movement? CORRECT ANS: Antenna involved in response to gravity Don't respond to light as eyes are covered In a graph of membrane permeability against time, the line for Na+ ions increases rapidly between 0.5 and 0.7ms Explain why CORRECT ANS: Na+ gated channel proteins open Na+ move into axon by facilitated diffusion Neurone depolarised Stimulates more Na+ channels to open Give 2 properties of stem cells CORRECT ANS: Undifferentiated Can keep dividing / replicating How might the insertion of DNA into a cell cause cancer? CORRECT ANS: DNA disrupts tumor suppressor gene Tumor suppressor gene not transcribed/inactivated Rate of cell division increases (not controlled) Succinate dehydrogenase catalyses a reaction in the Krebs Cycle In micrograph A there was a high amount of the enzyme In micrograph B there was a lower amount of the enzyme Which micrograph is of a slow muscle fibre and why? CORRECT ANS: A More succinate dehydrogenase So more aerobic respiration / mitochondria Explain the distribution of mitochondria in slow muscle fibres CORRECT ANS: Distributed near the surface Short diffusion path for O2 O2 for ETC of aerobic respiration in mitochondria You could use an optical microscope and a slide of stained muscle fibres to calculate the diameter of a muscle fibre Explain how CORRECT ANS: Use a graticule Calibrate against something of known size e.g ruler A student found the mean diameter of muscle fibres Explain two precautions that should have been taken when sampling these CORRECT ANS: Large sample size - representative Random sample - eliminate bias A graph shows blood glucose concentration against urine concentration measured using urine test (colour = range of 1-4) Evaluate the use of this urine test to measure blood glucose concentration CORRECT ANS: Positive correlation But range of results for particular values/overlap Subjective and arbitrary Explain how a DNA probe could be used to show if alleles of genes were the same CORRECT ANS: DNA probe has specific base sequence Complementary to the specific base sequence of the allele Bind to both alleles Label would show up in both Prey index is based on how much food is available to a predator Explain why this is better than biomass CORRECT ANS: Wolves don't eat all prey Inedible bits make up DIFFERENT PROPORTIONS In a graph of wolf numbers against number of animals in a given area, the line of best fit increases There are some outliers Explain what these shows about the factors affecting wolf numbers CORRECT ANS: Limited by prey When number of prey increase, number of wolves increases Large range so other factors involved Explain how acetylcholine contributes to a synapse being unidirectional CORRECT ANS: Acetylcholine receptors only on post synaptic membrane Acetylcholine released from pre-synaptic membrane Diffuses across synpatic cleft from high to low concentration Only binds to acetylcholine receptors Explain why the percentage of each base may differ in different parts of the chromosomes CORRECT ANS: Different genes Different base sequences In restriction mapping what would be true if some of the DNA was not digested fully CORRECT ANS: Large pieces of DNA present Add up to more than total length of original DNA Undigested added to original length Why might siRNA be useful in treating some diseases? CORRECT ANS: Some diseases are genetic siRNA inhibits translation and production of harmful protein In the first 40% of the time spent as a pupa, the RNA concentration decreases Suggest why CORRECT ANS: Tissues broken down RNA hydrolysed By lysozymes New RNA not made Why can increased intensity of exercise lead to increased heart rate? CORRECT ANS: CO2 produced in aerobic respiration CO2 concentration increases Chemoreceptors detect increase in CO2 Impulses to medulla More impulses to SAN along sympathetic nerve Explain why many transgenic eggs do not survive CORRECT ANS: Distrupts genes Inhibits translation of important protein Embryo foreign Attacked by immune system In a treatment for type 1 diabetes a virus is used to insert a functional insulin gene (tested in rats- successful) Evaluate the use of this treatment CORRECT ANS: Would be less injections Less restriction on diet Longer lasting Avoids highs/lows in blood glucose concentration Longer term effects not known Insulin may be rejected by body Don't know side effects in humans Rats are different to humans There is a graph of CAG repeats against age a genetic disorder develops. Evaluate the use of this graph to predict age of developing genetic disorder CORRECT ANS: Negative/positive correlation Wide range Overlap Suggests OTHER FACTORS involved A genetic fingerprint was run and CAG repeats of different length were separated How could the number of CAG repeats in each band be found? CORRECT ANS: Run known length of CAG repeats Compare Why is skin temperature not a good measure of core body temperature? CORRECT ANS: Fluctuates more affecting by sweating/radiation etc The percentage of population able to tolerate lactose is much higher in populations were dairy consumption is high Use natural selection to explain this CORRECT ANS: Random mutation produced allele for lactase Advantageous to produce lactase People with mutation survive, reproduce and pass on allele Allele frequency increases Describe the role of tropomyosin in muscle contraction CORRECT ANS: Moves out of the way when Ca2+ binds Allows actinomyosin bridge formation Describe the role of myosin in muscle contraction CORRECT ANS: Binds to actin binding sites Pulls actin filament along a short distance Unbinds from actin so can bind again further along This uses ATP In a graph of sucrose concentration against dopamine released (linked to desire to eat), as sucrose concentration increases, so does dopamine concentration How does this show positive feedback CORRECT ANS: Positive correlation Increase in sucrose leads to desire to eat more Eating leads to wanting to eat more Explain why at a certain concentration of sucrose the brain cannot distinguish between different concentrations CORRECT ANS: Refractory period leads to discrete/ limits frequency of action potentials Maximum action potential frequency exceeded, all concentrations seem the same A DNA probe is made complementary to the DNA base sequence of an exon, not an intron Explain why CORRECT ANS: Introns not translated Don't code for amino acids Only mutations in exons affect primary structure/tertiary structure Explain how an increase in light intensity can lead to a higher growth rate CORRECT ANS: Faster rate of LDR More NADH and ATP produced Faster rate of LIR More GP converted to TP More useful organic molecules formed More respiratory subtrates to produce ATP In June blue tits are born Explain why the mark-release-recapture method would NOT give reliable results in June CORRECT ANS: Young birds join population Population size increases Ratio of marked:unmarked decreases In June breeding pairs go into isolated territories Explain why the mark-release-recapture method would NOT give reliable results in June CORRECT ANS: Population size smaller as breeding pairs isolated Sample not representative Likely to catch all birds again Explain why DNA base sequencing can be used to estimate population of whales CORRECT ANS: DNA sequencing like marking Same DNA sequence means caught before What does the Hardy-Weinbery principle predict? CORRECT ANS: The frequency of alleles in a population Will remain constant over generations No mutations/large population/random mating White cats are deaf Explain why the Hardy-Weinberg principle cannot apply to white cats CORRECT ANS: Less likely to survive Allele frequency decreases Pioneer plants have seeds which can germinate when temperature fluctuates Explain the advantage of this CORRECT ANS: Bare soil temperature fluctuates More bare soil early on in successsion Explain how and why the CO2 concentrations change over 24 hours CORRECT ANS: When dark no photosynthesis Plants only respire net production of CO2 so increases When light, higher rate of photosynthesis than respiration so net uptake of CO2, decreases Explain the change of CO2 concentration with height in forest CORRECT ANS: Decreases Higher light intensity with height More CO2 taken up/photosynthesis Give 3 ways ATP is a suitable source of energy CORRECT ANS: Phosphorylates other molecules to make more reactive Rapidly resynthesised/hydrolysed in simple reaction Releases small amounts of energy so less energy lost as heat Why do humans synthesise more than their body weight in ATP each day? CORRECT ANS: ATP used for e.g. active transport ATP releases small amount of energy ATP cannot be stored Why is the NPP in plants higher in June than August? CORRECT ANS: Lower temperature Lower rate of respiration Less energy loss Photosynthesis less affected For chocolate fur cats must have the dominant allele H For cinnamon fur, cats need two copies of h allele Explain whether it is possible to produce only cats with chocolate fur CORRECT ANS: No as cats with chocolate fur could be heterozygous or homozygous Two chocolate cats could produce cinnamon kitten Possible if only HH genotypes Explain why random sampling is important CORRECT ANS: Avoids bias More representative Allows use of stats test When comparing A and B what should you say? CORRECT ANS: Talk about both e.g. A has range of 5 and B has range of 4 , A has larger range than B SAY 'AND' When looking at a graph what could you point out? CORRECT ANS: Correlation Outliers - show other factors involved Overlap Mode Range Birds have different shaped beaks Explain how this increases chance of survival CORRECT ANS: Different shape beak means can eat different food Reduces interspecific competition Why is the energy transfer from consumer to consumer more efficient than between producer and consumer? CORRECT ANS: More of consumer is digestible All eaten Less energy lost at heat How does marram grass act as pioneer plant? CORRECT ANS: Stabilises sand Less hostile In an investigation why is it important to use the same breed of pig? CORRECT ANS: Similar alleles Controls/genes not factor In an investigation into affect of temperature on growth, pigs were allowed to eat as much food as they wanted Why does this decrease reliability? CORRECT ANS: Different growth rates NOT due to temperature When a question says evaluate and you are given data what should you say? CORRECT ANS: How data supports e.g. correlation How data doesn't support e.g. overlap/range, sd bars overlap Problems with investigation: not on humans, small sample size, no control, only for x weeks, no information about