AQA biology a-Level Paper 2 Exam Questions with Answers, Exams of Nursing

Download AQA biology a-Level Paper 2 Exam Questions with Answers and more Exams Nursing in PDF only on Docsity! AQA biology a-Level Paper 2 Exam Questions with Answers Describe and explain the steps in the light dependent reaction of photosynthesis - Correct Answer 1. photoionization: light reaches chlorophyll in PSII, which is absorbed by an electron, which becomes excited and moves to a higher energy level. 2. the electron passes to a carrier protein in the thylakoid membrane, and is passed down a series of carrier molecules called an electron transfer chain. 3. as the electron moves down, energy is lost from the electron and is released as ATP. 4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which also produces hydrogen and oxygen. 5. the lost electron reaches PSI, which absorbs light energy and boosts another electron to a higher energy level (excitation). 6. this electron also goes down an electron transport chain. 7. this reaches the final electron acceptor which is a proton. they combine to form H and reduce NADP to NADPH. describe and explain the steps in the light independent reaction ff photosynthesis. - Correct Answer 1. CO2 diffuses into stromal and combines with ribose bisphosphate (RuBP) using the enzyme rubisco. 2. this forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules, glyercate-3-phosphate (G3P) . 3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for energy. 4. TP can be converted into useful organic substances. 5. TP can also be reformed into RuBP using ATP. describe glycolysis in respiration. give net formation. - Correct Answer 1. glucose is converted into phosphorylated glucose by 2ATP. this makes it very reactive, so it splits into 2 triose phosphate (TP). 2. 2TP is then oxidized by 2NAD and 4 ATP is formed to form pyruvate. 3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+ describe links reaction in respiration. give net formation. - Correct Answer 1. pyruvate diffuses into the matrix of mitochondria. 2. pyruvate is oxidized by NAD. CO2 is lost. this forms acetate. 3. acetate and co-enzyme A combine to form acetyl co-enzyme A. 4. NET: CO2, reduced NAD, acetyl co-enzyme A describe Krebs cycle in respiration. give net formation. - Correct Answer 1. acetyl co- enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon citric acid. 2. CO2 is lost (decarboxylation), molecule is oxidized by NAD and ATP is produce. this forms 5 carbon compound. 3. it is oxidized by 2NADH and FAD, and is decarboxylase. 4. this forms 4 carbon molecule again. describe oxidative phosphorylation in respiration. - Correct Answer 1. reduced coenzyme passes its H to a carrier protein in the ETC. this splits into a proton and electron. 2. the protons pass through the space between inner and outer mitochondrial membrane. 3. electrons pass through proteins on ETC. 4. protons return back via ATP synthase in the membrane, producing ATP. 5. the protons and electrons recombine to form H, which combines with O to form water. 6. oxygen is the last electron acceptor in the ETC. define biomass - Correct Answer the total mass of organisms in a given area what is the 'gross primary production' - Correct Answer the chemical energy stored in a plants biomass what is the 'net primary production' - Correct Answer the chemical energy stores in a plants biomass after respiratory losses have been considered. this energy is available to consumers. how can you calculate the net primary production? - Correct Answer NPP = GPP - R why is converting sunlight energy into biomass in producers inefficient? - Correct Answer some light isn't the correct wavelength to be absorbed some light doesn’t hit chloroplast some light is converted into heat energy some light energy is reflected describe the nitrogen cycle. - Correct Answer fixation: atmospheric nitrogen can be fixed by rhizobium bacteria. if struck by lightning, it becomes reactive and combines with oxygen to form NO. ammonification: saprobionts feed on organic matter and release ammonia, which then forms ammonium ions in the soil. nitrification: nitrifying bacteria convert ammonium ions into nitrite ions and then to nitrate ions. 4. 3 sodium move out for every 2 potassium in hence, the outward movement of Na+ is greater than the inward movement of K+. this creates an electrochemical gradient as the outside is more negative than inside. 5. K+ begins to diffuse back out while Na+ diffuses back in, although most Na+ gates are closed. describe the processes that occur when an action potential is formed. - Correct Answer 1. the energy of a stimulus causes some sodium voltage-gated channels in the axon membrane to open and so Na+ diffuses into axon, down electrochemical gradient. 2. this triggers a reversal in potential difference across the membrane because Na+ is positively charged. 3. as more Na+ goes in, more channels open and so even more Na+ goes in. 4. when action potential is +40mV the Na+ channels close and the K+ channels open. 5. K+ diffuses out of axon. 6. there is overshoot of electrical gradient- hyperpolarization. 7. K+ gates shut. resting potential is re-established. this is repolarization. describe the processes that occur during the passage of an action potential along an unmyelinated axon. - Correct Answer 1. at rest- the inside of axon is more negative than outside. 2. a stimulus causes influx of Na+ and so the charge of the axon is reversed- depolarized. 3. this causes localized electrical currents to open up the voltage-gated channels further along the axon, so more Na+ enters here and depolarizes this area. 4. in the initial area, Na+ gates close and K+ open, so K+ leave the axon down electrochemical gradient. depolarization moves along membrane. 5. outward movement of K+ and inward movement of Na+ continues until repolarization; return to resting state. why do action potentials travel faster down a militated axon? - Correct Answer myelin sheath prevents action potentials forming. action potentials form at the Nodes of Ranvier, and jump from node to node by salutatory conduction. in an unmyelinated axon, it takes longer as the events of depolarization take place all the way along an axon. what are factors that affect the speed of an action potential? - Correct Answer 1. myelin sheath 2. diameter of axon: the greater the diameter, the faster the speed, because there's less leakage of ions from a large axon, so membrane potentials are easier to maintain. 3. temperature: the higher the temperature, the greater the rate of diffusion of ions, and hence the faster the impulse. what is the purpose of the refractory period? - Correct Answer 1. Ensures action potentials travel in one direction only, since action potentials cannot move to a refractory region. 2. ensures action potentials are separated from one another. 3. limits the number of action potentials. spatial summation - Correct Answer a number of different presynaptic neurons collectively release enough neurotransmitters to exceed the threshold value of the postsynaptic neuron, triggering a new action potential. temporal summation - Correct Answer a single presynaptic neuron releases neurotransmitters many times over a short period. this exceeds the threshold value, triggering a new action potential. how do drugs affect synaptic transmission and action potentials? - Correct Answer 1. stimulate the nervous system by mimicking neurotransmitters, stimulating neurotransmitter release or inhibiting enzymes that break down neurotransmitters, and so create more action potentials. 2. inhibit the nervous system by inhibiting release of neurotransmitter or blocking Na+/K+ channels on postsynaptic neuron, hence creating less action potentials. describe the processes that occur during synaptic transmission. - Correct Answer 1. action potential arrives at end of presynaptic neuron. this stimulates Ca2+ channels to open so Ca2+ enter synaptic knob by facilitated diffusion. 2. this stimulates synaptic vesicles to fuse with presynaptic membrane, releasing acetylcholine into synaptic cleft. 3. acetylcholine binds to receptor sites on Na+ channel proteins on postsynaptic neuron membrane. this causes them to open to Na+ diffuse in. 4. influx of Na+ generates new action potential in postsynaptic neuron. 5. acetylcholinerase hydrolyses acetylcholine into choline and ethnic acid, which diffuses back across into presynaptic neuron. 6. ATP recombines ethnic acid and choline, which is stored in synaptic vesicles for later use. describe slow twitch fibres - Correct Answer contract more slowly and provide less powerful contractions but over a longer period. adapted for aerobic respiration to avoid lactic acid build up. adapted for endurance work. has lots of myoglobin, rich bloody supply and many mitochondria. describe fast twitch fibres - Correct Answer contract more rapidly and more powerful but over a shorter period of time. adapted for intense exercise have thicker and more numerous myosin filament, have more glycogen, have more enzymes to carry out anaerobic respiration, and has phosphocreatine. what is a neuromuscular junction - Correct Answer the point where motor neuron meets a skeletal muscle fiber. describe the processes that occur during muscle contraction - Correct Answer 1. action potential travels down T-tubules, which are in contact with the sarcoplasmic reticulum. 2. calcium ion protein channels on sarcoplasmic reticulum open and calcium ions diffuse out by diffusion, down a concentration gradient. 3. calcium ions cause tropomyosin to change shape and unblock the binding sites on actin. 4. ADP attaches to myosin head, so it changes shape and can now bind to the actin filament, forming a cross bridge. 5. once attached, myosin heads alters angle, pulling the actin along with it. ADP is released. 6. ATP attaches to myosin head, causing it to detach from actin. 7. calcium ions activate ATPase to hydrolyze ATP to ADP, which releases enough energy for the heads to return to initial position. 8. repeat what type of stimulus does a paining corpuscle respond to? - Correct Answer mechanical pressure when at rest, what occurs at a paining corpuscle? - Correct Answer the sodium ion channels on the membrane around the neuron are narrow and so don't allow Na+ to pass along them. it has resting potential. what happens when pressure is applied to paining corpuscle? - Correct Answer 1. it deforms, so membrane around neuron stretches. 2. this widens Na+ channels and so Na+ diffuses into neuron. 3. this changes the potential of the membrane, depolarizing it. a generator potential is formed. 4. generator potential forms an action potential. what kind of summation occurs in rod cells? - Correct Answer spatial summation what kind of summation occurs in cone cells? - Correct Answer temporal summation where are rod cells absent at? - Correct Answer the fovea where are cone cells concentrated at? - Correct Answer the fovea where are rod cells more highly distributed at? - Correct Answer periphery of the retina do rod cells give good or poor visual acuity? - Correct Answer poor visual acuity do cone cells give good or poor visual acuity? - Correct Answer good visual acuity how many types of rod and cone cells are there? - Correct Answer rod- 1 cone- 3, all responding to different wavelengths why does using nitrogen containing fertilizers result in reduced species diversity? - Correct Answer nitrogen rich soils favor the growth of grasses etc., which can outcompete other species, which die as a result. what is "leaching"? - Correct Answer the process by which nutrients are removed from the soil. rainwater will dissolve soluble nutrients and carry them deep into the soil, away from plant roots. the leached ions can reach rivers that drain into lakes. what is "eutrophication"? - Correct Answer the process by which nutrient concentrations increase in bodies of water, often as a result of leaching. may result in algae bloom, which blocks sunlight from reaching plants underneath, causing them to die. define population. - Correct Answer a group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed. define community. - Correct Answer all the populations of different species living and interacting in a particular place at the same time. define niche. - Correct Answer the role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment. dominance - Correct Answer occurs where heterozygote has a phenotype that is different from both homozygotes. neither allele is dominant over the other; they both contribute equally to the phenotype. sex linkage - Correct Answer alleles carried on the X chromosome. why are sex linked diseases more common in males than females? - Correct Answer because males only have one X chromosome, and so if there is a recessive allele there, then there will be no dominant allele on Y chromosome to "hide" it. multiple alleles - Correct Answer this is where there are several different alleles of a gene e.g. blood type: IA, IB (codominant), and IO (recessive). hybrid inheritance - Correct Answer involves 2 genes at different loci. epistasis - Correct Answer when one gene locus interacts with another gene at a different locus. linked genes - Correct Answer genes on the same chromosome Hardy-Weinberg principle - Correct Answer p2 + 2pq + q2 p2 = homozygous dominant q2 = homozygous recessive 2pq = heterozygous In any hardy-Weinberg problem, start with homozygous recessive individuals. what assumptions need to be in place to use the hardy Weinberg principle? - Correct Answer 1. No mutations 2. Population is isolated 3. No selection 4. Large population 5. Mating is random how can a population be separated and form different species? - Correct Answer 1. Populations become separated. physical barriers may come between two groups. 2. Therefore they stop interbreeding. 3. Populations adapt to new environment. Selection pressures will be different in different areas. 4. Allele frequencies will change in the different populations. 5. Over time they become so different that they can no longer interbreed. formula to calculate the mean density of individuals from quadrats - Correct Answer total no of individuals counted ------------------------------------ no of quadrats x area of quadrat allopatric speciation - Correct Answer When populations of a species become geographically isolated. Gene flow between them ceases (reproductive isolation). the new environment will trigger a change in the gene pool due to natural selection imposed on them. If the populations are relatively small, they may experience a founder effect. Selection and genetic drift will act differently on these two different genetic backgrounds, creating genetic differences between the two new species. sympatric speciation - Correct Answer become reproductively isolated from each other even though they occupy the same geographic range. Factors that could lead to them becoming reproductively isolated from each other are things like changes in courtship behavior, changes in feeding behavior, changes in coloration. The most common way this occurs is polyploidy. Rapid genetic changes can alter morphology, behavior, and habitat preferences. totipotent cells - Correct Answer cells that can mature into any kind of specialized body cell. can divide to form a whole organism. they are found in very early mammalian embryos. after this stage, some of the genes become switched off and so are not translated into RNA, hence specialized. pluripotent cells - Correct Answer can become any kind of specialized body cell, but cannot divide to form a whole organism. induced pluripotent stem cells - Correct Answer produced from omnipotent cells. genetically altered in labs (transcription factors) to make them have the characteristics of embryonic stem cells. they turn on the genes that were otherwise turned off. multipotent cells - Correct Answer can divide into some, but not all, specialized cells. omnipotent cells - Correct Answer divide to form just one type of cell. transcription factors - Correct Answer transcription factors bind to the DNA sequence at specific target sequences. RNA polymerase recognizes the complex formed and so transcribes the gene. methylation of DNA - Correct Answer addition of methyl groups to bases. added throughout life, sometimes in response to environmental factors e.g. diet. causes the DNA to wrap more tightly around histones, so transcriptional factors cannot bind to specific DNA sites and initiate transcription. acetylation of DNA - Correct Answer acetyl groups added to histones, so DNA is less tightly wound round it, making it easier for RNA polymerase and transcriptional factors to bind, so transcription can occur. oncogenes - Correct Answer mutated proto-oncogenes form oncogenes. oncogenes are permanently activated (switched off). explain how to produce DNA fragments with reverse transcriptase. - Correct Answer 1. reverse transcriptase forms canal from an mRNA strand. 2. single stranded canal is isolated when mRNA is hydrolyzed with an enzyme. 3. canal acts as a template for DNA nucleotides to bind to by complimentary base pairing. DNA polymerase joins them together. a copy of the gene is now formed. explain how to produce DNA fragments with restriction endonucleases. - Correct Answer 1. cuts gene at recognition site. this can result in blunt or sticky ends. 2. promoter gene and terminator gene also inserted. marker genes too. 3. same RE cut out complimentary recognition site in plasmid (vector). 4. DNA ligase is used to bind the nucleotides of the two DNA strands together. 5. plasmids introduced to host organisms. bacteria mixed with plasmids with calcium ions.