AQA A-level Biology paper 1.docx, Exams of Molecular biology

Download AQA A-level Biology paper 1.docx and more Exams Molecular biology in PDF only on Docsity! AQA A-level Biology paper 1 A vaccine can be used to produce immunity. Describe how memory cells are important in this process. (3) - ANSimportant because when individual is in contact with virus again, antibodies can be produced at a faster rate in a secondary immune response, and so the pathogen can be destroyed faster. abiotic - ANSnon-living artery structure - ANSthick muscle layer so that they can dilate and contract to smooth blood flow. thick elastic layer so artery can stretch and recoil with systole and diastole, smoothing blood flow. overall thickness of wall is large so that it doesn't burst under pressure. artificial active immunity - ANSinvolves inducing an immune response in an individual WITHOUT them suffering the symptoms of the disease. e.g. vaccinations memory cells produced Attaching lactase to the beads is a more efficient use of lactase than adding the lactase directly to cow's milk. Suggest three reasons why it is more efficient to attach lactase to the beads. - ANSlactase bead can be reused continuous process lactase not present in milk before cell fractionation, why is the tissue placed in a cold, isotonic buffer? - ANScold: reduce enzyme activity that may break down the organelles isotonic: same water potential as tissue, this prevents organelles shrinking/bursting due to osmotic loss/gain of water buffered: so the pH doesn't fluctuate, so that nothing alters the organelle structures or affects enzyme functioning biotic - ANSliving capillary structure - ANSone cell thick endothelium. allows rapid diffusion. numerous, highly branched, so provides a larger surface area. narrow lumen and diameter. spaces in lining to allow tissue fluid to form. courtship behaviour results in reproductive success by... - ANS1. allowing recognition of own species AQA A-level Biology paper 1 2. identifying those capable of breeding 3. forming a pair bond 4. synchronising mating define community - ANSall the populations of different species living and interacting in a particular place at the same time. define ecological niche - ANSThe position occupied by an organism in a particular ecosystem, dependent upon the resources it uses. The more resources that are taken into account then the more carefully defined the organism's niche will be, the organism will become more specialised. define ecology - ANSthe study of the inter-relationships between organisms and their environment, including abiotic and biotic factors. define ecosystem - ANSdynamic systems made up of a community and all the non- living factors of its environment. It includes all the living organisms that interact with one another and also with the physical and non-physical factors present. define genome - ANSthe complete set of genes in a cell define habitat - ANSthe place where an organism normally lives define population - ANSa group of individuals that occupy the same habitat at the same time and are potentially able to interbreed. define proteome - ANSthe full range of proteins that a cell is able to produce describe and explain the countercurrent exchange principle - ANS-the blood and the water flow in opposite directions -blood that is loaded with O2 meets water, which already has maximum O2 -blood with little O2 meets with water with O2 removed -so, diffusion concentration gradient established and maintained across the entire width of the gill lamellae -so, 80% of O2 in water absorbed into fish blood describe and explain why plant stomata links to gas exchange and its benefits - ANSstomata are like minute pores, on the underside of leaves. each has guard cells, which control the rate of gas exchange guard cells close when water loss is excessive AQA A-level Biology paper 1 describe the process of transcription - ANSDNA unwinds and separates (H bond between bases broken) template strands form due to exposed bases free RNA nucleotides align with template strand through complimentary base pairing RNA polymerase bonds the nucleotides together, forming a molecule of mRNA complimentary to the DNA mRNA leaves nucleus via nuclear pore splicing occurs- introns removed describe the process of translation - ANS1. mRNA associates with a ribosome in the cytoplasm 2. tRNA molecules with complimentary anticodons align with the first 2 mRNA codons 3. peptide bond forms between the amino acid molecules 4. the tRNA that bound to the first codon is free to leave the ribosome 5. the ribosome moves along the mRNA by one codon and now a new tRNA with a complimentary anticodon enters the ribosome 6. this continues until the ribosome reaches a stop codon describe the structure of cellulose - ANSmade up of straight chains of beta glucose the chains are parallel to each other, so H bonds form cross-linkages all the H bonds together strengthens the cellulose forms microfibrils describe the structure of starch - ANSchains of alpha glucose some chains are branched= amylopetcin some chains are coiled= amylose describe the test for proteins - ANSadd equal volumes of sample and sodium hydroxide to a test tube. add a few drops of dilute copper (II) sulfate and mix. if solution turns purple, protein is present. describe the transfer of sucrose into sieve elements - ANSsucrose is manufactured from photosynthesising cells. it diffuses by facilitated diffusion from photosynthesising cells to companion cells, down a concentration gradient. H+ actively transported into the spaces between cell walls. H+ diffuses into sieve tube elements. sucrose molecules also transported with them, through co-transport. directional selection - ANSselection favours individuals in one direction from the mean of the population. AQA A-level Biology paper 1 e.g. when environment changes, those with advantageous allele outside of the mean will be more likely to survive and breed. draw alpha and beta glucose - ANS draw how a dipeptide forms - ANS draw the structure of an amino acid - ANS explain cohesion-tension theory - ANSwater is drawn from cell to cell by osmosis. it moves across the root cortex to keep a constant column of water. this creates 'tension' on the column of water in the xylem. water shows cohesion due to its H bonding. this makes the column very strong. so, water is pulled up the xylem to replace the water lost by evaporation. water moves between the cells of a leaf along the water potential gradient. explain mass flow hypothesis - ANS1. sugars build up at source, lowering water potential of source cells. 2. water therefore enters cells by osmosis. 3. sugars are then actively transported into sieve tubes by transfer cells 4. this lowers water potential in sieve tube, so water enters by osmosis. 5. this causes high pressure potential at source at sink, sugars are unloaded by companion cells 6. this raises water potential explain predation - ANSpredators eat their prey, reducing prey population with fewer prey left, there is greater competition between predators for food some cant get the food and die, thereby reducing predator population the prey population therefore increases so, the predator population also increases features of specialised gas exchange surfaces - ANS- a large surface area to volume ratio - very thin therefore short diffusion pathway - selectively permeable - a transport system how can you investigate mass flow using aphids? - ANS1. cut across their mouthparts. the mouthparts act as a sampling tube that they collect the phloem contents. 2. If the phloem is punctured with a hollow tube then the sap oozes out, showing that there is high pressure (compression) inside the phloem (this is how maple syrup is tapped). AQA A-level Biology paper 1 3. If the xylem is punctured then air is sucked in, showing that there is low pressure (tension) inside the xylem. how can you investigate transport using radioactive tracers? - ANSa plant is supplied with 14C, which becomes incorporated into organic substances in the plant. The plant is then frozen in liquid nitrogen to kill and fix it quickly, and placed onto photographic film in the dark. The resulting autoradiograph shows the location of compounds containing 14C. this shows that organic compounds (presumably sugars) are transported downwards from the leaf to the roots. how do insects carry out gas exchange? - ANS1. insects contract their muscles, squeezing the trachea, enabling mass movement. 2. a diffusion gradient is established 3. The ends of tracheoles are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles. how do insects limit water loss? - ANS-small surface area to volume ratio -waterproof coverings -spiracles which can close how do viruses replicate? - ANSthey attach to their host cell with their attachment proteins. nucleic acids are injected into host cell. the genetic info contains "instructions" for the host cells metabolic processes to start producing the viral components, which are assembled into new viruses. how do xerophytes limit water loss? - ANS-thick waxy cuticle -rolled up leaves: traps water vapour -hairy leaves: traps moist air -stomata in pits/grooves: traps moist air -reduced surface area to volume ratio by trapping air, water potential gradient is reduced how does a scanning electron microscope work? - ANSit directs an electron beam onto a specimen surface rather than penetrating it. the beam is passed back and forth across a specimen in a regular pattern, depending on its contours a computer is used to build up a 3D image AQA A-level Biology paper 1 substrate level phosphorylation interspecific competition - ANSoccurs when individuals of DIFFERENT species compete for resources such as food, light, water etc. intraspecific competition - ANSoccurs when individuals of the SAME species compete for resources such as foo, light, water etc. large molecules often contain carbon. why? - ANSthey can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. natural active immunity - ANSresults from an individual becoming infected with a disease under normal circumstances. long term body produces its own antibodies predation - ANSone organism is consumed by another. red blood cells are biconcave discs. Explain one advantage of a biconcave disc over a spherical cell of the same volume in transporting oxygen. - ANSLarge (surface) area; For diffusion; stabilising selection - ANSif environmental conditions are the same, those with alleles closer to the mean are favored. they are more likely to survive and reproduce e.g. birth weight. structure of haemoglobin - ANS4 polypeptide chains - 2 alpha - 2 beta each chain has a haem group which contains a ferrous Fe2+ ion. suggest how chylomicrons leave the epithelial cell. - ANSby exocytosis because theyre too large to leave by other methods the 2 mechanisms that mean that meiosis will result in genetic variation - ANSindependent segregation crossing over There are large numbers of mitochondria in the epithelial cell. Explain how these organelles help the cell to absorb the products of digestion. (2) - ANSmitochondria provide the ATP this is needed for active transport of substances into the cell AQA A-level Biology paper 1 two ways in which pathogens can cause disease - ANSreleases toxins damages cell tissue vein structure - ANSmuscle layer is thinner, because they carry blood away from tissues, and so have less need to dilate. elastic layer is thinner because of lower blood pressure, which doesn't need recoil. overall thickness of wall is thinner due to low blood pressure. valves at regular intervals to ensure there's no backflow of blood. what are antibodies made up of? - ANS4 polypeptide chains: - 2 are 'heavy chains' - 2 are 'light chains' variable (binding) region what are fiberous proteins made up of? - ANSmade of long molecules arranged to form fibres (e.g. in keratin). Several helices may be wound around each other to form very strong fibres. what are globular proteins made up of? - ANSmade of chains folded into a compact structure. One of the most important classes are the enzymes. Although these folds are less regular than in a helix, they are highly specific and a particular protein will always be folded in the same way. what are the advantages of an electron microscope? - ANSelectron beam has a short wavelength and the microscope can therefore has high resolution. the negatively charged beam can be focused using electromagnets. what are the features of a successful vaccination programme? - ANS1. vaccine must be economically available in sufficient quantities 2. must have few side effects 3. available means of producing, storing and transporting the vaccine 4. must be possible to produce herd immunity what are the functions of collagen? - ANS1. Form the structure of bones 2. Makes up cartilage and connective tissue 3. Prevents blood that is being pumped at high pressure from bursting the walls of arteries 4. Is the main component of tendons, which connect skeletal muscles to bones what are the limitations of using a transmission electron microscope? - ANSthe whole system must be in vacuum, so living specimens cant be studied. AQA A-level Biology paper 1 complex staining process the image may contain artefacts what are the roles of lipids? - ANS1. source of energy 2. waterproofing 3. insulation 4. protection what are the two types of electron microscope? - ANStransmission electron microscope scanning electron microscope what does ATP synthase catalyse? - ANSthe formation of ATP from ADP what does dilute hydrochloric acid do in the benedicts test for non reducing sugars? - ANSit hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. what energy requiring processes need ATP? - ANSmetabolic processes movement active transport secretion activation of molecules what happens during crossing over? - ANSwhen the chromosomes align, the chromatids of each pair become twisted around one another tension is built and portions of chromatids are broken off, which rejoin with the chromatid of the homologous partner so, new genetic combinations of maternal and paternal alleles are produced what happens during independent segregation? - ANSduring meiosis 1 each chromosome aligns with its homologous partner at the equator of the cell the combination of maternal/paternal chromosomes aligns randomly one chromosome of each pair goes to daughter cell- by chance what is a 'sink' cell? - ANScells that use/store organic solutes what is a 'source' cell? - ANScells that photosynthesise and make sugars what is a reducing sugar? - ANSa sugar that can reduce (give electrons to) another chemical. AQA A-level Biology paper 1 what kind of protein is collagen? - ANSfiberous what kind of protein is haemoglobin? - ANSglobular what purpose does the structure of amylopectin serve? - ANSmore surface area for enzymes to work on, thus glucose molecules can be released at a much quicker rate. what purpose does the structure of amylose serve? - ANSmakes the molecule compact so it is stored more easily. what type of bond forms between the phosphate group and deoxyribose sugar in DNA? - ANSphosphodiester bond whats the difference between species richness and diversity index? - ANSSpecies richness measures only number of (different) species / does not measure number of individuals. where are proteases produced? - ANSstomach, pancreas, small intestine where is amylase produced? - ANSsalivary glands, pancreas, small intestine where is lactose produced? - ANSpancreas, small intestine where is maltase produced? - ANSepithelium of small intestine which has a longer wavelength: light or a beam of electrons? - ANSlight why can vaccinations not be effective? - ANS1. immunity may not be induced in people with defective immune systems 2. individuals may develop disease after the vaccination but before their immunity levels are high enough to prevent it. 3. pathogen may mutate frequently, so vaccines cant prevent them from harming people 4. certain pathogens conceal themselves from the body's immune system e.g. by hiding within cells 5. individuals may object to vaccinations due to religious, ethical or medical reasons why cant the highest resolution images not be produced by TEM? - ANSthere are difficulties preparing the specimen, which can limit resolution a higher energy electron beam may destroy the specimen why do animals need highly branched glycogen? - ANSbecause animals metabolic rate is faster than plants and so needs glucose to be released quicker. AQA A-level Biology paper 1 why do arterioles have thinner elastic layer than arteries? - ANSblood pressure is lower. why do veins have thinner walls than arteries? - ANSthinner walls because blood is at lower pressure, and so less stretch and recoil with each contraction of ventricles. why is ATP a good immediate energy source in a cell - ANSthe instability of the phosphate bonds. each ATP molecule releases less energy than glucose molecule, and so is smaller and more manageable the hydrolysis of ATP to ADP is a single reaction that releases immediate energy why is DNA stable? - ANS1. the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix 2. many hydrogen bonds link the base pairs together, so it adds strength overall. In a Venn diagram U means - ANSUnion - any number in side the circles Integer - ANSAll whole numbers (both positive and negative) and zero. Pentagon - ANS5 sided polygon Polygon - ANSa flat shape with many straight sides Quadrilateral - ANSa four-sided polygon Reciprocal - ANS1 divided by the number Rectangle - ANSa quadrilateral with four right angles significant figures - ANSAll the digits that can be known precisely in a measurement, plus a last estimated digit square - ANSA quadrilateral with 4 sides that are equal and has all 90 degree angles Squared Number - ANSA number multiplied by itself Trapezium - ANS2D one set of parallel lines. Quadrilateral < means - ANSLess than > means - ANSGreater than 1 to the power of anything still equals... - ANS1 AQA A-level Biology paper 1 A coloured in circle on a number line means... - ANSLess than or equal to or greater than or equal to A mixed number fraction is also called an? - ANSImproper fraction A number in standard form should be written in the form of? - ANSA x (10)n An open circle on a number line means.... - ANS> or < Anything to the power of 1 is... - ANSItself BIDMAS - ANSBrackets, Indices, Division, Multiplication, Addition Subtraction Factors of a number - ANSNumbers that divide into it For negative powers you need to... - ANSFlip it upside down (reciprocal) How many solutions do you end up with for a quadratic? - ANS2 How to find a fraction of something? - ANSDivide the number by the bottom and then multiply by the top How to solve an equation - ANSRearrange the equation so that all the x's are on one side If mixed numbers are negative then... - ANSPairs are positive Integer - ANSA whole number Iteration is.. - ANSRepeating a calculation in order to get closer approximations to the solution you want One other method of solving quadratics is? - ANSCompleting the square Prime number - ANSOnly divides by itself and one Quadratic formula is? - ANSx = -b +or- the square root of b squared - 4ac divided by 2a Surds are - ANSExpressions with irrational square roots that can't be written as fractions