AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100%, Exams of Biology

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AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS describe the structure of starch - CORRECT ANSWERS chains of alpha glucose some chains are branched= amylopetcin some chains are coiled= amylose what purpose does the structure of amylose serve? - CORRECT ANSWERS makes the molecule compact so it is stored more easily. what purpose does the structure of amylopectin serve? - CORRECT ANSWERS more surface area for enzymes to work on, thus glucose molecules can be released at a much quicker rate. how is the structure of starch suited to its function? - CORRECT ANSWERS 1. starch is insolube so it doesnt affect water potential 2. it is large enough that it doesnt diffuse out of cells 3. compact enough so that a lot of it can be stored in a small space 4. branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released how is the structure of glycogen suited to its function? - CORRECT ANSWERS 1. insoluble, so no effect on water potential of cell 2. insoluble, so doesnt diffuse out of cells 3. compact, a lot of it can be stored in a small space 4. very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released why do animals need highly branched glycogen? - CORRECT ANSWERS because animals metabolic rate is faster than plants and so needs glucose to be released quicker. describe the structure of cellulose - CORRECT ANSWERS made up of straight chains of beta glucose AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS the chains are parallel to each other, so H bonds form cross-linkages all the H bonds together strengthens the cellulose forms microfibrils draw alpha and beta glucose - CORRECT ANSWERS how does the structure of triglycerides relate to their properties? - CORRECT ANSWERS 1. triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, so its a good source of energy. 2. low mass to energy ratio, so theyre good energy storage molecules. 3. large and non-polar, therefore insoluble, therefore don't affect osmosis. 4. high ratio of hydrogen to oxygen atoms, so can release water when oxidised, hence provide a source of water what are the roles of lipids? - CORRECT ANSWERS 1. source of energy 2. waterproofing 3. insulation 4. protection how does the structure of phospholipids relate to their properties? - CORRECT ANSWERS 1. polar, therefore will position itself to form a bilayer 2. the structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. these are important in cell recognition. draw the structure of an amino acid - CORRECT ANSWERS draw how a dipeptide forms - CORRECT ANSWERS AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS how is DNA adapted to carrying out its function? - CORRECT ANSWERS 1. it is very stable, thus rarely mutates 2. the H bonds can easily be separated during DNA replication and protein synthesis 3. extremely large, thus carries a lot of genetic information 4. base pairing allows DNA to replicate and transfer info as mRNA. describe semi conservative replication - CORRECT ANSWERS - DNA helicase unwinds separates the two strands of DNA into single strands by breaking the H bonds between the bases - this therefore forms 2 base templates (the bases on each strand are exposed) - free complimentary nucleotides align with the bases according to complimentary base pairing - they are joined via condensation reaction with DNA polymerase - the new DNA molecule is formed what is meant by resolution - CORRECT ANSWERS the minimum distance apart that two objects can be in order for them to appear as separate items. before cell fractionation, why is the tissue placed in a cold, isotonic buffer? - CORRECT ANSWERS cold: 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 what are the advantages of an electron microscope? - CORRECT ANSWERS electron beam has a short wavelength and the microscope can therefore has high resolution. the negatively charged beam can be focused using electromagnets. AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS what are the limitations of using a transmission electron microscope? - CORRECT ANSWERS the whole system must be in vacuum, so living specimens cant be studied. complex staining process the image may contain artefacts what is the function of SER? - CORRECT ANSWERS synthesises, stores and transports lipids and carbohydrates what is the function of RER? - CORRECT ANSWERS provides a large surface area to synthesise proteins and glycoproteins provides a transport pathway for materials throughout the cell what is the function of golgi apparatus? - CORRECT ANSWERS add carbs to proteins to form glycoproteins produce secretory enzymes secrete carbohydrates transport, modify and store lipids form lysosomes what is meant by 'organ'? - CORRECT ANSWERS a combination of tissues that are coordinated to perform a variety of functions. large molecules often contain carbon. why? - CORRECT ANSWERS they can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. describe benedicts test for reducing sugars - CORRECT ANSWERS add equal volumes of the sugar sample and benedicts reagent. heat the mixture in a water bath for 5 minutes. brick red precipitate will form. AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS what is a reducing sugar? - CORRECT ANSWERS a sugar that can reduce (give electrons to) another chemical. describe the benedicts test for non reducing sugars - CORRECT ANSWERS with food sample, add an equal volume of dilute hydrochloric acid in a test tube. place test tube in water bath for 5 mins. add sodium hydrogencarbonate solution. heat resulting solution with an equal volume of benedicts. solution for 5 minutes. turns orange/brown. what does dilute hydrochloric acid do in the benedicts test for non reducing sugars? - CORRECT ANSWERS it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. describe binary fission - CORRECT ANSWERS the circular DNA molecule replicates and both copies attach to the cell membrane. plasmids also replicate cell membrane grows between the two DNA molecules, dividing the cytoplasm into two. a new cell wall forms between the two DNA molecules. two daughter cells are produced, each with a single copy of circular DNA and a variable number of plasmids. how do viruses replicate? - CORRECT ANSWERS they 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. describe cell mediated immunity - CORRECT ANSWERS 1. phagocytes injest pathogens. AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS 5. individuals may object to vaccinations due to religious, ethical or medical reasons what are antibodies made up of? - CORRECT ANSWERS 4 polypeptide chains: - 2 are 'heavy chains' - 2 are 'light chains' variable (binding) region how does HIV replicate? - CORRECT ANSWERS HIV attaches most commonly to T-helper cells the protein capsid fuses with the cell-surface membrane the RNA and enzymes of HIV enter T-helper cell reverse transcriptase converts the viruses RNA to DNA the new DNA enters nucleus is inserted into T-h cells DNA HIV DNA in nucleus creates mRNA using the cells enzymes, which contains the instructions for making new viral proteins. the viral proteins are assembled into new HIV features of specialised gas exchange surfaces - CORRECT ANSWERS - a large surface area to volume ratio - very thin therefore short diffusion pathway - selectively permeable - a transport system how do insects carry out gas exchange? - CORRECT ANSWERS 1. 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. AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS describe and explain the countercurrent exchange principle - CORRECT ANSWERS -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 how does the structure of a plant leaf link to gas exchange? - CORRECT ANSWERS -all cells are close to stomata, and therefore surface, therefore a short diffusion pathway -inter-connecting air spaces in the mesophyll so that gases can readily contact mesophyll cells describe and explain why plant stomata links to gas exchange and its benefits - CORRECT ANSWERS stomata 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 how do insects limit water loss? - CORRECT ANSWERS -small surface area to volume ratio -waterproof coverings -spiracles which can close how do xerophytes limit water loss? - CORRECT ANSWERS -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 AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS by trapping air, water potential gradient is reduced describe the process of inspiration - CORRECT ANSWERS external intercostals contract internal intercostals relax ribs move up and outwards, increasing thorax volume diaphragm contracts, further increasing thorax volume air pressure in lungs becomes lower than atmospheric pressure, so air is forced in describe the process of expiration - CORRECT ANSWERS internal intercostals contract external intercostals relax ribs movie in and downwards diaphragm relaxes this decreases thorax volume air pressure in lungs becomes greater than atmospheric pressure, so air is forced out structure of haemoglobin - CORRECT ANSWERS 4 polypeptide chains - 2 alpha - 2 beta each chain has a haem group which contains a ferrous Fe2+ ion. what is the vena cava connected to? - CORRECT ANSWERS right atrium what is aorta connected to? - CORRECT ANSWERS left ventricle what is pulmonary artery connected to? - CORRECT ANSWERS right ventricle what is pulmonary vein connected to? - CORRECT ANSWERS left atrium AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS what is the role of companion cells? - CORRECT ANSWERS they load/unload organic solutes into the sieve tube describe the transfer of sucrose into sieve elements - CORRECT ANSWERS sucrose 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. what is a 'source' cell? - CORRECT ANSWERS cells that photosynthesise and make sugars what is a 'sink' cell? - CORRECT ANSWERS cells that use/store organic solutes explain mass flow hypothesis - CORRECT ANSWERS 1. 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 how can you investigate mass flow using aphids? - CORRECT ANSWERS 1. cut across their mouthparts. the mouthparts act as a sampling tube that they collect the phloem contents. AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS 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). 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? - CORRECT ANSWERS a 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. define genome - CORRECT ANSWERS the complete set of genes in a cell define proteome - CORRECT ANSWERS the full range of proteins that a cell is able to produce describe the process of transcription - CORRECT ANSWERS DNA 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 - CORRECT ANSWERS 1. mRNA associates with a ribosome in the cytoplasm 2. tRNA molecules with complimentary anticodons align with the first 2 mRNA codons AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS 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 the 2 mechanisms that mean that meiosis will result in genetic variation - CORRECT ANSWERS independent segregation crossing over what happens during independent segregation? - CORRECT ANSWERS during 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 happens during crossing over? - CORRECT ANSWERS when 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 is ATP made up of? - CORRECT ANSWERS adenine ribose 3 phosphates how does ATP store energy? - CORRECT ANSWERS has 3 phosphates, the bonds between these are unstable and so have a low activation energy, hence easily broke. when they break, they release energy. AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS define community - CORRECT ANSWERS all the populations of different species living and interacting in a particular place at the same time. define habitat - CORRECT ANSWERS the place where an organism normally lives define ecological niche - CORRECT ANSWERS The 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. interspecific competition - CORRECT ANSWERS occurs when individuals of DIFFERENT species compete for resources such as food, light, water etc. intraspecific competition - CORRECT ANSWERS occurs when individuals of the SAME species compete for resources such as foo, light, water etc. predation - CORRECT ANSWERS one organism is consumed by another. explain predation - CORRECT ANSWERS predators 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 two ways in which pathogens can cause disease - CORRECT ANSWERS releases toxins damages cell tissue AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS A vaccine can be used to produce immunity. Describe how memory cells are important in this process. (3) - CORRECT ANSWERS important 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. Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (3) - CORRECT ANSWERS it enters via stomata, which are opened as guard cells open. if diffuses down a concentration gradient through the air spaces. There are large numbers of mitochondria in the epithelial cell. Explain how these organelles help the cell to absorb the products of digestion. (2) - CORRECT ANSWERS mitochondria provide the ATP this is needed for active transport of substances into the cell red blood cells are biconcave discs. Explain one advantage of a biconcave disc over a spherical cell of the same volume in transporting oxygen. - CORRECT ANSWERS Large (surface) area; For diffusion; Describe how oxygen in air in the alveoli enters the blood in capillaries. - CORRECT ANSWERS diffusion across alveoli epithelium 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. - CORRECT ANSWERS lactase bead can be reused continuous process lactase not present in milk what is a vaccine? - CORRECT ANSWERS Contains antigen / proteins / dead / weakened microorganism / pathogen / virus / bacteria; Stimulates production of antibodies / plasma cells / memory cells AQA A-LEVEL BIOLOGY PAPER 1 QUESTIONS AND ANSWERS NEWEST UPDATE 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED BEST COMPLETE SOLUTION GRADED A+ FOR SUCCESS where is amylase produced? - CORRECT ANSWERS salivary glands, pancreas, small intestine where is maltase produced? - CORRECT ANSWERS epithelium of small intestine where is lactose produced? - CORRECT ANSWERS pancreas, small intestine where are proteases produced? - CORRECT ANSWERS stomach, pancreas, small intestine describe the involvement of RER in producing chylomicrons - CORRECT ANSWERS RER synthesises proteins in the ribosomes, which are needed to form chylomicrons. suggest how chylomicrons leave the epithelial cell. - CORRECT ANSWERS by exocytosis because theyre too large to leave by other methods whats the difference between species richness and diversity index? - CORRECT ANSWERS Species richness measures only number of (different) species / does not measure number of individuals. directional selection - CORRECT ANSWERS selection favours individuals in one direction from the mean of the population. e.g. when environment changes, those with advantageous allele outside of the mean will be more likely to survive and breed. stabilising selection - CORRECT ANSWERS if 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. courtship behaviour results in reproductive success by... - CORRECT ANSWERS 1. allowing recognition of own species