AQA A-level Biology paper 1 Exam, Exams of Nursing

Download AQA A-level Biology paper 1 Exam and more Exams Nursing in PDF only on Docsity! AQA A-level Biology paper 1 AQA A-level Biology paper 1 Exam Questions Containing 134 Terms with Certified Answers 2024-2025. Large molecules often contain carbon. why? - Answer: they can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. 1 AQA A-level Biology paper 1 describe benedicts test for reducing sugars - Answer: 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. what is a reducing sugar? - Answer: a sugar that can reduce (give electrons to) another chemical. describe the benedicts test for non-reducing sugars - Answer: 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 hydrogen carbonate 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? - Answer: it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. describe the structure of starch - Answer: chains of alpha glucose some chains are branched= amylopectin some chains are coiled= amylose what purpose does the structure of amylose serve? - Answer: makes the molecule compact so it is stored more easily. 2 AQA A-level Biology paper 1 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 - Answer: draw how a dipeptide forms - Answer: what is meant by 'primary sequence' of a protein - Answer: The unique sequence of amino acids that make up a protein or polypeptide chain what is meant by 'secondary sequence' of a protein - Answer: The way in which the primary structure of a polypeptide chain folds e.g. alpha helix or beta pleated sheets. shape is held by H bonds. 5 AQA A-level Biology paper 1 what is meant by 'tertiary sequence' of a protein - Answer: This is the overall 3-D structure of the protein. The shape of the protein is held together by H bonds and ionic bonds and disulfide bridges. what is meant by 'quaternary sequence' of a protein - Answer: If a protein is made up of several polypeptide chains that are linked in various ways, the way they are arranged is called the quaternary structure. describe the test for proteins - Answer: add 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. what are fiberous proteins made up of? - Answer: made 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? - Answer: made 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 kind of protein is collagen? - Answer: fiberous 6 AQA A-level Biology paper 1 what kind of protein is haemoglobin? - Answer: globular what is haemoglobin made up of? - Answer: two α polypeptide chains two β polypeptide chains an inorganic prosthetic haem group (Fe2+) what is collagen made up of? describe its structure? - Answer: three polypeptide chains wound around each other each of the three chains is a coil itself Hydrogen bonds form between these coils Collagen molecules form further chains with other collagen molecules and form Covalent Cross Links with each other, which are staggered along the molecules to further increase stability. Collagen molecules wrapped around each other form Collagen Fibrils which themselves form Collagen Fibres. what are the functions of collagen? - Answer: 1. 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 type of bond forms between the phosphate group and deoxyribose sugar in DNA? - Answer: phosphodiester bond 7 AQA A-level Biology paper 1 transport, modify and store lipids form lysosomes what is meant by 'organ'? - Answer: a combination of tissues that are coordinated to perform a variety of functions. describe binary fission - Answer: 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? - Answer: 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 - Answer: 1. phagocytes injest pathogens. 2. the phagocyte places antigens from pathogen on its cell surface membrane, so it becomes an antigen presenting cell. 3. receptors of T-helper cells have a complimentary fit to these antigens. 10 AQA A-level Biology paper 1 4. this attachment activates T cells to divide rapidly by mitosis and form a clone of genetically identical cells. 5. the cloned T cells: a. develop into memory cells b. stimulate phagocytosis c. stimulate B cells to divide and secret their antibody d. activate cytotoxic T cells. describe humoral immunity - Answer: 1. the surface antigen of a pathogen is taken up by B cell 2. the B cell processes it and presents the antigen on its surface 3. T-helper cells attach to the processed antigens, thus activating the B cell 4. B cells divide by mitosis to produce a clone of plasma cells 5. these secrete the specific antibody that can bind to the pathogens antigen 6. the antigens destroy the pathogen 7. some B cells develop into memory cells what is passive immunity and how is it produced? - Answer: produced by the introduction of antibodies into individuals from an outside source. immunity is acquired immediately. no contact with pathogen/s needed. short term immunity: antibodies aren't replaced when broken down, memory cells not formed. e.g. anti-venom 11 AQA A-level Biology paper 1 what is active immunity and how is it produced? - Answer: produced by stimulating the production of antibodies by the individuals own immune system. contact with pathogen/s needed. immunity takes time to develop natural active immunity - Answer: results from an individual becoming infected with a disease under normal circumstances. long term body produces its own antibodies artificial active immunity - Answer: involves inducing an immune response in an individual WITHOUT them suffering the symptoms of the disease. e.g. vaccinations memory cells produced what are the features of a successful vaccination programme? - Answer: 1. 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 why can vaccinations not be effective? - Answer: 1. immunity may not be induced in people with defective immune systems 12 AQA A-level Biology paper 1 describe and explain why plant stomata links to gas exchange and its benefits - Answer: 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? - Answer: -small surface area to volume ratio -waterproof coverings -spiracles which can close how do xerophytes limit water loss? - Answer: -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 describe the process of inspiration - Answer: 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 - Answer: internal intercostals contract 15 AQA A-level Biology paper 1 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 - Answer: 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? - Answer: right atrium what is aorta connected to? - Answer: left ventricle what is pulmonary artery connected to? - Answer: right ventricle what is pulmonary vein connected to? - Answer: left atrium how is tissue fluid formed - Answer: high hydrostatic pressure at arterial end due to contractions of ventricles this causes tissue fluid to be forced out of the blood plasma this is ultrafiltration 16 AQA A-level Biology paper 1 describe the process of lipid digestion - Answer: in small intestine, bile salts combine with fat droplets and break them down smaller (emulsification). lipase enzymes from pancreas hydrolyse lipids into fatty acids, glycerol and monoglycerides. short chain fatty acids: diffuse directly into blood via epithelial cell longer chain fatty acids: combine with bile salts to form micelles, which break down into fatty acids and monoglycerides which diffuse into epithelial cells. once there, they recombine into triglycerides which can form chylomicrons. artery structure - Answer: thick 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. why do arterioles have thinner elastic layer than arteries? - Answer: blood pressure is lower. vein structure - Answer: muscle 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. 17 AQA A-level Biology paper 1 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? - Answer: 1. 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). 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? - Answer: 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. 20 AQA A-level Biology paper 1 define genome - Answer: the complete set of genes in a cell define proteome - Answer: the full range of proteins that a cell is able to produce describe the process of transcription - Answer: 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 - Answer: 1. 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 21 AQA A-level Biology paper 1 the 2 mechanisms that mean that meiosis will result in genetic variation - Answer: independent segregation crossing over what happens during independent segregation? - Answer: 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? - Answer: 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? - Answer: adenine ribose 3 phosphates how does ATP store energy? - Answer: 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. what does ATP synthase catalyse? - Answer: the formation of ATP from ADP 22 AQA A-level Biology paper 1 interact with one another and also with the physical and non-physical factors present. biotic - Answer: living abiotic - Answer: non-living define population - Answer: a group of individuals that occupy the same habitat at the same time and are potentially able to interbreed. define community - Answer: all the populations of different species living and interacting in a particular place at the same time. define habitat - Answer: the place where an organism normally lives define ecological niche - Answer: 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 - Answer: occurs when individuals of DIFFERENT species compete for resources such as food, light, water etc. intraspecific competition - Answer: occurs when individuals of the SAME species compete for resources such as foo, light, water etc. 25 AQA A-level Biology paper 1 predation - Answer: one organism is consumed by another. explain predation - Answer: 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 - Answer: releases toxins damages cell tissue A vaccine can be used to produce immunity. Describe how memory cells are important in this process. (3) - Answer: 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) - Answer: 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) - Answer: mitochondria provide the ATP this is needed for active transport of substances into the cell 26 AQA A-level Biology paper 1 red blood cells are biconcave discs. Explain one advantage of a biconcave disc over a spherical cell of the same volume in transporting oxygen. - Answer: Large (surface) area; For diffusion; Describe how oxygen in air in the alveoli enters the blood in capillaries. - Answer: 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. - Answer: lactase bead can be reused continuous process lactase not present in milk what is a vaccine? - Answer: Contains antigen / proteins / dead / weakened microorganism / pathogen / virus / bacteria; Stimulates production of antibodies / plasma cells / memory cells where is amylase produced? - Answer: salivary glands, pancreas, small intestine where is maltase produced? - Answer: epithelium of small intestine where is lactose produced? - Answer: pancreas, small intestine 27