Download AQA A-level Biology paper 1 Exam Questions and Answers June 2024 and more Exams Biology in PDF only on Docsity!
AQA A-level Biology paper
1 Exam Questions and
Answers June 2024
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. 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 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? - 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= amylopetcin
some chains are coiled= amylose what purpose does the structure of amylose serve? - Answer>> makes the molecule compact so it is stored more easily. what purpose does the structure of amylopectin serve? - Answer>> 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? - Answer>>
- starch is insolube so it doesnt affect water potential
- it is large enough that it doesnt diffuse out of cells
- compact enough so that a lot of it can be stored in a small space
- 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? - Answer>> 1. insoluble, so no effect on water potential of cell
- insoluble, so doesnt diffuse out of cells
- compact, a lot of it can be stored in a small space
- very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released why do animals need highly branched glycogen? - Answer>> because animals metabolic rate is faster than plants and so needs glucose to be released quicker. describe the structure of cellulose - Answer>> made 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
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. 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 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
- Makes up cartilage and connective tissue
- Prevents blood that is being pumped at high pressure from bursting the walls of arteries
- 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 why is DNA stable? - Answer>> 1. the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- many hydrogen bonds link the base pairs together, so it adds strength overall.
what are the limitations of using a transmission electron microscope? - Answer>> 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? - Answer>> synthesises, stores and transports lipids and carbohydrates what is the function of RER? - Answer>> 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? - Answer>> add carbs to proteins to form glycoproteins produce secretory enzymes secrete carbohydrates 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.
- the phagocyte places antigens from pathogen on its cell surface membrane, so it becomes an antigen presenting cell.
- receptors of T-helper cells have a complimentary fit to these antigens.
- this attachment activates T cells to divide rapidly by mitosis and form a clone of genetically identical cells.
- 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
- the B cell processes it and presents the antigen on its surface
- T-helper cells attach to the processed antigens, thus activating the B cell
- B cells divide by mitosis to produce a clone of plasma cells
- these secrete the specific antibody that can bind to the pathogens antigen
- the antigens destroy the pathogen
- 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.
- pathogen may mutate frequently, so vaccines cant prevent them from harming people
- certain pathogens conceal themselves from the body's immune system e.g. by hiding within cells
- individuals may object to vaccinations due to religious, ethical or medical reasons what are antibodies made up of? - Answer>> 4 polypeptide chains:
- 2 are 'heavy chains'
- 2 are 'light chains' variable (binding) region how does HIV replicate? - Answer>> 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 - Answer>> - 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? - Answer>> 1. insects contract their muscles, squeezing the trachea, enabling mass movement.
- a diffusion gradient is established
- 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. describe and explain the countercurrent exchange principle - Answer>> -the blood and the water flow in opposite directions -blood that is loaded with O2 meets water, which already has maximum O -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? - Answer>> -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 - 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
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 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. why do veins have thinner walls than arteries? - Answer>> thinner walls because blood is at lower pressure, and so less stretch and recoil with each contraction of ventricles. capillary structure - Answer>> one 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. how does water travel into/through plants? - Answer>> the water particles have higher water potential than the root hair cell, and so they enter the cell by osmosis down a water potential gradient. the water potential of the root hair cell is now higher than the cortex cell, and so water enters the cortex cell by osmosis. symplast pathway: water enters root hair cell by osmosis, and travels from the cytoplasm of one cell to another by plasmodesmata apoplast pathway: water enters the root by entering the spaces in cell walls. water moves up xylem due to H bonding in water. water travels until it reaches the casparian strip, where water needs to travel via symplast pathway. what is plasmodesmata? - Answer>> strands of cytoplasm linking one cell to another that passes through pores in cellulose cell walls explain cohesion-tension theory - Answer>> water is drawn from cell to cell by osmosis. it moves across the root cortex to
- 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.
- 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).
- 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. 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
- tRNA molecules with complimentary anticodons align with the first 2 mRNA codons
- peptide bond forms between the amino acid molecules
- the tRNA that bound to the first codon is free to leave the ribosome
- the ribosome moves along the mRNA by one codon and now a new tRNA with a complimentary anticodon enters the ribosome
- this continues until the ribosome reaches a stop codon 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 a transmission electron microscope work? - Answer>> it has an electron gun which produces a beam of electrons this is focused onto a specimen by condenser electromagnets the beam passes through the specimen some parts of the specimen absorb the electrons and appear dark and vice versa an image is produced why cant the highest resolution images not be produced by TEM?
- Answer>> there are difficulties preparing the specimen, which can limit resolution a higher energy electron beam may destroy the specimen how does a scanning electron microscope work? - Answer>> it 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 how to calibrate an eyepiece graticule? - Answer>> use a stage micrometer and align it with the eyepiece graticule. then, calculate the length of each subdivision define ecology - Answer>> the study of the inter-relationships between organisms and their environment, including abiotic and biotic factors. define ecosystem - Answer>> dynamic 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.
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. predation - Answer>> one organism is consumed by another. explain predation - Answer>> predators eat their prey, reducing prey population
