AQA AS LEVEL BIOLOGY 2023 with verified questions and answers

what is RNA? ribonucleic acid MRNA and TRNA single stranded shorter AU CG what are biological molecules? molecules made and used by living organisms eg. lipids, carbs, DNA, AT, water, inorganic ions what are the functions of carbohydrates? -energy source (respiration) -energy store (starch and glycogen) -structure (cellulose) ATP structure? 1 adenosine 3 phosphates ADP and energy= ATP condensation reaction using ATP synthase carries energy in bonds hydrolysis breaks down into ADP and energy using ATP hydrolase releases energy from phosphate group bonds what are the building blocks of carbohydrates called? monosaccharides why is ATP a good source of energy? immediate release, only need to break one bond releases small amounts of energy at a time, manageable examples of monosaccharides glucose, fructose, galactose uses of ATP? protein synthesis organelle synthesis dna replication mitosis active transport metabolic reactions movement homeostasis formula for monosaccharides? c6h12o6 -same formula but arranged differently role of water in biology? acts as a habitat for organisms make up cytoplasm, tissue fluid, blood, xylem and phloem water properties? dipolar partially positive hydrogen partially negative oxygen so separate water molecules form hydrogen bonds with eachother difference between alpha and beta glucose? on carbon 1, alpha glucose has an OH group on the bottom. beta glucose has it at the top. how are monosaccharides joined together? condensation reaction between 2 OH groups roles of water? -habitat, high shc so a lot of heat needs to be applied before evaporation due to hydrogen bonds. ice is less dense than water so floats up -solvent, dipolar so separate solutes by charge depending on partial charge. solute dissolves in water, useful for cytoplasm, diffusion and active transport ect -hydrostatic pressure, when pressurised, water provides a strong pushing force particularly in mass flow. supports turgidity -homeostasis, sweat on skin uses blood heat to evaporate, cooling individual. sweat is made up of hydrogen bonds,stable structure, large amount of heat to evaporate. LATENT HEAT OF EVAPORATION. bond in carbohydrate? glycosidic what are inorganic ions? salts or minerals don't contain carbon eg sodium and chloride ions examples of disaccharides sucrose, lactose (glucose + galactose), maltose (glucose + glucose) kingdoms of biology? animal, plant, bacteria, fungi, protocista animal and plant multicellular others are microorganisms viruses aren't living all organisms made up of cells eukaryotic vs prokaryotic eukaryotic - membrane bound organelles eg. nucleus prokaryotic - no membrane bound organelles, smaller ribosomes formula for disaccharides? c12h22o11 what are the 2 forms of reproduction? sexual- 2 parents each provide gamete which fuse to make zygote which develops into organism asexual- one parent to produce genetically identical offspring how are polymers separated? hydrolysis (addition of water) how does a zygote develop into an organism? stem cell, undifferentiated divides by mitosis to make more stem cells each cell differentiates into specialised each specialised divides by mitosis to make tissues different tissues for organ, and so on what is a polysaccharide? many monosaccharides joined together by condensation reaction/glycosidic bonds. structure of nucleus? contains DNA wrapped around histones to form chromatin double membrane called nuclear envelope with pores nucleolus produces ribosomes and mRNA nucleoplasm contains chromatin examples of polysaccharides -amylose, long chain of alpha glucose, makes starch/glycogen -cellulose, long chain of beta glucose properties of starch and glycogen as energy stores? -insoluble, doesn't affect water potential, cell won't shrink or burst -coiled, compact, fits inside cells better -branched/chained, easy to break down, glucose removed from the end endoplasmic reticulum? rough- has ribosomes ,protein synthesis, process and package smooth- makes lipids and carbs golgi apparatus? processes and packages proteins into vesicles digestive enzymes placed into lysozomes, vesicles with membranes structure of cellulose? -beta glucose arranged in straight chain (each alternative beta glucose rotated 180°) -many cellulose chains are cross linked by hydrogen bonds, form microfibrils -microfibrils crosslinked to make macrofibrils -hydrogen bonds are strong together, hard to break,makes cellulose strong -forms cell wall structure mitochondria? site of respiration, produces ATP which releases energy cristae- inner membrane has large surface area so more metabolic enzymes can attach matrix- middle liquid test for starch? iodine brown to blue/black chloroplast structure? absorbs light energy for photosynthesis to produce glucose double membrane thylakoid disks stack into granum thylakoid surrounded by stroma fluid large surface area test for reducing sugars heat with benedicts, turns brick red vacuole surrounded by membrane called tonoplast contains cell sap keeps cell turgid pushes chloroplasts to surface test for non reducing sugar? -heat with benedicts, no change -add dilute hcl (hydrolyses glycosidic bond) -add sodium hydrogen carbonate to neutralise -heat with benedicts, will turn brick red structure of bacteria? circular DNA and plasmids no membrane bound organelles smaller ribosomes cell wall made of murein some have slime capsule (protect from phagocytosis) and flagella (movement) types of proteins? globular and fibrous structure of virus? DNA or RNA if RNA, contains reverse transcriptase enzyme to convert it into DNA capsid phospholipid membrane attachment proteins to identify and attach to host what are globular proteins? have a specific 3d shape, soluble eg. haemoglobin how does a virus infect their host cell? uses attachment protein to attach send in DNA capsid which uses cell to make virus components producing copies and destroying host cell what are fibrous proteins? insoluble, inflexible and strong eg. keratin how do amino acids differ? have different r groups what is a chromosome? coiled DNA formed during interphase made of 2 sister chromatids joined by centromere 2 copies of same DNA molecule what is a homologous pair of chromosomes? 1 maternal 1 paternal same genes but different alleles how are amino acids joined? condensation reaction between carboxyl group and amine group. leaves bond between carbon and nitrogen, DIPEPTIDE primary structure of a protein? sequence of AA, polypeptide chain. change in sequence, bonds will be formed in different places in secondary. secondary structure? primary structure coils to form an alpha helix, hydrogen bonds form between amino acids tertiary structure? secondary structure folds again to form final 3d shape, held by ionic/hydrogen/disulfide bonds quarternary structure? more than one polypeptide chain, non protein can be involved quarternary structure examples? haemoglobin, antibodies, collagen collagen structure? -strong -primary structure glycine -secondary tight coil -tertiary coils again -quarternary three chains wrapped like rope protein test? biruet reagent, turns purple what is an enzyme? biological catalyst speeds up reaction without being used up lowers activation energy what makes an enzyme specific? specific active site, only complimentary substrates can bind and form enzyme substrate complexes lock and key model? active site is rigid, only exactly complimentary substrates fit induced fit model? shape of active site changes slightly so substrate fits exactly forming ES complex affect of substrate concentration on enzyme activity? more substrate, more chance of successful collisions, ES complex, increase rate increases until all enzymes are saturated affect of enzyme concentration on enzyme activity? more enzymes, more successful reactions, ES complexes continues until all the substrates are used up affect of temperature on enzyme activity? as temp increases, kinetic energy increases, molecules move faster more collisions, more ES complexes carries on until optimum after optimum, tertiary bonds break lose active site shape no longer complimentary denatured affect of ph on enzyme activity? if ph is changed away from optimum, bonds in tertiary structure break, enzyme denatured competitive inbibitor? similar shape to substrate fits in active site blocks ESCS from forming non competitive inhibitor binds on somewhere other than active site, changes the enzymes shape, prevents substrate from binding 3 types of lipids? triglycerides phospholipids cholesterol triglyceride structure 1 glycerol 3 fatty acids joined by ester bonds in condensation reaction COOC bond either saturated or unsaturated phospholipid stucture? 1 glycerol 2 fatty acids 1 phosphate group phosphate forms hydrophilic head fatty acid hydrophobic tail forms phospholipid bilayer what are nucleic acids? polymers made from nucleotides eg DNA and RNA what is DNA? deoxyribonucleic acid in all organisms carries genes, section of DNA coding for a protein building block of DNA? nucleotide (made of phosphate, deoxyribonucleic sugar, nitrogenous base) AT CG DNA structure? double helix sugar and phosphate condensation reaction hydrogen bonds between bases AT CG double strand coiled in double helix properties of DNA structure? double stranded, one strand acts as template for semi con replication helix, more compact sugar phosphate backbone protects bases hydrogen bonds weak, easy to break for replication complimentary Base pairing, ensures identical DNA copies made describe semi conservative replication? DNA double strand separated by DNA helicase, breaks h bonds one strand acts as template free nucleotides match up and bind to complimentary bases DNA polymerase joins sugar phosphate back of new strand scr evidence? bacteria DNA has 2 isotopes 14n and 15n 15n heavy 14n light nitrogen found in bases what does mitosis produce? two genetically identical diploids which have a full set of chromosomes what happens in interphase? dna replication protein and organelle synthesis what happens during prophase? chromatin condenses to make chromatids nuclear envelope breaks down spindle fibres form what happens during metaphase? chromosomes line up on cell equator attach to spindle fibres by centromere what happens during anaphase? spindle fibres pull sister chromatids by centromere to opposite poles sister chromatids make a v shape what happens during teleophase? chromatids uncoil to make chromatin again nuclear envelopes reform 2 identical nuclei formed in one cell what happens during cytokinesis? cytoplasm splits into 2 creating 2 identical sister cells what happens to chromosome number during mitosis? stays the same diploid what is cancer? formation of tumour due to uncontrolled mitosis/ cell division how does uncontrolled cell division occur? mutation of dna/ genes that regulate mitosis cell mutations can occur randomly or due to mutagens eg. radiation cancer cells are rapidly dividing spend less time in interphase and more time in mitosis treatments for cancer? surgery to remove tumour chemotherapy, drugs that inhibit mitosis in rapidly dividing cells radiotherapy, radiation used to kill cancer cells disadvantages of chemotherapy? kills off normal healthy cells eg hair skin rbcs causing hair loss,dry skin and tiredness needs to be given as regular doses to allow time for healthy cells to recover how do bacteria reproduce? binary fission (roughly splits cell into two parts) copy DNA and separate by asexual reproduction formula for magnification image/actual unit conversions? 1mm=1000 micrometers 1mm=1,000,000 nanometers why do mitochondria appear different shapes in images? viewed from different angles at different levels some cut transversely others cut through the middle of the cell why do electron microscopes have a higher resolution? electron beams have a shorter wavelength TEM and SEM differences? tem- electrons absorbed sem- electrons bounce off specimen advantages and disadvantages of TEM? good- highest magnification and resolution bad- artefacts made, only dead specimens, need to be thin, black and white, 2d image why do electron microscopes need to be in a vacuum? in air, oxygen molecules could collide with electrons and prevent electrons from reaching specimen advantages and disadvantages of SEM? good- 3d image bad- only dead specimens, black and white image, artefacts why does cell solution need to be cold, isotonic and ph buffered before homogenisation? cold- reduce enzyme activity which could damage organelles isotonic- no osmosis occurs so cells don't shrink or burst ph buffered- mantain constant ph why do cells need to be homogenised during cell fractionation? to break open cell membrane and release organelles so organelles can be studied in isolation why do cells need to be filtered during fractionation? remove membrane and whole cells what is cell ultra centrifugation? spun at low centrifugal force at first nucleus is largest so forms the first pellet at bottom pellet decanted and supernatant recentrifuged at higher speed next heaviest organelle leaves and so on organelles by size? nucleus chloroplast mitochondria er/golgi/lysozomes ribosomes factors affecting diffusion? surface area concentration gradient thickness temperature size of molecules define osmosis net movement of water molecules from a high water potential to a low water potential through a semi permeable membrane what affects water potential? amount of solute in liquid more solute, more negative wp what happens when an animal cell is surrounded by pure water? swell and burst high wp to low wp what happens when a plant cell is surrounded by pure water? swells but doesn't burst cell wall protects made of cellulose cell is turgid animal cell surrounded by glucose solution? shrinks flacid plant cell surrounded by glucose solution? water leaves cell wall prevents shrinking protoplast shrinks cell is plasmolysed describe active transport? molecules bind to carrier protein ATP breaks down to ADP, Pi and energy energy causes carrier protein to change shape carrier protein releases molecules on opposite side where there is a high con carrier protein releases pi to return to original shape small intestines adaptions for diffusion? micro villi large surface area capillaries near by for circulation, maintain concentration gradient epithelial layer one cell thick, short diffusion pathway active transport of glucose in the small intestine? sodium ions actively transported from the epithelial cells into the blood stream, creating a concentration gradient as concentration is lower in cell sodium ions move into epithelial cells through diffusion glucose is pulled in through a Co transport protein with sodium glucose builds up in cell, so moves into bloodstream by diffusion what is a pathogen? a microorganism that causes diseases bacteria produce toxins viruses divide inside cells making them burst body's defense against pathogens? barriers phagocytosis specific immune response what are the barriers to pathogens? skin, impermeable barrier made of keratin cilia and mucus in lungs stomach acid which denatures pathogens describe phagocytosis? pathogen releases chemicals that attract phagocyte phagocyte binds engulfs pathogen in phagocytic vacuoule lysozomes fuse and release digestive enzymes which break down pathogen by hydrolysis phagocyte presents pathogenic antigens on surface describe the specific immune response? phagocyte presents pathogen antigens on surface which stimulates t cells when binded t cells divide by mitosis to make helper, killer t cells killer cells kill infected cells helper t cells release chemical signals to stimulate b cells b cells divide by mitosis to make plasma and memory cells plasma cells make monoclonal antibodies memory cells long term immunity remain in blood what is an antigen? protein on surface of pathogen that stimulates an immune response how does the immune response lead to the production of antibodies? t cells stimulated helper t cells stimulate b cells b cells have antibodies on surface and divide to make plasma cells which produce more antibodies what is an antibody? globular protein made by plasma cells variable, hinge and constant regions variable region has different shape on each antibody bind to complimentary antigens forming antigen antibody complexes destroy pathogen hinge region gives flexibility constant region binds to phagocytes for phagocytosis how do memory t cells work? made during specific immune response remain in blood if person is infected by same pathogen, memory cells will recognise pathogen and produce antibodies RAPIDLY in LARGE AMOUNTS- immunity how does a vaccine produce immunity? injection of dead or weakened pathogens that stimulate an immune response leading to production of specific antibodies and memory cells active immunity? has memory cells long term immunity produces own antibodies occurs by vaccine or infection passive immunity? person given antibodies which eventually die no memory cells or long term immunity through placenta or breast milk or injection successful vaccination programme? low cost, safe, effective, long term immunity , easily produced ,no side effects produces herd immunity what is herd immunity? when a large proportion of the population is vaccinated , so most immune only few non immune so pathogen will have nowhere to go and die out less infection problems with vaccination programmes? doesn't work side effects no weak pathogen many strains in one vaccine antigenic variability cannot achieve herd immunity as some will not be vaccinated what is antigenic variability? pathogen mutates antigen changes shape memory cells not complimentary so don't recognise pathogen therefore pathogen can reharm what is a monoclonal antibody? one type of antibody complimentary to one antigen made by one type of plasma cell what are monoclonal antibodies used for? pregnancy tests identify specific antigens/antibodies in the persons blood how do monoclonal antibodies identify specific antigens in the blood? place antibodies on plate add persons blood if antigen is present in blood, it will bind to monoclonal antibodies 2nd set of monoclonal antibodies with enzyme attached is added 2nd antibody binds to antigen. if not, antigen won't bind test plate washed if antigen is present 2nd monoclonal antibodies attach and won't be washed away. will be washed away if antigen isn't present colourless substrate added which changes colour if enzyme is present, so antigen is present THE SAME FOR ANTIBODIES BUT ANTIGEN IS PLACED ON TEST PLATE INSTEAD!!!!!! why is test plate washed after 2nd set of enzymes bind in elisa test? to remove any unbound antibody enzyme conjugates could be a false positive how are monoclonal antibodies used in pregnancy testing? pregnant woman produces HCG hormone in urine if woman is pregnant, HCG in urine binds to antibodies on test strip forming HCG-ANTIBODY complex a blue line is positive result also bind to third part of strip as a control what is HIV? human immunodeficiency Virus HIV is the pathogen aids is the disease HIV spread by fluid to fluid contact HIV damages and destroys helper t cells so person cannot produce antibodies to kill the pathogen. no clonal selection or immune response what is AIDS? the symptoms/ disease caused by HIV when the number of helper t cells in the blood becomes critically low catch opportunistic infections because of lack of immunity how do microorganisms obtain nutrients and remove waste? nutrients move in by diffusion waste moves out by diffusion though SURFACE why are microorganisms able to perform exchange via their surface? large s/a to volume ratios short diffusion distance low demand why can't animals/plants perform exchange via surface? small s/a to volume ratio multicellular so large diffusion difference and high demand THEREFORE needs specialised exchange and transport systems why do fish have specialised gas exchange system? multicellular low s/a to volume ratio therefore cannot perform exchange on surface needs GILLS structure of fish gills? many Gill filaments and lamellae so large surface area lamellae are thin so have short diffusion distance ventilation brings in pure water and circulation brings in deoxygenated blood Gill arch made of cartilage and bone what is a countercurrent flow? water and blood in fish pass over in opposite directions deoxygrnated blood has low oxygen concentration water has high oxygen concentration therefore there will be a concentration gradient as oxygen is higher in water mantains concentration gradient all the way along lamellae as much oxygen diffuses into blood as possible why do insects have specialised gas exchange systems? multicellular so small surface area to volume ratio high demand and impermeable exoskeleton therefore cannot perform gas exchange on their surface tracheal system in insects? spiracles are openings on body surface have valves so open=gas exchanged closed=prevent water loss spiracles connect to trachea which connect to tracheoles (LARGE SA) which are directly connected to respiring cells to deliver oxygen and remove co2 how does gas exchange occur in tracheal system? at rest, down a concentration gradient by simple diffusion when active, by ventilation through spiracles inhaled and exhaled air function of lungs? site of mammal gas exchange gets oxygen to blood for respiration removes carbon dioxide from blood which is toxic function of trachea,bronchi,bronchioles? transport and filter air bronchioles control how much air reaching alveoli structure of trachea? c shaped cartilage to keep trachea from collapsing c shaped to give flexibility because of oesophagus lining made of goblet and ciliated epithelial cells which make mucus that trap pathogens cilia push mucus out of lungs structure of bronchioles? wall made of smooth muscle which contracts by itself when around noxious gases lining of goblet cells and cecs alveoli adaptation? large surface area, folded thin wall so short diffusion distance elastic tissue for stretch and recoil to increase surface area when breathing in and push air out VENTILATION MAINTAINS CONCENTRATION GRADIENT adaptation of capillaries? millions so large surface area thin wall so short diffusion distance narrow lumen to decrease diffusion distance circulation maintains low oxygen high co2 concentration gradient how does o2 move from the alveoli to the capillaries? diffusion passing through alveolar epithelium then capillary epithelium how does co2 move from capillaries to alveoli? capillary epithelium to alveolar epithelium through diffusion describe inspiration? external intercostal contract ribcage moves up and out diaphragm flattens DECREASE IN PRESSURE INCREASE IN VOLUME more air moves in, moves down pressure gradient