AQA A-level biology paper 3 Questions And Answers, Exams of Biology

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AQA A-level biology paper 3 Questions And Answers What are monomers? - The Answer Is Smaller units from which larger molecules are made What are examples of monomers? - The Answer Is Monosaccharides, amino acids and nucleotides What are polymers? - The Answer Is Molecules made from a large number of monomers joined together What is a condensation reaction? - The Answer Is A reaction that joins two molecules together with the formation of a chemical bind and involves the elimination of a molecule of water What is a hydrolysis reaction? - The Answer Is A covalent bond is broken by adding a molecule of water What is a monosaccharide? - The Answer Is The monomers from which larger carbohydrates are made AQA A-level biology paper 3 Questions And Answers What are examples of monosaccharides? - The Answer Is Glucose, fructose, galactose What are glucose's two isomers? - The Answer Is Alpha - OH below Beta - OH above What bond forms between monosaccharides? - The Answer Is Glycosidic bond How are disaccharides formed? - The Answer Is When a condensation reaction occurs between two monosaccharides - forms a glycosidic bond How is maltose formed? - The Answer Is A disaccharide is formed by the condensation of two glucose molecules. MALTASE breaks it down How is sucrose formed? - The Answer Is The condensation of a glucose molecule and a fructose molecule forms the disaccharide. SUCRASE breaks it down AQA A-level biology paper 3 Questions And Answers What is special about the structure of cellulose? - The Answer Is Every other beta glucose has to be inverted so it can join by a 1,4 glycosidic bond, meaning that hydrogen bonds form between the chains What can the hydrogen bonds on cellulose form? - The Answer Is Fibrils - gives them more tensile strength, support + ridgedity Why are straight chains important in cellulose? - The Answer Is Important in the hydrolysis of beta glucose (respiration) What is the test for reducing sugars? - The Answer Is Add benedicts (blue) Heat for 2 minutes Turns brick red if reducing sugars What is the test for non-reducing sugars? - The Answer Is Step 1: Boil in dilute HCl (to hydrolyse the non-reducing sugar). Step 2: Neutralise the solution by adding sodium hydrogen carbonate. Step 3: Repeat Benedict's test. AQA A-level biology paper 3 Questions And Answers The result will now be positive if a non-reducing sugar is present. If the solution remains blue, then no sugar is present. What is the test for starch? - The Answer Is Iodine solution is added Black-blue if present What are the two groups of lipids? - The Answer Is Triglyceride and phospholipid What bonds are formed between lipids? - The Answer Is Ester bonds How are triglycerides formed? - The Answer Is By the condensation of one molecule and glycerol and three fatty acids Also makes 3 water What are the properties of triglycerides? - The Answer Is Insoluble - doesn't affect water potential Metabolic water source - a high ratio of H+ to O2 atoms High ratio of carbon-hydrogen bonds to C-C - energy store AQA A-level biology paper 3 Questions And Answers Where does the ester bond form in a triglyceride? - The Answer Is Between glycerol and a fatty acid - OH- and H+ lost What is a saturated fatty acid? - The Answer Is A fatty acid with only single C-C bonds What is an unsaturated fatty acid? - The Answer Is A fatty acid with at least one double C=C bond What is a phospholipid? - The Answer Is A lipid containing glycerol, two fatty acids, and a phosphate group What is the structure of a phospholipid? - The Answer Is Hydrophilic head - soluble - phosphate head Hydrophobic tail - insoluble - fatty acid tail What type of molecule is a phospholipid? - The Answer Is Polar molecule - important in the phospholipid bilayer Positive + negative end AQA A-level biology paper 3 Questions And Answers What bonds are in the tertiary structure of an amino acid? - The Answer Is Disulphide bridges Ionic bonds Hydrogen bonds What is the quaternary structure of a protein? - The Answer Is Consists of more than one polypeptide chain Polypeptides can bind to a non-protein group (e.g. metal ion) An example is haemoglobin - 4 quaternary polypeptides What bonds are in the quaternary structure of an amino acid? - The Answer Is Non-covalent bonds such as Hydrophobic interactions Vanderwaals forces Hydrogen bonding What is the test for proteins? - The Answer Is Biuret test Add biuret solution so it forms a layer (blue) Shake it AQA A-level biology paper 3 Questions And Answers Positive - purple/violet precipitate What is an enzyme? - The Answer Is A biological catalyst that lowers the activation energy of reactions. What is the induced fit model? - The Answer Is the active site moulds around the substrate to form the enzyme-substrate complex. What is the active site of an enzyme determined by? - The Answer Is The primary and tertiary structure of an protein What factors affect rate of reaction? - The Answer Is Enzyme + substrate concentration pH Temperature Competitive inhibition Non-competitive inhibition How does enzyme concentration affect rate of reaction? - The Answer Is More active sites are available for complementary substrates AQA A-level biology paper 3 Questions And Answers Not enough substrates to go around - some active sites are left empty How does substrate concentration affect the rate of reaction? - The Answer Is More substrates are available for enzyme active sites Not enough active sites available How does pH affect enzyme activity? - The Answer Is Optimal pH - performs its best Too low/too high - deviates from its maximum rate Imbalance of H+ and OH- - disrupts active site How does temperature affect enzyme activity? - The Answer Is Increases collisions - more ESC Up to optimal temperature - afterwards, they will start to denature Will break the hydrogen bonds + therefore the tertiary structure How do competitive inhibitors affect enzyme activity? - The Answer Is Will compete with the substrate for the active site Specific to it AQA A-level biology paper 3 Questions And Answers What is the process of DNA replication? - The Answer Is 1.) DNA helicase unwinds a part of the DNA helix 2.) Free DNA nucleotides in line up with their complementary base on the template strand 3.) DNA polymerase will form phosphodiester bonds between the nucleotides 4.) This occurs in the 5' 3' direction so the lagging strand breaks into Okazaki fragments 5.) DNA ligase then synthesises them into full strands What is the structure of ATP? - The Answer Is Adenine (nitrogenous base); ribose (5- carbon sugar) and 3 phosphate groups It is purine What does ATP hydrolase do? - The Answer Is ATP -> ADP + Pi What does ATP synthase do? - The Answer Is ADP + Pi -> ATP (+energy) What are the properties of ATP? - The Answer Is Small - moves easily within the cells AQA A-level biology paper 3 Questions And Answers Water soluble - energy requiring processes can happen in aqueous environments Contains bonds between phosphates - immediate energy - large enough to be useful by not so large that energy is wasted as heat Releases energy in small quantities - energy not wasted Easily regenerated - can be recharged with energy What does Pi do? - The Answer Is Can be used to phosphorylate other compounds, often making them more reactive. What are the properties of water? - The Answer Is Metabolite Solvent Relatively high heat capacity Relatively large latent heat of vaporisation Cohesion Adhesion Dipolar molecule How does water being a metabolite benefit it? - The Answer Is Useful in many reactions such as condensation and hydrolysis reactions AQA A-level biology paper 3 Questions And Answers How does water being a solvent benefit it? - The Answer Is Helps cells transport and use substances like oxygen or nutrients. How does water having a high heat capacity benefit it? - The Answer Is Buffering changes in temperature - good buffer How does water having a large latent heat of vaporisation benefit it? - The Answer Is Provides a cooling effect with little loss of water through evaporation How does cohesion benefit water? - The Answer Is Supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air. How does adhesion benefit water? - The Answer Is Sticks to the walls of the xylem How does water being dipolar benefit it? - The Answer Is Allows other polar molecules to be readily dissolved into water. AQA A-level biology paper 3 Questions And Answers Membrane bound organelles What is the structure of the nucleus? - The Answer Is Nuclear envelope Nuclear pores Chromosomes Nucleolus What does the nucleus do? - The Answer Is It contains genetic material and controls the activities of the cell Where pre-mRNA is formed What is the cell surface membrane? - The Answer Is The plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environment. What does the cell surface membrane contain? - The Answer Is Phospholipids, proteins, cholesterol, glycolipids, glycoproteins What does the mitochondria contain? - The Answer Is enzymes needed for aerobic respiration AQA A-level biology paper 3 Questions And Answers Double membrane Cristae - large folds What do mitochondria do? - The Answer Is These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work What is the structure of a choloroplast? - The Answer Is Double membrane Thylakoid Stacks called grana Lamellae between them What do chloroplasts do? - The Answer Is This is where photosynthesis occurs, which makes food for the plant. They contain chlorophyll - a green pigment - which absorbs light needed for photosynthesis What is the structure of Golgi apparatus - The Answer Is Flattened membranous sacs (cisternae) AQA A-level biology paper 3 Questions And Answers What is the function of Golgi apparatus? - The Answer Is Modifies proteins Role in 'packaging + secretion of proteins Golgi vesicles - take proteins + get them ready for export What is the structure of lysosomes? - The Answer Is Membrane sac of digestive enzymes What is the function of lysosomes? - The Answer Is Break down materials and waste Host defence (destruction of bacteria by white blood cells) Lysozymes destroy pathogens What is the structure of a ribosome? - The Answer Is A larger part with a smaller part, both having rRNA mixed in 70S - plant cells 80S - animal cells What is the function of a ribosome? - The Answer Is Protein synthesis through translation of mRNA to polypeptides AQA A-level biology paper 3 Questions And Answers What is the function of the cell vacuole? - The Answer Is Helps to maintain pressure inside the cell and keep the cell rigid. This stops plants wilting. Also involved in the isolation of unwanted chemicals inside the cell. Store water, nutrients + waste What is a prokaryotic cell? - The Answer Is Cell without a nucleus or membrane bound organelles What type of DNA is in prokaryotic cells? - The Answer Is A single circular DNA molecule that is free in the cytoplasm and is not associated with proteins What else does a prokaryotic cell contain? - The Answer Is One or more plasmids A capsule surrounding the cell One or more flagella. What do virsues contain? - The Answer Is Genetic material - DNA or RNA Encased in a protein coat called a capsid AQA A-level biology paper 3 Questions And Answers Attachment proteins - allows it to inject genetic material How does an optical microscope work? - The Answer Is Light focused through the condenser lens, then through the specimen where certain wavelengths are filtered Light passes through the objective lens then to the eyepiece lens to produce a visible image Resolution and magnification of optical microscope? - The Answer Is Maximum magnification - 1500 Maximum resolution 200nanometers How does a transmission electron microscope work? - The Answer Is Electrons pass through the specimen Denser parts absorb more electrons - appear darker Resolution and magnification of a transmission microscope? - The Answer Is Maximum magnification - 500,000 Maximum resolution - 0.1nm Negatives of using a transmission microscope? - The Answer Is Cannot view live processes or specimens - AQA A-level biology paper 3 Questions And Answers interior is a vacuum - so electrons don't collide with air particles and ions as they could obscure the image Specimen has to be sliced very thinly Requires extensive staining process that can lead to artefacts (pieces of stain that look like organelles) How does a scannning electron microscope work? - The Answer Is Produced a 3D image - electrons 'bounce off' specimen and are detected at multiple detectors 1. Vacuum environment. 2. Artefacts are possible. Resolution and magnification of scanning microscope? - The Answer Is Maximum magnification - 100,000 Maximum resolution - 20nm How do you work out image size? - The Answer Is Actual size x magnification What are the principles of cell fractionalisation? - The Answer Is Used to separate cell components or to get a cell-free liquid Cells homogenised (squashed) to break open cells Then place them in a cold, isotonic + buffered solution AQA A-level biology paper 3 Questions And Answers What happens in anaphase? - The Answer Is Sister chromatids separate at the centromere and are pulled to opposite poles of the cell by the mitotic spindle What happens in telophase? - The Answer Is The spindle disappears and the nuclear envelope reformed Chromosomes start to decondense Cytokinesis occurs - cell division How does cancer occur? - The Answer Is Group of diseases Genes involved in the regulation of mitosis and the cell cycle are damaged which leads to uncontrolled mitosis This leads to the formation of a mass of abnormal cells - a tumour - which expands in size What do cancer treatments usually target? - The Answer Is Usually involves disrupting the cell cycle by: Preventing DNA from replicating - e.g. Cisplatin Inhibiting the metaphase stage of mitosis by interfering with spindle formation - e.g. Vinca Alkaloids AQA A-level biology paper 3 Questions And Answers What can uncontrolled mitosis cause? - The Answer Is Mutations can cause uncontrolled cell division, leading to the formation of tumours and of cancers Many cancer treatments are directed at controlling the rate of mitosis What happens in binary fission? - The Answer Is Replication of the circular DNA and of plasmids division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids. What are the stages of binary fission? - The Answer Is Happens in prokaryotes Circular DNA and plasmids are replicated Cytoplasm divides (cytokinesis) - single copy of circular DNA + variable plasmid copy numbers What does cholesterol in the cell membrane do? - The Answer Is Restrict movement + provide stability AQA A-level biology paper 3 Questions And Answers What is the fluid mosaic model? - The Answer Is Molecules can flow freely + many different types in the membrane What is simple diffusion? - The Answer Is Net movement of small, non-polar molecules from an area of high concentration to an area of low concentration. Passive process What is facilitated diffusion? - The Answer Is The movement of large/polar molecules through channel proteins/carrier proteins from an area of high concentration to an area of low concentration across a membrane. It is a passive process What is osmosis? - The Answer Is Osmosis is the net movement of water from an area of high water potential to an area of lower water potential across a semi-permeable membrane What is active trasnport? - The Answer Is Active transport is the net movement of particles through carrier proteins from an area of low concentration to an area of higher concentration - this process uses ATP AQA A-level biology paper 3 Questions And Answers What do cytotoxic T cells do? - The Answer Is Produce perforin which makes holes in the cell membrane - allows substances to enter and cause cell death Where do T cells mature? - The Answer Is Thymus What response are T-cells involved in? - The Answer Is Cell mediated response Where do B-cells mature? - The Answer Is Bone marrow What type of response are B-cells involved with? - The Answer Is Humoral What is an anitbody? - The Answer Is Protein that has binding sites complementary to antigens and destroy the pathogen Involved in humoral response What is the structure of an antibody? - The Answer Is - 4 polypeptide chains - quaternary AQA A-level biology paper 3 Questions And Answers Light chains and heavy chains - linked by disulphide bonds - antigen-binding sites. - constant (present in all) and variable regions (variable region dependant on antibody). - receptor binding site. What can the formation of an antibody-antigen complex lead to? - The Answer Is Destruction of the antigen, limited to agglutination and phagocytosis of bacterial cells. Produce the antibodies that have a specific shape to the antigens - so they can attach to the antigen + destroy the pathogen What do plasma cells do? - The Answer Is Produce the antibodies that have a specific shape to the antigens - so they can attach to the antigen + destroy the pathogen First contact - primary response Second contact - secondary response - memory cells What does vaccination involve? - The Answer Is Dead or inactive pathogen AQA A-level biology paper 3 Questions And Answers Initiates a primary response, leading to the formation of memory B cells Upon re-infection, secondary response is stimulated What is herd immunity? - The Answer Is When a majority of a population are vaccinated against a disease. This means that even people who have not been vaccinated are less likely to get it because there are fewer people to catch it from. What is active immunity? - The Answer Is Immunity that results from antibody production by immune system in response to presence of antigen - vaccination What is passive immunity? - The Answer Is Immunity that results from antibody production by immune system in response to presence of antigen - vaccination What is artificial passive immunity? - The Answer Is Injection of ready-made antibodies What is natural passive immunity? - The Answer Is Through antibody transfer across the placenta or in breast milk AQA A-level biology paper 3 Questions And Answers Ethical issues for and monoclonal antibodies? - The Answer Is Mice are used How does the ELISA test work? - The Answer Is Used in the detection of antigens 1. Antigen of interest is immobilised 2. Monoclonal antibodies added + if the antigen is there, they will bond 3. Apparatus is washed to remove unbound antigens 4. More monoclonal antibodies are added - have a colour which will bind to the antigen 5. Washed again 6. Complementary substrate to the enzyme is added - triggering a colour change - shows if they're present What is the general rule of surface area to volume ratio? - The Answer Is Larger than the organism - smaller the SA : V What is Fick's law? - The Answer Is Rate of diffusion = (SA * difference in conc.)/length of the diffusion path AQA A-level biology paper 3 Questions And Answers What is an adaption of a single celled organism? - The Answer Is They can exchange gases across body surface due to their large surface area What are the main three adaptations for gas exchange? - The Answer Is Large SA:V ratio Short diffusion path Large concentration gradient What is in the tracheal system of an insect? - The Answer Is Don't have lungs - have trachea Made up of trachea + tracheoles Spiracles - breath through O2 enters, CO2 leaves What are the adaptations of insects? - The Answer Is Gases enter = exit through spiracle Gas exchange through diffusion, CO2 conc from tracheoles to atmosphere Can do mass transport - contraction of abdominal muscles move gases along When in flight - muscle cells respire - anaerobically to produce lactate, lowering water potential so water moves from tracheoles into cells AQA A-level biology paper 3 Questions And Answers More air is drawn in to decrease volume in tracheoles How does gas exchange work in a fish? - The Answer Is Gill filaments - right angles to increase SA - increase rate of diffusion of oxygen from water to blood Lamella - in gill fragments - deep folds - high SA Gill bar - middle of the gill filaments What are some adaptations of fish? - The Answer Is Lamellae are folded so they have a large SA Lamellae + filaments are thin - increasing diffusion rate - shorter diffusion path Use countercurrent exchange to absorb oxygen into the blood Favourable conc. of oxygen is maintained across the whole length of the lamellae. How do insects reduce water loss? - The Answer Is Small SA:V ratio - minimise the area over which water is lost Waterproof coverings - over their body surfaces. In the case of insects this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle AQA A-level biology paper 3 Questions And Answers How are lipids broken down via lipase? - The Answer Is Hydrolyse lipids to monoglycerides + fatty acids Present in the small intestine What do bile salts do? - The Answer Is Bile salts made by the liver emulsify lipids Giving them a large SA so they're easily hydrolysed by lipases Products can remain associated with the bile salts to form micelles What are micelles? - The Answer Is Travel to the ileum + is broken down when in contact with the epithelium Products can then diffuse straight into the epithelium How are proteins broken down? - The Answer Is By: Endopeptidases Exopeptidases Membrane-bound dipeptidases AQA A-level biology paper 3 Questions And Answers How do endopeptidases work? - The Answer Is E.g. trypsin, chymotrypsin, pepsin Hydrolyse peptide bonds in the middle region of the polypeptide chain How do exopeptidases work? - The Answer Is Hydrolyse peptide bond on the terminal AA (end ones) How do membrane bound dipeptidases work? - The Answer Is Hydrolyse dipeptides into 2 AA How are amino acids and monosaccharides absorbed? - The Answer Is Co-transport Uses sodium ions Co transport sodium (down) + monosaccharides/AA (against) the epithelium (E) down the protein channel Sodium ions go from E to blood At the same time, potassium goes to E AA/MS go through a protein channel through facilitated diffusion What is haemoglobin? - The Answer Is Globular protein AQA A-level biology paper 3 Questions And Answers 4 polypeptide chains - quaternary structure 2 alpha, 2 beta Each haem chain contains Fe2+ Has 4 oxygen-binding sites What does haemoglobin do? - The Answer Is Carrier of oxygen through the blood to respiring tissues for aerobic respiration - to make ATP What is oxyhaemoglobin dissociation? - The Answer Is The release of oxygen from oxyhaemoglobin to the tissues What does an oxyhaemoglobin dissociation graph show? - The Answer Is The relationship between PPO2 (oxygen partial pressure) + percentage saturation of haemoglobin What does the bottom of the OHD graph show? - The Answer Is Low affinity (HG) - low oxygen concentration so less to bind to haemoglobin Deoxygenated blood (contracting skeletal muscles) What does the top of the OHD graph show? - The Answer Is High affinity (HG) - high oxygen concentration so more to bind to haemoglobin AQA A-level biology paper 3 Questions And Answers What is the coronary artery? - The Answer Is Carries oxygen to the heart muscle - so the heart can contract properly to pump blood What is the gross structure of the human heart? - The Answer Is Enters R atrium The tricuspid valve opens + DO blood enters the R ventricle DO blood then enters the pulmonary artery Blood is carried to the lungs where its OXY OXY blood then goes through the pulmonary vein to L atrium Then enters the L ventricle via the bicuspid valve L ventricle blood then enters the aorta + goes around the body What is cardiac diastole? - The Answer Is Atria and ventricles are all relaxed and the blood enters the atria increasing the volume of the atria + the pressure. As the blood enters, the pressure rises - so AV valves open and blood flows into ventricles down a pressure gradient - ventricles volume then increase What is atrial systole and ventricular diastole? - The Answer Is Atria contract (when abt 50% empty) to AQA A-level biology paper 3 Questions And Answers ensure all blood enters the ventricles. Blood entering the ventricles - ventricular diastole. Ventricular pressure slightly increases when blood enters - shutting the AV valves to prevent backflow What is ventricular systole? - The Answer Is Ventricles contract - contract harder due to thicker walls- further increasing ventricular pressure so it's more than that of the P artery/aorta. Semilunar valves open so blood flows into the P artery/aorta What is the structure of arteries? - The Answer Is Thick muscle layer - constriction + dilation can control blood volume Thick elastic layer - maintain blood pressure + allow stretch and recoil Thick wall prevents bursting during high pressures What is the structure of arterioles? - The Answer Is Thick muscle layer to restrict blood flow into capillaries - control blood flow Thinner elastic layer and wall than arteries What is the structure of veins? - The Answer Is Thin muscle layer AQA A-level biology paper 3 Questions And Answers Thin elastic layer + wall due to lower pressure Thin layer means they can be flattered - helping blood flow to the heart - larger SA Contain valves to prevent backflow - lower pressure What is the structure of capillaries? - The Answer Is No muscle or elastic layer Wall that is one cell thick - short diffusion path Form capillary beds - have narrow diameter - short diffusion distance What is the process of tissue fluid? - The Answer Is Blood enters the capillaries from the arteriole Increases volume which results in a high hydrostatic pressure (high pressure of liquid) at the arterial end Molecules (e.g. glucose, AA, fatty acids, ions, water, oxygen) are forced out forming TISSUE FLUID Large molecules (proteins) remain in capillaries - lowering the water potential (lower conc of water at the venule end) AQA A-level biology paper 3 Questions And Answers What is the source? - The Answer Is Where sugars are made What is the sink? - The Answer Is Where sugars are made What is the mass flow hypothesis? - The Answer Is Organic molecules (e.g. sucrose) are created by photosynthesis + are transported to the companion cells by facilitated diffusion Sucrose is then actively transported into the phloem/sieve tube elements by cotransport w hydrogen ions This decreases water potential as the solute conc increases - means water will enter the phloem from the xylem via osmosis Increases volume, increasing hydrostatic pressure Sugars used in respiring cells - increasing WP - so sugars exit by osmosis Decreasing hydrostatic pressure Hydrostatic gradient is made What is the ringing experiment? - The Answer Is A ring of bark & phloem are peeled & removed off a tree trunk. AQA A-level biology paper 3 Questions And Answers The result of removing the phloem is that the trunk swells above the removed section. Analysis of the liquid in this swelling shows it contains sugar. this shows that when the phloem is removed, the sugars cannot be transported & therefore proves the phloem transports the sugars. What is the tracing experiment? - The Answer Is Plants are provided w radioactively-labelled CO2 This is absorbed during photosynthesis to produce sugars - they become radioactively labelled Samples were then cut and places on X-ray film Section containing the RL sugars were detected - showed that the phloem transports organic substances What is the DNA like in prokaryotic cells? - The Answer Is Shirt, circular and not associated with histones What is the DNA like in eukaryotic cells? - The Answer Is Long, linear and associated with proteins called histones AQA A-level biology paper 3 Questions And Answers What other structures contain DNA? - The Answer Is Mitochondria and chloroplasts What is the DNA in mitochondria and chloroplasts like? - The Answer Is The same as in prokaryotes What is a gene? - The Answer Is A base sequence of DNA that codes for: The amino acid sequence of a polypeptide A functional RNA (including ribosomal RNA and tRNAs). What is a locus? - The Answer Is Location of a gene on a chromosome What is a triplet? - The Answer Is A sequence of 3 DNA bases that codes for a specific amino acid What are the characteristics of the genetic code? - The Answer Is Universal - same code for all organisms Degenerate - more codons than amino acids so some code for the same amino acid Non-overlapping - each base is only part of one codon AQA A-level biology paper 3 Questions And Answers complementary base pairs but ONLY ONE strand acts as a template Free mRNA nucleotides align and pair with their complementary base RNA polymerase joins the mRNA nucleotides together to form pre-mRNA What happens in spilicing? - The Answer Is Introns are removed The exons are attached back together via a condensation reaction - phosphodiester bonds mRNA is formed + it exits the nucleus through nuclear pores into the cytoplasm PROKARYOTIC CELLS DON'T HAVE INTRONS and therefore mRNA production is direct What happens in translation? - The Answer Is Ribosome attaches to the start codon of the mRNA (AUG) AQA A-level biology paper 3 Questions And Answers tRNA aligns the anticodon with the complementary mRNA codon The ribosome moves along the mRNA, which allows another tRNA to attach to the next codon The 2 amino acids attached to the tRNA molecules are joined by peptide bonds (which requires ATP) This process occurs until the ribosome reaches a stop codon which is where the ribosome detaches and translation ceases What is base substitution? - The Answer Is A single nucleotide base is replaced by another A nucleotide base is replaced with another - it is possible for this to not change the base on the DNA which would therefore mean no change to the amino acid sequence Can result in a silent mutation and no change to the primary structure AQA A-level biology paper 3 Questions And Answers What is base deletion? - The Answer Is The removal of a single nucleotide base A nucleotide base is deleted from the sequence - will cause a frameshift and therefore there will be a different tertiary structure and the whole enzyme will change Can change bonds between them What is base insertion? - The Answer Is Insertion of a single nucleotide base Will cause a frameshift as an extra nucleotide base has been added Can change bonds What is a silent mutation? - The Answer Is A mutation that doesn't result in any change What is a missense mutation? - The Answer Is A change to a single amino acid at the point of mutation AQA A-level biology paper 3 Questions And Answers What is Down syndrome? - The Answer Is A genetic disorder that causes an additional chromosome in the 21st pair, mild to moderate intellectual disability What is Klinefelter's syndrome (X, X, Y)? - The Answer Is A genetic disorder that occurs due to a person having two x chromosomes and one y chromosome, sparse body hair, enlarged breasts, wide hips, small testicles + cannot father children - can occur in egg + sperm What is polyploidy? - The Answer Is When a cell has more than two complete sets of chromosomes (in triploid + tetraploid) What is a diploid cell? - The Answer Is The parent cell at the start of the cell cycle (2n) Has a pair of chromosomes - one from each parent cell What are homologous chromosomes? - The Answer Is Chromosomes of a similar length with the same genes at the same loci AQA A-level biology paper 3 Questions And Answers What is meiosis? - The Answer Is Two nuclear divisions result usually in the formation of four haploid daughter cells from a single diploid parent cell Genetically different daughter cells result from the independent segregation of homologous chromosomes How does crossing over create more genetic diversity? - The Answer Is Allows for the exchange of genetic material What happens in crossing over? - The Answer Is A structure called a chiasma randomly forms + creates a point of contact between chromatids As a result of DNA replication, each chromosome duplicates to become a pair of sister chromatids The chiasma forms between the non-sister chromatids at a point which lies between two loci - allowing for the exchange of genetic material New combinations are called recombinants - different to parent cells due to crossing over AQA A-level biology paper 3 Questions And Answers What happens in prophase I? - The Answer Is Chromosomes shorten + thicken (condense) Pairs of homologous chromosomes line up closely together One centriole from each pair moves towards the opposite poles of the cell The nuclear membrane breaks down Another event that can take place in meiosis I is crossing over Crossing over What happens in metaphase I? - The Answer Is Chromosomes orientate themselves at the equator of the cell Pairs of homologous chromosomes align at the metaphase plate in a random nature What happens in anaphase I? - The Answer Is Chiasma breaks + the chromosomes are separated Spindle fibres contract + pull the chromosomes apart The random assortment + independent segregation of chromosomes during metaphase I + anaphase I result in the production of genetically different gametes AQA A-level biology paper 3 Questions And Answers What is genetic diversity? - The Answer Is The total number of different alleles in a population How can you measure genetic diversity? - The Answer Is The number of different alleles of genes in a species or population. Can be advantages - enables natural selection What is an allele? - The Answer Is Different forms of a gene What is antibiotic resistance? - The Answer Is Random mutation in the allele makes a resistant allele When exposed to the bacteria - only resistant ones can reproduce Resistance allele frequency increases over generations What are the different types of selection? - The Answer Is Directional Stabilising Disruptive AQA A-level biology paper 3 Questions And Answers What is directional selection? - The Answer Is Favours individuals at one end of the phenotypic range - one extreme e.g. long neck in giraffe Normal distribution curve shifts in this direction for the phenotype What is stabilising selection? - The Answer Is Favours intermediate variants and acts against extreme phenotypes Variation decreases over generations E.g. birth weight Average birth weight has a selective advantage - less complications More likely to survive and pass the allele to their offspring What do mutations lead to? - The Answer Is Random mutation can result in new alleles of a gene. Many mutations are harmful but the new allele of a gene might benefit its possessor, leading to increased reproductive success. AQA A-level biology paper 3 Questions And Answers The advantageous allele is inherited by members of the next generation. As a result, over many generations, the new allele increases in frequency in the population. What can natural selection cause? - The Answer Is Species that are better adapted to their environment. What types of adaptions can there be? - The Answer Is Anatomical Physiological Behavioural What is an example of anatomical, physiological or behavioural adaptations? - The Answer Is Hedgehogs Anatomical - spikes vs predators Physiological - hibernation + slow metabolism Behavioural - roll up in a ball in data AQA A-level biology paper 3 Questions And Answers What is species richness? - The Answer Is The number of different species in a community at a given time What is index of diversity? - The Answer Is The relationship between the number of species in a community and the number of individuals in each species Takes small groups into account What is the index of diversity formula? - The Answer Is D = N(N-1)/sum of n(n-1) N - amount of species n - number in species What are farming techniques that reduce biodiversity? - The Answer Is Monocultures - just wheat - reduce species diversity Ploughing Crop spraying Use uncultivated strips of land - provide food for birds etc Delayed harvesting of crops - allows seed dispersal Meadow conservation - conflicts with grass planting AQA A-level biology paper 3 Questions And Answers How can you work out genetic diversity? - The Answer Is The frequency of measurable or observable characteristics The base sequence of DNA The base sequence of mRNA The amino acid sequence of the proteins encoded by DNA and mRNA. What is the standard deviation formula? - The Answer Is S = √Σ (x-x̄)^2/(n-1) x - data points x̄ - mean n - number of values What is the first stage in the light dependant reaction? - The Answer Is Chlorophyll absorbs light, leading to the photoionisation of chlorophyll Photosystem II absorbs light and excites the electron inside, this causes the electrons to move into the ETC where it moves along via redox reactions AQA A-level biology paper 3 Questions And Answers What happens to the energy produced by the ETC? - The Answer Is Some of the energy from electrons released during photo ionisation is conserved in the production of ATP and reduced NADP The electrons release energy which forms a proton gradient to form How is ATP formed by the ETC? - The Answer Is The production of ATP involves electron transfer associated with the transfer of electrons down the electron transfer chain and passage of protons across chloroplast membranes and is catalysed by ATP synthase embedded in these membranes (chemiosmotic theory) The protons move to ATP synthase and they go through, causing the motor to turn + ADP + Pi -> ATP What is photolysis? - The Answer Is Photolysis of water produces protons, electrons and oxygen. H2O -> ½ O2 + 2e- + H+ What is the first stage of the light independent reaction? - The Answer Is Carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate AQA A-level biology paper 3 Questions And Answers 2x net ATP - two go in at the start + 4 come out What happens in anaerobic respiration in plants, microbes and yeast? - The Answer Is Pyruvate → ethanal → ethanol Each molecule of pyruvate is decarboxylated + converted to ethanal by pyruvate decarboxylase A molecule of carbon is given off during the conversion The ethanal accepts hydrogen atoms from the NADH + is reduced to ethanol - catalysed by ethanol dehydrogenase What happens in anaerobic respiration in animals? - The Answer Is Pyruvate → lactate In lactase fermentation, the pyruvate accepts the two H+ from NADH - catalysed by lactase dehydrogenase Pyruvate is reduced and converted to two molecules of lactase AQA A-level biology paper 3 Questions And Answers The NADH is reoxidised, meaning glycolysis can continue as the coenzyme can accept the hydrogen atoms that are released during the oxidation of TP What happens if respiration is aerobic? - The Answer Is The pyruvate from glycolysis enters the mitochondrial matrix by active transport. What is the link reaction? - The Answer Is Pyruvate (3C) → CO2 released + NAD+ is reduced → acetate (2C) → coenzyme A is added → forms acetyl coenzyme A (2C) What happens in the Krebs Cycle? - The Answer Is acetyl coenzyme A reacts with oxaloacetate (4C), releasing coenzyme A and producing citrate (6C) Decarboxylation to 5C compound + NAD+ is reduced to NADH Produces CO2 + NADH Decarboxylation occurs again in a 4C compound Produces CO2 + NADH AQA A-level biology paper 3 Questions And Answers 4C is oxidised into another 4C compound ATP is produced Substrate level phosphorylation 4C is oxidised to another 4C compound FAD reduced to FADH2+ 4C is used to regenerate oxloacetate Reducing NAD → NADH What are the products from the Krebs Cycle for one molecule of glucose (2x pyruvate) - The Answer Is 2x ATP 6x NADH 2x FADH2 4x CO20 Where does oxidative phosphorylation occur? - The Answer Is Inner mitochondrial membrane What happens in oxidative phosphorylation? - The Answer Is NADH → oxidised by electron transport proteins → produces protons + electrons AQA A-level biology paper 3 Questions And Answers How can biomass be measured in plants? - The Answer Is The mass of carbon or dry mass of tissue per given area OR By chemical energy store in dry biomass can be measured using calorimetry What is gross primary productivity? - The Answer Is Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume. What is net primary productivity? - The Answer Is Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account Where represents gross production and represents respiratory losses to the environment. How is energy transferred? - The Answer Is Through the food web Producer → primary consumer → secondary consumer → tertiary consumer Some is lost due to respiration + excretion AQA A-level biology paper 3 Questions And Answers How do you work out net primary productivity? - The Answer Is NPP = GPP - R R - respiratory losses How do you calculate the net production of consumers? - The Answer Is N= I - (F + R) I - chemical energy store in ingested food F - chemical energy lost to the environment in faeces + urine R - respiratory losses to the environment What is primary and secondary productivity - The Answer Is Primary and secondary productivity is the rate of primary or secondary production, respectively. It is measured as biomass in a given area in a given time eg kJ ha-1 year-1. What is a population? - The Answer Is The same species in an area What is a community? - The Answer Is All living organisms in an area at the same time AQA A-level biology paper 3 Questions And Answers What is an ecosystem? - The Answer Is A community in conjunction with the non- living components of the environment What are abiotic factors? - The Answer Is Non-living chemical + physical of an ecosystem What is respiratory substrate? - The Answer Is An organic molecule that can be oxidised by respiration, releasing energy to make ATP What is biomass? - The Answer Is Total mass of living matter within a biomass What is calorimetry? - The Answer Is A technique used to measure the quantity of heat gained or lost by a system What is the phosphorus cycle? - The Answer Is Environmental conditions e.g. erosion and weathering cause the release of phosphate ions by rocks into soil and bodies of water AQA A-level biology paper 3 Questions And Answers What is ammonification? - The Answer Is Organic nitrogen from decomposition of proteins, DNA, urea etc are converted to ammonium ions which are released into the soil Carried out by saprobionts: bacteria + fungi that can digest waste extracellularly What is nitrification? - The Answer Is When ammonium ions in the soil are oxidised to nitrates then nitrites by nitrifying bacteria NH4+ → NO2- → NO3- Two stage oxidation reaction What is denitification? - The Answer Is Converts nitrogen in compounds back to nitrogen gas Not useful as nitrogen gas cannot be absorbed by plants Anaerobic denitrifying bacteria AQA A-level biology paper 3 Questions And Answers What are fertilisers? - The Answer Is Replace the nitrates and phosphates lost by harvesting plants and removing livestock What are natural fertilisers? - The Answer Is Manure, seaweed, peat, guano etc Advantages: cheaper + free if it comes from your own livestock Disadvantage: exact minerals and proportions cant be controlled What are artificial fertilisers? - The Answer Is Contain exact amounts of minerals More water-soluble - more ions dissolve in the water surrounding the soil so higher absorption of inorganic ions This can lead to leaching and eutrophication What is leaching? - The Answer Is When water-soluble compounds (phosphate + nitrate) are washed away into bodies of water AQA A-level biology paper 3 Questions And Answers If nitrogen fertilisers leach, eutrophication can occur What is eutrophication? - The Answer Is Leached nitrates in the water cause algae to grow on the surface Lots of algae will block light - less light gets into the pond so the plants can't photosynthesise and therefore die Aerobic bacteria feed on dead plant matter + respire - using up the oxygen in the water Fish + other organisms will die due to lack of oxygen How do organisms increase their chance of survival? - The Answer Is By responding to environmental changes How do plants respond to environmental changes? - The Answer Is By producing chemicals or altering their growth What is tropism? - The Answer Is A directional growth response in plants AQA A-level biology paper 3 Questions And Answers What is negative taxis? - The Answer Is Movement away from a stimulus (cockroaches move away from light) What are 4 examples of taxis? - The Answer Is Chemotaxis - response to chemical Phototaxis - response to light Geotaxis - response to gravity Rheotaxis - response to movement What is kinesis? - The Answer Is A non-directional response to a stimulus What are 2 examples of kinesis? - The Answer Is Humans move around more when its cold outside to keep warm - but don't move away from the cold A woodlice may make more turns when searching for a favourable environment + vice versa - less when not searching What is a reflex? - The Answer Is Extremely rapid response that doesn't require thought Creates a protective effect AQA A-level biology paper 3 Questions And Answers What is the reflex arc? - The Answer Is Stimuli → receptors → sensory → relay → motor → muscle/organ/glands What are examples of receptors? - The Answer Is Eyes, skin, pancreas (alpha and beta cells) What is the threshold? - The Answer Is A certain amount of pressure to cause an action potential What is a stimulus? - The Answer Is Detectable change in the internal/external environment What is a receptor? - The Answer Is A cell or organ that detects a change in internal/external environments What is a co-ordinator? - The Answer Is Connects info between the receptor + the appropriate effector AQA A-level biology paper 3 Questions And Answers What is an effector? - The Answer Is A cell, tissue, organ or system that carries out a response What is a response? - The Answer Is A change brought about due to a stimulus What are auxins? - The Answer Is IAA ~ plant to grow in response to stimulus What is an example of a receptor? - The Answer Is Pacinian corpuscle What does the Pacinian corpuscle do? - The Answer Is Detects pressure What does the Pacinian corpuscle do at rest? - The Answer Is The sodium-potassium pump maintains resting potential At the resting state, channels are too narrow for Na+ to diffuse, so the resting potential is maintained What is resting potential? - The Answer Is The difference in electrical charge inside