AQA A Level Biology Paper 1 Exam, Exams of Biology

Download AQA A Level Biology Paper 1 Exam and more Exams Biology in PDF only on Docsity! AQA A Level Biology Paper 1 AQA A Level Biology Paper 1 Exam Containing 208 Questions and Answers 2024-2025. Water removed from the reactants joining two molecules together forming a chemical bond - Answer: Condensation The addition of water to the reactants to break a chemical bond between 2 molecules - Answer: Hydrolysis 1 AQA A Level Biology Paper 1 1. Add Benedict's reagent. 2. Heat the solution in a water bath for 5 minutes at 95 degrees Celsius. 3. Change from blue to brick red as CuO formed - Answer: Test for Reducing Sugars (3) Smaller units from which larger molecules are made - Answer: Monomer 1. Add 2cm³ of food sample then add 2cm³ of dilute HCl and heat. 2. Add 2cm³ of NaHCO3 then do test for reducing sugars. - Answer: Non-Reducing Sugars (2) Add drops of iodine to starch solution. Colour change to blue-black - Answer: Test for Starch (1) 1. Mix Test solution with ethanol. 2. Shake for 1 minute then add water. 3. Cloudy white emulsion - Answer: Test for Lipids (3) 1. Obtain equal volumes of test solution and NaOH then add a few drops of biuret solution (dilute copper (II) sulphate solution). 2. Colour change to mauve/purple - Answer: Test for Proteins (2) 1. Very high resolution. 2. Needs thin and dead specimen. 3. Artefacts can occur (remnant left on object during prep, such as air bubbles) 2 AQA A Level Biology Paper 1 minimising organelle size change due to osmosis. Buffered. Minimum changes in pH, so prevents enzymes in organelles denaturing. - Answer: Solution Required for cell fractionation (6 Marks) 1. Homogenisation. Breaking up cells by blending the sample to create a homogenate. 2. Filtering. Filtering the large, unwanted sil, producing the filtrate. 3. Ultracentrifugation. Spin in a centrifuge so components separate out by weight. Heavier near the bottom of the tube. 4. Supernatant is removed and spun again at higher speed. - Answer: Separation of Organelles From The Cells (4) The solution not including the pellet at the bottom of the test tube after centrifugation. - Answer: Supernatant 1. Cell wall forms, dividing the two genetically identical daughter cells. 2. Same circular DNA. - Answer: Binary Fission 3 Nuclei, Chloroplasts, Mitochondria, Lysosomes, Endoplasmic Reticulum, Ribosomes - Answer: Order of Organelles (Pass me a taco chief) - Answer: Mitosis acronym Cell grows and carrys out its normal function - Answer: Interphase 5 AQA A Level Biology Paper 1 Cells grow to normal size. Organelles replicate and genes are expressed to make proteins needed. - Answer: Interphase G1 DNA and histones replicated. - Answer: Interphase S Spindle fibres are made - Answer: Interphase G2 1. DNA winds up making chromosones from chromatin. 2. Centrioles appear at opposite poles of the cell. 3. Nucleolus disappears - Answer: Prophase (3) 1. Nuclear envelope disappears. 2. Chromosomes align along the equator of the cell. 3. Spindle fibres connect centrioles to chromosomes - Answer: Metaphase (3) 1. Spindle fibres contract pulling daughter chromosomes to opposite poles of the cell. - Answer: Anaphase (1) 1. Spindle fibres disperse. 2. Nuclear envelope forms. 3. Chromatids uncoil to chromatin - Answer: Telophase (3) 1. Cytoplasm constricts separating the cells into two. 2. Membrane forms creating two new genetically identical daughter cells. - Answer: Cytokinesis (2) 6 AQA A Level Biology Paper 1 number of cells in mitosis/total number of cells - Answer: Mitotic index 1. Circular DNA replicates and both copies attach to the cell membrane. 2. Plasmids also replicate. - Answer: Binary fission 1 (2) Cell membrane grows between the two DNA molecules and pinches them inwards dividing the cell into 2. - Answer: Binary Fission 2 (1) 1. Attach to host cell via attachment protein and inject nucleic acid into the cell. 2. This gives the instructions to construct the virus - Answer: Virus Replication 1 (2) 1. The virus is then assembled and leaves the cell, taking the phospholipid bilayer with it. 2. This creates holes in the cell and kills it. - Answer: Virus Replication 2 (2) Fluid: All the components can move around. Mosaic: Many different components all fit together - Answer: Fluid mosaic Structure [Fluid][Mosaic] (2) The passive transport of large molecules such as amino acids and sugars, but they require integral proteins to pass through. - Answer: Facilitated Diffusion The passive movement of particles from a high concentration to a region of low concentration, down a concentration gradient. - Answer: Diffusion 7 AQA A Level Biology Paper 1 Antibodies produced from cloned plasma B lymphocytes - Answer: Monoclonal Antibodies 1. Hydrogen bonds between DNA base pairs are broken 2. One DNA strand acts as a template 3. Free RNA nucleotides align by complementary base pairing (uracil is used instead of thymine) 4. RNA polymerase forms phosphodiester bonds between adjacent RNA nucleotides joining them together. 5. Pre-mRNA is spliced, removing introns then joining the exons. 6. mRNA moves out of nucleus via nuclear pore - Answer: Polypeptide synthesis (In nucleus) (6) [Transcription] Adaptation. How it works. Example. Repeat twice for 6 marks - Answer: 6 marker layout for Xerophytic plants 1. mRNA attaches to ribosome 2. tRNA molecule with complementary anticodon and desired amino acid moves to the ribosome and binds to the codon. 3. Amino acids join by peptide bonds with the use of ATP 4. tRNA released after amino acid joined to polypeptide 5. The ribosome moves along the mRNA to form the polypeptide - Answer: Polypeptide synthesis (In ribosomes) (5) [Translation] 10 AQA A Level Biology Paper 1 1. Substrate binds to active site 2. ESC forms 3. Active site changes shape slightly distorting hydrogen bonds in the substrate. 4. Reduces activation energy - Answer: Describe the Induced fit model of enzyme action and how an enzyme acts as a catalyst. (3 marks) A change in the nucleotide base sequence. - Answer: Mutations (Normal = BEAST) Substitution in a codon turns it into a stop codon - Answer: Substitution (Nonsense) Causing a different amino acid to be coded for - Answer: Missense (FEAST) Results in a codon coding for the same amino acid creating degenerate code. - Answer: Silent Nucleotide is gained from a DNA strand, creating a right frameshift. - Answer: Addition (BREAST) A nucleotide is lost so frameshift to the left. - Answer: Deletion (BEST) When one or more bases are repeated so shift to the right. - Answer: Duplication (BEEAST) 11 AQA A Level Biology Paper 1 A group of bases become separated from the DNA, then join back but inverted. - Answer: Inversion (BEATS) Breaks the end peptide bond - Answer: Exopeptidase Breaks the middle peptide bonds - Answer: Endopeptidase Tidal volume x Ventilation rate - Answer: pulmonary ventilation = 1. Proteins remain in the plasma 2. This reduces the water potential 3. Water moves to blood by osmosis 4. Returns to blood via lymphatic system - Answer: Tissue Fluid is formed from blood at the arteriolar end of a capillary bed. Explain how water from tissue fluid is returned to the circulatory system. (4) 1. Co-transport 2. Hydrolysis of ATP 3. Na+ and H+ bind to carrier protein 4. Protein changes shape and moves Na+ and H+ across membrane. - Answer: Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3. NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell. Use your knowledge of transport across cell membranes to suggest how NHE3 does this. (4) 12 AQA A Level Biology Paper 1 Environment conditions are stable Human birth weight - Answer: Stabilising Selection Transport of sap (a very concentrated solution of dissolved sucrose and amino acids) in the phloem vessels. - Answer: Translocation stroke volume x heart rate - Answer: Cardiac output 1. Phagosome fuses with lysosome; 2. Virus destroyed by lysozymes 3. Antigen (from virus) are displayed on the cell membrane - Answer: Describe how phagocytosis of a virus leads to presentation of its antigens. (2) 1. Transpiration. 2. Water leaves the leaf creating low pressure. 3. Water is sucked up from a high pressure (roots) to a low pressure. 4. Column of water does not break because of high tensile strength. 5. Strong lignin walls preventing xylem vessels from collapsing. - Answer: Xylem movement (5) 1. Sucrose actively transported to phloem vessels decreasing water potential. 2. Ions actively transported out of xylem vessel, increasing water potential. 3. Water diffuses from xylem to phloem. 4. Causes hydrostatic pressure so sap in phloem pushed downwards (mass flow). 15 AQA A Level Biology Paper 1 5. Sucrose is unloaded in the roots via active transport or diffusion. 6. Ions pumped into xylem via active tranport, decreasing water potential. 7. Osmosis from phloem to xylem 8. Water and ions made up by cohesion tension. - Answer: Mass flow Hypothesis (8) 1. The base sequence of DNA 2. The base sequence of mRNA 3. The amino acid sequence of proteins - Answer: State three comparisons of genetic diversity that the scientists used in order to generate classification Y. (3) 1. A reactant in hydrolysis, photosynthesis 2. High heat capacity so buffers changes in temperature. 3. Large latent heat of vaporisation so provides a cooling effect through evaporation. 4. Cohesion between water molecules so supports columns of water in plants. 5. Cohesion between water molecules so produces surface tension supporting small organisms - Answer: Explain five properties that make water important for organisms. (5) 1. Tracheoles have thin walls so short diffusion distance to cells 2. Large number of tracheoles so short diffusion distance to cells; 3. Large number of tracheoles so large surface area (for gas exchange) 16 AQA A Level Biology Paper 1 4. Body can be moved (by muscles) to move air so maintains diffusion/concentration gradient for oxygen/carbon dioxide - Answer: The adult damselfly uses a tracheal system for gas exchange. Explain three ways in which an insect's tracheal system is adapted for efficient gas exchange. (3) Glucose is high concentration in the ileum, low in the epithelial, but we want to increase the rate of transport. Sodium-potassium pump actively transports in a K+ to transport out Na+ creating a concentration gradient. Na+ and glucose pass through a co transporter in the phospholipid bilayer of the epithelial cell. - Answer: Co-Transport (Not mark scheme specific, only here as a guidance) Mitosis: 1. Division of body cells 2. results in 2 diploid daughter cells 3. genetically identical 4. used for growth, repair, and cell replacement Meiosis: 1. germline cells divide into sex cells 2. 4 haploid daughter cells 3. genetic variation due to: 4. crossing over 5. random orientation 6. used for sexual reproduction 17 AQA A Level Biology Paper 1 6. Starch molecule is branched and cellulose is unbranched - Answer: Compare and contrast the structure of starch and the structure of cellulose. (6) 1. Sucrose actively transported/co transported with H+ into phloem (cell) 2. By companion cells; 3. Lowers water potential in phloem and water enters from xylem by osmosis 4. Produces higher hydrostatic pressure 5. Mass flow to respiring cells 6. Unloaded from phloem by active transport - Answer: Describe the transport of carbohydrate in plants. (5) 1. Muscle contracts 2. Lumen constricts - Answer: Explain how an arteriolar can reduce the blood flow into capillaries. (2) 1 and 2. Adenine, ribose and 3 phosphates 3. Condensation reaction 4 Via ATP synthase - Answer: Describe how an ATP molecule is formed from its component molecules. (4) 1. Increasing Pi concentration, more ESCs are formed. 20 AQA A Level Biology Paper 1 2. At or above 40 mmol dm-3 all active sites occupied. - Answer: Explain the change in ATP concentration with increasing inorganic phosphate concentration. (2) 1. Larger organisms have a smaller surface area:volume ratio 2. Overcomes long diffusion pathway - Answer: Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake. (2) 1. Blood and water flow in opposite directions 2. Concentration gradient maintained along length of lamella - Answer: Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system. (2) 1. In fish, blood leaving (V) has more oxygen than water leaving (E) 2. But in humans, blood leaving (V) has less oxygen than air leaving (E) 3. So fish remove a greater proportion from the oxygen they take in. - Answer: A student studied Figure 3 and concluded that the fish gas exchange system is more efficient than the human gas exchange system. Use Figure 3 to justify this conclusion. (3) 1. Disinfect surfaces and instruments 2. Disinfect hands - Answer: Describe two precautions the student should take when clearing away after the dissection. (2) Feature: DNA 21 AQA A Level Biology Paper 1 Difference: DNA is circular in chloroplast but nuclear DNA is linear - Answer: Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell. (2) [Feature][Difference] 1. One glycerol and three fatty acids 2. Condensation reactions and removal of three molecules of water 3. Ester bonds formed - Answer: Describe how a triglyceride molecule is formed (3) 1. Spin supernatant at very high speeds 2. CENP-W separates depending on molecular mass - Answer: Explain how ultracentrifugation separates CENP-W from other molecules. (2) Sucrose - Answer: What is the only non-reducing dissacharide sugar ? A small repeating unit from which larger polymers are made. - Answer: What is a monomer? (1) 1. Filter and dry the precipitate 2. Find mass - Answer: Suggest another method other than colorimetry, that a student could use to measure the quantity of reducing sugar in a solution. (2) 1. Insoluble in water so doesn't affect water potential 2. Branched alpha helix so makes molecule compact 22 AQA A Level Biology Paper 1 Sodium ions 2. Co-transport of glucose into cells 3. Because sodium moved out by active transport via Na - K pump Phosphate ions 4. Joins nucleotides in the backbone of DNA 5. Used to produce ATP 6. Phosphorylates other compounds (glucose in glycolysis) making them more reactive - Answer: Describe the roles of iron ions, sodium ions, and phosphate ions in cells. (6) [Iron 1][Sodium 2-3][Phosphate 4-6] 1. Lysosomes 2. Fuse with vesicle 3. Releases hydrolytic enzymes (lyzozymes) - Answer: U. marinum cells ingest bacteria and digest them in the cytoplasm. Describe the role of one named organelle in digesting these bacteria. 1. Resolution too low 2. Because wavelength of light is too long - Answer: Explain why it is not possible to determine the identity of the structures labelled X using an optical microscope. (2) 1. DNA in nucleus is code for protein 2. Ribosomes on rough endoplasmic reticulum produce protein 3. Mitochondria produce ATP for protein synthesis 4. Golgi apparatus package/modify protein 25 AQA A Level Biology Paper 1 5. Golgi vessicles transport proteins and undergo exocytosis when they fuse with cell surface membrane - Answer: Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. Do not include details of transcription and translation in your answer. (5) 70s ribosomes - Answer: Name an organelle found in both a chloroplast and a prokaryotic cell. (1) 1. TEM use electrons and optical use light 2. TEM allows a greater resolution 3. So with TEM smaller organelles can be observed 4. TEM view only dead specimens whereas optical can view live specimens 5. TEM does not show colour and optical does 6. TEM requires thinner specimens 7. TEM requires a more complex and more time consuming preparation 8. TEM focuses using magnets and optical uses glass lenses - Answer: Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. (8) 1. Break open cells and produce homogenate; 2. Remove unbroken cells and larger debris; - Answer: (Ultracentrifugation) Explain why the biologist used a blender and then filtered the mixture. (2) 26 AQA A Level Biology Paper 1 Cytoplasm of red blood cell is filled with haemoglobin. - Answer: No organelles are visible in the cytoplasm of this red blood cell. Suggest why. (1) 1. Membrane has phospholipid bilayer 2. Stain binds to phosphate or glycerol 3. On inside and outside of membrane. - Answer: Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines. Suggest an explanation for the appearance of the cell-surface membrane as two dark lines. (3) 1. Add drop of water to glass slide 2. Obtain thin section of plant tissue and place on slide 3. Stain with iodine in potassium iodide. 4. Lower cover slip using mounted needle. - Answer: Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical light microscope. (4) 1. Examine over 20 cells 2. Repeat the count to ensure figures are correct - Answer: Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate. (2) 27 AQA A Level Biology Paper 1 2. They could then identify potential antigens to use in the vaccine - Answer: Determining the genome of the viruses could allow scientists to develop a vaccine. Explain how. (2) 1. Bind to antigen 2. Antibodies cause agglutination - Answer: Describe and explain the role of antibodies in stimulating phagocytosis. Do not include details about the process of phagocytosis. (2) 1. Bacterium binds to surface protein on a specific B cell. 2. B cell divides by mitosis and differentiates into plasma cells that produce specific antibodies. 3. Division stimulated by cytokines 4. Plasma cells release antibodies 5. Some B cells become memory cells 6. Memory cells produce antibodies faster - Answer: In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis. (6) 1. Active involves memory cells, passive does not 2. Active involves production of antibody by plasma cells and memory cells 3. Passive involves antibody introduced into body from outside such as antivenom 4. Active: long term, because antibody produced in response to antigen 5. Passive: short term, because antibody given is broken down 30 AQA A Level Biology Paper 1 6. Active can take time to develop, passive is fast acting. - Answer: Describe the difference between active and passive immunity. (6) 1. Micelles contain bile salts and fatty acids 2. Make fatty acids more soluble in water 3. Fatty acids absorbed by simple lipid diffusion 4. Triglycerides reformed in cells 5. Vesicles move to cell membrane - Answer: Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5) 1. Structure is determined by position of amino acid and R group 2. Primary structure is sequence of amino acids 3. Secondary structure formed by hydrogen bonding between amino acids (alpha helix and B-pleated sheet) 4. Tertiary structure formed by interactions between R groups such as hydrogen bonds, disulphide bridges and ionic bonds 5. Quaternary structure contains >1 polypeptide chain and/or prosthetic. - Answer: Describe how the structure of a protein depends on the amino acids it contains. (6) 1. Peptide bonds are hydrolysed 2. Endopeptidase act in the middle of polypeptide 3. Exopeptidases act at end of polypeptide 31 AQA A Level Biology Paper 1 4. Dipeptidase acts on dipeptide producing single amino acids - Answer: Describe the role of enzymes in the digestion of proteins in a mammal. (4) 1. Modifies triglycerides 2. Combines triglycerides with proteins 3. Packaged for release to undergo exocytosis - Answer: Suggest how the Golgi apparatus is involved in the absorption of lipids. (3) 1. Thin so small diffusion pathway 2. Flat so large surface area:volume ratio - Answer: Explain how two features of the body of the tubifex worm allow efficient gas exchange. (2) 1. More oxygen dissociation 2. By decreasing blood pH - Answer: Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin. (2) 1. Binding of first oxygen changes the quaternary structure of haemoglobin 2. Creates another binding site on Fe - Answer: Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why. (2) 1. High rate of transpiration 2. Water lost through stomata causing high tension in xylem 32 AQA A Level Biology Paper 1 2. Large number of samples - Answer: Give two ways the students would have ensured their index of diversity was representative of each habitat. (2) 1. Set up grid system with coordinates 2. Place large number of quadrats at coordinates selected at random 3. Count number of estimate percentage cover of native plant in quadrats 4. Repeat at same time each year for many years - Answer: Describe how you would investigate the effect of an invasion by a non-native species of plant (a biotic environmental factor) over many years on the abundance of a native species of plant in a community. (4) 1. Inbreeding 2. Founder effect 3. Bottleneck effect - Answer: Some populations of animals that have never been hunted show very low levels of genetic diversity. Other than hunting, suggest three reasons why populations might show very low levels of genetic diversity. (3) 1. Random fusion of gametes 2. Produces new allele combinations - Answer: Genetic variation within a species is increased during meiosis by crossing over and the independent segregation of homologous chromosomes. Apart from mutation, explain one other way genetic variation within a species is increased. (2) 1. Too many copies of chromosomes 2. Homologous chromosomes do not separate evenly. 35 AQA A Level Biology Paper 1 3. So no meiosis - Answer: The offspring produced from farmed trout (produce diploid egg cells) are sterile. Suggest and explain why. (3) 1. Homologous chromosomes pair 2. One of each pair goes to each to opposite poles - Answer: Explain how the chromosome number is halved during meiosis (2) 1. Homologous pairs of chromosomes form a bivalent 2. Chiasmata form and crossing over occurs 3. Equal lengths of non-sister chromatids or alleles are exchanged 4. Producing new combinations of alleles - Answer: Crossing over greatly increases genetic diversity in this species of moss. Describe the process of crossing over and explain how it increases genetic diversity. (4) 1. In meiosis I/II 2. Nondisjunction occurs meaning homologous chromosomes do not separate 3. Leading to diploid gametes which are fertilised by haploid gametes 4. Forming 3 chromosomes in zygote - Answer: Describe how the change in chromosome number in Patau syndrome was produced. (4) 1. Use random sample of seeds from each population 2. Use large enough sample to be representative of whole population 3. Indication of what size was measured eg mass 4. Calculate a mean and standard deviation for each population 5. Use the student's t-test 36 AQA A Level Biology Paper 1 6. Analyse whether there is a significant difference between the means of the two populations - Answer: An environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree. He was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside. Describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees. 1. W has 4 nuclei since it is at the end of 2nd division of meiosis 2. Z has 2 nuclei since it is at the end of 1st division of meiosis 3. W shows haploid cells 4. Cells in W contain half the mass of DNA of cells in Z - Answer: Figure 6 shows an image from an optical microscope of meiosis occurring in a flower bud of a flowering plant. W and Z are undergoing meiosis. Explain the appearance of W and Z. (4) 1. Two samples of bacteria were grown - one in a nutrient broth containing N14 (light) and the other N15 (heavy) 2. A sample of DNA from each batch was centrifuged. DNA in N15 settled lower than the DNA from the N14. 3. Bacteria containing N15 is then put in broth only N14 and then left to replicate 4. If the replication was conservative, there would be two separate bands 37 AQA A Level Biology Paper 1 5. Repeat this step with test tube 3, 4, and 5 to produce 0.5M, 0.25M, 0.125M respectively. - Answer: Make 5 serial dilutions of a sucrose concentration with an initial concentration of 2M. Dilute each by a factor of 2. (5) 1. Variable regions 2. Hinge protein 3. Constant regions 4. Light chain 5. Disulphide bridge 6. Heavy chain - Answer: Label an antibody (6) 1. When Hb binds with the first O2 molecule, its quaternary shape changes producing more active sites. 2. As Hb becomes more saturated, it gets harder for more molecules to join, hence the plateau. - Answer: Explain the sigmoidal shape of an oxygen dissociation curve. (2) 1. Endothelium becomes damaged due to high BP 2. Fats and macrophages from the blood clump together under the lining forming fatty streaks 3. Over time, more white blood cells fats, and connective tissue build up and harden forming a fibrous plaque called an atheroma 4. This plaque blocks the lumen of the artery and restricts blood flow, which causes blood pressure to increase 40 AQA A Level Biology Paper 1 5. Coronary artery disease occurs where cardiomyocytes do not receive oxygen for aerobic respiration, leading to cardiac muscle tissue dying, thus a myocardial infarction. - Answer: Describe how an atheroma in the coronary artery leads to myocardial infarction. (5) 1. Atheroma plaques damage and weaken arteries 2. Blood travels though weakened artery at high BP, causing it to push the inner layers through the outer layers, creating a balloon-like swelling, 3. This is called an aneurysm - Answer: Describe how an aneurysm occurs. (3) 1. Atheroma plaque ruptures through the endothelium 2. This damages the walls and leaves a rough surface 3. Platelets and fibrin form a blood clot here 4. Blood clot causes a blockage, or becomes dislodged and causes a blockage elsewhere - Answer: Describe how thrombosis occurs. (4) 1. High blood cholesterol and poor diet 2. Cigarette smoking 3. High blood pressure - Answer: Factors that increase the risk of cardiovascular disease. (3) 1. Temperature 2. Humidity 3. Wind speed 4. Light intensity - Answer: Factors that affect transpiration rate (4) 41 AQA A Level Biology Paper 1 1. If a ring of bark (only phloem removed) is removed for a tree, a bulge forms above the ring. 2. A radioactive tracer can trace 14C 3. Pressure in the phloem can be investigated using aphids. 4. Metabolic inhibitor is out into the phloem, then translocation stops. Evidence that ATP is involved. - Answer: Evidence for mass flow. (4) 1. Sugar travels to many different sinks, not just one with the highest water potential, as the model suggests. 2. The sieve plates would create a barrier to mass flow. A lot of pressure would be needed for the solutes to get through at a reasonable rate. - Answer: Evidence against mass flow (2). 1. Sterlilise an inoculating loop by placing the loop under a Bunsen burner until loop turns orange-red. 2. Open the culture bottle, dip the loop in, then flame the neck of the bottle to sterilise and put on the lid. 3. Open agar plate slightly and spread the culture onto the agar, then further spread with a sterile spreader. 4. Then, add the antibiotic strip and lightly press down to ensure the strip is in contact with the culture. 5. Put the lid on, tape vertically, invert and add name label. Incubate at 25 degrees celsius. 42 AQA A Level Biology Paper 1 1. Cell membranes: phospholipid bilayer allowing simple lipid diffusion 2. Energy source: Made into acetyl CoA to enter krebs 3. Waterproofing: insoluble in water e.g waxy cuticle 4. Protection: fat is stored around delicate organs eg. heart 5. Insulation: Electrical and thermal insulation. - Answer: Describe and outline 5 functions of lipids. (5) 1. Structural: Keratin 2. Enzymes: Pepsin 3. Transport: Carrier and integral protein 4. Hormones: ADH 5. Antibodies - Answer: Describe and outline 5 functions that proteins hold within an organism. (5) 1. Complementary base pairing allows for replication with accuracy 2. Bases held together by hydrogen bonds are easily broken during replication. 3. Large molecule so can carry a lot of information 4. Double helix tightly coiled so compact 5. Double stranded allows semi- conservative replication - Answer: How is DNA adapted to its function? (5) 1. Reactant in photosynthesis 2. Binds to carrier protein in active transport 3. Sliding filament theory 45 AQA A Level Biology Paper 1 4. Phosphorylation of molecules making them more unstable - Answer: Outline 4 uses of ATP (4) Produces and transports lipids - Answer: Describe the function of the SER (1) 1. Modifies proteins by adding carbohydrates or lipids 2. Modifies proteins to produce enzymes 3. Transports, stores and modifies lipids 4. Packages proteins into vesicles in preparation for their transport within/out of a cell 5. Secretes carbohydrates 6. Forms lysosomes - Answer: Describe the function of the golgi apparatus (6) Blue —> green —> yellow —> orange —> brick red - Answer: Qualitative Benedict's Positive Test colour changes 46