AQA A LEVEL BIOLOGY Paper 1 2022 With Complete Solutions

Capsule (slime) - ANSWER Protects the bacteria from attack by cells of the immune system. Flagellum - ANSWER Rotates to make the cell move. Viruses - ANSWER Acellular. Invade and reproduce inside the cells of other organisms. What is magnification? - ANSWER How much bigger the image is that the specimen. What is resolution? - ANSWER The ability of the microscope to distinguish between two points that are close together. Light/optical microscopes - ANSWER Uses light. Max resolution of 0.2micrometers Max magnification of x1,500 Electron microscopes - ANSWER Use electrons. Vacuum only so no living specimen. Max resolution of 0.0002micrometers Max magnification of x1,500,000 TEM - ANSWER Uses electromagnets to focus a beam of electrons through the specimen. Thin specimen only. SEM - ANSWER Scans a beam of electrons across the specimen. 3-D image. Can be used on a thick specimen - but lower resolution than TEM. What is the process of cell fractionation? - ANSWER 1 Homogenisation - Play cells in ice-cold, isotonic, buffer solution and grind up in a blender. 2 Filtration - filter the solution through a gauze to separate out any debris. 3 Ultracentrifugation - pour the cell fragments into a tube and put the tube into a centrifuge. Spin at a low speed. The heaviest organelles (nucleus) will fall to the bottom and will form the pellets. The rest of the organelles stay suspended in the supernatant. The supernatant is drained off poured into another tube and spun again at a higher speed. The heaviest organelles (mitochondria) will fall to the bottom, forming a pellet. The process repeats. 3.4.4 Genetic Diversity and Adaptation - ANSWER What is an allele? - ANSWER Different versions of a gene. What is genetic diversity? - ANSWER The number of different alleles of genes in a species or population. How is genetic diversity increased? - ANSWER Mutations in DNA. Gene flow. What allows natural selection to take place? - ANSWER Genetic diversity. What is a genetic bottleneck? - ANSWER An event that causes a big reduction in a population. What are the effects of a genetic bottleneck? - ANSWER Reduces the number of different alleles in the gene pool so reduces genetic diversity. What is a type of genetic bottleneck? - ANSWER The founder effect. Describes what happens when just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool. What is the effect of natural selection? - ANSWER Increases advantageous alleles in a population. Natural selection leads to... - ANSWER Adaption Types of adaptations: - ANSWER Structural, physiological, behavioral What is directional selection? - ANSWER Favours individuals at one end of the phenotypic range. What is stabilising selection? - ANSWER Selection favouring average individuals. RP6 (aseptic techniques). - ANSWER Aseptic techniques - preventing contamination by unwanted microorganisms, regularly disinfect work surface, use sterile equipment, wash hands with soap and water. 3.3.2 Gas Exchange - ANSWER State the two adaptations of gas exchange surfaces. - ANSWER Thin so short diffusion distance Large surface area Describe the gas exchange system in fish. - ANSWER Countercurrent (blood flows through the lamellae in one direction and water flows over in the opposite direction, maintains a high concentration gradient). Water enters the fish through its mouth and passes through the gills. Each gill is made of lots of thin plates called gill filaments which are covered in lots of lamellae, which increase the surface area. Lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion. Describe the gas exchange system in insects. - ANSWER Use tracheae. Air moves into tracheae through spiracles. Oxygen travels down the concentration gradient towards the cells. The tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells. Carbon dioxide moves down its concentration gradient towards the spiracles to be released into the atmosphere. Insects use rhythmic abdominal movements to move air in and out of the spiracles. Describe the gas exchange system in dicotyledonous plants. - ANSWER Mesophyll cell surface, large surface area, are inside the leaf, gases move into and out of the leaf via stomata. Guard cells control the opening/closing of stomata. How do insects and plants control water loss? - ANSWER Insects - Close spiracles using muscles. Have a waterproof waxy cuticle all over body. Have tiny hairs around the spiracles. Plants - if the plant gets dehydrated the guard cells lose water and become flaccid which closes the pore. Give some examples of xerophytic adaptations. - ANSWER Sunken stomata to trap moist air. Curled leaves with stomata inside to protect them from wind which decreases evaporation and maintains humidity inside. A reduced number of stomata so there are fewer places for water to escape. Waxy waterproof cuticles on leaves and stems to reduce evaporation. What is the structure of the human gas exchange system? - ANSWER Trachea. Bronchi. Bronchioles. Alveoli. (Ribcage, intercostal muscles, diaphragm). What is the process of inspiration? - ANSWER Active process. External intercostal and diaphragm muscles contract. Ribcage moves upwards and outwards diaphragm flattens, volume of thoracic cavity increases. Lung pressure decreases. Air flows down the pressure gradient into the lungs. What is the process of expiration? - ANSWER Passive process. External intercostal and diaphragm muscles relax. Rib cage moves downwards and inwards and diaphragm becomes curved again. Volume of thoracic cavity decreases so air pressure increases. Air is forced down the pressure gradient and out of the lungs. Where does gaseous exchange occur in humans? - ANSWER Alveoli. How are alveoli adapted for gas exchange? - ANSWER Lots of them, large surface area. Epithelium is one cell thick, short diffusion pathway. How does gas exchange take place in the alveoli? - ANSWER Oxygen diffuses out of the alveoli, across the alveolar epithelium and capillary endothelium, into Hb in the blood. Carbon dioxide diffuses into the alveoli from the blood, and is breathed out. 3.1.4 Proteins - ANSWER What is a protein made up of? - ANSWER Amino acids (monomers). What is the general structure of an amino acid? - ANSWER (NH2)(R) - C - (H)(COOH) How are two amino acids joined? - ANSWER Peptide bond formed by a condensation reaction (molecule of water eliminated). What is the primary structure of a protein? - ANSWER Sequence of amino acids in the polypeptide chain. What is the secondary structure of a protein? - ANSWER Hydrogen bonding forms between amino acids and so make it coil or fold into alpha helix or beta pleated sheet. What is the tertiary structure of a protein? - ANSWER More bonds form (hydrogen and ionic bonds). Forms final 3D structure (for single chain proteins). What is the quaternary structure of a protein? - ANSWER Made up of several different polypeptide chains held together by bonds. What are the different functions of proteins? - ANSWER Structural proteins. Transport proteins. Antibodies. Enzymes. Outline a method for the biuret test. - ANSWER Add a few drops of NaOH solution to the test sample. Add some copper(||) sulphate solution. If the protein is present the solution turns purple if there is no protein the solution will stay blue. What is an enzyme? - ANSWER A biological catalyst. Catalyses metabolic reactions. How do enzymes work? - ANSWER They lower the activation energy to speed up the rate of reaction. Describe the 'lock and key' model. - ANSWER This is where the substrate fits into the enzyme in the same way the key fits into a lock. Describe the 'induced fit' model. - ANSWER The substrate doesn't only have to be the right shape to fit the active site but also has to make the active site change shape in the right way. Factors affecting enzyme activity: - ANSWER Temperature, pH, enzyme concentration, substrate concentration. How does a competitive inhibitor work? - ANSWER A competitive inhibitor is of similar shape to the substrate, and is complementary to the active site. They attach to the active site before the substrate thus blocking it, but interact weakly so they dont stay permanently - compete for active site. How does a non-competitive inhibitor work? - ANSWER They bind to another binding site other than the active site and alter the shape of the enzyme so the substrate can no longer bind to the active site. 3.1.2 Carbohydrates - ANSWER What are the monomers that make up carbohydrates? - ANSWER Monosaccharides. How are two monosaccharides joined? - ANSWER By a condensation reaction, forming a glycosidic bond (eliminating a water molecule). Maltose is made up of... - ANSWER 2 glucose molecules. Lactose is made up of... - ANSWER Glucose and galactose. Sucrose is made up of... - ANSWER Fructose and glucose. What are the two isomers of glucose? - ANSWER Alpha and beta glucose. How does alpha-glucose differ from beta-glucose? - ANSWER In alpha-glucose, the hydroxyl group is placed below the plane of the ring of carbons; in beta-glucose, the hydroxyl group is placed above the plane of the ring. Outline a method for the Benedict's test. - ANSWER Add Benedict's reagent to a sample and heat it in a water bath has been brought to the boil. If the test is positive it will form a coloured precipitate. (Blue -> brick red) - could filter the precipitate and weigh it to compare amount of reducing sugar. For non reducing sugar: Add dilute hydrochloric acid and carefully heat in a water bath that's been brought to the boil. Neutralise with sodium hydrogen carbonate. Carry out Benedict's test as normal. What is the structure of starch? - ANSWER Contains two polysaccharides of alpha glucose (amylose and amylopectin). Amylose - Long unbranched chain of alpha glucose. Coiled, compact, good for storage. Amylopectin - Long branched chain of alpha glucose, Sidebranches allow enzymes to reach the glycosidic bonds easily so glucose released quickly. Insoluble in water so doesn't affect water potential of cell. What test can be used for starch? - ANSWER Iodine test. Add iodine dissolved in potassium iodide solution to the test sample. If starch is present the sample changes from brown-orange to a blue-black colour. Describe the structure of glycogen. - ANSWER Similar to amylopectin. Lots of sidebranches so glucose can be released quickly. Very compact molecule so good for storage. What is cellulose used for? - ANSWER Cell walls. (Structural support) Describe the structure of cellulose. - ANSWER Straight cellulose chains made of beta glucose. Chains linked together by hydrogen bonds to form strong fibres called microfibrils. 3.3.4 Mass Transport - ANSWER What is haemoglobin? - ANSWER Quaternary, globular protein What is haemoglobin made up of? - ANSWER 4 polypeptide chains. One haem group per chain, contains iron ion. How many oxygen molecules can hemoglobin carry? - ANSWER 4 Haemoglobin has a ____ affinity for oxygen - ANSWER High. What does haemoglobin form when it binds to oxygen? - ANSWER Oxyhaemoglobin. What is the equation for the reaction between Hb and O2? - ANSWER Hb + 4O2 —> HbO8 What does 'partial pressure of oxygen' (pO2) mean? - ANSWER A measure of oxygen concentration. Greater concentration -> higher pO2 What happens when there's a high pO2? - ANSWER Oxygen loads onto haemoglobin to form oxyhaemoglobin. What happens when there's a low pO2? - ANSWER Oxyhaemoglobin unloads it's oxygen. How is oxyhaemoglobin formed in the lungs? - ANSWER Oxygen enters blood capillaries at alveoli. Alveoli have high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin. What happens to oxyhaemoglobin when cells respire? - ANSWER Cells use oxygen, lowers pO2. Red blood cells deliver oxyhaemoglobin to respiring tissues, unloads oxygen. Evaluate the function of haemoglobin. - ANSWER In lungs, high pO2, so haemoglobin binds with oxygen to form oxyhaemoglobin (high affinity for oxygen in lungs). At respiring cells (using up oxygen), lower pO2, so oxyhaemoglobin unloads oxygen at cells (low affinity for oxygen). What does the Bohr effect cause? - ANSWER A shift in curve towards right. What happens to pCO2 when cells are respiring? - ANSWER Increases. How does haemoglobin differ at high altitudes? - ANSWER Haemoglobin has higher affinity for oxygen. What is the general pattern of blood circulation in a mammal? - ANSWER Right side of heart: Heart, pulmonary artery, lungs, pulmonary vein, heart. Back to left side. Left side: Heart, aorta, body (renal artery, renal vein) vena cava, heart. Back to right side. Which two words describe the mammalian circulatory system? - ANSWER Closed, double. What is the function of the coronary arteries? - ANSWER Supply oxygenated blood to the heart muscle. How does the structure of the heart relate to its function? - ANSWER AV valves, prevent backflow of blood from ventricles to atria. SL valves, prevent backflow of blood from arteries to ventricles. Left has thicker muscular wall, generates high blood pressure for blood to travel around body. Right has thinner muscular wall, generates lower blood pressure, blood travels to lungs, high blood pressure would damage alveoli.